Wave turbulent statistics in non-weak wave turbulence
Naoto Yokoyama
2011-05-08T23:59:59.000Z
In wave turbulence, it has been believed that statistical properties are well described by the weak turbulence theory, in which nonlinear interactions among wavenumbers are assumed to be small. In the weak turbulence theory, separation of linear and nonlinear time scales derived from the weak nonlinearity is also assumed. However, the separation of the time scales is often violated even in weak turbulent systems where the nonlinear interactions are actually weak. To get rid of this inconsistency, closed equations are derived without assuming the separation of the time scales in accordance with Direct-Interaction Approximation (DIA), which has been successfully applied to Navier--Stokes turbulence. The kinetic equation of the weak turbulence theory is recovered from the DIA equations if the weak nonlinearity is assumed as an additional assumption. It suggests that the DIA equations is a natural extension of the conventional kinetic equation to not-necessarily-weak wave turbulence.
Wave turbulence served up on a plate
Pablo Cobelli; Philippe Petitjeans; Agnes Maurel; Vincent Pagneux; Nicolas Mordant
2009-10-28T23:59:59.000Z
Wave turbulence in a thin elastic plate is experimentally investigated. By using a Fourier transform profilometry technique, the deformation field of the plate surface is measured simultaneously in time and space. This enables us to compute the wavevector-frequency Fourier ($\\mathbf k, \\omega$) spectrum of the full space-time deformation velocity. In the 3D ($\\mathbf k, \\omega$) space, we show that the energy of the motion is concentrated on a 2D surface that represents a nonlinear dispersion relation. This nonlinear dispersion relation is close to the linear dispersion relation. This validates the usual wavenumber-frequency change of variables used in many experimental studies of wave turbulence. The deviation from the linear dispersion, which increases with the input power of the forcing, is attributed to weak non linear effects. Our technique opens the way for many new extensive quantitative comparisons between theory and experiments of wave turbulence.
Fossil turbulence and fossil turbulence waves can be dangerous
Carl H Gibson
2012-11-25T23:59:59.000Z
Turbulence is defined as an eddy-like state of fluid motion where the inertial-vortex forces of the eddies are larger than any other forces that tend to damp the eddies out. By this definition, turbulence always cascades from small scales where vorticity is created to larger scales where turbulence fossilizes. Fossil turbulence is any perturbation in a hydrophysical field produced by turbulence that persists after the fluid is no longer turbulent at the scale of the perturbation. Fossil turbulence patterns and fossil turbulence waves preserve and propagate energy and information about previous turbulence. Ignorance of fossil turbulence properties can be dangerous. Examples include the Osama bin Laden helicopter crash and the Air France 447 Airbus crash, both unfairly blamed on the pilots. Observations support the proposed definitions, and suggest even direct numerical simulations of turbulence require caution.
Wave VelocityWave Velocity Diff t f ti l l itDifferent from particle velocity
Yoo, S. J. Ben
Wave VelocityWave Velocity v=/T =f Diff t f ti l l itDifferent from particle velocity Depends on the medium in which the wave travelsDepends on the medium in which the wave travels stringaonvelocity F v of Waves11-8. Types of Waves Transverse wave Longitudinal wave Liu UCD Phy1B 2014 37 #12;Sound Wave
Turbulent round jet under gravity waves
Ryu, Yong Uk
2002-01-01T23:59:59.000Z
The behavior of a neutrally buoyant horizontal turbulent round jet under a wavy environment was investigated. Progressive waves with different wave amplitudes in an intermediate water depth were used. The Particle Image Velocimetry (PIV) technique...
Wave turbulence buildup in a vibrating plate
Auliel, Maria Ines; Mordant, Nicolas
2015-01-01T23:59:59.000Z
We report experimental and numerical results on the buildup of the energy spectrum in wave turbulence of a vibrating thin elastic plate. Three steps are observed: first a short linear stage, then the turbulent spectrum is constructed by the propagation of a front in wave number space and finally a long time saturation due to the action of dissipation. The propagation of a front at the second step is compatible with scaling predictions from the Weak Turbulence Theory.
Laminated Wave Turbulence: Generic Algorithms I
E. Kartashova; A. Kartashov
2006-09-07T23:59:59.000Z
The model of laminated wave turbulence presented recently unites both types of turbulent wave systems - statistical wave turbulence (introduced by Kolmogorov and brought to the present form by numerous works of Zakharov and his scientific school since nineteen sixties) and discrete wave turbulence (developed in the works of Kartashova in nineteen nineties). The main new feature described by this model is the following: discrete effects do appear not only in the long-wave part of the spectral domain (corresponding to small wave numbers) but all through the spectra thus putting forth a novel problem - construction of fast algorithms for computations in integers of order $10^{12}$ and more. In this paper we present a generic algorithm for polynomial dispersion functions and illustrate it by application to gravity and planetary waves.
Wave Packets and Turbulent Peter Jordan1
Dabiri, John O.
Wave Packets and Turbulent Jet Noise Peter Jordan1 and Tim Colonius2 1 D´epartement Fluides-control efforts is incomplete. Wave packets are intermittent, advecting disturbances that are correlated over review evidence of the existence, energetics, dynamics, and acous- tic efficiency of wave packets. We
Aspects of wave turbulence in preheating
Crespo, José A.; De Oliveira, H.P., E-mail: jaacrespo@gmail.com, E-mail: oliveira@dft.if.uerj.br [Universidade do Estado do Rio de Janeiro, Instituto de Física - Departamento de Física Teórica, Rio de Janeiro, RJ, CEP 20550-013 Brazil. (Brazil)
2014-06-01T23:59:59.000Z
In this work we have studied the nonlinear preheating dynamics of several inflationary models. It is well established that after a linear stage of preheating characterized by the parametric resonance, the nonlinear dynamics becomes relevant driving the system towards turbulence. Wave turbulence is the appropriated description of this phase since the matter contents are fields instead of usual fluids. Turbulence develops due to the nonlinear interations of waves, here represented by the small inhomogeneities of the scalar fields. We present relevant aspects of wave turbulence such as the Kolmogorov-Zakharov spectrum in frequency and wave number that indicates the energy transfer through scales. From the power spectrum of the matter energy density we were able to estimate the temperature of the thermalized system.
Multifractal statistics of Lagrangian velocity and acceleration in turbulence
L. Biferale; G. Boffetta; A. Celani; B. J. Devenish; A. Lanotte; F. Toschi
2004-03-11T23:59:59.000Z
The statistical properties of velocity and acceleration fields along the trajectories of fluid particles transported by a fully developed turbulent flow are investigated by means of high resolution direct numerical simulations. We present results for Lagrangian velocity structure functions, the acceleration probability density function and the acceleration variance conditioned on the instantaneous velocity. These are compared with predictions of the multifractal formalism and its merits and limitations are discussed.
Turbulent round jet under gravity waves
Ryu, Yong Uk
2002-01-01T23:59:59.000Z
) Turbulent shear stress &u'w'&/&u, & versus z/x. . . 26 3-5 Overlapped mean axial velocity &u&/&u, & versus zJx of the case of A = 0. 5 cm at six locations corresponding to figure 3-4(a) . . 28 3-6 Horizontal turbulent velocity &u' &' /&u, & versus zJx... of the case of A = 0. 5 cm with z, = 0 at. the moving jet centerline in the range of (a) x/D = 40 - 95, (b) x/D = 40 ? 57, and (c) x/D = 64 - 95 . . 30 3-7 Vertical turbulent velocity &w' & /&u, & versus z Jx of the case of A = 0. 5 cm FIGURE Page with z...
Irregular wave induced velocities in shallow water
Sultan, Nels John
1991-01-01T23:59:59.000Z
probabil- ity density function. This thesis applies this expanded distribution to fluid particle velocities instead of wave elevations. Ochi (1982) presents a review of recent ad- vances in the stochastic analysis of random seas. He notes that the first..., (Longuet-Higgins 1963), that purely linear waves will have a Gaussian distribu- tion. Therefore, any deviation from a Gaussian distribution must be attributed to wave nonlinearities. Ochi (1982) discusses a series of experiments by Honda and Mitsuyasu...
He, Jiansen; Marsch, Eckart; Chen, Christopher H K; Wang, Linghua; Pei, Zhongtian; Zhang, Lei; Salem, Chadi S; Bale, Stuart D
2015-01-01T23:59:59.000Z
Magnetohydronamic turbulence is believed to play a crucial role in heating the laboratorial, space, and astrophysical plasmas. However, the precise connection between the turbulent fluctuations and the particle kinetics has not yet been established. Here we present clear evidence of plasma turbulence heating based on diagnosed wave features and proton velocity distributions from solar wind measurements by the Wind spacecraft. For the first time, we can report the simultaneous observation of counter-propagating magnetohydrodynamic waves in the solar wind turbulence. Different from the traditional paradigm with counter-propagating Alfv\\'en waves, anti-sunward Alfv\\'en waves (AWs) are encountered by sunward slow magnetosonic waves (SMWs) in this new type of solar wind compressible turbulence. The counter-propagating AWs and SWs correspond respectively to the dominant and sub-dominant populations of the imbalanced Els\\"asser variables. Nonlinear interactions between the AWs and SMWs are inferred from the non-orth...
Discrete wave turbulence of rotational capillary water waves
Adrian Constantin; Elena Kartashova; Erik Wahlén
2010-05-12T23:59:59.000Z
We study the discrete wave turbulent regime of capillary water waves with constant non-zero vorticity. The explicit Hamiltonian formulation and the corresponding coupling coefficient are obtained. We also present the construction and investigation of resonance clustering. Some physical implications of the obtained results are discussed.
Simultaneous temperature and velocity Lagrangian measurements in turbulent thermal convection
Liot, O; Zonta, F; Chibbaro, S; Coudarchet, T; Gasteuil, Y; Pinton, J -F; Salort, J; Chillà, F
2015-01-01T23:59:59.000Z
We report joint Lagrangian velocity and temperature measurements in turbulent thermal convection. Measurements are performed using an improved version (extended autonomy) of the neutrally-buoyant instrumented particle that was used by to performed experiments in a parallelepipedic Rayleigh-Benard cell. The temperature signal is obtained from a RFtransmitter. Simultaneously, we determine particle's position and velocity with one camera, which grants access to the Lagrangian heat flux. Due to the extended autonomy of the present particle, we obtain well converged temperature and velocity statistics, as well as pseudo-eulerian maps of velocity and heat flux. Present experimental results have also been compared with the results obtained by a corresponding campaign of Direct Numerical Simulations and Lagrangian Tracking of massless tracers. The comparison between experimental and numerical results show the accuracy and reliability of our experimental measurements. Finally, the analysis of lagrangian velocity and t...
Gülder, Ömer L.
Contribution of small scale turbulence to burning velocity of flamelets in the thin reaction zone the turbulent burning velocity under the conditions corresponding to the thin reaction zones regime. Approaches turbulence on flam- elet burning velocity. An expression was derived to estimate the contribution of flame
Laminated Wave Turbulence: Generic Algorithms II
Elena Kartashova; Alexey Kartashov
2006-11-17T23:59:59.000Z
The model of laminated wave turbulence puts forth a novel computational problem - construction of fast algorithms for finding exact solutions of Diophantine equations in integers of order $10^{12}$ and more. The equations to be solved in integers are resonant conditions for nonlinearly interacting waves and their form is defined by the wave dispersion. It is established that for the most common dispersion as an arbitrary function of a wave-vector length two different generic algorithms are necessary: (1) one-class-case algorithm for waves interacting through scales, and (2) two-class-case algorithm for waves interacting through phases. In our previous paper we described the one-class-case generic algorithm and in our present paper we present the two-class-case generic algorithm.
Wave Turbulence in Superfluid 4 Energy Cascades, Rogue Waves & Kinetic Phenomena
Fominov, Yakov
Outline Wave Turbulence in Superfluid 4 He: Energy Cascades, Rogue Waves & Kinetic Phenomena Conference, Chernogolovka, 3 August 2009 McClintock Efimov Ganshin Kolmakov Mezhov-Deglin Wave Turbulence in Superfluid 4 He #12;Outline Outline 1 Introduction Motivation 2 Modelling wave turbulence Need for models
Cloud-Scale Vertical Velocity and Turbulent Dissipation Rate Retrievals
Shupe, Matthew
2013-05-22T23:59:59.000Z
Time-height fields of retrieved in-cloud vertical wind velocity and turbulent dissipation rate, both retrieved primarily from vertically-pointing, Ka-band cloud radar measurements. Files are available for manually-selected, stratiform, mixed-phase cloud cases observed at the North Slope of Alaska (NSA) site during periods covering the Mixed-Phase Arctic Cloud Experiment (MPACE, late September through early November 2004) and the Indirect and Semi-Direct Aerosol Campaign (ISDAC, April-early May 2008). These time periods will be expanded in a future submission.
Cloud-Scale Vertical Velocity and Turbulent Dissipation Rate Retrievals
DOE Data Explorer [Office of Scientific and Technical Information (OSTI)]
Shupe, Matthew
Time-height fields of retrieved in-cloud vertical wind velocity and turbulent dissipation rate, both retrieved primarily from vertically-pointing, Ka-band cloud radar measurements. Files are available for manually-selected, stratiform, mixed-phase cloud cases observed at the North Slope of Alaska (NSA) site during periods covering the Mixed-Phase Arctic Cloud Experiment (MPACE, late September through early November 2004) and the Indirect and Semi-Direct Aerosol Campaign (ISDAC, April-early May 2008). These time periods will be expanded in a future submission.
Nazarenko, Sergey
Gravity Wave Turbulence in Wave Tanks: Space and Time Statistics Sergei Lukaschuk,1,* Sergey the first simultaneous space-time measurements for gravity wave turbulence in a large laboratory flume. We found that the slopes of k and ! wave spectra depend on wave intensity. This cannot be explained by any
Laminated Wave Turbulence: Generic Algorithms III
Elena Kartashova; Alexey Kartashov
2007-01-11T23:59:59.000Z
Model of laminated wave turbulence allows to study statistical and discrete layers of turbulence in the frame of the same model. Statistical layer is described by Zakharov-Kolmogorov energy spectra in the case of irrational enough dispersion function. Discrete layer is covered by some system(s) of Diophantine equations while their form is determined by wave dispersion function. This presents a very special computational challenge - to solve Diophantine equations in many variables, usually 6 to 8, in high degrees, say 16, in integers of order $10^{16}$ and more. Generic algorithms for solving this problem in the case of {\\it irrational} dispersion function have been presented in our previous papers. In this paper we present a new generic algorithm for the case of {\\it rational} dispersion functions. Special importance of this case is due to the fact that in wave systems with rational dispersion the statistical layer does not exist and the general energy transport is governed by the discrete layer alone.
Theory of High Frequency Acoustic Wave Scattering by Turbulent Flames
Lieuwen, Timothy C.
combustion processes that occur in a wide range of processing, power generating and propulsion applicationsTheory of High Frequency Acoustic Wave Scattering by Turbulent Flames TIM LIEUWEN* School an analysis of acoustic wave scattering by turbulent premixed flames with moving, convoluted fronts that have
Fluctuations of energy flux in wave turbulence Eric Falcon,1
Falcon, Eric
Fluctuations of energy flux in wave turbulence ´Eric Falcon,1 S´ebastien Auma^itre,2 Claudio Falc gravity and capillary wave turbulence in a statistically stationary regime displays fluctuations much interactions transfer kinetic energy toward small scales where viscous dissipation takes place
Toward a wave turbulence formulation of statistical nonlinear optics
Garnier, Josselin
Toward a wave turbulence formulation of statistical nonlinear optics Josselin Garnier,1, * Mietek optical waves have been reported in the literature. This article is aimed at providing a generalized wave, the process of optical wave thermalization to thermo- dynamic equilibrium, which slows down significantly
Wave-Turbulence Interactions in a Breaking Mountain Wave Craig Epifanio and Tingting Qian
#12;Dissipation of Mean Wave Energy · Mean wave energy E is just the total energy (kinetic + available · The dissipation of mean wave energy is caused by the turbulent momentum fluxes--specifically, by their tendency
Study of Nonlinear Interaction and Turbulence of Alfven Waves in LAPD Experiments
Boldyrev, Stanislav; Perez, Jean Carlos
2013-11-29T23:59:59.000Z
The complete project had two major goals — investigate MHD turbulence generated by counterpropagating Alfven modes, and study such processes in the LAPD device. In order to study MHD turbulence in numerical simulations, two codes have been used: full MHD, and reduced MHD developed specialy for this project. Quantitative numerical results are obtained through high-resolution simulations of strong MHD turbulence, performed through the 2010 DOE INCITE allocation. We addressed the questions of the spectrum of turbulence, its universality, and the value of the so-called Kolmogorov constant (the normalization coefficient of the spectrum). In these simulations we measured with unprecedented accuracy the energy spectra of magnetic and velocity fluctuations. We also studied the so-called residual energy, that is, the difference between kinetic and magnetic energies in turbulent fluctuations. In our analytic work we explained generation of residual energy in weak MHD turbulence, in the process of random collisions of counterpropagating Alfven waves. We then generalized these results for the case of strong MHD turbulence. The developed model explained generation of residual energy is strong MHD turbulence, and verified the results in numerical simulations. We then analyzed the imbalanced case, where more Alfven waves propagate in one direction. We found that spectral properties of the residual energy are similar for both balanced and imbalanced cases. We then compared strong MHD turbulence observed in the solar wind with turbulence generated in numerical simulations. Nonlinear interaction of Alfv´en waves has been studied in the upgraded Large Plasma Device (LAPD). We have simulated the collision of the Alfven modes in the settings close to the experiment. We have created a train of wave packets with the apltitudes closed to those observed n the experiment, and allowed them to collide. We then saw the generation of the second harmonic, resembling that observed in the experiment.
Wave turbulence revisited: Where does the energy flow?
L. V. Abdurakhimov; I. A. Remizov; A. A. Levchenko; G. V. Kolmakov; Y. V. Lvov
2014-04-03T23:59:59.000Z
Turbulence in a system of nonlinearly interacting waves is referred to as wave turbulence. It has been known since seminal work by Kolmogorov, that turbulent dynamics is controlled by a directional energy flux through the wavelength scales. We demonstrate that an energy cascade in wave turbulence can be bi-directional, that is, can simultaneously flow towards large and small wavelength scales from the pumping scales at which it is injected. This observation is in sharp contrast to existing experiments and wave turbulence theory where the energy flux only flows in one direction. We demonstrate that the bi-directional energy cascade changes the energy budget in the system and leads to formation of large-scale, large-amplitude waves similar to oceanic rogue waves. To study surface wave turbulence, we took advantage of capillary waves on a free, weakly charged surface of superfluid helium He-II at temperature 1.7K. Although He-II demonstrates non-classical thermomechanical effects and quantized vorticity, waves on its surface are identical to those on a classical Newtonian fluid with extremely low viscosity. The possibility of directly driving a charged surface by an oscillating electric field and the low viscosity of He-II have allowed us to isolate the surface dynamics and study nonlinear surface waves in a range of frequencies much wider than in experiments with classical fluids.
Internal wave energy radiated from a turbulent mixed layer
Munroe, James R., E-mail: jmunroe@mun.ca [Department of Physics and Physical Oceanography, Memorial University of Newfoundland, St. John's, Newfoundland A1B 3X7 (Canada); Sutherland, Bruce R., E-mail: bsuther@ualberta.ca [Departments of Physics and Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2R3 (Canada)
2014-09-15T23:59:59.000Z
We examine mixed-layer deepening and the generation of internal waves in stratified fluid resulting from turbulence that develops in response to an applied surface stress. In laboratory experiments the stress is applied over the breadth of a finite-length tank by a moving roughened conveyor belt. The turbulence in the shear layer is characterized using particle image velocimetry to measure the kinetic energy density. The internal waves are measured using synthetic schlieren to determine their amplitudes, frequencies, and energy density. We also perform fully nonlinear numerical simulations restricted to two dimensions but in a horizontally periodic domain. These clearly demonstrate that internal waves are generated by transient eddies at the integral length scale of turbulence and which translate with the background shear along the base of the mixed layer. In both experiments and simulations we find that the energy density of the generated waves is 1%–3% of the turbulent kinetic energy density of the turbulent layer.
Effect of turbulent velocity on the \\HI intensity fluctuation power spectrum from spiral galaxies
Dutta, Prasun
2015-01-01T23:59:59.000Z
We use numerical simulations to investigate effect of turbulent velocity on the power spectrum of \\HI intensity from external galaxies when (a) all emission is considered, (b) emission with velocity range smaller than the turbulent velocity dispersion is considered. We found that for case (a) the intensity fluctuation depends directly only on the power spectrum of the column density, whereas for case (b) it depends only on the turbulent velocity fluctuation. We discuss the implications of this result in real observations of \\HI fluctuations.
Crust and Upper Mantle P Wave Velocity Structure Beneath Valles...
Crust and Upper Mantle P Wave Velocity Structure Beneath Valles Caldera, New Mexico- Results from the Jemez Teleseismic Tomography Experiment Jump to: navigation, search OpenEI...
Soliton Turbulence in Shallow Water Ocean Surface Waves
Costa, Andrea; Resio, Donald T; Alessio, Silvia; Chrivì, Elisabetta; Saggese, Enrica; Bellomo, Katinka; Long, Chuck E
2014-01-01T23:59:59.000Z
We analyze shallow water wind waves in Currituck Sound, North Carolina and experimentally confirm, for the first time, the presence of $soliton$ $turbulence$ in ocean waves. Soliton turbulence is an exotic form of nonlinear wave motion where low frequency energy may also be viewed as a $dense$ $soliton$ $gas$, described theoretically by the soliton limit of the Korteweg-deVries (KdV) equation, a $completely$ $integrable$ $soliton$ $system$: Hence the phrase "soliton turbulence" is synonymous with "integrable soliton turbulence." For periodic/quasiperiodic boundary conditions the $ergodic$ $solutions$ of KdV are exactly solvable by $finite$ $gap$ $theory$ (FGT), the basis of our data analysis. We find that large amplitude measured wave trains near the energetic peak of a storm have low frequency power spectra that behave as $\\sim\\omega^{-1}$. We use the linear Fourier transform to estimate this power law from the power spectrum and to filter $densely$ $packed$ $soliton$ $wave$ $trains$ from the data. We apply ...
Wavefield Analysis of Rayleigh Waves for Near-Surface Shear-Wave Velocity
Zeng, Chong
2011-05-18T23:59:59.000Z
Shear (S)-wave velocity is a key property of near-surface materials and is the fundamental parameter for many environmental and engineering geophysical studies. Directly acquiring accurate S-wave velocities from a seismic ...
Spectral Cascade and Energy Dissipation in Kinetic Alfven Wave Turbulence
Lin, Zhihong
Spectral Cascade and Energy Dissipation in Kinetic Alfv´en Wave Turbulence Xi Cheng, Zhihong Lin energy sources at large spatial scales. The energy of these non- linearly interacting Alfven waves. 2000). The wave-particle energy exchange rates of these channels depend on the spectral properties near
Turbulent Flow and Transport Modeling by Long Waves and Currents
Kim, Dae Hong
2010-10-12T23:59:59.000Z
This dissertation presents models for turbulent flow and transport by currents and long waves in large domain. From the Navier-Stokes equations, a fully nonlinear depth-integrated equation model for weakly dispersive, ...
Weiss, M.; Zarzalis, N. [Division of Combustion Technology, Engler-Bunte-Institute, University of Karlsruhe (TH), Karlsruhe (Germany); Suntz, R. [Institute for Chemical Technology, University of Karlsruhe (TH), Karlsruhe (Germany)
2008-09-15T23:59:59.000Z
Effects of turbulent flame stretch on mean local laminar burning velocity of flamelets, u{sub n}, were investigated experimentally in an explosion vessel at normal temperature and pressure. In this context, the wrinkling, A{sub t}/A{sub l}, and the burning velocity, u{sub t}, of turbulent flames were measured simultaneously. With the flamelet assumption the mean local laminar burning velocity of flamelets, u{sub n}=u{sub t} x (A{sub t}/A{sub l}){sup -1}, was calculated for different turbulence intensities. The results were compared to the influence of stretch on spherically expanding laminar flames. For spherically expanding laminar flames the stretched laminar burning velocity, u{sub n}, varied linearly with the Karlovitz stretch factor, yielding Markstein numbers that depend on the mixture composition. Six different mixtures with positive and negative Markstein numbers were investigated. The measurements of the mean local laminar burning velocity of turbulent flamelets were used to derive an efficiency parameter, I, which reflects the impact of the Markstein number and turbulent flame stretch - expressed by the turbulent Karlovitz stretch factor - on the local laminar burning velocity of flamelets. The results showed that the efficiency is reduced with increasing turbulence intensity and the reduction can be correlated to unsteady effects. (author)
Surface Wave Enhanced Turbulence as an important source energy
;Surface wave energy input (mW/m/m, Wang & Huang, 2004) 9/15/2006 11 #12;Wind energy is more important: 1Surface Wave Enhanced Turbulence as an important source energy maintaining/regulating Thermohaline #12;New energetic theory of THC 1) Mechanical energy is required for overcoming friction/dissipation 2
P wave velocity variations in the Coso region, California, derived...
times Jump to: navigation, search OpenEI Reference LibraryAdd to library Journal Article: P wave velocity variations in the Coso region, California, derived from local earthquake...
The Turbulence Velocity Power Spectrum of Neutral Hydrogen in the Small Magellanic Cloud
Chepurnov, Alexey; Lazarian, Alex; Stanimirovic, Snezana
2015-01-01T23:59:59.000Z
We present the results of the Velocity Coordinate Spectrum (VCS) technique to calculate the velocity power spectrum of turbulence in the Small Magellanic Cloud (SMC) in 21cm emission. We have obtained a velocity spectral index of -3.85 and an injection scale of 2.3 kpc. The spectral index is steeper than the Kolmogorov index which is expected for shock-dominated turbulence which is in agreement with past works on the SMC gas dynamics. The injection scale of 2.3 kpc suggests that tidal interactions with the Large Magellanic Cloud are the dominate driver of turbulence in this dwarf galaxy. This implies turbulence maybe driven by multiple mechanisms in galaxies in addition to supernova injection and that galaxy-galaxy interactions may play an important role.
Estimating propagation velocity through a surface acoustic wave sensor
Xu, Wenyuan (Oakdale, MN); Huizinga, John S. (Dellwood, MN)
2010-03-16T23:59:59.000Z
Techniques are described for estimating the propagation velocity through a surface acoustic wave sensor. In particular, techniques which measure and exploit a proper segment of phase frequency response of the surface acoustic wave sensor are described for use as a basis of bacterial detection by the sensor. As described, use of velocity estimation based on a proper segment of phase frequency response has advantages over conventional techniques that use phase shift as the basis for detection.
Arctic sea ice velocity field: General circulation and turbulent-like fluctuations
Boyer, Edmond
that are activated intermittently within the ice pack. Citation: Rampal, P., J. Weiss, D. Marsan, and M. BourgoinArctic sea ice velocity field: General circulation and turbulent-like fluctuations P. Rampal,1,2 J the Arctic sea ice velocity field as the superposition of a mean field and fluctuations. We study how
Andrejczuk, M; Blyth, A
2015-01-01T23:59:59.000Z
This article discusses a potential impact of turbulent velocity fluctuations of the air on a drizzle formation in Cumulus clouds. Two different representations of turbulent velocity fluctuations for a microphysics formulated in a Lagrangian framework are discussed - random walk model and the interpolation, and its effect on microphysical properties of the cloud investigated. Turbulent velocity fluctuations significantly enhances velocity differences between colliding droplets, especially those having small sizes. As a result drizzle forms faster in simulations including a representation of turbulence. Both representations of turbulent velocity fluctuations, random walk and interpolation, have similar effect on droplet spectrum evolution, but interpolation of the velocity does account for a possible anisotropy in the air velocity. All discussed simulations show relatively large standard deviation ($\\sim$1${\\mu}m$) of the cloud droplet distribution from the onset of cloud formation is observed. Because coalesen...
Excitation of Langmuir wave turbulence in high-frequency (HF) pump waves over Gakona, Alaska
Rokusek, Daniel L
2007-01-01T23:59:59.000Z
(cont.) Investigated in this thesis are the excitation and observation of Langmuir wave turbulence caused by the parametric decay instability (PDI) in high-frequency space plasma heating experiments conducted at the NSF/DoD ...
Weak and strong wave turbulence spectra for elastic thin plate
Naoto Yokoyama; Masanori Takaoka
2013-02-15T23:59:59.000Z
Variety of statistically steady energy spectra in elastic wave turbulence have been reported in numerical simulations, experiments, and theoretical studies. Focusing on the energy levels of the system, we have performed direct numerical simulations according to the F\\"{o}ppl--von K\\'{a}rm\\'{a}n equation, and successfully reproduced the variability of the energy spectra by changing the magnitude of external force systematically. When the total energies in wave fields are small, the energy spectra are close to a statistically steady solution of the kinetic equation in the weak turbulence theory. On the other hand, in large-energy wave fields, another self-similar spectrum is found. Coexistence of the weakly nonlinear spectrum in large wavenumbers and the strongly nonlinear spectrum in small wavenumbers are also found in moderate energy wave fields.
Gradual eddy-wave crossover in superfluid turbulence
L'vov, Victor S; Rudenko, Oleksii
2008-01-01T23:59:59.000Z
We revise the theory of superfluid turbulence near the absolute zero of temperature and suggest a model with differential approximation for the energy fluxes in the k-space carried by the collective hydrodynamic motions of quantized vortex lines and by their individual uncorrelated motions known as Kelvin waves. The model predicts energy spectra of the hydrodynamic and the Kelvin waves components of the system, which experience a smooth crossover between different regimes of motion over a finite range of scales.
Gradual eddy-wave crossover in superfluid turbulence
Victor S. L'vov; Sergey V. Nazarenko; Oleksii Rudenko
2008-07-08T23:59:59.000Z
We revise the theory of superfluid turbulence near the absolute zero of temperature and suggest a model with differential approximation for the energy fluxes in the k-space carried by the collective hydrodynamic motions of quantized vortex lines and by their individual uncorrelated motions known as Kelvin waves. The model predicts energy spectra of the hydrodynamic and the Kelvin waves components of the system, which experience a smooth crossover between different regimes of motion over a finite range of scales.
Nonlocal resonances in weak turbulence of gravity-capillary waves
Quentin Aubourg; Nicolas Mordant
2015-03-13T23:59:59.000Z
We report a laboratory investigation of weak turbulence of water surface waves in the gravity-capillary crossover. By using time-space resolved profilometry and a bicoherence analysis, we observe that the nonlinear processes involve 3-wave resonant interactions. By studying the solutions of the resonance conditions we show that the nonlinear interaction is dominantly 1D and involves collinear wave vectors. Furthermore taking into account the spectral widening due to weak nonlinearity explains that nonlocal interactions are possible between a gravity wave and high frequency capillary ones. We observe also that nonlinear 3-wave coupling is possible among gravity waves and we raise the question of the relevance of this mechanism for oceanic waves.
"Fast" evolution of wave turbulence Victor Shrira & Sergei Annenkov
Fominov, Yakov
"Fast" evolution of wave turbulence Victor Shrira & Sergei Annenkov Department of Mathematics then its adjustment occurs on the "fast" (dynamical) -2 timescale, rather than the kinetic -4 timescale are NOT violated ? We show by DNS that the fast evolution still occurs. We generalize the KE to describe
On electromagnetic waves with a negative group velocity
Makarov, V. P.; Rukhadze, A. A.; Samokhin, A. A. [Russian Academy of Sciences, Prokhorov Institute of General Physics (Russian Federation)
2010-12-15T23:59:59.000Z
Recent publications devoted to the electrodynamics of media in which waves with a negative group velocity can exist are discussed. The properties of such waves have been studied from the beginning of the past century, and the most important results in this field were obtained by Soviet physicists in the 1940s-1950s. However, in most recent publications, this circumstance has not been taken into account.
Role of the basin boundary conditions in gravity wave turbulence
Luc Deike; Benjamin Miquel; Pablo Gutiérrez-Matus; Timothée Jamin; Benoit Semin; Sébastien Aumaitre; Michael Berhanu; Eric Falcon; Félicien BONNEFOY
2014-12-16T23:59:59.000Z
Gravity wave turbulence is studied experimentally in a large wave basin where irregular waves are generated unidirectionally. The role of the basin boundary conditions (absorbing or reflecting) and of the forcing properties are investigated. To that purpose, an absorbing sloping beach opposite to the wavemaker can be replaced by a reflecting vertical wall. We observe that the wave field properties depend strongly on these boundary conditions. Quasi-one dimensional field of nonlinear waves propagate before to be damped by the beach whereas a more multidirectional wave field is observed with the wall. In both cases, the wave spectrum scales as a frequency-power law with an exponent that increases continuously with the forcing amplitude up to a value close to -4, which is the value predicted by the weak turbulence theory. The physical mechanisms involved are probably different according to the boundary condition used, but cannot be easily discriminated with only temporal measurements. We have also studied freely decaying gravity wave turbulence in the closed basin. No self-similar decay of the spectrum is observed, whereas its Fourier modes decay first as a time power law due to nonlinear mechanisms, and then exponentially due to linear viscous damping. We estimate the linear, nonlinear and dissipative time scales to test the time scale separation that highlights the important role of a large scale Fourier mode. By estimation of the mean energy flux from the initial decay of wave energy, the Kolmogorov-Zakharov constant is evaluated and found to be compatible with a recent theoretical value.
Role of the basin boundary conditions in gravity wave turbulence
Luc Deike; Benjamin Miquel; Pablo Gutiérrez-Matus; Timothée Jamin; Benoit Semin; Michael Berhanu; Eric Falcon; Félicien Bonnefoy
2015-09-02T23:59:59.000Z
Gravity wave turbulence is studied experimentally in a large wave basin where irregular waves are generated unidirectionally. The role of the basin boundary conditions (absorbing or reflecting) and of the forcing properties are investigated. To that purpose, an absorbing sloping beach opposite to the wavemaker can be replaced by a reflecting vertical wall. We observe that the wave field properties depend strongly on these boundary conditions. Quasi-one dimensional field of nonlinear waves propagate before to be damped by the beach whereas a more multidirectional wave field is observed with the wall. In both cases, the wave spectrum scales as a frequency-power law with an exponent that increases continuously with the forcing amplitude up to a value close to -4, which is the value predicted by the weak turbulence theory. The physical mechanisms involved are probably different according to the boundary condition used, but cannot be easily discriminated with only temporal measurements. We have also studied freely decaying gravity wave turbulence in the closed basin. No self-similar decay of the spectrum is observed, whereas its Fourier modes decay first as a time power law due to nonlinear mechanisms, and then exponentially due to linear viscous damping. We estimate the linear, nonlinear and dissipative time scales to test the time scale separation that highlights the important role of a large scale Fourier mode. By estimation of the mean energy flux from the initial decay of wave energy, the Kolmogorov-Zakharov constant is evaluated and found to be compatible with a recent theoretical value.
Spectrum of Kelvin-wave turbulence in superfluids
Victor S. L'vov; Sergey Nazarenko
2010-02-03T23:59:59.000Z
We derive a type of kinetic equation for Kelvin waves on quantized vortex filaments with random large-scale curvature, that describes step-by-step (local) energy cascade over scales caused by 4-wave interactions. Resulting new energy spectrum $E\\Sb{LN}(k)\\propto k^{-5/3}$ must replace in future theory (e.g. in finding the quantum turbulence decay rate) the previously used spectrum $E\\Sb {KS}(k)\\propto k^{-7/5}$, which was recently shown to be inconsistent due to nonlocality of the 6-wave energy cascade.
VELOCITY FIELD OF A ROUND TURBULENT TRANSVERSE JET Suman Muppidi
Mahesh, Krishnan
- bulent jet in a laminar crossflow. The velocity ratio is 5.7 and the Reynolds number is 5000. Mean Jets in crossflow, also called `transverse jets' are defined as the flow field where a jet of fluid enters and interacts with a crossflowing fluid. Examples of jets in crossflow are fuel injectors
Turbulent velocity profiles in a tilted heat pipe J. Salort, X. Riedinger,
Paris-Sud XI, Université de
Turbulent velocity profiles in a tilted heat pipe J. Salort, X. Riedinger, E. Rusaouen, J the ther- mal behavior of a square heat pipe, depending on its inclination angle and the applied heat flux (stresses). Heat pipes, or gravital flows in vertical or inclined Also at College of Engineering
Enhanced turbulence due to the superposition of internal gravity waves and a coastal upwelling jet
Enhanced turbulence due to the superposition of internal gravity waves and a coastal upwelling jet instability. Yet enhanced turbulence is observed in the upwelling jet, typically as long, thin patches), Enhanced turbulence due to the superposition of internal gravity waves and a coastal upwelling jet, J
Compressional-wave and shear-wave velocities from long-spaced sonic waveforms
Lake, Leonard Cornelius
1986-01-01T23:59:59.000Z
COMPRESSIONAL-WAVE AND SHEAR-WAVE VELOCITIES FROM LONG- SPACED SONIC WAVEFORMS A Thesis LEONARD CORNELIUS LAKE Submitted to the Graduate College of Texas AdtM University in partial fulftllment of the requirements for thc degree of MASTER... OF SCIENCE Mav 19S6 Major Subject: Geophystcs COMPRESSIONAL-WAVE AND SHEAR-WAVE VELOCITIES FROM LONG- SPACED SONIC WAVEFORMS A Thesis LEONARD CORNELIUS LAKE Approved as to style and content by: erry W. neer (C)tairman of Commtttee) R bert. R. Unterb...
Turbulence and internal waves in numerical models of the equatorial undercurrents system
Pham, Hieu T.
2010-01-01T23:59:59.000Z
w ? field at t = 80; (b) Wave energy flux p ? w ? across thestress u ? w ? and (f) wave energy flux p ? w ? . Thefor dissipation of the internal wave energy by turbulence is
Turbulence and internal waves in numerical models of the equatorial undercurrents system
Pham, Hieu T.
2010-01-01T23:59:59.000Z
w ? field at t = 80; (b) Wave energy flux p ? w ? across thethe shear layer is wave energy and not turbulence. ) Thestress u ? w ? and (f) wave energy flux p ? w ? . The
Kowal, Grzegorz; Lazarian, A., E-mail: kowal@astro.wisc.ed, E-mail: lazarian@astro.wisc.ed [Department of Astronomy, University of Wisconsin, 475 North Charter Street, Madison, WI 53706 (United States)
2010-09-01T23:59:59.000Z
We study compressible magnetohydrodynamic turbulence, which holds the key to many astrophysical processes, including star formation and cosmic-ray propagation. To account for the variations of the magnetic field in the strongly turbulent fluid, we use wavelet decomposition of the turbulent velocity field into Alfven, slow, and fast modes, which presents an extension of the Cho and Lazarian decomposition approach based on Fourier transforms. The wavelets allow us to follow the variations of the local direction of the magnetic field and therefore improve the quality of the decomposition compared to the Fourier transforms, which are done in the mean field reference frame. For each resulting component, we calculate the spectra and two-point statistics such as longitudinal and transverse structure functions as well as higher order intermittency statistics. In addition, we perform a Helmholtz- Hodge decomposition of the velocity field into incompressible and compressible parts and analyze these components. We find that the turbulence intermittency is different for different components, and we show that the intermittency statistics depend on whether the phenomenon was studied in the global reference frame related to the mean magnetic field or in the frame defined by the local magnetic field. The dependencies of the measures we obtained are different for different components of the velocity; for instance, we show that while the Alfven mode intermittency changes marginally with the Mach number, the intermittency of the fast mode is substantially affected by the change.
Universal Velocity Profile for Coherent Vortices in Two-Dimensional Turbulence
M. Chertkov; I. Kolokolov; V. Lebedev
2009-12-29T23:59:59.000Z
Two-dimensional turbulence generated in a finite box produces large-scale coherent vortices coexisting with small-scale fluctuations. We present a rigorous theory explaining the $\\eta=1/4$ scaling in the $V\\propto r^{-\\eta}$ law of the velocity spatial profile within a vortex, where $r$ is the distance from the vortex center. This scaling, consistent with earlier numerical and laboratory measurements, is universal in its independence of details of the small-scale injection of turbulent fluctuations and details of the shape of the box.
Measurements of parallel electron velocity distributions using whistler wave absorption
Thuecks, D. J.; Skiff, F.; Kletzing, C. A. [Department of Physics and Astronomy, University of Iowa, 203 Van Allen Hall, Iowa City, Iowa 52242 (United States)
2012-08-15T23:59:59.000Z
We describe a diagnostic to measure the parallel electron velocity distribution in a magnetized plasma that is overdense ({omega}{sub pe} > {omega}{sub ce}). This technique utilizes resonant absorption of whistler waves by electrons with velocities parallel to a background magnetic field. The whistler waves were launched and received by a pair of dipole antennas immersed in a cylindrical discharge plasma at two positions along an axial background magnetic field. The whistler wave frequency was swept from somewhat below and up to the electron cyclotron frequency {omega}{sub ce}. As the frequency was swept, the wave was resonantly absorbed by the part of the electron phase space density which was Doppler shifted into resonance according to the relation {omega}-k{sub ||v||} = {omega}{sub ce}. The measured absorption is directly related to the reduced parallel electron distribution function integrated along the wave trajectory. The background theory and initial results from this diagnostic are presented here. Though this diagnostic is best suited to detect tail populations of the parallel electron distribution function, these first results show that this diagnostic is also rather successful in measuring the bulk plasma density and temperature both during the plasma discharge and into the afterglow.
Turbulent structure of high-density suspensions formed under waves Michael P. Lamb
; KEYWORDS: wave boundary layer, oscillatory, high-density suspension, fluid mud, turbulent kinetic energy on the interactions between turbulent wave boundary layers and a predominantly silt-sized sediment bed. Under a wide, and sediment concentration revealed that the wave boundary layer, while typically >1 cm thick in sediment
Paris-Sud XI, Université de
Gravity wave turbulence revealed by horizontal vibrations of the container B. Issenmann and E: December 20, 2012) We experimentally study the role of the forcing on gravity-capillary wave turbulence that the frequency power-law exponent of the gravity wave spectrum depends on the forcing parameters. By horizontally
Photospheric Logarithmic Velocity Spirals as MHD Wave Generation Mechanisms
Mumford, S J
2015-01-01T23:59:59.000Z
High-resolution observations of the solar photosphere have identified a wide variety of spiralling motions in the plasma. These spirals vary in properties, but are observed to be abundant on the solar surface. In this work these spirals are studied for their potential as magnetohydrodynamic (MHD) wave generation mechanisms. The inter-granular lanes, where these spirals are commonly observed, are also regions where the magnetic field strength is higher than average. This combination of magnetic field and spiralling plasma is a recipe for the generation of Alfv\\'en waves and other MHD waves. This work employs numerical simulations of a self-similar magnetic flux tube embedded in a realistic, gravitationally stratified, solar atmosphere to study the effects of a single magnetic flux tube perturbed by a logarithmic velocity spiral driver. The expansion factor of the logarithmic spiral driver is varied, multiple simulations are run for a range of values of the expansion factor centred around observational data. Th...
Stress-wave velocity of wood-based panels: Effect of moisture,
Stress-wave velocity of wood-based panels: Effect of moisture, product type, and material direction Guangping Han Qinglin Wu Xiping Wang Abstract The effect of moisture on longitudinal stress-wave veloc- ity, particleboard, and southern pine lumber was evaluated. It was shown that the stress-wave velocity decreased
Huynh, Long Quang
1994-01-01T23:59:59.000Z
An empirical model has been developed to predict the mean-velocity profile of a turbulent boundary layer under the influence of surface curvature. The model proposed is able to determine the profiles for both a convex and concave curvature...
Huynh, Long Quang
1994-01-01T23:59:59.000Z
An empirical model has been developed to predict the mean-velocity profile of a turbulent boundary layer under the influence of surface curvature. The model proposed is able to determine the profiles for both a convex and concave curvature...
TURBULENCE-INDUCED RELATIVE VELOCITY OF DUST PARTICLES. IV. THE COLLISION KERNEL
Pan, Liubin [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Padoan, Paolo, E-mail: lpan@cfa.harvard.edu, E-mail: ppadoan@icc.ub.edu [ICREA and Institut de Ciències del Cosmos, Universitat de Barcelona, IEEC-UB, Martí Franquès 1, E-08028 Barcelona (Spain)
2014-12-20T23:59:59.000Z
Motivated by its importance for modeling dust particle growth in protoplanetary disks, we study turbulence-induced collision statistics of inertial particles as a function of the particle friction time, ?{sub p}. We show that turbulent clustering significantly enhances the collision rate for particles of similar sizes with ?{sub p} corresponding to the inertial range of the flow. If the friction time, ?{sub p,} {sub h}, of the larger particle is in the inertial range, the collision kernel per unit cross section increases with increasing friction time, ?{sub p,} {sub l}, of the smaller particle and reaches the maximum at ?{sub p,} {sub l} = ?{sub p,} {sub h}, where the clustering effect peaks. This feature is not captured by the commonly used kernel formula, which neglects the effect of clustering. We argue that turbulent clustering helps alleviate the bouncing barrier problem for planetesimal formation. We also investigate the collision velocity statistics using a collision-rate weighting factor to account for higher collision frequency for particle pairs with larger relative velocity. For ?{sub p,} {sub h} in the inertial range, the rms relative velocity with collision-rate weighting is found to be invariant with ?{sub p,} {sub l} and scales with ?{sub p,} {sub h} roughly as ? ?{sub p,h}{sup 1/2}. The weighting factor favors collisions with larger relative velocity, and including it leads to more destructive and less sticking collisions. We compare two collision kernel formulations based on spherical and cylindrical geometries. The two formulations give consistent results for the collision rate and the collision-rate weighted statistics, except that the spherical formulation predicts more head-on collisions than the cylindrical formulation.
Parallel electric field generation by Alfven wave turbulence
Bian, N H; Brown, J C
2010-01-01T23:59:59.000Z
{This work aims to investigate the spectral structure of the parallel electric field generated by strong anisotropic and balanced Alfvenic turbulence in relation with the problem of electron acceleration from the thermal population in solar flare plasma conditions.} {We consider anisotropic Alfvenic fluctuations in the presence of a strong background magnetic field. Exploiting this anisotropy, a set of reduced equations governing non-linear, two-fluid plasma dynamics is derived. The low-$\\beta$ limit of this model is used to follow the turbulent cascade of the energy resulting from the non-linear interaction between kinetic Alfven waves, from the large magnetohydrodynamics (MHD) scales with $k_{\\perp}\\rho_{s}\\ll 1$ down to the small "kinetic" scales with $k_{\\perp}\\rho_{s} \\gg 1$, $\\rho_{s}$ being the ion sound gyroradius.} {Scaling relations are obtained for the magnitude of the turbulent electromagnetic fluctuations, as a function of $k_{\\perp}$ and $k_{\\parallel}$, showing that the electric field develops ...
Enhanced Turbulence due to the Superposition of Internal Gravity Waves and a Coastal Upwelling Jet
Enhanced Turbulence due to the Superposition of Internal Gravity Waves and a Coastal Upwelling Jet to shear instability. Yet, enhanced turbulence is observed in the upwelling jet, typically as long, thin), the latter during upwelling conditions (summer). Linear internal gravity waves (IGW) also have significant
Geddes, Cameron Guy Robinson
Warm wave breaking of nonlinear plasma waves with arbitrary phase velocities C. B. Schroeder, E, collisionless plasma is developed to analyze nonlinear plasma waves excited by intense drive beams. The maximum amplitude and wavelength are calculated for nonrelativistic plasma temperatures and arbitrary plasma wave
Anomalous shear wave delays and surface wave velocities at Yellowstone Caldera, Wyoming
Daniel, R.G.; Boore, D.M.
1982-04-10T23:59:59.000Z
To investigate the effects of a geothermal area on the propagation of intermediate-period (1--30 s) teleseismic body waves and surface waves, a specially designed portable seismograph system was operated in Yellowstone Caldera, Wyoming. Travel time residuals, relative to a station outside the caldera, of up to 2 s for compressional phases are in agreement with short-period residuals for P phases measured by other investigators. Travel time delays for shear arrivals in the intermediate-period band range from 2 to 9 s and decrease with increasing dT/d..delta... Measured Rayleigh wave phase velocities are extremely low, ranging from 3.2 km/s at 27-s period to 2.0 km/s at 7-s period; the estimated uncertainty associated with these values is 15%. We propose a model for compressional and shear velocities and Poisson's ratio beneath the Yellowstone caldera which fits the teleseismic body and surface wave data: it consists of a highly anomalous crust with an average shear velocity of 3.0 km/s overlying an upper mantle with average velocity of 4.1 km/s. The high average value of Poisson's ratio in the crust (0.34) suggests the presence of fluids there; Poisson's ratio in the mantle between 40 and approximately 200 km is more nearly normal (0.29) than in the crust. A discrepancy between normal values of Poisson's ratio in the crust calculated from short-period data and high values calculated from teleseismic data can be resolved by postulating a viscoelastic crustal model with frequency-dependent shear velocity and attenuation.
Statistical analysis of the velocity and scalar fields in reacting turbulent wall-jets
Z. Pouransari; L. Biferale; A. V. Johansson
2015-02-21T23:59:59.000Z
The concept of local isotropy in a chemically reacting turbulent wall-jet flow is addressed using direct numerical simulation (DNS) data. Different DNS databases with isothermal and exothermic reactions are examined. The chemical reaction and heat release effects on the turbulent velocity, passive scalar and reactive species fields are studied using their probability density functions (PDF) and higher order moments for velocities and scalar fields, as well as their gradients. With the aid of the anisotropy invariant maps for the Reynolds stress tensor the heat release effects on the anisotropy level at different wall-normal locations are evaluated and found to be most accentuated in the near-wall region. It is observed that the small-scale anisotropies are persistent both in the near-wall region and inside the jet flame. Two exothermic cases with different Damkohler number are examined and the comparison revealed that the Damkohler number effects are most dominant in the near-wall region, where the wall cooling effects are influential. In addition, with the aid of PDFs conditioned on the mixture fraction, the significance of the reactive scalar characteristics in the reaction zone is illustrated. We argue that the combined effects of strong intermittency and strong persistency of anisotropy at the small scales in the entire domain can affect mixing and ultimately the combustion characteristics of the reacting flow.
Statistical analysis of the velocity and scalar fields in reacting turbulent wall-jets
Pouransari, Z; Johansson, A V
2015-01-01T23:59:59.000Z
The concept of local isotropy in a chemically reacting turbulent wall-jet flow is addressed using direct numerical simulation (DNS) data. Different DNS databases with isothermal and exothermic reactions are examined. The chemical reaction and heat release effects on the turbulent velocity, passive scalar and reactive species fields are studied using their probability density functions (PDF) and higher order moments for velocities and scalar fields, as well as their gradients. With the aid of the anisotropy invariant maps for the Reynolds stress tensor the heat release effects on the anisotropy level at different wall-normal locations are evaluated and found to be most accentuated in the near-wall region. It is observed that the small-scale anisotropies are persistent both in the near-wall region and inside the jet flame. Two exothermic cases with different Damkohler number are examined and the comparison revealed that the Damkohler number effects are most dominant in the near-wall region, where the wall cooli...
Fourier analysis of wave turbulence in a thin elastic plate
Nicolas Mordant
2010-06-18T23:59:59.000Z
The spatio-temporal dynamics of the deformation of a vibrated plate is measured by a high speed Fourier transform profilometry technique. The space-time Fourier spectrum is analyzed. It displays a behavior consistent with the premises of the Weak Turbulence theory. A isotropic continuous spectrum of waves is excited with a non linear dispersion relation slightly shifted from the linear dispersion relation. The spectral width of the dispersion relation is also measured. The non linearity of this system is weak as expected from the theory. Finite size effects are discussed. Despite a qualitative agreement with the theory, a quantitative mismatch is observed which origin may be due to the dissipation that ultimately absorbs the energy flux of the Kolmogorov-Zakharov casade.
HIERARCHICAL STRUCTURE OF MAGNETOHYDRODYNAMIC TURBULENCE IN POSITION-POSITION-VELOCITY SPACE
Burkhart, Blakesley; Lazarian, A. [Astronomy Department, University of Wisconsin, Madison, 475 N. Charter St., WI 53711 (United States); Goodman, Alyssa [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-78, Cambridge, MA 02138 (United States); Rosolowsky, Erik [University of British Columbia, Okanagan Campus, 3333 University Way, Kelowna BC V1V 1V7 (Canada)
2013-06-20T23:59:59.000Z
Magnetohydrodynamic turbulence is able to create hierarchical structures in the interstellar medium (ISM) that are correlated on a wide range of scales via the energy cascade. We use hierarchical tree diagrams known as dendrograms to characterize structures in synthetic position-position-velocity (PPV) emission cubes of isothermal magnetohydrodynamic turbulence. We show that the structures and degree of hierarchy observed in PPV space are related to the presence of self-gravity and the global sonic and Alfvenic Mach numbers. Simulations with higher Alfvenic Mach number, self-gravity and supersonic flows display enhanced hierarchical structure. We observe a strong dependency on the sonic and Alfvenic Mach numbers and self-gravity when we apply the statistical moments (i.e., mean, variance, skewness, kurtosis) to the leaf and node distribution of the dendrogram. Simulations with self-gravity, larger magnetic field and higher sonic Mach number have dendrogram distributions with higher statistical moments. Application of the dendrogram to three-dimensional density cubes, also known as position-position-position (PPP) cubes, reveals that the dominant emission contours in PPP and PPV are related for supersonic gas but not for subsonic. We also explore the effects of smoothing, thermal broadening, and velocity resolution on the dendrograms in order to make our study more applicable to observational data. These results all point to hierarchical tree diagrams as being a promising additional tool for studying ISM turbulence and star forming regions for obtaining information on the degree of self-gravity, the Mach numbers and the complicated relationship between PPV and PPP data.
Falcon, Eric
Fluctuations of the Energy Flux in Wave Turbulence S. Auma^itre , E. Falcon,§ and S. Fauve SPEC, DSM, CEA.falcon@univ-paris-diderot.fr The key governing parameter of wave turbulence is the energy flux that drives the waves and cascades of energy among different scales through the weak interaction between waves. It was understood first
Three-dimensional P and S waves velocity structures of the Coso...
search OpenEI Reference LibraryAdd to library Journal Article: Three-dimensional P and S waves velocity structures of the Coso geothermal area, California, from...
Falcon, Eric
2014-01-01T23:59:59.000Z
energy flux are in good agreement with wave turbulence theory. The Kolmogorov-Zakharov constant waves interact with each other, they can develop a regime of wave turbulence where the wave energyPHYSICAL REVIEW E 89, 023003 (2014) Energy flux measurement from the dissipated energy in capillary
Abdou, Mohamed
turbulent open channel water flows B. Freeze, S. Smolentsev *, N. Morley, M. Abdou UCLA, Department Abstract Interfacial heat transport in open channel turbulent flows is strongly dependent on surface waves and mass transport across a flowing liquid interface has become an increasingly important topic during
Turbulence and internal waves in tidal flow over topography
Gayen, Bishakhdatta
2012-01-01T23:59:59.000Z
M. C. 2006 An estimate of tidal energy lost to turbulence atcant loss of low-mode tidal energy at 28.9 ? . Geophys. Res.of turbulent kinetic energy over a tidal cycle. Maximum T KE
Investigations of the cascade of Langmuir wave turbulence over HAARP Observatory in Gakona, Alaska
Burton, Laura M
2007-01-01T23:59:59.000Z
This thesis investigates the cascade lines from Langmuir wave turbulence as a result of Parametric Decay Instability (PDI) in the ionosphere. This effect is studied using a high-frequency (HF) heater located at the NSF/DoD ...
Wave Turbulence on the Surface of a Ferrofluid in a Magnetic Field Francois Boyer and Eric Falcon*
Falcon, Eric
Wave Turbulence on the Surface of a Ferrofluid in a Magnetic Field Franc¸ois Boyer and Eric Falcon the observation of wave turbulence on the surface of a ferrofluid mechanically forced and submitted to a static normal magnetic field. We show that magnetic surface waves arise only above a critical field. The power
Paris-Sud XI, Université de
Wave turbulence on the surface of a ferrofluid submitted to a magnetic field Fran¸cois Boyer the observation of wave turbulence on the surface of a ferrofluid mechanically forced and submitted to a static normal magnetic field. We show that magnetic surface waves arise only above a critical field. The power
Medium-induced jet evolution: wave turbulence and energy loss
Leonard Fister; Edmond Iancu
2014-09-06T23:59:59.000Z
We study the gluon cascade generated via successive medium-induced branchings by an energetic parton propagating through a dense QCD medium. We focus on the high-energy regime where the energy $E$ of the leading particle is much larger than the characteristic medium scale $\\omega_c=\\hat q L^2/2$, with $\\hat q$ the jet quenching parameter and $L$ the distance travelled through the medium. In this regime the leading particle loses only a small fraction $\\sim\\alpha_s(\\omega_c/E)$ of its energy and can be treated as a steady source of radiation for gluons with energies $\\omega\\le\\omega_c$. For this effective problem with a source, we obtain exact analytic solutions for the gluon spectrum and the energy flux. The solutions exhibit wave turbulence: the basic physical process is a continuing fragmentation which is `quasi-democratic' (i.e. quasi-local in energy) and which provides an energy transfer from the source to the medium at a rate (the energy flux $\\mathcal{F}$) which is quasi-independent of $\\omega$. The locality of the branching process implies a spectrum of the Kolmogorov-Obukhov type, i.e. a power-law spectrum which is a fixed point of the branching process and whose strength is proportional to the energy flux: $D(\\omega)\\sim\\mathcal{F}/\\sqrt\\omega$ for $\\omega\\ll\\omega_c$. Via this turbulent flow, the gluon cascade loses towards the medium an energy $\\Delta E\\sim\\alpha_s^2\\omega_c$, which is independent of the initial energy $E$ of the leading particle and of the details of the thermalization mechanism at the low-energy end of the cascade. This energy is carried away by very soft gluons, which propagate at very large angles with respect to the jet axis. Our predictions for the value of $\\Delta E$ and for its angular distribution appear to agree quite well, qualitatively and even semi-quantitatively, with the phenomenology of di-jet asymmetry in nucleus-nucleus collisions at the LHC.
Preventing transition to turbulence using streamwise traveling waves: theoretical analysis
Jovanovic, Mihailo
. INTRODUCTION Fluid motion is usually classified as either laminar or turbulent; flows that are smooth force on a vehicle moving through a fluid in the laminar regime. Sensorless flow control represents and ordered (laminar) may become complex and disordered (turbulent) as the flow strength increases
MAGNETOHYDRODYNAMIC WAVES AND CORONAL HEATING: UNIFYING EMPIRICAL AND MHD TURBULENCE MODELS
Sokolov, Igor V.; Van der Holst, Bart; Oran, Rona; Jin, Meng; Manchester, Ward B. IV; Gombosi, Tamas I. [Department of AOSS, University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109 (United States)] [Department of AOSS, University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109 (United States); Downs, Cooper [Predictive Science Inc., 9990 Mesa Rim Road, Suite 170, San Diego, CA 92121 (United States)] [Predictive Science Inc., 9990 Mesa Rim Road, Suite 170, San Diego, CA 92121 (United States); Roussev, Ilia I. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States)] [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Evans, Rebekah M., E-mail: igorsok@umich.edu [NASA Goddard Space Flight Center, Space Weather Lab, 8800 Greenbelt Road, Greenbelt, MD 20771 (United States)
2013-02-10T23:59:59.000Z
We present a new global model of the solar corona, including the low corona, the transition region, and the top of the chromosphere. The realistic three-dimensional magnetic field is simulated using the data from the photospheric magnetic field measurements. The distinctive feature of the new model is incorporating MHD Alfven wave turbulence. We assume this turbulence and its nonlinear dissipation to be the only momentum and energy source for heating the coronal plasma and driving the solar wind. The difference between the turbulence dissipation efficiency in coronal holes and that in closed field regions is because the nonlinear cascade rate degrades in strongly anisotropic (imbalanced) turbulence in coronal holes (no inward propagating wave), thus resulting in colder coronal holes, from which the fast solar wind originates. The detailed presentation of the theoretical model is illustrated with the synthetic images for multi-wavelength EUV emission compared with the observations from SDO AIA and STEREO EUVI instruments for the Carrington rotation 2107.
Electromagnetic plane waves with negative phase velocity in charged black strings
Sharif, M., E-mail: msharif.math@pu.edu.pk; Manzoor, R., E-mail: rubabmanzoor9@yahoo.com [University of the Punjab, Department of Mathematics (Pakistan)
2013-02-15T23:59:59.000Z
We investigate the propagation regions of electromagnetic plane waves with negative phase velocity in the ergosphere of static charged black strings. For such a propagation, some conditions for negative phase velocity are established that depend on the metric components and the choice of the octant. We conclude that these conditions remain unaffected by the negative values of the cosmological constant.
Wave-induced velocities inside a model seagrass bed
Luhar, Mitul
Laboratory measurements reveal the flow structure within and above a model seagrass meadow (dynamically similar to Zostera marina) forced by progressive waves. Despite being driven by purely oscillatory flow, a mean current ...
The life-cycle of drift-wave turbulence driven by small scale instability
Colm Connaughton; Sergey Nazarenko; Brenda Quinn
2010-12-16T23:59:59.000Z
We demonstrate theoretically and numerically the zonal-flow/drift-wave feedback mechanism for the LH transition in an idealised model of plasma turbulence driven by a small scale instability. Zonal flows are generated by a secondary modulational instability of the modes which are directly driven by the primary instability. The zonal flows then suppress the small scales thereby arresting the energy injection into the system, a process which can be described using nonlocal wave turbulence theory. Finally, the arrest of the energy input results in saturation of the zonal flows at a level which can be estimated from the theory and the system reaches stationarity without damping of the large scales.
Integrated Study of the Nonlinear Dynamics of Collisional Drift Wave Turbulence
George R. Tynan
2012-04-24T23:59:59.000Z
An existing linear magnetized plasma device, the Controlled Shear Decorrelation experiment (CSDX) was used to study the transition from a state of coherent wave like activity to a state of turbulent activity using the magnetic field and thus magnetization of the plasma as the control parameter. The results show the onset of coherent drift waves consistent with linear stability analysis. As the magnetization is raised, at first multiple harmonics appear, consistent with wave steepening. This period is then followed by the beginning of nonlinear interactions between different wave modes, which then results in the formation of narrow frequency but distributed azimuthal wave number fluctuations that are consistent with the formation of long-lived coherent nonlinear structures within the plasmas. These structures, termed quasicoherent modes, persist as the magnetic field is raised. Measurements of turbulent momentum flux indicate that the plasma is also forming an azimuthally symmetric radially sheared fluid flow that is nonlinearly driven by smaller scaled turbulent fluctuations. Further increases in the magnetic field result in the breakup of the quasicoherent mode, and the clear formation of the sheared flow. Numerical simulations of the experiment reproduce the formation of the sheared flow via a vortex merging process, and confirm that the experiment is providing the first clear experimental evidence of the formation of sheared zonal flows from drift turbulent fluctuations in a magnetized plasma.
Compressible Turbulence and Interactions with Shock Waves and...
Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)
problems in various disciplines, including supernova explosions, inertial confinement fusion, hypersonic flight and propulsion, and shock wave lithotripsy....
Wave-Turbulence Mixing for Upper Ocean Multifractal Thermal
Chu, Peter C.
) width ~ 0.8 km #12;Data Observation · Coastal Monitoring Buoy (CMB) - U.S. Naval Oceanographic Office) Frequency is around 4 CPH #12;Isopycnal Displacement turbulence-Dominated (00-05 GMT Aug 1) #12;Power depth #12;Structure Function (Power Law) IW-T type #12;Structure Function (Power Law) T type #12
Extensional wave attenuation and velocity in partially-saturated sand in the sonic frequency range
Liu, Z.; Rector, J.W.; Nihei, K.T.; Tomutsa, L.; Myer, L.R.; Nakagawa, S.
2002-06-17T23:59:59.000Z
Extensional wave attenuation and velocity measurements on a high permeability Monterey sand were performed over a range of gas saturations for imbibition and degassing conditions. These measurements were conducted using extensional wave pulse propagation and resonance over a 1 - 9 kHz frequency range for a hydrostatic confining pressure of 8.3 MPa. Analysis of the extensional wave data and the corresponding X-ray CT images of the gas saturation show strong attenuation resulting from the presence of the gas (QE dropped from 300 for the dry sand to 30 for the partially-saturated sand), with larger attenuation at a given saturation resulting from heterogeneous gas distributions. The extensional wave velocities are in agreement with Gassmann theory for the test with near-homogeneous gas saturation and with a patchy saturation model for the test with heterogeneous gas saturation. These results show that partially-saturated sands under moderate confining pressure can produce strong intrinsic attenuation for extensional waves.
Excitation of solitons by an external resonant wave with a slowly varying phase velocity
Aranson, I.; Meerson, B. [Hebrew Univ., Jerusalem (Israel). Racah Inst. of Physics; Tajima, Toshiki [Texas Univ., Austin, TX (United States)
1992-02-01T23:59:59.000Z
A novel mechanism is proposed for the excitation of solitons in nonlinear dispersive media. The mechanism employs an external pumping wave with a varying phase velocity, which provides a continuous resonant excitation of a nonlinear wave in the medium. Two different schemes of a continuous resonant growth (continuous phase-locking) of the induced nonlinear wave are suggested. The first of them requires a definite time dependence of the pumping wave phase velocity and is relatively sensitive to the initial wave phase. The second employs the dynamic autoresonance effect and is insensitive to the exact time dependence of the pumping wave phase velocity. It is demonstrated analytically and numerically, for a particular example of a driven Korteweg-de Vries (KdV) equation with periodic boundary conditions, that as the nonlinear wave grows, it transforms into a soliton, which continues growing and accelerating adiabatically. A fully nonlinear perturbation theory is developed for the driven KdV equation to follow the growing wave into the strongly nonlinear regime and describe the soliton formation.
A Two-component Transport Model for Solar Wind Fluctuations: Waves plus Quasi-2D Turbulence
Oughton, Sean
component. Thus, it would seem appropriate, and advantageous, to develop an energy-containing style modelA Two-component Transport Model for Solar Wind Fluctuations: Waves plus Quasi-2D Turbulence Sean for the transport of solar wind fluctuations, based on the assumption that they can be well-represented using two
Internal wave energy radiated from a turbulent mixed layer James R. Munroe1, a)
Sutherland, Bruce
Internal wave energy radiated from a turbulent mixed layer James R. Munroe1, a) and Bruce R in the shear layer is characterized using particle image velocimetry to measure the kinetic energy den- sity, and energy density. We also perform fully nonlinear numer- ical simulations restricted to two dimensions
Turbulent combined wave-current boundary layer model for application in coastal waters
Humbyrd, Chelsea Joy
2012-01-01T23:59:59.000Z
Accurately predicting transport processes, including sediment transport, in the coastal environment is impossible without correct current velocity and shear stress information. A combined wave-current boundary layer theory ...
PDF of velocity and turbulent frequency or the joint PDF of velocity, wave vector, and turbulent implemented in conjunction with several velocity models. The complete model yields good comparisons and reaction are treated without mod- eling assumption [3, 4]. In contrast, standard moment closure methods
Kinetic Alfvén wave turbulence and formation of localized structures
Sharma, R. P. [Centre for Energy Studies, Indian Institute of Technology Delhi, Delhi 110016 (India)] [Centre for Energy Studies, Indian Institute of Technology Delhi, Delhi 110016 (India); Modi, K. V. [Centre for Energy Studies, Indian Institute of Technology Delhi, Delhi 110016 (India) [Centre for Energy Studies, Indian Institute of Technology Delhi, Delhi 110016 (India); Mechanical Engineering Department, Government Engineering College Valsad, Gujarat 396001 (India)
2013-08-15T23:59:59.000Z
This work presents non-linear interaction of magnetosonic wave with kinetic Alfvén wave for intermediate ?-plasma (m{sub e}/m{sub i}???1). A set of dimensionless equations have been developed for analysis by considering ponderomotive force due to pump kinetic Alfvén wave in the dynamics of magnetosonic wave. Stability analysis has been done to study modulational instability or linear growth rate. Further, numerical simulation has been carried out to study the nonlinear stage of instability and resulting power spectrum applicable to solar wind around 1 AU. Due to the nonlinearity, background density of magnetosonic wave gets modified which results in localization of kinetic Alfvén wave. From the obtained results, we observed that spectral index follows k{sup ?3.0}, consistent with observation received by Cluster spacecraft for the solar wind around 1 AU. The result shows the steepening of power spectrum which may be responsible for heating and acceleration of plasma particles in solar wind.
Turbulence and internal waves in tidal flow over topography
Gayen, Bishakhdatta
2012-01-01T23:59:59.000Z
Flow over sloping topography including streamwise vari-5 Flow over sloping topography without streamwise vari-of internal waves at sloping topography. Here, C p denotes
Asgari-Targhi, M.; Van Ballegooijen, A. A. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street MS-15, Cambridge, MA 02138 (United States)
2012-02-10T23:59:59.000Z
It has been suggested that the solar corona may be heated by dissipation of Alfven waves that propagate up from the solar photosphere. According to this theory, counterpropagating Alfven waves are subject to nonlinear interactions that lead to turbulent decay of the waves and heating of the chromospheric and coronal plasma. To test this theory, better models for the dynamics of Alfven waves in coronal loops are required. In this paper, we consider wave heating in an active region observed with the Solar Dynamics Observatory in 2010 May. First a three-dimensional (3D) magnetic model of the region is constructed, and ten magnetic field lines that match observed coronal loops are selected. For each loop we construct a 3D magnetohydrodynamic model of the Alfven waves near the selected field line. The waves are assumed to be generated by footpoint motions inside the kilogauss magnetic flux elements at the two ends of the loop. Based on such models, we predict the spatial and temporal profiles of the heating along the selected loops. We also estimate the temperature fluctuations resulting from such heating. We find that the Alfven wave turbulence model can reproduce the observed characteristics of the hotter loops in the active region core, but the loops at the periphery of the region have large expansion factors and are predicted to be thermally unstable.
Electromagnetic wave propagation with negative phase velocity in regular black holes
Sharif, M., E-mail: msharif.math@pu.edu.pk; Manzoor, R., E-mail: rubabmanzoor9@yahoo.com [University of the Punjab, Department of Mathematics (Pakistan)
2012-12-15T23:59:59.000Z
We discuss the propagation of electromagnetic plane waves with negative phase velocity in regular black holes. For this purpose, we consider the Bardeen model as a nonlinear magnetic monopole and the Bardeen model coupled to nonlinear electrodynamics with a cosmological constant. It turns out that the region outside the event horizon of each regular black hole does not support negative phase velocity propagation, while its possibility in the region inside the event horizon is discussed.
Basile Gallet; Sergey Nazarenko; Bérengère Dubrulle
2015-04-21T23:59:59.000Z
In field theory, particles are waves or excitations that propagate on the fundamental state. In experiments or cosmological models one typically wants to compute the out-of-equilibrium evolution of a given initial distribution of such waves. Wave Turbulence deals with out-of-equilibrium ensembles of weakly nonlinear waves, and is therefore well-suited to address this problem. As an example, we consider the complex Klein-Gordon equation with a Mexican-hat potential. This simple equation displays two kinds of excitations around the fundamental state: massive particles and massless Goldstone bosons. The former are waves with a nonzero frequency for vanishing wavenumber, whereas the latter obey an acoustic dispersion relation. Using wave turbulence theory, we derive wave kinetic equations that govern the coupled evolution of the spectra of massive and massless waves. We first consider the thermodynamic solutions to these equations and study the wave condensation transition, which is the classical equivalent of Bose-Einstein condensation. We then focus on nonlocal interactions in wavenumber space: we study the decay of an ensemble massive particles into massless ones. Under rather general conditions, these massless particles accumulate at low wavenumber. We study the dynamics of waves coexisting with such a strong condensate, and we compute rigorously a nonlocal Kolmogorov-Zakharov solution, where particles are transferred non-locally to the condensate, while energy cascades towards large wave numbers through local interactions. This nonlocal cascading state constitute the intermediate asymptotics between the initial distribution of waves and the thermodynamic state reached in the long-time limit.
Non-Gaussian properties of second-order wave orbital velocity
Alberello, Alberto; Gramstad, Odin; Babanin, Alexander V; Toffoli, Alessandro
2015-01-01T23:59:59.000Z
A stochastic second-order wave model is applied to assess the statistical properties of wave orbital velocity in random sea states below the water surface. Directional spreading effects as well as the dependency of the water depth are investigated by means of a Monte-Carlo approach. Unlike for the surface elevation, sub-harmonics dominate the second-order contribution to orbital velocity. We show that a notable set-down occurs for the most energetic and steepest groups. This engenders a negative skewness in the temporal evolution of the orbital velocity. A substantial deviation of the upper and lower tails of the probability density function from the Gaussian distribution is noticed, velocities are faster below the wave trough and slower below the wave crest when compared with linear theory predictions. Second-order nonlinearity effects strengthen with reducing the water depth, while weaken with the broadening of the wave spectrum. The results are confirmed by laboratory data. Corresponding experiments have b...
Van Nguyen, Linh; Chainais, Pierre
2015-01-01T23:59:59.000Z
The study of turbulent flows calls for measurements with high resolution both in space and in time. We propose a new approach to reconstruct High-Temporal-High-Spatial resolution velocity fields by combining two sources of information that are well-resolved either in space or in time, the Low-Temporal-High-Spatial (LTHS) and the High-Temporal-Low-Spatial (HTLS) resolution measurements. In the framework of co-conception between sensing and data post-processing, this work extensively investigates a Bayesian reconstruction approach using a simulated database. A Bayesian fusion model is developed to solve the inverse problem of data reconstruction. The model uses a Maximum A Posteriori estimate, which yields the most probable field knowing the measurements. The DNS of a wall-bounded turbulent flow at moderate Reynolds number is used to validate and assess the performances of the present approach. Low resolution measurements are subsampled in time and space from the fully resolved data. Reconstructed velocities ar...
Guido Ciraolo; Cristel Chandre; Ricardo Lima; Marco Pettini; Michel Vittot
2006-07-31T23:59:59.000Z
In this article we present an application of a method of control of Hamiltonian systems to the chaotic velocity diffusion of a cold electron beam interacting with electrostatic waves. We numerically show the efficiency and robustness of the additional small control term in restoring kinetic coherence of the injected electron beam.
Variation of seismic-wave velocities in westerly granite under stress
Al-Shaibani, Abdulaziz Muhareb
1994-01-01T23:59:59.000Z
stresses and about 3% along the direction of the minimum stresses and showed an anisotropy of about 6%. The shear-wave velocity increased by different amounts in different directions. The amount of increase ranged from 3.4% to about 6%. The anisotropy in S...
perovskite phase suggests slow longitudinal elastic-wave velocities propagating along the
Hansell, Dennis
perovskite phase suggests slow longitudinal elastic-wave velocities propagating along the [010] direction. In addition, it is also inferred that the post-perovskite phase forms a platy crystal habit) observed in the D region (1, 2) is possibly caused by the preferred orientation of the post-perovskite
Inversion of OBC seismic data for P- and S-wave velocities.
Hall, Guy R
using cubic polynomials. The output of the processing flow are P- and S- wave interval-velocity in depth models that can be used for pre-depth stack migration. The processing scheme I develop is very simple compared with traditional schemes...
Julia, J; Nyblade, A; Hansen, S; Rodgers, A; Matzel, E
2009-07-06T23:59:59.000Z
In this project, we are developing models of lithospheric structure for a wide variety of tectonic regions throughout Eurasia and the Middle East by regionalizing 1D velocity models obtained by jointly inverting P-wave and S-wave receiver functions with Rayleigh wave group and phase velocities. We expect the regionalized velocity models will improve our ability to predict travel-times for local and regional phases, such as Pg, Pn, Sn and Lg, as well as travel-times for body-waves at upper mantle triplication distances in both seismic and aseismic regions of Eurasia and the Middle East. We anticipate the models will help inform and strengthen ongoing and future efforts within the NNSA labs to develop 3D velocity models for Eurasia and the Middle East, and will assist in obtaining model-based predictions where no empirical data are available and for improving locations from sparse networks using kriging. The codes needed to conduct the joint inversion of P-wave receiver functions (PRFs), S-wave receiver functions (SRFs), and dispersion velocities have already been assembled as part of ongoing research on lithospheric structure in Africa. The methodology has been tested with synthetic 'data' and case studies have been investigated with data collected at an open broadband stations in South Africa. PRFs constrain the size and S-P travel-time of seismic discontinuities in the crust and uppermost mantle, SRFs constrain the size and P-S travel-time of the lithosphere-asthenosphere boundary, and dispersion velocities constrain average S-wave velocity within frequency-dependent depth-ranges. Preliminary results show that the combination yields integrated 1D velocity models local to the recording station, where the discontinuities constrained by the receiver functions are superimposed to a background velocity model constrained by the dispersion velocities. In our first year of this project we will (i) generate 1D velocity models for open broadband seismic stations in the western half of the study area (Eurasia and the Middle East) and (ii) identify well located seismic events with event-station paths isolated to individual tectonic provinces within the study area and collect broadband waveforms and source parameters for the selected events. The 1D models obtained from the joint inversion will then be combined with published geologic terrain maps to produce regionalized models for distinctive tectonic areas within the study area, and the models will be validated through full waveform modeling of well-located seismic events recorded at local and regional distances.
The relation between seismic P- and S-wave velocity dispersion in saturated rocks
Mavko, G. [Stanford Univ., CA (United States). Dept. of Geophysics] [Stanford Univ., CA (United States). Dept. of Geophysics; Jizba, D. [CSTJF, Pau (France)] [CSTJF, Pau (France)
1994-01-01T23:59:59.000Z
Seismic velocity dispersion in fluid-saturated rocks appears to be dominated by two mechanisms: the large scale mechanism modeled by Biot, and the local flow or squirt mechanism. The two mechanisms can be distinguished by the ratio of P- to S-wave dispersions, or more conveniently, by the ratio of dynamic bulk to shear compliance dispersions derived from the wave velocities. The authors` formulation suggests that when local flow dominates, the dispersion of the shear compliance will be approximately 4/15 the dispersion of the compressibility. When the Biot mechanism dominates, the constant of proportionality is much smaller. Their examination of ultrasonic velocities from 40 sandstones and granites shows that most, but not all, of the samples were dominated by local flow dispersion, particularly at effective pressures below 40 MPa.
MHD Waves and Coronal Heating: Unifying Empirical and MHD Turbulence Models
Sokolov, Igor V; Oran, Rona; Downs, Cooper; Roussev, Ilia I; Jin, Meng; Manchester, Ward B; Evans, Rebekah M; Gombosi, Tamas I
2012-01-01T23:59:59.000Z
We present a new global model of the solar corona, including the low corona, the transition region and the top of chromosphere. The realistic 3D magnetic field is simulated using the data from the photospheric magnetic field measurements. The distinctive feature of the new model is incorporating the MHD Alfven wave turbulence. We assume this turbulence and its non-linear dissipation to be the only momentum and energy source for heating the coronal plasma and driving the solar wind. The difference between the turbulence dissipation efficiency in coronal holes and that in closed field regions is because the non-linear cascade rate degrades in strongly anisotropic turbulence in coronal holes (no inward propagating wave), thus resulting in colder coronal holes with the bi-modal solar wind originating from them. The detailed presentation of the theoretical model is illustrated with the synthetic images for multi-wavelength EUV emission compared with the observations from SDO AIA and Stereo EUVI instruments for the...
Miguel D. Bustamante; Brenda Quinn
2013-09-02T23:59:59.000Z
A robust energy transfer mechanism is found in nonlinear wave systems, which favours transfers towards modes interacting via non-resonant triads, applicable in meteorology, nonlinear optics and plasma wave turbulence. Transfer efficiency is maximal when the frequency mismatch of the non-resonant triad balances the system's nonlinear frequency: at intermediate levels of oscillation amplitudes an instability is triggered that explores unstable manifolds of periodic orbits, so turbulent cascades are most efficient at intermediate nonlinearity. Numerical simulations confirm analytical predictions.
Shen, Yang
P-wave velocity structure of the crust and uppermost mantle beneath Iceland from local earthquake and uppermost mantle beneath Iceland, the keys to understanding the magma plumbing system of the hotspot develop a three-dimensional P-wave velocity model of the Icelandic crust and uppermost mantle from
Nonlinear three-mode interaction and drift-wave turbulence in a tokamak edge plasma
Batista, A.M.; Caldas, I.L.; Lopes, S.R.; Viana, R.L.; Horton, W.; Morrison, P.J. [Instituto de Fisica, Universidade de Sao Paulo, Caixa Postal 66318, 05315-970, Sao Paulo, SP (Brazil); Departamento de Fisica, Universidade Federal do Parana, 81531-990, Curitiba, Parana (Brazil); Department of Physics and Institute for Fusion Studies, University of Texas at Austin, Austin, Texas, 78712 (United States)
2006-04-15T23:59:59.000Z
A three-wave interaction model with quadratic nonlinearities and linear growth/decay rates is used to investigate the occurrence of drift-wave turbulence driven by pressure gradients in the edge plasma of a tokamak. Model parameters are taken from a typical set of measurements of the floating electrostatic potential in the tokamak edge region. Some aspects of the temporal dynamics exhibited by the three-wave interaction model are investigated, with special emphasis on a chaotic regime found for a wide range of the wave decay rate. An intermittent transition from periodic to chaotic behavior is observed and some statistical properties, such as the interburst and laminar length interval durations, are explored.
Extensional wave attenuation and velocity in partially saturated sand in the sonic frequency range
Liu, Z.; Rector, J.W.; Nihei, K.T.; Tomutsa, L.; Myer, L.R.; Nakagawa, S.
2001-08-10T23:59:59.000Z
Extensional wave attenuation and velocity measurements on a high permeability Monterey sand were performed over a range of gas saturations for imbibition and degassing conditions. These measurements were conducted using extensional wave pulse propagation and resonance over a 1-9 kHz frequency range for a hydrostatic confining pressure of 8.3 MPa. Analysis of the extensional wave data and the corresponding X-ray CT images of the gas saturation show strong attenuation resulting from the presence of the gas (Q{sub E} dropped from 300 for the dry sand to 30 for the partially-saturated sand), with larger attenuation at a given saturation resulting from heterogeneous gas distributions. The extensional wave velocities are in agreement with Gassmann theory for the test with near-homogeneous gas saturation and with a patchy saturation model for the test with heterogeneous gas saturation. These results show that partially-saturated sands under moderate confining pressure can produce strong intrinsic attenuation for extensional waves.
Accurate seismic phase-velocities from interfering surface-waves using homomorphic deconvolution
Szerbiak, Robert Bruce
1981-01-01T23:59:59.000Z
-deconvolution-technique results, with SN = 3 92 95 99 LIST OF FIGURES Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figur e Figure Figuze Figure 4 5 6 7 8 9 10... IL -1. 0 0 0 0. 2 0. 4 0. 0 0. 8 1. 0 TllNE (SEC) Fig. 1. Surface-wave simulation. Two methods used in computing phase-velocity are: 1) the one-station method uses two passages of the same wave to compute phase differences of the phase spectrum...
American Society for Testing and Materials. Philadelphia
2011-01-01T23:59:59.000Z
1.1 This practice covers a procedure for measuring the ultrasonic velocities in the outer wall of polyethylene storage tanks. An angle beam lateral longitudinal (LCR) wave is excited with wedges along a circumferential chord of the tank wall. A digital ultrasonic flaw detector is used with sending-receiving search units in through transmission mode. The observed velocity is temperature corrected and compared to the expected velocity for a new, unexposed sample of material which is the same as the material being evaluated. The difference between the observed and temperature corrected velocities determines the degree of UV exposure of the tank. 1.2 The practice is intended for application to the outer surfaces of the wall of polyethylene tanks. Degradation typically occurs in an outer layer approximately 3.2-mm (0.125-in.) thick. Since the technique does not interrogate the inside wall of the tank, wall thickness is not a consideration other than to be aware of possible guided (Lamb) wave effects or reflection...
Rossby and Drift Wave Turbulence and Zonal Flows: the Charney-Hasegawa-Mima model and its extensions
Colm Connaughton; Sergey Nazarenko; Brenda Quinn
2014-07-07T23:59:59.000Z
A detailed study of the Charney-Hasegawa-Mima model and its extensions is presented. These simple nonlinear partial differential equations suggested for both Rossby waves in the atmosphere and also drift waves in a magnetically-confined plasma exhibit some remarkable and nontrivial properties, which in their qualitative form survive in more realistic and complicated models, and as such form a conceptual basis for understanding the turbulence and zonal flow dynamics in real plasma and geophysical systems. Two idealised scenarios of generation of zonal flows by small-scale turbulence are explored: a modulational instability and turbulent cascades. A detailed study of the generation of zonal flows by the modulational instability reveals that the dynamics of this zonal flow generation mechanism differ widely depending on the initial degree of nonlinearity. A numerical proof is provided for the extra invariant in Rossby and drift wave turbulence -zonostrophy and the invariant cascades are shown to be characterised by the zonostrophy pushing the energy to the zonal scales. A small scale instability forcing applied to the model demonstrates the well-known drift wave - zonal flow feedback loop in which the turbulence which initially leads to the zonal flow creation, is completely suppressed and the zonal flows saturate. The turbulence spectrum is shown to diffuse in a manner which has been mathematically predicted. The insights gained from this simple model could provide a basis for equivalent studies in more sophisticated plasma and geophysical fluid dynamics models in an effort to fully understand the zonal flow generation, the turbulent transport suppression and the zonal flow saturation processes in both the plasma and geophysical contexts as well as other wave and turbulence systems where order evolves from chaos.
S wave velocity structure below central Mexico using highresolution surface wave tomography
Clayton, Robert W.
to the coast and found significant difference between the two paths in the period range of 5 to 35 s. [4 regions; they also show a wellresolved lowvelocity zone just below the active part of the Trans Mexican zone. This knowledge is also critical in understanding amplification of seismic waves as they propagate
Nicoud, Franck
and transpiration is identified. Note that M M cf/2 so that for typical ``low speed'' values of M 0.05 and cf 0 or cooling, Eq. 4 can be rewritten in the form: UVD 2 W 1 WU 1 O M2 . 5 The first-order term in Eq. 5 , i parameter is W Vinj , the characteristic transpiration velocity being in wall units. Thus, the ``mixing
Anomalous scaling of low-order structure functions of turbulent velocity
S. Y. Chen; B. Dhruva; S. Kurien; K. R. Sreenivasan; M. A. Taylor
2004-11-30T23:59:59.000Z
It is now believed that the scaling exponents of moments of velocity increments are anomalous, or that the departures from Kolmogorov's (1941) self-similar scaling increase nonlinearly with the increasing order of the moment. This appears to be true whether one considers velocity increments themselves or their absolute values. However, moments of order lower than 2 of the absolute values of velocity increments have not been investigated thoroughly for anomaly. Here, we discuss the importance of the scaling of non-integer moments of order between +2 and -1, and obtain them from direct numerical simulations at moderate Reynolds numbers (Taylor microscale Reynolds numbers $R_\\lambda \\le$ 450) and experimental data at high Reynolds numbers ($R_\\lambda \\approx$ 10,000). The relative difference between the measured exponents and Kolmogorov's prediction increases as the moment order decreases towards -1, thus showing that the anomaly that is manifest in high-order moments is present in low-order moments as well. This conclusion provides a motivation for seeking a theory of anomalous scaling as the order of the moment vanishes. Such a theory does not have to consider rare events--which may be affected by non-universal features such as shear--and so may be regarded as advantageous to consider and develop.
Two-fluid description of wave-particle interactions in strong Buneman turbulence
Che, H. [NASA/Goddard Space Flight Center, Greenbelt, Maryland 20771 (United States)
2014-06-15T23:59:59.000Z
To understand the nature of anomalous resistivity in magnetic reconnection, we investigate turbulence-induced momentum transport and energy dissipation while a plasma is unstable to the Buneman instability in force-free current sheets. Using 3D particle-in-cell simulations, we find that the macroscopic effects generated by wave-particle interactions in Buneman instability can be approximately described by a set of electron fluid equations. We show that both energy dissipation and momentum transport along electric current in the current layer are locally quasi-static, but globally dynamic and irreversible. Turbulent drag dissipates both the streaming energy of the current sheet and the associated magnetic energy. The net loss of streaming energy is converted into the electron component heat conduction parallel to the magnetic field and increases the electron Boltzmann entropy. The growth of self-sustained Buneman waves satisfies a Bernoulli-like equation that relates the turbulence-induced convective momentum transport and thermal momentum transport. Electron trapping and de-trapping drive local momentum transports, while phase mixing converts convective momentum into thermal momentum. The drag acts like a micro-macro link in the anomalous heating processes. The decrease of magnetic field maintains an inductive electric field that re-accelerates electrons, but most of the magnetic energy is dissipated and converted into the component heat of electrons perpendicular to the magnetic field. This heating process is decoupled from the heating of Buneman instability in the current sheets. Ion heating is weak but ions play an important role in assisting energy exchanges between waves and electrons. Cold ion fluid equations together with our electron fluid equations form a complete set of equations that describes the occurrence, growth, saturation and decay of the Buneman instability.
S. S. Zilitinkevich; T. Elperin; N. Kleeorin; V. L'vov; I. Rogachevskii
2009-08-18T23:59:59.000Z
We advance our prior energy- and flux-budget turbulence closure model (Zilitinkevich et al., 2007, 2008) for the stably stratified atmospheric flows and extend it accounting for additional vertical flux of momentum and additional productions of turbulent kinetic energy, turbulent potential energy (TPE) and turbulent flux of potential temperature due to large-scale internal gravity waves (IGW). Main effects of IGW are following: the maximal value of the flux Richardson number (universal constant 0.2-0.25 in the no-IGW regime) becomes strongly variable. In the vertically homogeneous stratification, it increases with increasing wave energy and can even exceed 1. In the heterogeneous stratification, when IGW propagate towards stronger stratification, the maximal flux Richardson number decreases with increasing wave energy, reaches zero and then becomes negative. In other words, the vertical flux of potential temperature becomes counter-gradient. IGW also reduce anisotropy of turbulence and increase the share of TPE in the turbulent total energy. Depending on the direction (downward or upward), IGW either strengthen or weaken the total vertical flux of momentum. Predictions from the proposed model are consistent with available data from atmospheric and laboratory experiments, direct numerical simulations and large-eddy simulations.
1 Green's Functions for Surface Waves in a Generic Velocity Structure 1 and Green's functions have been well established 14 for many decades. However, or Green's function surface displacement. We address this gap in the 19 literature
P. N. Appleton; K. C. Xu; W. Reach; M. A. Dopita; Y. Gao; N. Lu; C. C. Popescu; J. W. Sulentic; R. J. Tuffs; M. S. Yun
2006-02-25T23:59:59.000Z
We present the discovery of strong mid-infrared emission lines of molecular hydrogen of apparently high velocity dispersion (~870 km/s) originating from a group-wide shock wave in Stephan's Quintet. These Spitzer Space Telescope observations reveal emission lines of molecular hydrogen and little else. this is the first time an almost pure H_2 line spectrum has been seen in an extragalactic object. Along with the absence of PAH features and very low excitation ionized gas tracers, the spectra resemble shocked gas seen in Galactic supernova remnants, but on a vast scale. The molecular emission extends over 24 kpc along the X-ray emitting shock-front, but has ten times the surface luminosity as the soft X-rays, and about one-third the surface luminosity of the IR continuum. We suggest that the powerful H_2 emission is generated by the shock wave caused when a high-velocity intruder galaxy collides with filaments of gas in the galaxy group. Our observations suggest a close connection between galaxy-scale shock-waves and strong broad H_2 emission lines, like those seen in the spectra of Ultraluminous Infrared Galaxies where high-speed collisions between galaxy disks are common.
V. S. Ptuskin; I. V. Moskalenko; F. C. Jones; A. W. Strong; V. N. Zirakashvili
2006-01-21T23:59:59.000Z
The physical processes involved in diffusion of Galactic cosmic rays in the interstellar medium are addressed. We study the possibility that the nonlinear MHD cascade sets the power-law spectrum of turbulence which scatters charged energetic particles. We find that the dissipation of waves due to the resonant interaction with cosmic ray particles may terminate the Kraichnan-type cascade below wavelengths 10^13 cm. The effect of this wave dissipation has been incorporated in the GALPROP numerical propagation code in order to asses the impact on measurable astrophysical data. The energy-dependence of the cosmic-ray diffusion coefficient found in the resulting self-consistent model may explain the peaks in the secondary to primary nuclei ratios observed at about 1 GeV/nucleon.
Waves and vortices in the inverse cascade regime of stratified turbulence with or without rotation
Herbert, Corentin; Rosenberg, Duane; Pouquet, Annick
2015-01-01T23:59:59.000Z
We study the partition of energy between waves and vortices in stratified turbulence, with or without rotation, for a variety of parameters, focusing on the behavior of the waves and vortices in the inverse cascade of energy towards the large scales. To this end, we use direct numerical simulations in a cubic box at a Reynolds number Re=1000, with the ratio between the Brunt-V\\"ais\\"al\\"a frequency N and the inertial frequency f varying from 1/4 to 20, together with a purely stratified run. The Froude number, measuring the strength of the stratification, varies within the range 0.02 energy spectra and fluxes exhibit characteristics of an inverse cascade, even though their energy is not conserved. Surprisingly, the slow vortices still dominate when the ratio N/f increases, also in the stratified case, although less and less so. However, when N/f increases, the inverse cascade of the slow modes becomes we...
Measurement of shear wave velocity of heavy oil De-hua Han, Jiajin Liu, University of Houston
1 Measurement of shear wave velocity of heavy oil De-hua Han, Jiajin Liu, University of Houston modulus and therefore no shear wave can propagate through fluids. But heavy oils have properties that are much complex than lighter oils. At low temperatures, heavy oils are extremely viscous and begin to act
Wardaya, P. D., E-mail: pongga.wardaya@utp.edu.my; Noh, K. A. B. M., E-mail: pongga.wardaya@utp.edu.my; Yusoff, W. I. B. W., E-mail: pongga.wardaya@utp.edu.my [Petroleum Geosciences Department, Universiti Teknologi PETRONAS, Tronoh, Perak, 31750 (Malaysia); Ridha, S. [Petroleum Engineering Department, Universiti Teknologi PETRONAS, Tronoh, Perak, 31750 (Malaysia); Nurhandoko, B. E. B. [Wave Inversion and Subsurface Fluid Imaging Research Laboratory (WISFIR), Dept. of Physics, Institute of Technology Bandung, Bandung, Indonesia and Rock Fluid Imaging Lab, Bandung (Indonesia)
2014-09-25T23:59:59.000Z
This paper discusses a new approach for investigating the seismic wave velocity of rock, specifically carbonates, as affected by their pore structures. While the conventional routine of seismic velocity measurement highly depends on the extensive laboratory experiment, the proposed approach utilizes the digital rock physics view which lies on the numerical experiment. Thus, instead of using core sample, we use the thin section image of carbonate rock to measure the effective seismic wave velocity when travelling on it. In the numerical experiment, thin section images act as the medium on which wave propagation will be simulated. For the modeling, an advanced technique based on artificial neural network was employed for building the velocity and density profile, replacing image's RGB pixel value with the seismic velocity and density of each rock constituent. Then, ultrasonic wave was simulated to propagate in the thin section image by using finite difference time domain method, based on assumption of an acoustic-isotropic medium. Effective velocities were drawn from the recorded signal and being compared to the velocity modeling from Wyllie time average model and Kuster-Toksoz rock physics model. To perform the modeling, image analysis routines were undertaken for quantifying the pore aspect ratio that is assumed to represent the rocks pore structure. In addition, porosity and mineral fraction required for velocity modeling were also quantified by using integrated neural network and image analysis technique. It was found that the Kuster-Toksoz gives the closer prediction to the measured velocity as compared to the Wyllie time average model. We also conclude that Wyllie time average that does not incorporate the pore structure parameter deviates significantly for samples having more than 40% porosity. Utilizing this approach we found a good agreement between numerical experiment and theoretically derived rock physics model for estimating the effective seismic wave velocity of rock.
Upper-hybrid wave-driven Alfvenic turbulence in magnetized dusty plasmas
Misra, A. P. [Department of Physics, Umeaa University, SE-901 87 Umeaa (Sweden); Banerjee, S. [Department of Mathematics, Politecnico di Torino, 10129 Torino (Italy)
2011-03-15T23:59:59.000Z
The nonlinear dynamics of coupled electrostatic upper-hybrid (UH) and Alfven waves (AWs) is revisited in a magnetized electron-ion plasma with charged dust impurities. A pair of nonlinear equations that describe the interaction of UH wave envelopes (including the relativistic electron mass increase) and the density as well as the compressional magnetic field perturbations associated with the AWs are solved numerically to show that many coherent solitary patterns can be excited and saturated due to modulational instability of unstable UH waves. The evolution of these solitary patterns is also shown to appear in the states of spatiotemporal coherence, temporal as well as spatiotemporal chaos, due to collision and fusion among the patterns in stochastic motion. Furthermore, these spatiotemporal features are demonstrated by the analysis of wavelet power spectra. It is found that a redistribution of wave energy takes place to higher harmonic modes with small wavelengths, which, in turn, results in the onset of Alfvenic turbulence in dusty magnetoplasmas. Such a scenario can occur in the vicinity of Saturn's magnetosphere as many electrostatic solitary structures have been observed there by the Cassini spacecraft.
New insights into the decay of ion waves to turbulence, ion heating, and soliton generation
Chapman, T., E-mail: chapman29@llnl.gov; Banks, J. W.; Berger, R. L.; Cohen, B. I.; Williams, E. A. [Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551 (United States)] [Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551 (United States); Brunner, S. [Centre de Recherches en Physique des Plasmas, Association EURATOM-Confédération Suisse, Ecole Polytechnique Fédéral de Lausanne, CRPP-PPB, CH-1015 Lausanne (Switzerland)] [Centre de Recherches en Physique des Plasmas, Association EURATOM-Confédération Suisse, Ecole Polytechnique Fédéral de Lausanne, CRPP-PPB, CH-1015 Lausanne (Switzerland)
2014-04-15T23:59:59.000Z
The decay of a single-frequency, propagating ion acoustic wave (IAW) via two-ion wave decay to a continuum of IAW modes is found to result in a highly turbulent plasma, ion soliton production, and rapid ion heating. Instability growth rates, thresholds, and sensitivities to plasma conditions are studied via fully kinetic Vlasov simulations. The decay rate of IAWs is found to scale linearly with the fundamental IAW potential amplitude ?{sub 1} for ZT{sub e}/T{sub i}?20, beyond which the instability is shown to scale with a higher power of ?{sub 1}, where Z is the ion charge number and T{sub e} (T{sub i}) is the electron (ion) thermal temperature. The threshold for instability is found to be smaller by an order of magnitude than linear theory estimates. Achieving a better understanding of the saturation of stimulated Brillouin scatter levels observed in laser-plasma interaction experiments is part of the motivation for this study.
Short Note Green's Functions for Surface Waves in a Generic Velocity Structure by Victor C. Tsai displacement/stress eigenfunctions and Green's functions have been well established for many decades. However on frequency, or Green's function surface displacement. We address this gap in the liter- ature and here
Vertical vibration of a circular footing on a linear-wave-velocity B. B. GUZINA and R. Y. S. PAKy
Guzina, Bojan
Vertical vibration of a circular footing on a linear-wave-velocity half-space B. B. GUZINAÃ and R. Y. S. PAKy An exact treatment is presented for the problem of a rigid surface foundation vibrating; soilastructure interaction; vibration. Les auteurs abordent le probleÁme de la vibra- tion verticale de
Brauchler, R.; Doetsch, J.; Dietrich, P.; Sauter, M.
2012-01-10T23:59:59.000Z
In this study, hydraulic and seismic tomographic measurements were used to derive a site-specific relationship between the geophysical parameter p-wave velocity and the hydraulic parameters, diffusivity and specific storage. Our field study includes diffusivity tomograms derived from hydraulic travel time tomography, specific storage tomograms, derived from hydraulic attenuation tomography, and p-wave velocity tomograms, derived from seismic tomography. The tomographic inversion was performed in all three cases with the SIRT (Simultaneous Iterative Reconstruction Technique) algorithm, using a ray tracing technique with curved trajectories. The experimental set-up was designed such that the p-wave velocity tomogram overlaps the hydraulic tomograms by half. The experiments were performed at a wellcharacterized sand and gravel aquifer, located in the Leine River valley near Göttingen, Germany. Access to the shallow subsurface was provided by direct-push technology. The high spatial resolution of hydraulic and seismic tomography was exploited to derive representative site-specific relationships between the hydraulic and geophysical parameters, based on the area where geophysical and hydraulic tests were performed. The transformation of the p-wave velocities into hydraulic properties was undertaken using a k-means cluster analysis. Results demonstrate that the combination of hydraulic and geophysical tomographic data is a promising approach to improve hydrogeophysical site characterization.
Joint migration velocity analysis of PP-and PS-waves for VTI media Pengfei Cai1
Tsvankin, Ilya
estimated, accurate depth images can be obtained by migrating the recorded PP and PS data. INTRODUCTION Prestack depth migration (PSDM) and reflection tomography in the migrated domain are widely used in PJoint migration velocity analysis of PP- and PS-waves for VTI media Pengfei Cai1 and Ilya Tsvankin2
Ecological collapse and the emergence of traveling waves at the onset of shear turbulence
Shih, Hong-Yan; Goldenfeld, Nigel
2015-01-01T23:59:59.000Z
The transition to turbulence exhibits remarkable spatio-temporal behavior that continues to defy detailed understanding. Near the onset to turbulence in pipes, transient turbulent regions decay either directly or, at higher Reynolds numbers through splitting, with characteristic time-scales that exhibit a super-exponential dependence on Reynolds number. Here we report numerical simulations of transitional pipe flow, showing that a zonal flow emerges at large scales, activated by anisotropic turbulent fluctuations; in turn, the zonal flow suppresses the small-scale turbulence leading to stochastic predator-prey dynamics. We show that this "ecological" model of transitional turbulence reproduces the super-exponential lifetime statistics and phenomenology of pipe flow experiments. Our work demonstrates that a fluid on the edge of turbulence is mathematically analogous to an ecosystem on the edge of extinction, and provides an unbroken link between the equations of fluid dynamics and the directed percolation univ...
Incrocci, Thomas Paul
1970-01-01T23:59:59.000Z
. . . . . . . . , . . . ~ . ~ INTRODUCTION BACKGROUND TO THE PROBLEM Theory of Mountain Waves Mountain Waves and Clear Air Turbulence (CAT). Page iv v vi viii The Vertical Propagation and Transfer of Energy of Mountain Waves into the Stratosphere The Influence of Wind... and the prevailing wind directions favorable for the development of extensive mountain wave activity in the surrounding areas (Wind directions taken from Harrison and Sowa, 1966). 24 Nid-tropospheric conditions for 1200 GNT on 19 March 1966 28 Nid...
Multi-scale interaction of driftWave turbulence with large scale shear flows
McDevitt, Christopher J.
2008-01-01T23:59:59.000Z
then to impose outgoing wave energy boundary conditions [Appendix A, this outgoing wave energy condition implies thatMHD. Appendix A: Outgoing Wave Energy Boundary Conditions In
Anomalous electron-ion energy coupling in electron drift wave turbulence
Zhao, Lei
annulus arises due to a wave energy flux differential acrossprincipal collisionless wave energy dissipation channel inOn the other hand, wave energy can be dissipated by ion
Anomalous electron-ion energy coupling in electron drift wave turbulence
Zhao, Lei
an additional means for wave energy to be transferred to theAlso zonal flow dissipate wave energy through zonal flowclassical theorem for wave energy evolution in a strongly
On breaking waves and turbulence at the air-sea interface /
Sutherland, Peter Jesse
2013-01-01T23:59:59.000Z
transfer equation of wave energy or action, which has threeSurface impulse and wave energy dissipation rates, Journalaverage rate of gravity wave energy loss per unit area by
Incrocci, Thomas Paul
1970-01-01T23:59:59.000Z
troposphere of the average profiles of L and Ri for those cases with wind components less than 10 m sec normal to the mountain tops 43 INTRODUCTION The problem of stratospheric turbulence was vividly brought to light when the supersonic XB-70 airplane...AN INVESTIGATION OF THE RELATIONSHIPS BETWEEN MOUNTAIN WAVES AND CLEAR AIR TURBULENCE ENCOUNTERED BY TIIE XB-70 AIRPLANE IN THE STRATOSPHERE A Thesis by THOMAS PAUL INCROCCI Submitted to the Graduate College of Texas A&M University...
Multi-scale interaction of driftWave turbulence with large scale shear flows
McDevitt, Christopher J.
2008-01-01T23:59:59.000Z
pro?le, killing the free energy source of the turbulence.environmentally benign source of energy free from many ofin fact act as a source of free energy for the convective
Anisotropic turbulent model for solar coronal heating
B. Bigot; S. Galtier; H. Politano
2008-08-26T23:59:59.000Z
Context : We present a self-consistent model of solar coronal heating, originally developed by Heyvaert & Priest (1992), in which we include the dynamical effect of the background magnetic field along a coronal structure by using exact results from wave MHD turbulence (Galtier et al. 2000). Aims : We evaluate the heating rate and the microturbulent velocity for comparison with observations in the quiet corona, active regions and also coronal holes. Methods :The coronal structures are assumed to be in a turbulent state maintained by the slow erratic motions of the magnetic footpoints. A description for the large-scale and the unresolved small-scale dynamics are given separately. From the latter, we compute exactly (or numerically for coronal holes) turbulent viscosites that are finally used in the former to close self-consistently the system and derive the heating flux expression. Results : We show that the heating rate and the turbulent velocity compare favorably with coronal observations. Conclusions : Although the Alfven wave turbulence regime is strongly anisotropic, and could reduce a priori the heating efficiency, it provides an unexpected satisfactory model of coronal heating for both magnetic loops and open magnetic field lines.
Tariq, Sabeen; Mirza, Arshad M. [Department of Physics, Theoretical Plasma Physics Group, Quaid-i-Azam University, Islamabad 45320 (Pakistan); Masood, W. [Theoretical Plasma Physics Division, PINSTECH, P.O. Box. Nilore, Islamabad 44000, Pakistan and National Center for Physics (NCP), Islamabad 45320 (Pakistan)
2010-10-15T23:59:59.000Z
The propagation of high and low frequency (in comparison with the cyclotron frequency) electrostatic drift-waves is investigated in a nonuniform, dense magnetoplasma (composed of electrons and ions), in the presence of parallel shear flow, by employing the quantum magnetohydrodynamic (QMHD) model. Using QMHD model, a new set of equations is presented in order to investigate linear properties of electrostatic drift-waves with sheared plasma flows for dense plasmas. In this regard, dispersion relations for coupled electron-thermal and drift-ion acoustic modes are derived and several interesting limiting cases are discussed. For instance, it is found that sheared ion flow parallel to the external magnetic field can drive the quantum drift-ion acoustic wave unstable, etc. The present investigation may have relevance in dense astrophysical environments where quantum effects are significant.
Four Lectures on Turbulent Combustion
Peters, Norbert
Four Lectures on Turbulent Combustion N. Peters Institut f¨ur Technische Mechanik RWTH Aachen Turbulent Combustion: Introduction and Overview 1 1.1 Moment Methods in Modeling Turbulence with Combustion and Velocity Scales . . . . . . . . . . . 11 1.4 Regimes in Premixed Turbulent Combustion
Futatani, S. [France-Japan Magnetic Fusion Laboratory, CNRS, France; Bos, W.J.T. [CNRS, Ecole Centrale de Lyon, Universite Claude Bernard Lyon; Del-Castillo-Negrete, Diego B [ORNL; Schneider, Kai [Universite d'Aix-Marseille; Benkadda, S. [France-Japan Magnetic Fusion Laboratory, CNRS, France; Farge, Marie [Laboratoire de Meteorologie Dynamique-CNRL, Ecole Normale Superieure
2011-01-01T23:59:59.000Z
We assess two techniques for extracting coherent vortices out of turbulent flows: the wavelet based Coherent Vorticity Extraction (CVE) and the Proper Orthogonal Decomposition (POD). The former decomposes the flow field into an orthogonal wavelet representation and subsequent thresholding of the coefficients allows one to split the flow into organized coherent vortices with non-Gaussian statistics and an incoherent random part which is structureless. POD is based on the singular value decomposition and decomposes the flow into basis functions which are optimal with respect to the retained energy for the ensemble average. Both techniques are applied to direct numerical simulation data of two-dimensional drift-wave turbulence governed by Hasegawa Wakatani equation, considering two limit cases: the quasi-hydrodynamic and the quasi-adiabatic regimes. The results are compared in terms of compression rate, retained energy, retained enstrophy and retained radial flux, together with the enstrophy spectrum and higher order statistics. (c) 2010 Published by Elsevier Masson SAS on behalf of Academie des sciences.
Wang, Hongjuan; Gong, Jiancun; Wu, Ning; Lin, Jun
2015-01-01T23:59:59.000Z
We numerically study the detailed evolutionary features of the wave-like disturbance and its propagation in the eruption. This work is a follow-up to Wang et al., using significantly upgraded new simulations. We focus on the contribution of the velocity vortices and the fast shock reflection and refraction in the solar corona to the formation of the EUV waves. Following the loss of equilibrium in the coronal magnetic structure, the flux rope exhibits rapid motions and invokes the fast-mode shock forward of the rope, which then produces the type II radio burst. The expansion of the fast shock, which is associated with outward motion, takes place in various directions, and the downward expansion shows the reflection and the refraction as a result of the non-uniform background plasma. The reflected component of the fast shock propagates upward and the refracted component propagates downward. As the refracted component reaches the boundary surface, a weak echo is excited. The Moreton wave is invoked as the fast s...
Tokam, A K; Tabod, C T; Nyblade, A A; Julia, J; Wiens, D A; Pasyanos, M E
2010-02-18T23:59:59.000Z
The Cameroon Volcanic Line (CVL) is a major geologic feature that cuts across Cameroon from the south west to the north east. It is a unique volcanic lineament which has both an oceanic and a continental sector and consists of a chain of Tertiary to Recent, generally alkaline volcanoes stretching from the Atlantic island of Pagalu to the interior of the African continent. The oceanic sector includes the islands of Bioko (formerly Fernando Po) and Sao Tome and Principe while the continental sector includes the Etinde, Cameroon, Manengouba, Bamboutos, Oku and Mandara mountains, as well as the Adamawa and Biu Plateaus. In addition to the CVL, three other major tectonic features characterize the region: the Benue Trough located northwest of the CVL, the Central African Shear Zone (CASZ), trending N70 degrees E, roughly parallel to the CVL, and the Congo Craton in southern Cameroon. The origin of the CVL is still the subject of considerable debate, with both plume and non-plume models invoked by many authors (e.g., Deruelle et al., 2007; Ngako et al, 2006; Ritsema and Allen, 2003; Burke, 2001; Ebinger and Sleep, 1998; Lee et al, 1994; Dorbath et al., 1986; Fairhead and Binks, 1991; King and Ritsema, 2000; Reusch et al., 2010). Crustal structure beneath Cameroon has been investigated previously using active (Stuart et al, 1985) and passive (Dorbath et al., 1986; Tabod, 1991; Tabod et al, 1992; Plomerova et al, 1993) source seismic data, revealing a crust about 33 km thick at the south-western end of the continental portion of the CVL (Tabod, 1991) and the Adamawa Plateau, and thinner crust (23 km thick) beneath the Garoua Rift in the north (Stuart et al, 1985) (Figure 1). Estimates of crustal thickness obtained using gravity data show similar variations between the Garoua rift, Adamawa Plateau, and southern part of the CVL (Poudjom et al., 1995; Nnange et al., 2000). In this study, we investigate further crustal structure beneath the CVL and the adjacent regions in Cameroon using 1-D shear wave velocity models obtained from the joint inversion of Rayleigh wave group velocities and P-receiver functions for 32 broadband seismic stations. From the 1-D shear wave velocity models, we obtain new insights into the composition and structure of the crust and upper mantle across Cameroon. After briefly reviewing the geological framework of Cameroon, we describe the data and the joint inversion method, and then interpret variations in crustal structure found beneath Cameroon in terms of the tectonic history of the region.
Coastal Wave Generation and Wave Breaking over Terrain: Two Problems in Mesoscale Wave Dynamics
Qian, Tingting
2010-07-14T23:59:59.000Z
Two problems in mesoscale wave dynamics are addressed: (i) wave-turbulence interaction in a breaking mountain wave and (ii) gravity wave generation associated with coastal heating gradients. The mean and turbulent structures in a breaking mountain...
Coastal Wave Generation and Wave Breaking over Terrain: Two Problems in Mesoscale Wave Dynamics
Qian, Tingting
2010-07-14T23:59:59.000Z
Two problems in mesoscale wave dynamics are addressed: (i) wave-turbulence interaction in a breaking mountain wave and (ii) gravity wave generation associated with coastal heating gradients. The mean and turbulent structures in a breaking mountain...
Signature of a universal statistical description for drift-wave plasma turbulence
Anderson, Johan; Xanthopoulos, Pavlos [Max-Planck-Institut fuer Plasmaphysik, IPP-Euratom Association, Teilinstitut Greifswald, D-17491 Greifswald (Germany)
2010-11-15T23:59:59.000Z
This letter provides a theoretical interpretation of numerically generated probability density functions (PDFs) of intermittent plasma transport events. Specifically, nonlinear gyrokinetic simulations of ion-temperature-gradient turbulence produce the time series of heat flux that manifestly exhibit non-Gaussian PDFs with enhanced tails. It is demonstrated that, after the removal of autocorrelations, the numerical PDFs can be matched with predictions from a fluid theoretical setup based on the instanton method. This result points to a universality in the modeling of intermittent stochastic process offering a predictive capability.
Sermeus, J.; Glorieux, C., E-mail: christ.glorieux@fys.kuleuven.be [Laboratory for Acoustics and Thermal Physics, KU Leuven, University of Leuven, Celestijnenlaan 200D, B-3001 Heverlee (Belgium); Sinha, R.; Vereecken, P. M. [IMEC, Kapeldreef 75, B-3001 Leuven (Belgium); Center for Surface Chemistry and Catalysis, KU Leuven, University of Leuven, Kasteelpark Arenberg 23, B-3001 Leuven (Belgium); Vanstreels, K. [IMEC, Kapeldreef 75, B-3001 Leuven (Belgium)
2014-07-14T23:59:59.000Z
MnO{sub 2} is a material of interest in the development of high energy-density batteries, specifically as a coating material for internal 3D structures, thus ensuring rapid energy deployment. Its electrochemical properties have been mapped extensively, but there are, to the best of the authors' knowledge, no records of the elastic properties of thin film MnO{sub 2}. Impulsive stimulated thermal scattering (ISTS), also known as the heterodyne diffraction or transient grating technique, was used to determine the Young's modulus (E) and porosity (?) of a 500?nm thick MnO{sub 2} coating on a Si(001) substrate. ISTS is an all optical method that is able to excite and detect surface acoustic waves (SAWs) on opaque samples. From the measured SAW velocity dispersion, the Young's modulus and porosity were determined to be E?=?25?±?1?GPa and ?=42±1%, respectively. These values were confirmed by independent techniques and determined by a most-squares analysis of the carefully fitted SAW velocity dispersion. This study demonstrates the ability of the presented technique to determine the elastic parameters of a thin, porous film on an anisotropic substrate.
Optical-Fiber Gravitational Wave Detector: Dynamical 3-Space Turbulence Detected
Reginald T Cahill
2007-07-16T23:59:59.000Z
Preliminary results from an optical-fiber gravitational wave interferometric detector are reported. The detector is very small, cheap and simple to build and operate. It is assembled from readily available opto-electronic components. A parts list is given. The detector can operate in two modes: one in which only instrument noise is detected, and data from a 24 hour period is reported for this mode, and in a 2nd mode in which the gravitational waves are detected as well, and data from a 24 hour period is analysed. Comparison shows that the instrument has a high S/N ratio. The frequency spectrum of the gravitational waves shows a pink noise spectrum, from 0 to 0.1Hz.
Lyakhovsky, Vladimir
1987-01-01T23:59:59.000Z
-elastic isotropic models (Zaichenko et al. 1984; Schukin 1984). Interpretation of seismic results based on the Hooke in seismic zones implies that the traditional interpretation of geophysical investigations basedGeophys. J. R. astr. SOC.(1987) 91,429437 On the relation between seismic wave velocity and stress
Naoto Yokoyama; Masanori Takaoka
2014-12-09T23:59:59.000Z
A single-wavenumber representation of nonlinear energy spectrum, i.e., stretching energy spectrum is found in elastic-wave turbulence governed by the F\\"oppl-von K\\'arm\\'an (FvK) equation. The representation enables energy decomposition analysis in the wavenumber space, and analytical expressions of detailed energy budget in the nonlinear interactions are obtained for the first time in wave turbulence systems. We numerically solved the FvK equation and observed the following facts. Kinetic and bending energies are comparable with each other at large wavenumbers as the weak turbulence theory suggests. On the other hand, the stretching energy is larger than the bending energy at small wavenumbers, i.e., the nonlinearity is relatively strong. The strong correlation between a mode $a_{\\bm{k}}$ and its companion mode $a_{-\\bm{k}}$ is observed at the small wavenumbers. Energy transfer shows that the energy is input into the wave field through stretching-energy transfer at the small wavenumbers, and dissipated through the quartic part of kinetic-energy transfer at the large wavenumbers. A total-energy flux consistent with the energy conservation is calculated directly by using the analytical expression of the total-energy transfer, and the forward energy cascade is observed clearly.
The dynamics of transition to turbulence in plane Couette flow
Viswanath, D
2007-01-01T23:59:59.000Z
In plane Couette flow, the incompressible fluid between two plane parallel walls is driven by the motion of those walls. The laminar solution, in which the streamwise velocity varies linearly in the wall-normal direction, is known to be linearly stable at all Reynolds numbers ($Re$). Yet, in both experiments and computations, turbulence is observed for $Re \\gtrsim 360$. In this article, we show that when the laminar flow is perturbed on to the transition {\\it threshold}, the flow approaches either steady or traveling wave solutions. These solutions exhibit some aspects of turbulence but are not fully turbulent even at $Re=4000$. However, these solutions are linearly unstable and flows that evolve along their unstable directions become fully turbulent. The solution approached by a threshold perturbation depends upon the nature of the perturbation. Surprisingly, the positive eigenvalue that corresponds to one family of solutions decreases in magnitude with increasing $Re$, with the rate of decrease given by $Re...
Reynolds number of transition and large-scale properties of strong turbulence
Yakhot, Victor
2014-01-01T23:59:59.000Z
A turbulent flow is characterized by velocity fluctuations excited in an extremely broad interval of wave numbers $k> \\Lambda_{f}$ where $\\Lambda_{f}$ is a relatively small set of the wave-vectors where energy is pumped into fluid by external forces. Iterative averaging over small-scale velocity fluctuations from the interval $\\Lambda_{f}statistics of spatial velocity derivatives. The calculated relation $Re(\\Lambda_{f})=Re_{tr}$ "selects" the lowest - order non-linearity as the only relevant one. This means that in the infra-red limit $k\\rightarrow \\Lambda_{f...
Residual energy in magnetohydrodynamic turbulence and in the solar wind
Stanislav Boldyrev; Jean Carlos Perez; Vladimir Zhdankin
2011-08-30T23:59:59.000Z
Recent observations indicate that kinetic and magnetic energies are not in equipartition in the solar wind turbulence. Rather, magnetic fluctuations are more energetic and have somewhat steeper energy spectrum compared to the velocity fluctuations. This leads to the presence of the so-called residual energy E_r=E_v-E_b in the inertial interval of turbulence. This puzzling effect is addressed in the present paper in the framework of weak turbulence theory. Using a simple model of weakly colliding Alfv\\'en waves, we demonstrate that the kinetic-magnetic equipartition indeed gets broken as a result of nonlinear interaction of Alfv\\'en waves. We establish that magnetic energy is indeed generated more efficiently as a result of these interactions, which proposes an explanation for the solar wind observations.
He Jiansen; Tu Chuanyi [School of Earth and Space Sciences, Peking University, Beijing 100871 (China); Marsch, Eckart [Max-Planck-Institut fuer Sonnensystemforschung, 37191 Katlenburg-Lindau (Germany); Yao Shuo, E-mail: jshept@gmail.com [School of Geophysics and Information Technology, China University of Geoscience (Beijing), Beijing 100083 (China)
2012-01-20T23:59:59.000Z
To determine the wave modes prevailing in solar wind turbulence at kinetic scales, we study the magnetic polarization of small-scale fluctuations in the plane perpendicular to the data sampling direction (namely, the solar wind flow direction, V{sub SW}) and analyze its orientation with respect to the local background magnetic field B{sub 0,local}. As an example, we take only measurements made in an outward magnetic sector. When B{sub 0,local} is quasi-perpendicular to V{sub SW}, we find that the small-scale magnetic-field fluctuations, which have periods from about 1 to 3 s and are extracted from a wavelet decomposition of the original time series, show a polarization ellipse with right-handed orientation. This is consistent with a positive reduced magnetic helicity, as previously reported. Moreover, for the first time we find that the major axis of the ellipse is perpendicular to B{sub 0,local}, a property that is characteristic of an oblique Alfven wave rather than oblique whistler wave. For an oblique whistler wave, the major axis of the magnetic ellipse is expected to be aligned with B{sub 0,local}, thus indicating significant magnetic compressibility, and the polarization turns from right to left handedness as the wave propagation angle ({theta}{sub kB}) increases toward 90 Degree-Sign . Therefore, we conclude that the observation of a right-handed polarization ellipse with orientation perpendicular to B{sub 0,local} seems to indicate that oblique Alfven/ion-cyclotron waves rather than oblique fast-mode/whistler waves dominate in the 'dissipation' range near the break of solar wind turbulence spectra occurring around the proton inertial length.
Fineberg, Jay
rates: turbulent transport when no wave breaking occurs and bubble dominated transport when wave is correlated with measured acoustic emissions, indicating that bubble creation and dynamics dominate air carbon ( 38 000 gigatons) than the atmosphere and 38 times more than the total vegetative carbon
Talbot, L.; Cheng, R.K. [Lawrence Berkeley Laboratory, CA (United States)
1993-12-01T23:59:59.000Z
Turbulent combustion is the dominant process in heat and power generating systems. Its most significant aspect is to enhance the burning rate and volumetric power density. Turbulent mixing, however, also influences the chemical rates and has a direct effect on the formation of pollutants, flame ignition and extinction. Therefore, research and development of modern combustion systems for power generation, waste incineration and material synthesis must rely on a fundamental understanding of the physical effect of turbulence on combustion to develop theoretical models that can be used as design tools. The overall objective of this program is to investigate, primarily experimentally, the interaction and coupling between turbulence and combustion. These processes are complex and are characterized by scalar and velocity fluctuations with time and length scales spanning several orders of magnitude. They are also influenced by the so-called {open_quotes}field{close_quotes} effects associated with the characteristics of the flow and burner geometries. The authors` approach is to gain a fundamental understanding by investigating idealized laboratory flames. Laboratory flames are amenable to detailed interrogation by laser diagnostics and their flow geometries are chosen to simplify numerical modeling and simulations and to facilitate comparison between experiments and theory.
Gravitational Waves from Neutron Stars: A Review
Lasky, Paul D
2015-01-01T23:59:59.000Z
Neutron stars are excellent emitters of gravitational waves. Squeezing matter beyond nuclear densities invites exotic physical processes, many of which violently transfer large amounts of mass at relativistic velocities, disrupting spacetime and generating copious quantities of gravitational radiation. I review mechanisms for generating gravitational waves with neutron stars. This includes gravitational waves from radio and millisecond pulsars, magnetars, accreting systems and newly born neutron stars, with mechanisms including magnetic and thermoelastic deformations, various stellar oscillation modes and core superfluid turbulence. I also focus on what physics can be learnt from a gravitational wave detection, and where additional research is required to fully understand the dominant physical processes at play.
Gravitational Waves from Neutron Stars: A Review
Paul D. Lasky
2015-08-26T23:59:59.000Z
Neutron stars are excellent emitters of gravitational waves. Squeezing matter beyond nuclear densities invites exotic physical processes, many of which violently transfer large amounts of mass at relativistic velocities, disrupting spacetime and generating copious quantities of gravitational radiation. I review mechanisms for generating gravitational waves with neutron stars. This includes gravitational waves from radio and millisecond pulsars, magnetars, accreting systems and newly born neutron stars, with mechanisms including magnetic and thermoelastic deformations, various stellar oscillation modes and core superfluid turbulence. I also focus on what physics can be learnt from a gravitational wave detection, and where additional research is required to fully understand the dominant physical processes at play.
Swigler, David Townley
2010-10-12T23:59:59.000Z
A laboratory experiment was performed to investigate the three-dimensional turbulence and kinematic properties that develop due to a breaking solitary and an irregular shallow water bathymetry. A large basin equipped with a piston-type wavemaker...
Procaccia, Itamar
PHYSICAL REVIEW LETTERS Submitted 21 May 1997 Exact Result for the 3rd Order Correlations conservation. This law states that the energy flux expressed as a spatial derivative of the 3rd order velocity as a second spatial derivative of the 3rd order velocity correlator with the rate of helicity dissipation
Turbulent burning rates of methane and methane-hydrogen mixtures
Fairweather, M. [School of Process, Environmental and Materials Engineering, University of Leeds, Leeds LS2 9JT (United Kingdom); Ormsby, M.P.; Sheppard, C.G.W. [School of Mechanical Engineering, University of Leeds, Leeds LS2 9JT (United Kingdom); Woolley, R. [Department of Mechanical Engineering, University of Sheffield, Sheffield S1 3JD (United Kingdom)
2009-04-15T23:59:59.000Z
Methane and methane-hydrogen (10%, 20% and 50% hydrogen by volume) mixtures have been ignited in a fan stirred bomb in turbulence and filmed using high speed cine schlieren imaging. Measurements were performed at 0.1 MPa (absolute) and 360 K. A turbulent burning velocity was determined for a range of turbulence velocities and equivalence ratios. Experimental laminar burning velocities and Markstein numbers were also derived. For all fuels the turbulent burning velocity increased with turbulence velocity. The addition of hydrogen generally resulted in increased turbulent and laminar burning velocity and decreased Markstein number. Those flames that were less sensitive to stretch (lower Markstein number) burned faster under turbulent conditions, especially as the turbulence levels were increased, compared to stretch-sensitive (high Markstein number) flames. (author)
Turbulent Energy Transport in Nonradiative Accretion Flows
Steven A. Balbus
2003-09-24T23:59:59.000Z
Just as correlations between fluctuating radial and azimuthal velocities produce a coherent stress contributing to the angular momentum transport in turbulent accretion disks, correlations in the velocity and temperature fluctuations produce a coherent energy flux. This nonadvective energy flux is always of secondary importance in thin radiative disks, but cannot be neglected in nonradiative flows, in which it completes the mean field description of turbulence. It is, nevertheless, generally ignored in accretion flow theory, with the exception of models explicitly driven by thermal convection, where it is modeled phenomenologically. This flux embodies both turbulent thermal convection as well as wave transport, and its presence is essential for a proper formulation of energy conservation, whether convection is present or not. The sign of the thermal flux is likely to be outward in real systems, but the restrictive assumptions used in numerical simulations may lead to inward thermal transport, in which case qualitatively new effects may be exhibited. We find, for example, that a static solution would require inward, not outward, thermal transport. Even if it were present, thermal convection would be unlikely to stifle accretion, but would simply add to the outward rotational energy flux that must already be present.
Victor S. Lvov; Sergey Nazarenko
2009-09-16T23:59:59.000Z
Both the Kelvin wave and the Kolmogorov turbulence interpretations presented in the PRL, [v. 103, 084501 (2009) by J. Yepez, G. Vahala, L.Vahala and M. Soe, arXiv:0905.0159] are misleading, and much more theoretical analysis needs to be done for the interpretation of the important numerical results obtained by the authors. A way to do this is suggested.
Sato, Yuki
to the initial onset of a single vortex motion. We place a flow tube in one arm of a matter wave interferometer and directly monitor the order-parameter phase difference across the tube's ends. When a vortex initially quantum interference device to probe the initial onset of the motion of a single vortex line driven
P and S wave velocity and VP///VS in the wake of the Yellowstone hot spot
Humphreys, Eugene
magmatism occurred at the eastern Snake River Plain $610 m.y. B.P. Data are teleseismic P and S travel time. The dominant structure is a zone which extends beneath the Snake River Plain to a depth of $190 km that is high to density. Specifically, we infer that the low-velocity mantle beneath the Snake River Plain is partially
Hall, Maclin S. (Marietta, GA); Jackson, Theodore G. (Atlanta, GA); Knerr, Christopher (Lawrenceville, GA)
1998-02-17T23:59:59.000Z
An improved system for measuring the velocity of ultrasonic signals within the plane of moving web-like materials, such as paper, paperboard and the like. In addition to velocity measurements of ultrasonic signals in the plane of the web in the MD and CD, one embodiment of the system in accordance with the present invention is also adapted to provide on-line indication of the polar specific stiffness of the moving web. In another embodiment of the invention, the velocity of ultrasonic signals in the plane of the web are measured by way of a plurality of ultrasonic transducers carried by synchronously driven wheels or cylinders, thus eliminating undue transducer wear due to any speed differences between the transducers and the web. In order to provide relatively constant contact force between the transducers and the webs, the transducers are mounted in a sensor housings which include a spring for biasing the transducer radially outwardly. The sensor housings are adapted to be easily and conveniently mounted to the carrier to provide a relatively constant contact force between the transducers and the moving web.
Hall, M.S.; Jackson, T.G.; Knerr, C.
1998-02-17T23:59:59.000Z
An improved system for measuring the velocity of ultrasonic signals within the plane of moving web-like materials, such as paper, paperboard and the like. In addition to velocity measurements of ultrasonic signals in the plane of the web in the MD and CD, one embodiment of the system in accordance with the present invention is also adapted to provide on-line indication of the polar specific stiffness of the moving web. In another embodiment of the invention, the velocity of ultrasonic signals in the plane of the web are measured by way of a plurality of ultrasonic transducers carried by synchronously driven wheels or cylinders, thus eliminating undue transducer wear due to any speed differences between the transducers and the web. In order to provide relatively constant contact force between the transducers and the webs, the transducers are mounted in a sensor housings which include a spring for biasing the transducer radially outwardly. The sensor housings are adapted to be easily and conveniently mounted to the carrier to provide a relatively constant contact force between the transducers and the moving web. 37 figs.
Numerical Study of a Turbulent Hydraulic Jump
Zhao, Qun
Numerical Study of a Turbulent Hydraulic Jump Qun Zhao, Shubhra Misra, Ib. A. Svendsen and James T of a Turbulent Hydraulic Jump p.1/14 #12;Objective Our ultimate goal is to study the breaking waves. Numerical Study of a Turbulent Hydraulic Jump p.2/14 #12;A moving bore Qiantang Bore China (Courtesy of Dr J
Simple Models for Turbulent Self-Regulation in Galaxy Disks
Curtis Struck; Daniel C. Smith
1999-07-29T23:59:59.000Z
We propose that turbulent heating, wave pressure and gas exchanges between different regions of disks play a dominant role in determining the preferred, quasi-equilibrium, self-similar states of gas disks on large-scales. We present simple families of analytic, thermohydrodynamic models for these global states, which include terms for turbulent pressure and Reynolds stresses. Star formation rates, phase balances, and hydrodynamic forces are all tightly coupled and balanced. The models have stratified radial flows, with the cold gas slowly flowing inward in the midplane of the disk, and with the warm/hot phases that surround the midplane flowing outward. The models suggest a number of results that are in accord with observation, as well as some novel predictions, including the following. 1) The large-scale gas density and thermal phase distributions in galaxy disks can be explained as the result of turbulent heating and spatial couplings. 2) The turbulent pressures and stresses that drive radial outflows in the warm gas also allow a reduced circular velocity there. This effect was observed by Swaters, Sancisi and van der Hulst in NGC 891, a particularly turbulent edge-on disk. The models predict that the effect should be universal in such disks. 3) They suggest that a star formation rate like the phenomenological Schmidt Law is the natural result of global thermohydrodynamical balance, and may not obtain in disks far from equilibrium. (Abridged)
Studies of Turbulence in Shallow Sediment Laden Flow With Superimposed Rainfall
Barfield, B. J.
1968-01-01T23:59:59.000Z
to the partial differential equation were the particle fall velocity and the turbulent diffusion coefficient. The diffusion coefficient used was the product of the mean square velocity and the Eulerian time scale of turbulence. A 4O ft. recirculating research...
FLOW CONDITIONING DESIGN IN TURBULENT
near the nozzle exit influenced by different flow conditioner (vs. nozzle) designs? How are velocity in the flow conditioner? Will more screens reduce free-surface fluctuations? #12;4 Objectives · Quantify effect of flow conditioner designs in terms of mean velocity and turbulence intensity just upstream
The Effect of Magnetic Turbulence Energy Spectra and
Ng, Chung-Sang
The Effect of Magnetic Turbulence Energy Spectra and Pickup Ions on the Heating of the Solar Wind ABVSW Z2: average turbulence energy with Z+ 2 = Z- 2 : turbulence correlation length T: solar wind of Alaska Fairbanks #12;MHD turbulence Energy cascade possible only if two Alfvén wave packets propagating
Experimental investigation of velocity biasing in laser Doppler anemometry
Wiedner, Brian Gregory
1988-01-01T23:59:59.000Z
Tech University; Chair of Advisory Commettee: Dr. Gerald L. Morrison The effects of several velocity bias reduction schemes were invest- igated using a 3-D laser Doppler anemometer and counter type (burst) signal processors. Amongst these schemes... of Sample Size on Effects of Sample Size on Effects of Sample Size on Effects of Sample Size on Velocity and Reynolds Stresses Axial Mean Velocity Radial Mean Velocity Axial Turbulence Intensity Radial Turbulence Intensity Axial/Radial Correlation...
Elena Amato; Pasquale Blasi
2006-06-23T23:59:59.000Z
Particle acceleration at astrophysical shocks may be very efficient if magnetic scattering is self-generated by the same particles. This nonlinear process adds to the nonlinear modification of the shock due to the dynamical reaction of the accelerated particles on the shock. Building on a previous general solution of the problem of particle acceleration with arbitrary diffusion coefficients (Amato & Blasi, 2005), we present here the first semi-analytical calculation of particle acceleration with both effects taken into account at the same time: charged particles are accelerated in the background of Alfven waves that they generate due to the streaming instability, and modify the dynamics of the plasma in the shock vicinity.
Sandia Energy - Measuring Inflow and Wake Flow Turbulence Using...
Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)
that characterizes inflow and wake flow velocity and turbulence around a vertical axis turbine deployed at the Roza Canal, Yakima, Washington. The ADV was mounted on a...
LaCure, Mari Mae
2010-04-29T23:59:59.000Z
Waves is the supporting document to the Master of Fine Arts thesis exhibition of the same title. Exhibited March 7-12 2010 in the Art and Design Gallery at the University of Kansas, Waves was comprised of a series of mixed media drawings...
Rogue Wave Modes for the Long Wave-Short Wave Resonance Kwok Wing CHOW*(1)
1 Rogue Wave Modes for the Long Wave-Short Wave Resonance Model Kwok Wing CHOW*(1) , Hiu Ning CHAN.45.Yv; 47.35.Fg ABSTRACT The long wave-short wave resonance model arises physically when the phase velocity of a long wave matches the group velocity of a short wave. It is a system of nonlinear evolution
SUR LES CASCADES D'ENERGIE EN ECOULEMENTS TURBULENTS CASCADE OF ENERGY IN TURBULENT FLOWS
Rosa, Ricardo M. S.
SUR LES CASCADES D'Â´ENERGIE EN Â´ECOULEMENTS TURBULENTS CASCADE OF ENERGY IN TURBULENT FLOWS CIPRIAN energy is transferred from low wave number modes to high wave number modes (L. Onsager (1945)). Such a transfer of energy occurs in a spectral range beyond that of injection of energy, and it underlies the so
Experimental study of internal wave generation by convection in water
Bars, Michael Le; Perrard, Stéphane; Ribeiro, Adolfo; Rodet, Laetitia; Aurnou, Jonathan M; Gal, Patrice Le
2015-01-01T23:59:59.000Z
We experimentally investigate the dynamics of water cooled from below at 0^oC and heated from above. Taking advantage of the unusual property that water's density maximum is at about 4^oC, this set-up allows us to simulate in the laboratory a turbulent convective layer adjacent to a stably stratified layer, which is representative of atmospheric and stellar conditions. High precision temperature and velocity measurements are described, with a special focus on the convectively excited internal waves propagating in the stratified zone. Most of the convective energy is at low frequency, and corresponding waves are localized to the vicinity of the interface. However, we show that some energy radiates far from the interface, carried by shorter horizontal wavelength, higher frequency waves. Our data suggest that the internal wave field is passively excited by the convective fluctuations, and the wave propagation is correctly described by the dissipative linear wave theory.
Can we characterize turbulence in premixed flames?
Lipatnikov, A.N. [Department of Applied Mechanics, Chalmers University of Technology, Gothenburg, 412 96 (Sweden)
2009-06-15T23:59:59.000Z
Modeling of premixed turbulent combustion involves averaging reaction rates in turbulent flows. The focus of most approaches to resolving this problem has been placed on determining the dependence of the mean rate w of product creation on the laminar flame speed S{sub L}, the rms turbulence velocity u', etc. The goal of the present work is to draw attention to another issue: May the input quantity u{sup '} for a model of w= w(u'/S{sub L},..) be considered to be known? The point is that heat release substantially affects turbulence and, hence, turbulence characteristics in premixed flames should be modeled. However, standard moment methods for numerically simulating turbulent flows do not allow us to evaluate the true turbulence characteristics in a flame. For instance, the Reynolds stresses in premixed flames are affected not only by turbulence itself, but also by velocity jump across flamelets. A common way to resolving this problem consists of considering the Reynolds stresses conditioned on unburned (or burned) mixture to be the true turbulence characteristics. In the present paper, this widely accepted but never proved hypothesis is put into question, first, by considering simple model constant-density problems (flame motion in an oscillating one-dimensional laminar flow; flame stabilized in a periodic shear, one-dimensional, laminar flow; turbulent mixing). In all the cases, the magnitude of velocity fluctuations, calculated using the conditioned Reynolds stresses, is affected by the intermittency of reactants and products and, hence, is not the true rms velocity. Second, the above claim is further supported by comparing balance equations for the mean and conditioned Reynolds stresses. The conditioned Reynolds stresses do not characterize the true turbulence in flames, because conditional averaging cuts off flow regions characterized by either high or low velocities. (author)
Vertical stratified turbulent transport mechanism indicated by remote sensing
Carl H. Gibson; R. Norris Keeler; Valery G. Bondur
2007-12-02T23:59:59.000Z
Satellite and shipboard data reveal the intermittent vertical information transport mechanism of turbulence and internal waves that mixes the ocean, atmosphere, planets and stars.
Advances in compressible turbulent mixing
Dannevik, W.P.; Buckingham, A.C.; Leith, C.E. [eds.
1992-01-01T23:59:59.000Z
This volume includes some recent additions to original material prepared for the Princeton International Workshop on the Physics of Compressible Turbulent Mixing, held in 1988. Workshop participants were asked to emphasize the physics of the compressible mixing process rather than measurement techniques or computational methods. Actual experimental results and their meaning were given precedence over discussions of new diagnostic developments. Theoretical interpretations and understanding were stressed rather than the exposition of new analytical model developments or advances in numerical procedures. By design, compressibility influences on turbulent mixing were discussed--almost exclusively--from the perspective of supersonic flow field studies. The papers are arranged in three topical categories: Foundations, Vortical Domination, and Strongly Coupled Compressibility. The Foundations category is a collection of seminal studies that connect current study in compressible turbulent mixing with compressible, high-speed turbulent flow research that almost vanished about two decades ago. A number of contributions are included on flow instability initiation, evolution, and transition between the states of unstable flow onset through those descriptive of fully developed turbulence. The Vortical Domination category includes theoretical and experimental studies of coherent structures, vortex pairing, vortex-dynamics-influenced pressure focusing. In the Strongly Coupled Compressibility category the organizers included the high-speed turbulent flow investigations in which the interaction of shock waves could be considered an important source for production of new turbulence or for the enhancement of pre-existing turbulence. Individual papers are processed separately.
Simultaneous and instantaneous measurement of velocity and density in rayleigh-taylor mixing layers
Kraft, Wayne Neal
2009-05-15T23:59:59.000Z
-driven turbulence in a statistically steady gas channel of helium and air ( 6 . 0 03 . 0 ? ? t A ). The capability of the diagnostic to simultaneously and instantaneously measure turbulent velocity and density fluctuations allows for a unique investigation...
The Effect of Magnetic Turbulence Energy Spectral
Ng, Chung-Sang
The Effect of Magnetic Turbulence Energy Spectral Scaling on the Heating of the Solar Wind C. S. Ng #12;MHD turbulence Energy cascade possible only if two Alfvén wave packets propagating in opposite directions collide · Time scales: Eddy turn-over time N ~1/ kvk Alfvén time A ~1/ kVA N N Energy cascade
Theory of laminated turbulence: open questions
E. Kartashova
2006-11-17T23:59:59.000Z
Theory of laminated turbulnece includes continuous layer of turbulence (statistical description, kinetic equations, Zakharov-Kolmogorov spectra, etc) AND discrete layer of turbulence (isolated groups of interacting waves, no statisticaldescription). This theory is presented, examples of possible applications are given, important open questions are formulated.
Lin, Andrew Tien-Shun
for the presence of gas hydrate are strong. In this study, we perform velocity analysis of the 6 4-component OBS of the velocities are observed. We then investigate the large scale gas hydrate content through rock physic modeling, and the acoustic veloci- ties predicted for a set of gas hydrate, quartz and clay contents are com- pared
Quantum Turbulence Matthew S. Paoletti
Texas at Austin. University of
critically review the diverse theoretical, computational, and experimental approaches from the point of view distinction between the velocity statistics of quantum and classical turbulence is exhibited and used of experimental observers. Similarities and differences between the general properties of classical and quantum
Bedforms in a turbulent stream.Part 1: Turbulent flow over topography
A. Fourrière; P. Claudin; B. Andreotti
2008-11-14T23:59:59.000Z
In the context of subaqueous ripple and dune formation, we present here a Reynolds averaged calculation of the turbulent flow over a topography. We perform a weakly non-linear expansion of the velocity field, sufficiently accurate to recover the separation of streamlines and the formation of a recirculation bubble above some aspect ratio. The basal stresses are investigated in details; in particular, we show that the phase shift of the shear stress with respect to the topography, responsible for the formation of bedforms, appears in an inner boundary layer where shear stress and pressure gradients balance. We study the sensitivity of the calculation with respect to (i) the choice of the turbulence closure, (ii) the motion of the bottom (growth or propagation), (iii) the physics at work in the surface layer, responsible for the hydrodynamic roughness of the bottom, (iv) the aspect ratio of the bedform and (v) the effect of the free surface, which can be interpreted in terms of standing gravity waves excited by topography. The most important effects are those of points (iii) to (v). We show that the dynamical mechanisms controlling the hydrodynamical roughness (mixing due to roughness elements, viscosity, sediment transport, etc) have an influence on the basal shear stress when the thickness of the surface layer is comparable to that of the inner layer. We evidence that non-linear effects tend to oppose linear ones and are of the same order for bedform aspect ratios of the order of 1/10. We show that the influence of the free surface on the basal shear stress is dominant when the wavelength is large compared to the flow depth, so that the inner layer extends throughout the flow and in the resonant conditions, and when the downstream material velocity balances the upstream wave propagation.
ON QUIET-TIME SOLAR WIND ELECTRON DISTRIBUTIONS IN DYNAMICAL EQUILIBRIUM WITH LANGMUIR TURBULENCE
Zaheer, S. [Permanent address: Department of Physics, Forman Christian College, Lahore, Punjab 54000, Pakistan. (Pakistan); Yoon, P. H. [Also at SSR, KHU, Yongin, Korea. (Korea, Republic of)
2013-10-01T23:59:59.000Z
A recent series of papers put forth a self-consistent theory of an asymptotically steady-state electron distribution function and Langmuir turbulence intensity. The theory was developed in terms of the ? distribution which features Maxwellian low-energy electrons and a non-Maxwellian energetic power-law tail component. The present paper discusses a generalized ? distribution that features a Davydov-Druyvesteyn type of core component and an energetic power-law tail component. The physical motivation for such a generalization is so that the model may reflect the influence of low-energy electrons interacting with low-frequency kinetic Alfvénic turbulence as well as with high-frequency Langmuir turbulence. It is shown that such a solution and the accompanying Langmuir wave spectrum rigorously satisfy the balance requirement between the spontaneous and induced emission processes in both the particle and wave kinetic equations, and approximately satisfy the similar balance requirement between the spontaneous and induced scattering processes, which are nonlinear. In spite of the low velocity modification of the electron distribution function, it is shown that the resulting asymptotic velocity power-law index ?, where f{sub e} ? v {sup –?} is close to the average index observed during the quiet-time solar wind condition, i.e., ? ? O(6.5) whereas ?{sub average} ? 6.69, according to observation.
Phase mixing vs. nonlinear advection in drift-kinetic plasma turbulence
Schekochihin, A A; Highcock, E G; Dellar, P J; Dorland, W; Hammett, G W
2015-01-01T23:59:59.000Z
A scaling theory of long-wavelength electrostatic turbulence in a magnetised, weakly collisional plasma (e.g., drift-wave turbulence driven by temperature gradients) is proposed, with account taken both of the nonlinear advection of the perturbed particle distribution by fluctuating ExB flows and of its phase mixing, which is caused by the streaming of the particles along the mean magnetic field and, in a linear problem, would lead to Landau damping. A consistent theory is constructed in which very little free energy leaks into high velocity moments of the distribution, rendering the turbulent cascade in the energetically relevant part of the wave-number space essentially fluid-like. The velocity-space spectra of free energy expressed in terms of Hermite-moment orders are steep power laws and so the free-energy content of the phase space does not diverge at infinitesimal collisionality (while it does for a linear problem); collisional heating due to long-wavelength perturbations vanishes in this limit (also i...
Energy spectra of finite temperature superfluid helium-4 turbulence
Kivotides, Demosthenes [Department of Aeronautics, Imperial College London, London SW7 2AZ (United Kingdom)
2014-10-15T23:59:59.000Z
A mesoscopic model of finite temperature superfluid helium-4 based on coupled Langevin-Navier-Stokes dynamics is proposed. Drawing upon scaling arguments and available numerical results, a numerical method for designing well resolved, mesoscopic calculations of finite temperature superfluid turbulence is developed. The application of model and numerical method to the problem of fully developed turbulence decay in helium II, indicates that the spectral structure of normal-fluid and superfluid turbulence is significantly more complex than that of turbulence in simple-fluids. Analysis based on a forced flow of helium-4 at 1.3 K, where viscous dissipation in the normal-fluid is compensated by the Lundgren force, indicate three scaling regimes in the normal-fluid, that include the inertial, low wavenumber, Kolmogorov k{sup ?5/3} regime, a sub-turbulence, low Reynolds number, fluctuating k{sup ?2.2} regime, and an intermediate, viscous k{sup ?6} range that connects the two. The k{sup ?2.2} regime is due to normal-fluid forcing by superfluid vortices at high wavenumbers. There are also three scaling regimes in the superfluid, that include a k{sup ?3} range that corresponds to the growth of superfluid vortex instabilities due to mutual-friction action, and an adjacent, low wavenumber, k{sup ?5/3} regime that emerges during the termination of this growth, as superfluid vortices agglomerate between intense normal-fluid vorticity regions, and weakly polarized bundles are formed. There is also evidence of a high wavenumber k{sup ?1} range that corresponds to the probing of individual-vortex velocity fields. The Kelvin waves cascade (the main dynamical effect in zero temperature superfluids) appears to be damped at the intervortex space scale.
Rothstein, Jonathan
An analysis of superhydrophobic turbulent drag reduction mechanisms using direct numerical October 2009; accepted 22 April 2010; published online 11 June 2010 Superhydrophobic surfaces combine the drag reducing performance of superhydrophobic surfaces in turbulent channel flow. Slip velocities, wall
Resonant Interactions in Rotating Homogeneous Three-dimensional Turbulence
Q. Chen; S. Chen; G. L. Eyink; D. D. Holm
2004-04-29T23:59:59.000Z
Direct numerical simulations of three-dimensional (3D) homogeneous turbulence under rapid rigid rotation are conducted to examine the predictions of resonant wave theory for both small Rossby number and large Reynolds number. The simulation results reveal that there is a clear inverse energy cascade to the large scales, as predicted by 2D Navier-Stokes equations for resonant interactions of slow modes. As the rotation rate increases, the vertically-averaged horizontal velocity field from 3D Navier-Stokes converges to the velocity field from 2D Navier-Stokes, as measured by the energy in their difference field. Likewise, the vertically-averaged vertical velocity from 3D Navier-Stokes converges to a solution of the 2D passive scalar equation. The energy flux directly into small wave numbers in the $k_z=0$ plane from non-resonant interactions decreases, while fast-mode energy concentrates closer to that plane. The simulations are consistent with an increasingly dominant role of resonant triads for more rapid rotation.
Lunar Laser-Ranging Detection of Light-Speed Anisotropy and Gravitational Waves
Reginald T Cahill
2010-02-03T23:59:59.000Z
The Apache Point Lunar Laser-ranging Operation (APOLLO), in NM, can detect photon bounces from retro-reflectors on the moon surface to 0.1ns timing resolution. This facility enables not only the detection of light speed anisotropy, which defines a local preferred frame of reference - only in that frame is the speed of light isotropic, but also fluctuations/turbulence (gravitational waves) in the flow of the dynamical 3-space relative to local systems/observers. So the APOLLO facility can act as an effective "gravitational wave" detector. A recently published small data set from November 5, 2007, is analysed to characterise both the average anisotropy velocity and the wave/turbulence effects. The results are consistent with some 13 previous detections, with the last and most accurate being from the spacecraft earth-flyby Doppler-shift NASA data.
TURBULENT FRBRNNING MVK130 Turbulent Combustion
TURBULENT FÖRBRÄNNING MVK130 Turbulent Combustion Poäng: 3.0 Betygskala: TH Valfri för: M4 to combustion, McGraw-Hill 1996. #12;
Gravitational Collapse in Turbulent Molecular Clouds. II. Magnetohydrodynamical Turbulence
F. Heitsch; M. -M. Mac Low; R. S. Klessen
2000-09-14T23:59:59.000Z
Hydrodynamic supersonic turbulence can only prevent local gravitational collapse if the turbulence is driven on scales smaller than the local Jeans lengths in the densest regions, a very severe requirement (Paper I). Magnetic fields have been suggested to support molecular clouds either magnetostatically or via magnetohydrodynamic (MHD) waves. Whereas the first mechanism would form sheet-like clouds, the second mechanism not only could exert a pressure onto the gas counteracting the gravitational forces, but could lead to a transfer of turbulent kinetic energy down to smaller spatial scales via MHD wave interactions. This turbulent magnetic cascade might provide sufficient energy at small scales to halt local collapse. We test this hypothesis with MHD simulations at resolutions up to 256^3 zones, done with ZEUS-3D. We first derive a resolution criterion for self-gravitating, magnetized gas: in order to prevent collapse of magnetostatically supported regions due to numerical diffusion, the minimum Jeans length must be resolved by four zones. Resolution of MHD waves increases this requirement to roughly six zones. We then find that magnetic fields cannot prevent local collapse unless they provide magnetostatic support. Weaker magnetic fields do somewhat delay collapse and cause it to occur more uniformly across the supported region in comparison to the hydrodynamical case. However, they still cannot prevent local collapse for much longer than a global free-fall time.
'ITENUATiON AND VELOCITY OF BEREA SANDSTONE MEASURED IN THE FREQUENCY DOMAIN T. J. Shank!and1 Institutde.Usingmeasurementsinthefrequencydomainwe havemeasuredqualityfactorQandtraveltimesofdirectand side-reflectedelasticwavesin a 1.8mlongsampleofBerea sandstoneDVM. Possibletravelpathsinadditiontodirecttransmissioninclude sidewall reflectionsandsurfacewaves. 391 #12;392 Shanklandetal.:AttenuationandVelocityofSandstone
Overview of the TurbSim Stochastic Inflow Turbulence Simulator
Kelley, N. D.; Jonkman, B. J.
2005-09-01T23:59:59.000Z
The TurbSim stochastic inflow turbulence code was developed to provide a numerical simulation of a full-field flow that contains coherent turbulence structures that reflect the proper spatiotemporal turbulent velocity field relationships seen in instabilities associated with nocturnal boundary layer flows that are not represented well by the IEC Normal Turbulence Models (NTM). Its purpose is to provide the wind turbine designer with the ability to drive design code (FAST or MSC.ADAMS) simulations of advanced turbine designs with simulated inflow turbulence environments that incorporate many of the important fluid dynamic features known to adversely affect turbine aeroelastic response and loading.
A Dynamical Model of Plasma Turbulence in the Solar Wind
Howes, G G
2015-01-01T23:59:59.000Z
A dynamical approach, rather than the usual statistical approach, is taken to explore the physical mechanisms underlying the nonlinear transfer of energy, the damping of the turbulent fluctuations, and the development of coherent structures in kinetic plasma turbulence. It is argued that the linear and nonlinear dynamics of Alfven waves are responsible, at a very fundamental level, for some of the key qualitative features of plasma turbulence that distinguish it from hydrodynamic turbulence, including the anisotropic cascade of energy and the development of current sheets at small scales. The first dynamical model of kinetic turbulence in the weakly collisional solar wind plasma that combines self-consistently the physics of Alfven waves with the development of small-scale current sheets is presented and its physical implications are discussed. This model leads to a simplified perspective on the nature of turbulence in a weakly collisional plasma: the nonlinear interactions responsible for the turbulent casca...
A sufficient condition for Gaussian departure in turbulence
Daniela Tordella; Michele Iovieno; Peter Roger Bailey
2007-10-17T23:59:59.000Z
The interaction of two isotropic turbulent fields of equal integral scale but different kinetic energy generates the simplest kind of inhomogeneous turbulent field. In this paper we present a numerical experiment where two time decaying isotropic fields of kinetic energies $E_1$ and $E_2$ initially match over a narrow region. Within this region the kinetic energy varies as a hyperbolic tangent. The following temporal evolution produces a shearless mixing. The anisotropy and intermittency of velocity and velocity derivative statistics is observed. In particular the asymptotic behavior in time and as a function of the energy ratio $E_1/E_2 \\to \\infty$ is discussed. This limit corresponds to the maximum observable turbulent energy gradient for a given $E_1$ and is obtained through the limit $E_2 \\to 0$. A field with $E_1/E_2 \\to \\infty$ represents a mixing which could be observed near a surface subject to a very small velocity gradient separating two turbulent fields, one of which is nearly quiescent. In this condition the turbulent penetration is maximum and reaches a value equal to 1.2 times the nominal mixing layer width. The experiment shows that the presence of a turbulent energy gradient is sufficient for the appearance of intermittency and that during the mixing process the pressure transport is not negligible with respect to the turbulent velocity transport. These findings may open the way to the hypothesis that the presence of a gradient of turbulent energy is the minimal requirement for Gaussian departure in turbulence.
Turbulence Induced Transport in Tokamaks
Caldas, I. L.; Marcus, F. A.; Heller, M. V. A. P.; Guimaraes-Filho, Z. O. [Instituto de Fisica, Universidade de Sao Paulo, Caixa Postal 66318, 05315-970, Sao Paulo, SP (Brazil); Batista, A. M. [Departamento de Matematica e Estatistica, Universidade Estadual de Ponta Grossa, Ponta Grossa, PR (Brazil); Viana, R. L.; Lopes, S. R. [Departamento de Fisica, Universidade Federal do Parana, 81531-990, Curitiba, PR (Brazil); Morrison, P. J.; Horton, W. [Department of Physics, University of Texas at Austin, Austin, Texas, 78712 (United States); Institute for Fusion Studies, The University of Texas at Austin, Austin, Texas, 78712 (United States)
2006-12-04T23:59:59.000Z
This report is concerned with plasma edge turbulence and its relation to anomalous particle transport in tokamaks. First, experimental evidence of turbulence driven particle transport and measurements of the gradients of the equilibrium profiles in the Brazilian tokamaks TBR and TCABR are presented. Next, diffusion in a two drift-wave system is discussed. In this nonintegrable system, particle transport is associated with the onset of chaotic orbits. Finally, numerical evidence suggesting that a nonlinear three-mode interaction could contribute to the intermittent plasma fluctuations observed in tokamaks is presented.
The Origin of Molecular Cloud Turbulence
Padoan, Paolo; Haugboelle, Troels; Nordlund, Ake
2015-01-01T23:59:59.000Z
Turbulence is ubiquitous in molecular clouds (MCs), but its origin is still unclear because MCs are usually assumed to live longer than the turbulence dissipation time. It has been shown that interstellar medium (ISM) turbulence is likely driven by SN explosions, but it has never been demonstrated that SN explosions can establish and maintain a turbulent cascade inside MCs consistent with the observations. In this work, we carry out a simulation of SN-driven turbulence in a volume of (250 pc)^3, specifically designed to test if SN driving alone can be responsible for the observed turbulence inside MCs. We find that SN driving establishes velocity scaling consistent with the usual scaling laws of supersonic turbulence. This also means that previous idealized simulations of MC turbulence, driven with a random, large-scale volume force, were correctly adopted as appropriate models for MC turbulence, despite the artificial driving. We also find the same scaling laws extend to the interior of MCs, and their normal...
B. V. Chirikov; V. G. Davidovsky
2000-06-15T23:59:59.000Z
The results of numerical experiments on the structure of chaotic attractors in the Khalatnikov - Kroyter model of two freedoms are presented. This model was developed for a qualitative description of the wave turbulence of the second sound in helium. The attractor dimension, size, and the maximal Lyapunov exponent in dependence on the single dimensionless parameter $F$ of the model are found and discussed. The principal parameter $F$ is similar to the Reynolds number in hydrodynamic turbulence. We were able to discern four different attractors characterized by a specific critical value of the parameter ($F=F_{cr}$), such that the attractor exists for $F>F_{cr}$ only. A simple empirical relation for this dependence on the argument ($F-F_{cr}$) is presented which turns out to be universal for different attractors with respect to the dimension and dimensionless Lyapunov exponents. Yet, it differs as to the size of attractor. In the main region of our studies the dependence of all dimensionless characteristics of the chaotic attractor on parameter $F$ is very slow (logarithmic) which is qualitatively different as compared to that of a multi-freedom attractor, e.g., in hydrodynamic turbulence (a power law). However, at very large $F\\sim 10^7$ the transition to a power-law dependence has been finally found, similar to the multi-freedom attractor. Some unsolved problems and open questions are also discussed.
Diffusion Processes in Turbulent Magnetic Fields
Alex Lazarian
2007-07-05T23:59:59.000Z
We study of the effect of turbulence on diffusion processes within magnetized medium. While we exemplify our treatment with heat transfer processes, our results are quite general and are applicable to different processes, e.g. diffusion of heavy elements. Our treatment is also applicable to describing the diffusion of cosmic rays arising from magnetic field wandering. In particular, we find that when the energy injection velocity is smaller than the Alfven speed the heat transfer is partially suppressed, while in the opposite regime the effects of turbulence depend on the intensity of driving. In fact, the scale $l_A$ at which the turbulent velocity is equal the Alfven velocity is a new important parameter. When the electron mean free path $\\lambda$ is larger than $l_A$, the stronger the the turbulence, the lower thermal conductivity by electrons is. The turbulent motions, however, induces their own advective transport, that can provide effective diffusivity. For clusters of galaxies, we find that the turbulence is the most important agent for heat transfer. We also show that the domain of applicability of the subdiffusion concept is rather limited.
Turbulent transport phenomena in a channel with periodic rib turbulators
Liou, T.M.; Hwang, J.J.; Chen, S.H. (National Tsing Hua University, Hsinchu (Taiwan))
1992-09-01T23:59:59.000Z
Periodic fully developed turbulent flow in a 2D channel with rib turbulators on two opposite walls has been studied numerically and experimentally. In numerical predictions, an algebraic Reynolds stress turbulence model is adopted, and a smoothed hybrid central/skew upstream difference scheme is developed. In experiments, the laser-Doppler velocimetry and laser holographic interferometry are employed to measure the local flow and heat transfer characteristics. The results are obtained with the ratio of pitch to rib height 5, 10, 15, and 20, for Reynolds number of 3.3 x 10 exp 4 and are presented in terms of the reattachment length, mean velocity and turbulent kinetic energy profiles, isotherm patterns, and distributions of local pressure recovery and Nusselt number. A detailed comparison with experimental data shows that the present calculations have an improvement over the previous work in the prediction of periodic ribbed-wall flow and heat transfer. In addition, regions susceptible to hot spots are identified by examining the distributions of the local Nusselt number. Furthermore, the enhancement of mean Nusselt number is documented in terms of relative contributions of the increased turbulence intensity and surface area provided by the ribs. 32 refs.
Hybrid Vlasov-Maxwell simulations of two-dimensional turbulence in plasmas
Valentini, F.; Servidio, S.; Veltri, P. [Dipartimento di Fisica, Università della Calabria, I-87036 Rende (CS) (Italy); Perrone, D. [LESIA, Observatoire de Paris, 92190 Meudon (France); Califano, F. [Dipartimento di Fisica and CNISM, Università di Pisa, 56127 Pisa (Italy); Matthaeus, W. H. [Department of Physics and Astronomy, Bartol Research Institute, University of Delaware, Newark, Delaware 19716 (United States)
2014-08-15T23:59:59.000Z
Turbulence in plasmas is a very challenging problem since it involves wave-particle interactions, which are responsible for phenomena such as plasma dissipation, acceleration mechanisms, heating, temperature anisotropy, and so on. In this work, a hybrid Vlasov-Maxwell numerical code is employed to study local kinetic processes in a two-dimensional turbulent regime. In the present model, ions are treated as a kinetic species, while electrons are considered as a fluid. As recently reported in [S. Servidio, Phys. Rev. Lett. 108, 045001 (2012)], nearby regions of strong magnetic activity, kinetic effects manifest through a deformation of the ion velocity distribution function that consequently departs from the equilibrium Maxwellian configuration. Here, the structure of turbulence is investigated in detail in phase space, by evaluating the high-order moments of the particle velocity distribution, i.e., temperature, skewness, and kurtosis. This analysis provides quantitative information about the non-Maxwellian character of the system dynamics. This departure from local thermodynamic equilibrium triggers several processes commonly observed in many astrophysical and laboratory plasmas.
Alfvenic Turbulence in the Extended Solar Corona: Kinetic Effects and Proton Heating
S. R. Cranmer; A. A. van Ballegooijen
2003-05-08T23:59:59.000Z
We present a model of magnetohydrodynamic (MHD) turbulence in the extended solar corona that contains the effects of collisionless dissipation and anisotropic particle heating. Measurements made by UVCS/SOHO have revived interest in the idea that ions are energized by the dissipation of ion cyclotron resonant waves, but such high-frequency (i.e., small wavelength) fluctuations have not been observed. A turbulent cascade is one possible way of generating small-scale fluctuations from a pre-existing population of low-frequency MHD waves. We model this cascade as a combination of advection and diffusion in wavenumber space. The dominant spectral transfer occurs in the direction perpendicular to the background magnetic field. As expected from earlier models, this leads to a highly anisotropic fluctuation spectrum with a rapidly decaying tail in parallel wavenumber. The wave power that decays to high enough frequencies to become ion cyclotron resonant depends on the relative strengths of advection and diffusion in the cascade. For the most realistic values of these parameters, though, there is insufficient power to heat protons and heavy ions. The dominant oblique fluctuations (with dispersion properties of kinetic Alfven waves) undergo Landau damping, which implies strong parallel electron heating. We discuss the probable nonlinear evolution of the electron velocity distributions into parallel beams and discrete phase-space holes (similar to those seen in the terrestrial magnetosphere) which can possibly heat protons via stochastic interactions.
Signatures of fast and slow magnetohydrodynamic shocks in turbulent molecular clouds
Lehmann, Andrew
2015-01-01T23:59:59.000Z
The character of star formation is intimately related to the supersonic magnetohydrodynamic (MHD) turbulent dynamics of the giant molecular clouds in which stars form. A significant amount of the turbulent energy dissipates in low-velocity shock waves. These shocks cause molecular line cooling of the compressed and heated gas, and so their radiative signatures probe the nature of the turbulence. In MHD fluids the three distinct families of shocks---fast, intermediate and slow---differ in how they compress and heat the molecular gas, and so observational differences between them may also distinguish driving modes of turbulent regions. Here we use a two-fluid model to compare the characteristics of one-dimensional fast and slow MHD shocks propagating at low speeds (a few km/s) in molecular clouds. Fast MHD shocks are magnetically driven, forcing ion species to stream through the neutral gas ahead of the shock front. This magnetic precursor heats the gas sufficiently to create a large, warm transition zone where...
Modelling of turbulent stratified flames
Darbyshire, Oliver Richard
) shows data with a negative correlation, (b) shows data with no correlation and (c) shows data with a positive correlation. . . . . . . . . 44 3.3 Flow chart of the SIMPLE algorithm. . . . . . . . . . . . . . . . . . . . . 50 3.4 Schematic of the V... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 4.1 Comparison of predicted and measured velocities (m/s) and turbulence kinetic energy (m2/s2) for the cold flow ORACLES experiment. . . . . . 64 4.2 Comparison of cold flow results for the V-flame case. Mean axial velocity is shown on the left...
Penetration of lower hybrid current drive waves in tokamaks
Horton, W. [The University of Texas at Austin, Austin, Texas 78712 (United States) [The University of Texas at Austin, Austin, Texas 78712 (United States); Aix-Marseille University, 58, Bd Charles Livon, 13284 Marseille (France); Goniche, M.; Peysson, Y.; Decker, J.; Ekedahl, A.; Litaudon, X. [CEA, IRFM, F-13108 Saint-Paul-Lez Durance (France)] [CEA, IRFM, F-13108 Saint-Paul-Lez Durance (France)
2013-11-15T23:59:59.000Z
Lower hybrid (LH) ray propagation in toroidal plasma is shown to be controlled by combination of the azimuthal spectrum launched by the antenna, the poloidal variation of the magnetic field, and the scattering of the waves by the drift wave fluctuations. The width of the poloidal and radial radio frequency wave spectrum increases rapidly as the rays penetrate into higher density and scatter from the drift waves. The electron temperature gradient (ETG) spectrum is particularly effective in scattering the LH waves due to its comparable wavelengths and phase velocities. ETG turbulence is also driven by the radial gradient of the electron current profile giving rise to an anomalous viscosity spreading the LH driven plasma currents. The LH wave scattering is derived from a Fokker-Planck equation for the distribution of the ray trajectories with diffusivities derived from the drift wave fluctuations. The condition for chaotic diffusion for the rays is derived. The evolution of the poloidal and radial mode number spectrum of the lower hybrid waves are both on the antenna spectrum and the spectrum of the drift waves. Antennas launching higher poloidal mode number spectra drive off-axis current density profiles producing negative central shear [RS] plasmas with improved thermal confinement from ETG transport. Core plasma current drive requires antennas with low azimuthal mode spectra peaked at m = 0 azimuthal mode numbers.
Combustion-turbulence interaction in the turbulent boundary layer over a hot surface
Ng, T.T.; Cheng, R.K.; Robben, F.; Talbot, L.
1982-01-01T23:59:59.000Z
The turbulence-combustion interaction in a reacting turbulent boundary layer over a heated flat plate was studied. Ethylene/air mixture with equivalence ratio of 0.35 was used. The free stream velocity was 10.5 m/s and the wall temperature was 1250/sup 0/K. Combustion structures visualization was provided by high-speed schlieren photographs. Fluid density statistics were deduced from Rayleigh scattering intensity measurements. A single-component laser Doppler velocimetry system was used to obtain mean and root-mean-square velocity distributions, the Reynolds stress, the streamwise and the cross-stream turbulent kinetic energy diffusion, and the production of turbulent kinetic energy by Reynolds stress. The combustion process was dominated by large-scale turbulent structures of the boundary layer. Combustion causes expansion of the boundary layer. No overall self-similarity is observed in either the velocity or the density profiles. Velocity fluctuations were increased in part of the boundary layer and the Reynolds stress was reduced. The turbulent kinetic energy diffusion pattern was changed significantly and a modification of the boundary layer assumption will be needed when dealing with this problem analytically. 11 figures, 1 table.
Effects of electron drift on the collisionless damping of kinetic Alfv\\'en waves in the solar wind
Tong, Yuguang; Chen, Christopher H K; Salem, Chadi S; Verscharen, Daniel
2015-01-01T23:59:59.000Z
The collisionless dissipation of anisotropic Alfv\\'enic turbulence is a promising candidate to solve the solar wind heating problem. Extensive studies examined the kinetic properties of Alfv\\'en waves in simple Maxwellian or bi-Maxwellian plasmas. However, the observed electron velocity distribution functions in the solar wind are more complex. In this study, we analyze the properties of kinetic Alfv\\'en waves in a plasma with two drifting electron populations. We numerically solve the linearized Maxwell-Vlasov equations and find that the damping rate and the proton-electron energy partition for kinetic Alfv\\'en waves are significantly modified in such plasmas, compared to plasmas without electron drifts. We suggest that electron drift is an important factor to take into account when considering the dissipation of Alfv\\'enic turbulence in the solar wind or other $\\beta \\sim 1$ astrophysical plasmas.
Magnetohydrodynamic lattice Boltzmann simulations of turbulence and rectangular jet flow
Riley, Benjamin Matthew
2009-05-15T23:59:59.000Z
Magnetohydrodynamic (MHD) investigations of decaying isotropic turbulence and rectangular jets (RJ) are carried out. A novel MHD lattice Boltzmann scheme that combines multiple relaxation time (MRT) parameters for the velocity field with a single...
Charecterization of inertial and pressure effects in homogeneous turbulence
Bikkani, Ravi Kiran
2005-11-01T23:59:59.000Z
and anisotropy components and invariants are examined. In the second part of the thesis, the velocity gradient dynamics in turbulent flows are studied with the help of inviscid 3D Burgers equations and restricted Euler equations. The analytical asymptotic...
Concepts in strong Langmuir turbulence theory
DuBois, D.F.; Rose, H.A.
1990-01-01T23:59:59.000Z
Some of the basic concepts of strong Langmuir turbulence (SLT) theory are reviewed. In SLT system, a major fraction of the turbulent energy is carried by local, time-dependent, nonlinear excitations called cavitons. Modulational instability, localization of Langmuir fields by density fluctuations, caviton nucleation, collapse, and burnout and caviton correlations are reviewed. Recent experimental evidence will be presented for SLT phenomena in the interaction of powerful HF waves with the ionosphere and in laser-plasma interaction experiments. 38 refs., 11 figs.
Incloud turbulence structure of marine stratocumulus N. Riemer,1
of turbulent kinetic energy is dominantly driven by wind shear. Citation: Ching, J., N. Riemer, M. Dunn, and M3 Received 10 August 2010; revised 14 September 2010; accepted 20 September 2010; published 6) in July 2005, and identifies the dominant sources of turbulent kinetic energy. We used vertical veloc- ity
RESEARCH ARTICLE Particles for tracing turbulent liquid helium
Lathrop, Daniel P.
RESEARCH ARTICLE Particles for tracing turbulent liquid helium Gregory P. Bewley Æ K. R of local flow velocities in turbulent liquid helium, using tracer particles. We survey and evaluate, we note that cryogenic helium is attractive for experimental studies because its kinematic viscosity
Stress Wave Source Characterization: Impact, Fracture, and Sliding Friction
McLaskey, Gregory Christofer
2011-01-01T23:59:59.000Z
717-725. Graff, K. (1975). Wave Motion in Elastic Solids (and deterioration on stress wave velocities in concrete,Greenspan, M. (1981) Surface-wave displacement: absolute
New perspectives on superparameterization for geophysical turbulence
Majda, Andrew J. [Center for Atmosphere Ocean Science, Courant Institute of Mathematical Sciences, New York University, 251 Mercer St., New York, NY 10012 (United States); Center for Prototype Climate Modelling, NYU Abu Dhabi, Abu Dhabi (United Arab Emirates); Grooms, Ian, E-mail: grooms@cims.nyu.edu [Center for Atmosphere Ocean Science, Courant Institute of Mathematical Sciences, New York University, 251 Mercer St., New York, NY 10012 (United States)
2014-08-15T23:59:59.000Z
This is a research expository paper regarding superparameterization, a class of multi-scale numerical methods designed to cope with the intermittent multi-scale effects of inhomogeneous geophysical turbulence where energy often inverse-cascades from the unresolved scales to the large scales through the effects of waves, jets, vortices, and latent heat release from moist processes. Original as well as sparse space–time superparameterization algorithms are discussed for the important case of moist atmospheric convection including the role of multi-scale asymptotic methods in providing self-consistent constraints on superparameterization algorithms and related deterministic and stochastic multi-cloud parameterizations. Test models for the statistical numerical analysis of superparameterization algorithms are discussed both to elucidate the performance of the basic algorithms and to test their potential role in efficient multi-scale data assimilation. The very recent development of grid-free seamless stochastic superparameterization methods for geophysical turbulence appropriate for “eddy-permitting” mesoscale ocean turbulence is presented here including a general formulation and illustrative applications to two-layer quasigeostrophic turbulence, and another difficult test case involving one-dimensional models of dispersive wave turbulence. This last test case has randomly generated solitons as coherent structures which collapse and radiate wave energy back to the larger scales, resulting in strong direct and inverse turbulent energy cascades.
WAVE-ENERGY DENSITY AND WAVE-MOMENTUM DENSITY OF EACH SPECIES OF A COLLISION-LESS PLASMA
Cary, John R.
2012-01-01T23:59:59.000Z
case, the electrons have negative wave energy for 2w ne w wave energy for 2w .w > 0 nl Hence, unstable waves with negative phase velocity,
DETERMINATION OF NON-THERMAL VELOCITY DISTRIBUTIONS FROM SERTS LINEWIDTH OBSERVATIONS
Coyner, Aaron J. [Department of Physics, Catholic University of America, 620 Michigan Avenue, Washington, DC 20064 (United States); Davila, Joseph M., E-mail: aaron.j.coyner@nasa.gov [Code 671, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
2011-12-01T23:59:59.000Z
Non-thermal velocities obtained from the measurement of coronal Extreme Ultraviolet (EUV) linewidths have been consistently observed in solar EUV spectral observations and have been theorized to result from many plausible scenarios including wave motions, turbulence, or magnetic reconnection. Constraining these velocities can provide a physical limit for the available energy resulting from unresolved motions in the corona. We statistically determine a series of non-thermal velocity distributions from linewidth measurements of 390 emission lines from a wide array of elements and ionization states observed during the Solar Extreme Ultraviolet Research Telescope and Spectrograph 1991-1997 flights covering the spectral range 174-418 A and a temperature range from 80,000 K to 12.6 MK. This sample includes 248 lines from active regions, 101 lines from quiet-Sun regions, and 41 lines were observed from plasma off the solar limb. We find a strongly peaked distribution corresponding to a non-thermal velocity of 19-22 km s{sup -1} in all three of the quiet-Sun, active region, and off-limb distributions. For the possibility of Alfven wave resonance heating, we find that velocities in the core of these distributions do not provide sufficient energy, given typical densities and magnetic field strengths for the coronal plasma, to overcome the estimated coronal energy losses required to maintain the corona at the typical temperatures working as the sole mechanism. We find that at perfect efficiency 50%-60% of the needed energy flux can be produced from the non-thermal velocities measured.
TURBULENT FRBRNNING MVK 130 Turbulent Combustion
TURBULENT FÖRBRÄNNING MVK 130 Turbulent Combustion Antal poäng: 3.0. Valfri för: M4. Kursansvarig program med hänsyn till de modeller som används. Litteratur S.R. Turns: An introduction to combustion, Mc
Azimuthally Anisotropic 3D Velocity Continuation
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Burnett, William; Fomel, Sergey
2011-01-01T23:59:59.000Z
We extend time-domain velocity continuation to the zero-offset 3D azimuthally anisotropic case. Velocity continuation describes how a seismic image changes given a change in migration velocity. This description turns out to be of a wave propagation process, in which images change along a velocity axis. In the anisotropic case, the velocity model is multiparameter. Therefore, anisotropic image propagation is multidimensional. We use a three-parameter slowness model, which is related to azimuthal variations in velocity, as well as their principal directions. This information is useful for fracture and reservoir characterization from seismic data. We provide synthetic diffraction imaging examples to illustratemore »the concept and potential applications of azimuthal velocity continuation and to analyze the impulse response of the 3D velocity continuation operator.« less
Local Energy Velocity of Classical Fields
I. V. Drozdov; A. A. Stahlhofen
2007-04-19T23:59:59.000Z
It is proposed to apply a recently developed concept of local wave velocities to the dynamical field characteristics, especially for the canonical field energy density. It is shown that local energy velocities can be derived from the lagrangian directly. The local velocities of zero- and first- order for energy propagation has been obtained for special cases of scalar and vector fields. Some important special cases of these results are discussed.
Inhomogeneous distribution of droplets in cloud turbulence
Itzhak Fouxon; Yongnam Park; Roei Harduf; Changhoon Lee
2014-10-30T23:59:59.000Z
We solve the problem of spatial distribution of inertial particles that sediment in turbulent flow with small ratio of acceleration of fluid particles to acceleration of gravity $g$. The particles are driven by linear drag and have arbitrary inertia. The pair-correlation function of concentration obeys a power-law in distance with negative exponent. Divergence at zero signifies singular distribution of particles in space. Independently of particle size the exponent is ratio of integral of energy spectrum of turbulence times the wavenumber to $g$ times numerical factor. We find Lyapunov exponents and confirm predictions by direct numerical simulations of Navier-Stokes turbulence. The predictions include typical case of water droplets in clouds. This significant progress in the study of turbulent transport is possible because strong gravity makes the particle's velocity at a given point unique.
Propagating and stationary superfluid turbulent fronts
Castiglione, J.; Murphy, P.J.; Tough, J.T.; Hayot, F. [Ohio State Univ., Columbus, OH (United States)] [and others
1995-09-01T23:59:59.000Z
The authors have observed that the critical heat current for the transition to superfluid turbulence in weakly nonuniform circular channels depends strongly on the flow direction. This observation is particularly surprising since no other property of the turbulence appears to have such a dependence. In a nonuniform channel the critical heat current is associated with a stationary front between the laminar and turbulent flow. The authors propose a new model for super-fluid turbulent fronts which explains the asymmetry of the critical heat currents in a simple way. The model is based on the subcritical nature of the transition, and the generic description of such a bifurcation by the Ginzburg-Landau equation. As a bonus, the model also explains a long-standing problem in superfluid physics-the nature of propagating fronts in uniform channels. The results of this analysis of both the uniform and nonuniform channel data also provide new information about the vortex line drift velocity.
Turbulent Fluxes in Stably Stratified Boundary Layers
L'vov, Victor S; Rudenko, Oleksii; 10.1088/0031-8949/2008/T132/014010
2008-01-01T23:59:59.000Z
We present an extended version of an invited talk given on the International Conference "Turbulent Mixing and Beyond". The dynamical and statistical description of stably stratified turbulent boundary layers with the important example of the stable atmospheric boundary layer in mind is addressed. Traditional approaches to this problem, based on the profiles of mean quantities, velocity second-order correlations, and dimensional estimates of the turbulent thermal flux run into a well known difficulty, predicting the suppression of turbulence at a small critical value of the Richardson number, in contradiction with observations. Phenomenological attempts to overcome this problem suffer from various theoretical inconsistencies. Here we present an approach taking into full account all the second-order statistics, which allows us to respect the conservation of total mechanical energy. The analysis culminates in an analytic solution of the profiles of all mean quantities and all second-order correlations removing t...
Planar Richtmyer-Meshkov instabilities and transition to turbulence
Grinstein, Fernando F [Los Alamos National Laboratory; Gowardhan, Akshay [Los Alamos National Laboratory; Ristorcelli, Ray [Los Alamos National Laboratory
2011-01-21T23:59:59.000Z
Extensive recent work has demonstrated that predictive under-resolved simulations of the velocity fields in turbulent flows are possible without resorting to explicit subgrid models. When using a class of physics-capturing high-resolution finite-volume numerical algorithms. This strategy is denoted implicit large eddy simulation (ILES, MILES). The performance of ILES in the substantially more difficult problem of under-resolved material mixing driven by under-resolved velocity fields and initial conditions (ICs) is a focus of the present work. Progress is presented in analyzing the effects of IC combined spectral content and thickness parametrizations. In the large eddy simulation (LES). the large energy containing structures are resolved, the smaller, presumably more isotropic, structures are filtered out, and effects of subgrid scales (SGS) are modeled. ILES effectively addresses the seemingly insurmountable issues posed to LES by under-resolution. by relying on the use of SGS modeling and filtering provided implicitly by a class of physics capturing numerics; extensive verification and validation in areas of engineering. geophysics. and astrophysics has been reported. In many areas of interest such as. inertial confinement fusion. understanding the collapse of the outer cores of supernovas. and supersonic combustion engines, vorticity is introduced at material interfaces by the impulsive loading of shock waves. and turbulence is generated via Richtmyer-Meshkov instabilities (RMI). Given that ILES is based on locally-adaptive, non-oscillatory. finite-volume methods it is naturally suited to emulate shock physics. The unique combination of shock and turbulence emulation capabilities supports direct use of ILES as an effective simulation anzatz for RMI. Here, we further test this approach using a particular strategy based on a nominally-inviscid, Schmidt number {approx} 1, simulation model that uses the LANL RAGE code to investigate planar RMI. Issues of initial material interface characterization and modeling difficulties, and effects of IC resolved spectral content on transitional and late-time turbulent mixing were examined in our previous work. The focus here is to carry out a systematic analysis of effects of combined IC spectral content and thickness.
Outflow Driven Turbulence in Molecular Clouds
Jonathan J. Carroll; Adam Frank; Eric G. Blackman; Andrew J. Cunningham; Alice C. Quillen
2008-05-30T23:59:59.000Z
In this paper we explore the relationship between protostellar outflows and turbulence in molecular clouds. Using 3-D numerical simulations we focus on the hydrodynamics of multiple outflows interacting within a parsec scale volume. We explore the extent to which transient outflows injecting directed energy and momentum into a sub-volume of a molecular cloud can be converted into random turbulent motions. We show that turbulence can readily be sustained by these interactions and show that it is possible to broadly characterize an effective driving scale of the outflows. We compare the velocity spectrum obtained in our studies to that of isotropically forced hydrodynamic turbulence finding that in outflow driven turbulence a power law is indeed achieved. However we find a steeper spectrum (beta ~ 3) is obtained in outflow driven turbulence models than in isotropically forced simulations (beta ~ 2). We discuss possible physical mechanisms responsible for these results as well and their implications for turbulence in molecular clouds where outflows will act in concert with other processes such as gravitational collapse.
Optical Turbulence Characterization at LAMOST Site: Observations and Models
Liu, L -Y; Yao, Y -Q; Vernin, J; Chadid, M; Wang, H -S; Yin, J; Wang, Y -P
2015-01-01T23:59:59.000Z
Atmospheric optical turbulence seriously limits the performance of high angular resolution instruments. An 8-night campaign of measurements was carried out at the LAMOST site in 2011, to characterize the optical turbulence. Two instruments were set up during the campaign: a Differential Image Motion Monitor (DIMM) used to measure the total atmospheric seeing, and a Single Star Scidar (SSS) to measure the vertical profiles of the turbulence C_n^2(h) and the horizontal wind velocity V(h). The optical turbulence parameters are also calculated with the Weather Research and Forecasting (WRF) model coupled with the Trinquet-Vernin model, which describes optical effects of atmospheric turbulence by using the local meteorological parameters. This paper presents assessment of the optical parameters involved in high angular resolution astronomy. Its includes seeing, isoplanatic angle, coherence time, coherence etendue, vertical profiles of optical turbulence intensity _n^2(h)$ and horizontal wind speed V(h). The median...
Model turbulent floods with the Smagorinski large eddy closure
A. J. Roberts; D. J. Georgiev; D. V. Strunin
2008-05-21T23:59:59.000Z
Floods, tides and tsunamis are turbulent, yet conventional models are based upon depth averaging inviscid irrotational flow equations. We propose to change the base of such modelling to the Smagorinksi large eddy closure for turbulence in order to appropriately match the underlying fluid dynamics. Our approach allows for large changes in fluid depth to cater for extreme inundations. The key to the analysis underlying the approach is to choose surface and bed boundary conditions that accommodate a constant turbulent shear as a nearly neutral mode. Analysis supported by slow manifold theory then constructs a model for the coupled dynamics of the fluid depth and the mean turbulent lateral velocity. The model resolves the internal turbulent shear in the flow and thus may be used in further work to rationally predict erosion and transport in turbulent floods.
The deterministic chaos and random noise in turbulent jet
Yao, Tian-Liang [Key Laboratory of Coal Gasification and Energy Chemical Engineering of Ministry of Education, East China University of Science and Technology, P.O. Box 272, Shanghai 200237 (China); Shanghai Institute of Space Propulsion, Shanghai 201112 (China); Shanghai Engineering Research Center of Space Engine, Shanghai Institute of Space Propulsion, Shanghai 201112 (China); Liu, Hai-Feng, E-mail: hfliu@ecust.edu.cn; Xu, Jian-Liang; Li, Wei-Feng [Key Laboratory of Coal Gasification and Energy Chemical Engineering of Ministry of Education, East China University of Science and Technology, P.O. Box 272, Shanghai 200237 (China)
2014-06-01T23:59:59.000Z
A turbulent flow is usually treated as a superposition of coherent structure and incoherent turbulence. In this paper, the largest Lyapunov exponent and the random noise in the near field of round jet and plane jet are estimated with our previously proposed method of chaotic time series analysis [T. L. Yao, et al., Chaos 22, 033102 (2012)]. The results show that the largest Lyapunov exponents of the round jet and plane jet are in direct proportion to the reciprocal of the integral time scale of turbulence, which is in accordance with the results of the dimensional analysis, and the proportionality coefficients are equal. In addition, the random noise of the round jet and plane jet has the same linear relation with the Kolmogorov velocity scale of turbulence. As a result, the random noise may well be from the incoherent disturbance in turbulence, and the coherent structure in turbulence may well follow the rule of chaotic motion.
Interpreting Power Anisotropy Measurements in Plasma Turbulence
Chen, C H K; Horbury, T S; Schekochihin, A A
2009-01-01T23:59:59.000Z
A relationship between power anisotropy and wavevector anisotropy in turbulent fluctuations is derived. This can be used to interpret plasma turbulence measurements, for example in the solar wind. If fluctuations are anisotropic in shape then the ion gyroscale break point in spectra in the directions parallel and perpendicular to the magnetic field would not occur at the same frequency, and similarly for the electron gyroscale break point. This is an important consideration when interpreting solar wind observations in terms of anisotropic turbulence theories. Model magnetic field power spectra are presented assuming a cascade of critically balanced Alfven waves in the inertial range and kinetic Alfven waves in the dissipation range. The variation of power anisotropy with scale is compared to existing solar wind measurements and the similarities and differences are discussed.
Wave-wave interactions in solar type III radio bursts
Thejappa, G. [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States); MacDowall, R. J. [NASA/Goddard Space Flight Center, Greenbelt MD 20771 (United States)
2014-02-11T23:59:59.000Z
The high time resolution observations from the STEREO/WAVES experiment show that in type III radio bursts, the Langmuir waves often occur as localized magnetic field aligned coherent wave packets with durations of a few ms and with peak intensities well exceeding the strong turbulence thresholds. Some of these wave packets show spectral signatures of beam-resonant Langmuir waves, down- and up-shifted sidebands, and ion sound waves, with frequencies, wave numbers, and tricoherences satisfying the resonance conditions of the oscillating two stream instability (four wave interaction). The spectra of a few of these wave packets also contain peaks at f{sub pe}, 2f{sub pe} and 3 f{sub pe} (f{sub pe} is the electron plasma frequency), with frequencies, wave numbers and bicoherences (computed using the wavelet based bispectral analysis techniques) satisfying the resonance conditions of three wave interactions: (1) excitation of second harmonic electromagnetic waves as a result of coalescence of two oppositely propagating Langmuir waves, and (2) excitation of third harmonic electromagnetic waves as a result of coalescence of Langmuir waves with second harmonic electromagnetic waves. The implication of these findings is that the strong turbulence processes play major roles in beam stabilization as well as conversion of Langmuir waves into escaping radiation in type III radio bursts.
Turbulent Particle Acceleration in the Diffuse Cluster Plasma
J. A. Eilek; J. C. Weatherall
1999-06-30T23:59:59.000Z
In situ particle acceleration is probably occuring in cluster radio haloes. This is suggested by the uniformity and extent of the haloes, given that spatial diffusion is slow and that radiative losses limit particle lifetimes. Stochastic acceleration by plasma turbulence is the most likely mechanism. Alfven wave turbulence has been suggested as the means of acceleration, but it is too slow to be important in the cluster environment. We propose, instead, that acceleration occurs via strong lower-hybrid wave turbulence. We find that particle acceleration will be effective in clusters if only a small fraction of the cluster energy density is in this form.
The Spatial Scaling Laws of Compressible Turbulence
Sun, Bohua
2015-01-01T23:59:59.000Z
This Letter proposed spatial scaling laws of the density-weighted energy spectrum of compressible flow in terms of dissipation rate, wave number and the Mach number. The study has shown the compressible turbulence energy spectrum does not show the complete similarity, but incomplete similarity as $E(k,Ma)=(C+\\frac{D}{\\ln{Ma}})\
Interstellar Turbulence, Cloud Formation and Pressure Balance
Enrique Vazquez-Semadeni
1998-10-23T23:59:59.000Z
We discuss HD and MHD compressible turbulence as a cloud-forming and cloud-structuring mechanism in the ISM. Results from a numerical model of the turbulent ISM at large scales suggest that the phase-like appearance of the medium, the typical values of the densities and magnetic field strengths in the intercloud medium, as well as Larson's velocity dispersion-size scaling relation in clouds may be understood as consequences of the interstellar turbulence. However, the density-size relation appears to only hold for the densest simulated clouds, there existing a large population of small, low-density clouds, which, on the other hand, are hardest to observe. We then discuss several tests and implications of a fully dynamical picture of interstellar clouds. The results imply that clouds are transient, constantly being formed, distorted and disrupted by the turbulent velocity field, with a fraction of these fluctuations undergoing gravitational collapse. Simulated line profiles and estimated cloud lifetimes are consistent with observational data. In this scenario, we suggest it is quite unlikely that quasi-hydrostatic structures on any scale can form, and that the near pressure balance between clouds and the intercloud medium is an incidental consequence of the density field driven by the turbulence and in the presence of appropriate cooling, rather than a driving or confining mechanism.
The Joint Cascade of Energy and Helicity in Three-Dimensional Turbulence
Qiaoning Chen; Shiyi Chen; Gregory L. Eyink
2002-06-18T23:59:59.000Z
Three-dimensional (3D) turbulence has both energy and helicity as inviscid constants of motion. In contrast to two-dimensional (2D) turbulence, where a second inviscid invariant--the enstrophy--blocks the energy cascade to small scales, in 3D there is a joint cascade of both energy and helicity simultaneously to small scales. The basic cancellation mechanism which permits a joint cascade of energy and helicity is illuminated by means of the helical decomposition of the velocity into positively and negatively polarized waves. This decomposition is employed in the present study both theoretically and also in a numerical simulation of homogeneous and isotropic 3D turbulence. It is shown that the transfer of energy to small scales produces a tremendous growth of helicity separately in the + and - helical modes at high wavenumbers, diverging in the limit of infinite Reynolds number. However, because of a tendency to restore reflection invariance at small scales, the net helicity from both modes remains finite in that limit. The net helicity flux is shown to be constant all the way up to the Kolmogorov wavenumber: there is no shorter inertial-range for helicity cascade than for energy cascade. The transfer of energy and helicity between + and - modes, which permits the joint cascade, is shown to be due to two distinct physical processes, advection and vortex stretching.
N. V. Antonov; N. M. Gulitskiy
2015-01-21T23:59:59.000Z
Inertial-range asymptotic behavior of a vector (e.g., magnetic) field, passively advected by a strongly anisotropic turbulent flow, is studied by means of the field theoretic renormalization group and the operator product expansion. The advecting velocity field is Gaussian, not correlated in time, with the pair correlation function of the form $\\propto \\delta(t-t') / k_{\\bot}^{d-1+\\xi}$, where $k_{\\bot}=|{\\bf k}_{\\bot}|$ and ${\\bf k}_{\\bot}$ is the component of the wave vector, perpendicular to the distinguished direction (`direction of the flow') -- the $d$-dimensional generalization of the ensemble introduced by Avellaneda and Majda [{\\it Commun. Math. Phys.} {\\bf 131}: 381 (1990)]. The stochastic advection-diffusion equation for the transverse (divergence-free) vector field includes, as special cases, the kinematic dynamo model for magnetohydrodynamic turbulence and the linearized Navier--Stokes equation. In contrast to the well known isotropic Kraichnan's model, where various correlation functions exhibit anomalous scaling behavior with infinite sets of anomalous exponents, here the dependence on the integral turbulence scale $L$ has a logarithmic behavior: instead of power-like corrections to ordinary scaling, determined by naive (canonical) dimensions, the anomalies manifest themselves as polynomials of logarithms of $L$. The key point is that the matrices of scaling dimensions of the relevant families of composite operators appear nilpotent and cannot be diagonalized. The detailed proof of this fact is given for correlation functions of arbitrary order.
Kaminski, Edouard
Second-order model of entrainment in planar turbulent jets at low Reynolds number S. Paillat and E.1063/1.4767535 Investigations on the local entrainment velocity in a turbulent jet Phys. Fluids 24, 105110 (2012); 10-order model of entrainment in planar turbulent jets at low Reynolds number S. Paillata) and E. Kaminski
Evidence of Shock-Driven Turbulence in the Solar Chromosphere
K. P. Reardon; F. Lepreti; V. Carbone; A. Vecchio
2008-09-24T23:59:59.000Z
We study the acoustic properties of the solar chromosphere in the high-frequency regime using a time sequence of velocity measurements in the chromospheric Ca II 854.2 nm line taken with the Interferometric Bidimensional Spectrometer (IBIS). We concentrate on quiet-Sun behavior, apply Fourier analysis, and characterize the observations in terms of the probability density functions (PDFs) of velocity increments. We confirm the presence of significant oscillatory fluctuation power above the cutoff frequency and find that it obeys a power-law distribution with frequency up to our 25 mHz Nyquist limit. The chromospheric PDFs are non-Gaussian and asymmetric and they differ among network, fibril, and internetwork regions. This suggests that the chromospheric high-frequency power is not simply the result of short-period waves propagating upward from the photosphere but rather is the signature of turbulence generated within the chromosphere from shock oscillations near the cutoff frequency. The presence of this pervasive and broad spectrum of motions in the chromosphere is likely to have implications for the excitation of coronal loop oscillations.
Turbulence in a three-dimensional deflagration model for Type Ia supernovae: I. Scaling properties
Ciaraldi-Schoolmann, F; Niemeyer, J C; Roepke, F K; Hillebrandt, W
2009-01-01T23:59:59.000Z
We analyze the statistical properties of the turbulent velocity field in the deflagration model for Type Ia supernovae. In particular, we consider the question of whether turbulence is isotropic and consistent with the Kolmogorov theory at small length scales. Using numerical data from a high-resolution simulation of a thermonuclear supernova explosion, spectra of the turbulence energy and velocity structure functions are computed. We show that the turbulent velocity field is isotropic at small length scales and follows a scaling law that is consistent with the Kolmogorov theory until most of the nuclear fuel is burned. At length scales greater than a certain characteristic scale, turbulence becomes anisotropic. Here, the radial velocity fluctuations follow the scaling law of the Rayleigh-Taylor instability, whereas the angular component still obeys Kolmogorov scaling. In the late phase of the explosion, this characteristic scale drops below the numerical resolution of the simulation. The analysis confirms th...
ENSEMBLE SIMULATIONS OF PROTON HEATING IN THE SOLAR WIND VIA TURBULENCE AND ION CYCLOTRON RESONANCE
Cranmer, Steven R. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
2014-07-01T23:59:59.000Z
Protons in the solar corona and heliosphere exhibit anisotropic velocity distributions, violation of magnetic moment conservation, and a general lack of thermal equilibrium with the other particle species. There is no agreement about the identity of the physical processes that energize non-Maxwellian protons in the solar wind, but a traditional favorite has been the dissipation of ion cyclotron resonant Alfvén waves. This paper presents kinetic models of how ion cyclotron waves heat protons on their journey from the corona to interplanetary space. It also derives a wide range of new solutions for the relevant dispersion relations, marginal stability boundaries, and nonresonant velocity-space diffusion rates. A phenomenological model containing both cyclotron damping and turbulent cascade is constructed to explain the suppression of proton heating at low alpha-proton differential flow speeds. These effects are implemented in a large-scale model of proton thermal evolution from the corona to 1 AU. A Monte Carlo ensemble of realistic wind speeds, densities, magnetic field strengths, and heating rates produces a filled region of parameter space (in a plane described by the parallel plasma beta and the proton temperature anisotropy ratio) similar to what is measured. The high-beta edges of this filled region are governed by plasma instabilities and strong heating rates. The low-beta edges correspond to weaker proton heating and a range of relative contributions from cyclotron resonance. On balance, the models are consistent with other studies that find only a small fraction of the turbulent power spectrum needs to consist of ion cyclotron waves.
Fast wave evanescence in filamentary boundary plasmas
Myra, J. R. [Lodestar Research Corporation, Boulder, Colorado 80027 (United States)] [Lodestar Research Corporation, Boulder, Colorado 80027 (United States)
2014-02-15T23:59:59.000Z
Radio frequency waves for heating and current drive of plasmas in tokamaks and other magnetic confinement devices must first traverse the scrape-off-layer (SOL) before they can be put to their intended use. The SOL plasma is strongly turbulent and intermittent in space and time. These turbulent properties of the SOL, which are not routinely taken into account in wave propagation codes, can have an important effect on the coupling of waves through an evanescent SOL or edge plasma region. The effective scale length for fast wave (FW) evanescence in the presence of short-scale field-aligned filamentary plasma turbulence is addressed in this paper. It is shown that although the FW wavelength or evanescent scale length is long compared with the dimensions of the turbulence, the FW does not simply average over the turbulent density; rather, the average is over the exponentiation rate. Implications for practical situations are discussed.
Turbulence and Sound-field POD Analysis of a Turbulent Jet J. B. Freund
Dabiri, John O.
Division of Engineering and Applied Science California Institute of Technology colonius-validated direct numerical simulation database. Norms are defined based on near-field volume integrals of pressure, turbulence kinetic energy, streamwise velocity, and total enthalpy, two-dimensional integrals of streamswise
THE FATE OF PLANETESIMALS IN TURBULENT DISKS WITH DEAD ZONES. I. THE TURBULENT STIRRING RECIPE
Okuzumi, Satoshi [Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551 (Japan); Ormel, Chris W., E-mail: okuzumi@geo.titech.ac.jp [Astronomy Department, University of California, Berkeley, CA 94720 (United States)
2013-07-01T23:59:59.000Z
Turbulence in protoplanetary disks affects planet formation in many ways. While small dust particles are mainly affected by the aerodynamical coupling with turbulent gas velocity fields, planetesimals and larger bodies are more affected by gravitational interaction with gas density fluctuations. For the latter process, a number of numerical simulations have been performed in recent years, but a fully parameter-independent understanding has not been yet established. In this study, we present simple scaling relations for the planetesimal stirring rate in turbulence driven by magnetorotational instability (MRI), taking into account the stabilization of MRI due to ohmic resistivity. We begin with order-of-magnitude estimates of the turbulence-induced gravitational force acting on solid bodies and associated diffusion coefficients for their orbital elements. We then test the predicted scaling relations using the results of recent ohmic-resistive MHD simulations by Gressel et al. We find that these relations successfully explain the simulation results if we properly fix order-of-unity uncertainties within the estimates. We also update the saturation predictor for the density fluctuation amplitude in MRI-driven turbulence originally proposed by Okuzumi and Hirose. Combination of the scaling relations and saturation predictor allows us to know how the turbulent stirring rate of planetesimals depends on disk parameters such as the gas column density, distance from the central star, vertical resistivity distribution, and net vertical magnetic flux. In Paper II, we apply our recipe to planetesimal accretion to discuss its viability in turbulent disks.
The Temperature of Interstellar Clouds from Turbulent Heating
Liubin Pan; Paolo Padoan
2008-10-22T23:59:59.000Z
To evaluate the effect of turbulent heating in the thermal balance of interstellar clouds, we develop an extension of the log-Poisson intermittency model to supersonic turbulence. The model depends on a parameter, d, interpreted as the dimension of the most dissipative structures. By comparing the model with the probability distribution of the turbulent dissipation rate in a simulation of supersonic and super-Alfvenic turbulence, we find a best-fit value of d=1.64. We apply this intermittency model to the computation of the mass-weighted probability distribution of the gas temperature of molecular clouds, high-mass star-forming cores, and cold diffuse HI clouds. Our main results are: i) The mean gas temperature in molecular clouds can be explained as the effect of turbulent heating alone, while cosmic ray heating may dominate only in regions where the turbulent heating is low; ii) The mean gas temperature in high-mass star-forming cores with typical FWHM of ~6 km/s (corresponding to a 1D rms velocity of 2.5 km/s) may be completely controlled by turbulent heating, which predicts a mean value of approximately 36 K, two to three times larger than the mean gas temperature in the absence of turbulent heating; iii) The intermittency of the turbulent heating can generate enough hot regions in cold diffuse HI clouds to explain the observed CH+ abundance, if the rms velocity on a scale of 1 pc is at least 3 km/s, in agreement with previous results based on incompressible turbulence. Because of its importance in the thermal balance of molecular clouds and high-mass star-forming cores, the process of turbulent heating may be central in setting the characteristic stellar mass and in regulating molecular chemical reactions.
Kumar S. Gupta; Siddhartha Sen
2010-06-05T23:59:59.000Z
We demonstrate the possibility of a turbulent flow of electrons in graphene in the hydrodynamic region, by calculating the corresponding turbulent probability density function. This is used to calculate the contribution of the turbulent flow to the conductivity within a quantum Boltzmann approach. The dependence of the conductivity on the system parameters arising from the turbulent flow is very different from that due to scattering.
Penetration and scattering of lower hybrid waves by density fluctuations
Horton, W. [Institute for Fusion Studies, University of Texas at Austin (United States); Goniche, M.; Peysson, Y.; Decker, J.; Ekedahl, A.; Litaudon, X. [CEA, IRFM, F-13108 St-Paul-Lez-Durance (France)
2014-02-12T23:59:59.000Z
Lower Hybrid [LH] ray propagation in toroidal plasma is controlled by a combination of the azimuthal spectrum launched from the antenna, the poloidal variation of the magnetic field, and the scattering of the waves by the density fluctuations. The width of the poloidal and radial RF wave spectrum increases rapidly as the rays penetrate into higher density and scatter from the turbulence. The electron temperature gradient [ETG] spectrum is particularly effective in scattering the LH waves due to its comparable wavelengths and parallel phase velocities. ETG turbulence is also driven by the radial gradient of the electron current density giving rise to an anomalous viscosity spreading the LH-driven plasma currents. The scattered LH spectrum is derived from a Fokker-Planck equation for the distribution of the ray trajectories with a diffusivity proportional to the fluctuations. The LH ray diffusivity is large giving transport in the poloidal and radial wavenumber spectrum in one - or a few passes - of the rays through the core plasma.
Analysis of the effects of energy deposition on shock-driven turbulent mixing
Haines, Brian M.; Grinstein, Fernando F.; Welser-Sherrill, Leslie; Fincke, James R.; Doss, Forrest W. [Los Alamos National Laboratory, MS T087, Los Alamos, New Mexico 87545 (United States)] [Los Alamos National Laboratory, MS T087, Los Alamos, New Mexico 87545 (United States)
2013-07-15T23:59:59.000Z
We perform simulations of laser-driven turbulence experiments with energy deposition, modeling situations where energy is deposited in a mixing layer before or after it is reshocked. Such situations are experienced in, e.g., inertial confinement fusion capsules. We show that the timing of the energy deposition has a significant impact on the development of turbulent flow and corresponding turbulent material mixing. In particular, if the energy is deposited before the shock wave begins interacting with the mixing layer, the development of turbulence and turbulent mixing are inhibited. If, however, the energy is deposited after the shock wave has interacted with a portion of the mixing layer, turbulence generation and turbulent mixing are enhanced.
Mazzucato, E.; Bell, R. E.; Ethier, S.; Hosea, J. C.; Kaye, S. M.; LeBlanc, B. P.; Lee, W. W.; Ryan, P. M.; Smith, D. R.; Wang, W. X.; Wilson, J. R.
2009-03-26T23:59:59.000Z
Various theories and numerical simulations support the conjecture that the ubiquitous problem of anomalous electron transport in tokamaks may arise from a short-scale turbulence driven by the electron temperature gradient. To check whether this turbulence is present in plasmas of the National Spherical Torus Experiment (NSTX), measurements of turbulent fluctuations were performed with coherent scattering of electromagnetic waves. Results from plasmas heated by high harmonic fast waves (HHFW) show the existence of density fluctuations in the range of wave numbers k??e=0.1-0.4, corresponding to a turbulence scale length of the order of the collisionless skin depth. Experimental observations and agreement with numerical results from the linear gyro-kinetic GS2 code indicate that the observed turbulence is driven by the electron temperature gradient. These turbulent fluctuations were not observed at the location of an internal transport barrier driven by a negative magnetic shear.
Recent Advances in Wave Travel Time Based Methodology for Structural Health Monitoring
Southern California, University of
identify wave velocity profiles of vertically propagating shear and torsional waves through the building monitoring, seismic interferometry, wave travel time 1. INTRODUCTION The ability to monitor the health
LARGE EDDY SIMULATION OF TURBULENT BOUNDARY LAYERS OVER ROUGH BEDS
Pawlak, Geno
that determines the response of the boundary layer is not clear. One method to characterize the irregular nature with different spectral slopes using 2D 10 % loading square waves as basis functions. These square waves can) is then used to simulate the turbulent boundary layer over the rough beds. The LES solver is first validated
On numerical turbulence generation for test-particle simulations
Tautz, R. C. [Zentrum fuer Astronomie und Astrophysik, Technische Universitaet Berlin, Hardenbergstrasse 36, D-10623 Berlin (Germany); Dosch, A. [Center for Space Plasmas and Aeronomic Research, University of Alabama in Huntsville, 320 Sparkman Drive, Huntsville, Alabama 35805 (United States)
2013-02-15T23:59:59.000Z
A modified method is presented to generate artificial magnetic turbulence that is used for test-particle simulations. Such turbulent fields are obtained from the superposition of a set of wave modes with random polarizations and random directions of propagation. First, it is shown that the new method simultaneously fulfils requirements of isotropy, equal mean amplitude and variance for all field components, and vanishing divergence. Second, the number of wave modes required for a stochastic particle behavior is investigated by using a Lyapunov approach. For the special case of slab turbulence, it is shown that already for 16 wave modes the particle behavior agrees with that shown for considerably larger numbers of wave modes.
Modeling Compressed Turbulence
Israel, Daniel M. [Los Alamos National Laboratory
2012-07-13T23:59:59.000Z
From ICE to ICF, the effect of mean compression or expansion is important for predicting the state of the turbulence. When developing combustion models, we would like to know the mix state of the reacting species. This involves density and concentration fluctuations. To date, research has focused on the effect of compression on the turbulent kinetic energy. The current work provides constraints to help development and calibration for models of species mixing effects in compressed turbulence. The Cambon, et al., re-scaling has been extended to buoyancy driven turbulence, including the fluctuating density, concentration, and temperature equations. The new scalings give us helpful constraints for developing and validating RANS turbulence models.
Rossby wave radiation by an eddy on the polar beta-plane
Zhang, Yang
2015-01-01T23:59:59.000Z
Results from the laboratory experiments on the evolution of vortices (eddies) generated in a rotating tank with topographic beta-effect are presented. The surface elevation and velocity fields are measured by the Altimetric Imaging Velocimetry. The experiments are supplemented by shallow water numerical simulations as well as a linear theory which describes the Rossby wave radiation by travelling vortices. The cyclonic vortices observed in the experiments travel to the northwest and continuously radiate Rossby waves. Measurements show that initially axisymmetric vortices develop a dipolar component which enables them to perform translational motion. A pattern of alternating zonal jets to the west of the vortex is created by Rossby waves with approximately zonal crests. Energy spectra of the flows in the wavenumber space indicate that a wavenumber similar to that introduced by Rhines for turbulent flows on the beta-plane can be introduced here. The wavenumber is based on the translational speed of a vortex rat...
Statistical theory of turbulent incompressible multimaterial flow
Kashiwa, B.
1987-10-01T23:59:59.000Z
Interpenetrating motion of incompressible materials is considered. ''Turbulence'' is defined as any deviation from the mean motion. Accordingly a nominally stationary fluid will exhibit turbulent fluctuations due to a single, slowly moving sphere. Mean conservation equations for interpenetrating materials in arbitrary proportions are derived using an ensemble averaging procedure, beginning with the exact equations of motion. The result is a set of conservation equations for the mean mass, momentum and fluctuational kinetic energy of each material. The equation system is at first unclosed due to integral terms involving unknown one-point and two-point probability distribution functions. In the mean momentum equation, the unclosed terms are clearly identified as representing two physical processes. One is transport of momentum by multimaterial Reynolds stresses, and the other is momentum exchange due to pressure fluctuations and viscous stress at material interfaces. Closure is approached by combining careful examination of multipoint statistical correlations with the traditional physical technique of kappa-epsilon modeling for single-material turbulence. This involves representing the multimaterial Reynolds stress for each material as a turbulent viscosity times the rate of strain based on the mean velocity of that material. The multimaterial turbulent viscosity is related to the fluctuational kinetic energy kappa, and the rate of fluctuational energy dissipation epsilon, for each material. Hence a set of kappa and epsilon equations must be solved, together with mean mass and momentum conservation equations, for each material. Both kappa and the turbulent viscosities enter into the momentum exchange force. The theory is applied to (a) calculation of the drag force on a sphere fixed in a uniform flow, (b) calculation of the settling rate in a suspension and (c) calculation of velocity profiles in the pneumatic transport of solid particles in a pipe.
Turbulent drag reduction through oscillating discs
Wise, Daniel J
2014-01-01T23:59:59.000Z
The changes of a turbulent channel flow subjected to oscillations of wall flush-mounted rigid discs are studied by means of direct numerical simulations. The Reynolds number is $R_\\tau$=$180$, based on the friction velocity of the stationary-wall case and the half channel height. The primary effect of the wall forcing is the sustained reduction of wall-shear stress, which reaches a maximum of 20%. A parametric study on the disc diameter, maximum tip velocity, and oscillation period is presented, with the aim to identify the optimal parameters which guarantee maximum drag reduction and maximum net energy saving, computed by taking into account the power spent to actuate the discs. This may be positive and reaches 6%. The Rosenblat viscous pump flow is used to predict the power spent for disc motion in the turbulent channel flow and to estimate localized and transient regions over the disc surface subjected to the turbulent regenerative braking effect, for which the wall turbulence exerts work on the discs. The...
Analytic Model of the Universal Structure of Turbulent Boundary Layers
Victor S. L'vov; Itamar Procaccia; Oleksii Rudenko
2006-06-21T23:59:59.000Z
Turbulent boundary layers exhibit a universal structure which nevertheless is rather complex, being composed of a viscous sub-layer, a buffer zone, and a turbulent log-law region. In this letter we present a simple analytic model of turbulent boundary layers which culminates in explicit formulae for the profiles of the mean velocity, the kinetic energy and the Reynolds stress as a function of the distance from the wall. The resulting profiles are in close quantitative agreement with measurements over the entire structure of the boundary layer, without any need of re-fitting in the different zones.
Turbulent density fluctuations in the solar wind
Ingale, Madhusudan
2015-01-01T23:59:59.000Z
Treatments of the radio scattering due to density turbulence in the solar wind typically employ asymptotic approximations to the phase structure function. We use a general structure function (GSF) that straddles the asymptotic limits and quantify the relative error introduced by the approximations. We show that the regimes where GSF predictions are accurate than those of its asymptotic approximations is not only of practical relevance, but are where inner scale effects influence the estimate of the scatter-broadening. Thus we propose that GSF should henceforth be used for scatter broadening calculations and estimates of quantities characterizing density turbulence in the solar corona and solar wind. In the next part of this thesis we use measurements of density turbulence in the solar wind from previously publish observations of radio wave scattering and interplanetary scintillations. Density fluctuations are inferred using the GSF for radio scattering data and existing analysis methods for IPS. Assuming that...
Cosmic-ray diffusion in magnetized turbulence
Tautz, R C
2015-01-01T23:59:59.000Z
The problem of cosmic-ray scattering in the turbulent electromagnetic fields of the interstellar medium and the solar wind is of great importance due to the variety of applications of the resulting diffusion coefficients. Examples are diffusive shock acceleration, cosmic-ray observations, and, in the solar system, the propagation of coronal mass ejections. In recent years, it was found that the simple diffusive motion that had been assumed for decades is often in disagreement both with numerical and observational results. Here, an overview is given of the interaction processes of cosmic rays and turbulent electromagnetic fields. First, the formation of turbulent fields due to plasma instabilities is treated, where especially the non-linear behavior of the resulting unstable wave modes is discussed. Second, the analytical and the numerical side of high-energy particle propagation will be reviewed by presenting non-linear analytical theories and Monte-Carlo simulations. For the example of the solar wind, the im...
Clustering of Aerosols in Atmospheric Turbulent Flow
T. Elperin; N. Kleeorin; M. A. Liberman; V. L'vov; I. Rogachevskii
2007-02-15T23:59:59.000Z
A mechanism of formation of small-scale inhomogeneities in spatial distributions of aerosols and droplets associated with clustering instability in the atmospheric turbulent flow is discussed. The particle clustering is a consequence of a spontaneous breakdown of their homogeneous space distribution due to the clustering instability, and is caused by a combined effect of the particle inertia and a finite correlation time of the turbulent velocity field. In this paper a theoretical approach proposed in Phys. Rev. E 66, 036302 (2002) is further developed and applied to investigate the mechanisms of formation of small-scale aerosol inhomogeneities in the atmospheric turbulent flow. The theory of the particle clustering instability is extended to the case when the particle Stokes time is larger than the Kolmogorov time scale, but is much smaller than the correlation time at the integral scale of turbulence. We determined the criterion of the clustering instability for the Stokes number larger than 1. We discussed applications of the analyzed effects to the dynamics of aerosols and droplets in the atmospheric turbulent flow.
Che, H.; Goldstein, M. L. [NASA/Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
2014-11-10T23:59:59.000Z
The formation of the observed core-halo feature in the solar wind electron velocity distribution function is a long-time puzzle. In this Letter, based on the current knowledge of nanoflares, we show that the nanoflare-accelerated electron beams are likely to trigger a strong electron two-stream instability that generates kinetic Alfvén wave and whistler wave turbulence, as we demonstrated in a previous paper. We further show that the core-halo feature produced during the origin of kinetic turbulence is likely to originate in the inner corona and can be preserved as the solar wind escapes to space along open field lines. We formulate a set of equations to describe the heating processes observed in the simulation and show that the core-halo temperature ratio of the solar wind is insensitive to the initial conditions in the corona and is related to the core-halo density ratio of the solar wind and to the quasi-saturation property of the two-stream instability at the time when the exponential decay ends. This relation can be extended to the more general core-halo-strahl feature in the solar wind. The temperature ratio between the core and hot components is nearly independent of the heliospheric distance to the Sun. We show that the core-halo relative drift previously reported is a relic of the fully saturated two-stream instability. Our theoretical results are consistent with the observations while new tests for this model are provided.
Overview of the TurbSim Stochastic Inflow Turbulence Simulator: Version 1.10
Kelley, N. D.; Jonkman, B. J.
2006-09-01T23:59:59.000Z
The Turbsim stochastic inflow turbulence code was developed to provide a numerical simulation of a full-field flow that contains coherent turbulence structures that reflect the proper spatiotemporal turbulent velocity field relationships seen in instabilities associated with nocturnal boundary layer flows. This report provides the user with an overview of how the TurbSim code has been developed and some of the theory behind that development.
Modification of turbulent structure in channel flows by microbubble injection close to the wall
Gutierrez Torres, Claudia del Carmen
2005-11-01T23:59:59.000Z
An investigation of turbulent structure modification of a boundary layer for a fully developed channel flow by microbubble injection close to the upper wall was carried out using Particle Image Velocimetry (PIV). Two-dimensional velocity components...
Foukzon, Jaykov
2008-01-01T23:59:59.000Z
Advanced numerical-analytical study of the three-dimensional nonlinear stochastic partial differential equation, analogous to that proposed by V. N. Nikolaevski to describe longitudinal seismic waves, is presented. The equation has a threshold of short-wave instability and symmetry, providing long-wave dynamics. Proposed new mechanism for quantum "super chaos" generating in nonlinear dynamical systems. The hypothesis is said, that strong physical turbulence could be identified with quantum chaos of considered type.
Subgrid models for mass and thermal diffusion in turbulent mixing
Sharp, David H [Los Alamos National Laboratory; Lim, Hyunkyung [STONY BROOK UNIV; Li, Xiao - Lin [STONY BROOK UNIV; Gilmm, James G [STONY BROOK UNIV
2008-01-01T23:59:59.000Z
We are concerned with the chaotic flow fields of turbulent mixing. Chaotic flow is found in an extreme form in multiply shocked Richtmyer-Meshkov unstable flows. The goal of a converged simulation for this problem is twofold: to obtain converged solutions for macro solution features, such as the trajectories of the principal shock waves, mixing zone edges, and mean densities and velocities within each phase, and also for such micro solution features as the joint probability distributions of the temperature and species concentration. We introduce parameterized subgrid models of mass and thermal diffusion, to define large eddy simulations (LES) that replicate the micro features observed in the direct numerical simulation (DNS). The Schmidt numbers and Prandtl numbers are chosen to represent typical liquid, gas and plasma parameter values. Our main result is to explore the variation of the Schmidt, Prandtl and Reynolds numbers by three orders of magnitude, and the mesh by a factor of 8 per linear dimension (up to 3200 cells per dimension), to allow exploration of both DNS and LES regimes and verification of the simulations for both macro and micro observables. We find mesh convergence for key properties describing the molecular level of mixing, including chemical reaction rates between the distinct fluid species. We find results nearly independent of Reynolds number for Re 300, 6000, 600K . Methodologically, the results are also new. In common with the shock capturing community, we allow and maintain sharp solution gradients, and we enhance these gradients through use of front tracking. In common with the turbulence modeling community, we include subgrid scale models with no adjustable parameters for LES. To the authors' knowledge, these two methodologies have not been previously combined. In contrast to both of these methodologies, our use of Front Tracking, with DNS or LES resolution of the momentum equation at or near the Kolmogorov scale, but without resolving the Batchelor scale, allows a feasible approach to the modeling of high Schmidt number flows.
Wave Mechanics and the Fifth Dimension
Paul S. Wesson; James M. Overduin
2013-01-28T23:59:59.000Z
Replacing 4D Minkowski space by 5D canonical space leads to a clearer derivation of the main features of wave mechanics, including the wave function and the velocity of de Broglie waves. Recent tests of wave-particle duality could be adapted to investigate whether de Broglie waves are basically 4D or 5D in nature.
Large-eddy simulation of a wind turbine wake in turbulent
Firestone, Jeremy
Large-eddy simulation of a wind turbine wake in turbulent neutral shear flow Shengbai Xie, Cristina-similar velocity profile existing in the wake after a wind turbine? How does the wake influence the vertical? Motivation #12; Large-eddy simulation for turbulent flow field Actuator-line model for wind turbine ui
Interpolation between DarcyWeisbach and Darcy for laminar and turbulent flows
Walter, M.Todd
Interpolation between DarcyWeisbach and Darcy for laminar and turbulent flows W.L. Hogarth a, *, J the square of the velocity is proportional to the hydraulic gradient and if the flow is laminar, whichWeisbach; Porous media; Open channels; Turbulent flow; Laminar flow 1. Introduction Grassed waterways
Interpolation between DarcyWeisbach and Darcy for laminar and turbulent flows
Interpolation between DarcyWeisbach and Darcy for laminar and turbulent flows W.L. Hogarth a,*, J is laminar, which is the usual case, the velocity is proportional to the hydraulic gradient. This last result: Darcy; DarcyWeisbach; Porous media; Open channels; Turbulent flow; Laminar flow 1. Introduction Grassed
Wavelet analyses using parallel computing for plasma turbulence studies
Fujisawa, A.; Inagaki, S.; Matsuoka, K.; Itoh, S.-I. [Research Institute for Applied Mechanics and Itoh Research Center for Plasma Turbulence, Kyushu University, Kasuga-kouen, Kasuga 816-8580 (Japan); Shimizu, A.; Itoh, K. [National Institute for Fusion Science, Oroshi-cho, Toki-shi 509-52 (Japan); Nagashima, Y.; Yamada, T. [Graduate School of Frontier Sciences, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa-shi, Chiba 277-8561 (Japan)
2010-10-15T23:59:59.000Z
The wavelet analyses have been carried out, using a cluster of personal computer, on the signal of electric field fluctuations measured with heavy ion beam probes in the compact helical system stellarator. The results have revealed the intermittent characteristics of turbulence and of the nonlinear couplings between elemental waves of turbulence. The usage of parallel computing is found to successfully reduce the calculation time as inversely proportional to the CPU number used the cluster, which shows the nature of 'embarrassingly parallel computation'. The present example of the wavelet analyses clearly demonstrates the importance of the advanced analyzing methods and the parallel computation for the modern studies of plasma turbulence.
Measurements of Turbulence at Two Tidal Energy Sites in Puget Sound, WA
Thomson, Jim; Polagye, Brian; Durgesh, Vibhav; Richmond, Marshall C.
2012-06-05T23:59:59.000Z
Field measurements of turbulence are pre- sented from two sites in Puget Sound, WA (USA) that are proposed for electrical power generation using tidal current turbines. Rapidly sampled data from multiple acoustic Doppler instruments are analyzed to obtain statistical mea- sures of fluctuations in both the magnitude and direction of the tidal currents. The resulting turbulence intensities (i.e., the turbulent velocity fluctuations normalized by the harmonic tidal currents) are typically 10% at the hub- heights (i.e., the relevant depth bin) of the proposed turbines. Length and time scales of the turbulence are also analyzed. Large-scale, anisotropic eddies dominate the energy spectra, which may be the result of proximity to headlands at each site. At small scales, an isotropic turbulent cascade is observed and used to estimate the dissipation rate of turbulent kinetic energy. Data quality and sampling parameters are discussed, with an emphasis on the removal of Doppler noise from turbulence statistics.
Axel Brandenburg
2008-08-07T23:59:59.000Z
Aspects of turbulence in protostellar accretion discs are being reviewed. The emergence of dead zones due to poor ionization and alternatives to the magneto-rotational instability are discussed. The coupling between dust and gas in protostellar accretion discs is explained and turbulent drag is compared with laminar drag in the Stokes and Epstein regimes. Finally, the significance of magnetic field generation in turbulent discs is emphasized in connection with driving outflows and with star-disc coupling.
COLLISIONLESS DAMPING AT ELECTRON SCALES IN SOLAR WIND TURBULENCE
TenBarge, J. M.; Howes, G. G. [Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242 (United States); Dorland, W., E-mail: jason-tenbarge@uiowa.edu [Department of Physics, University of Maryland, College Park, MA 20742-3511 (United States)
2013-09-10T23:59:59.000Z
The dissipation of turbulence in the weakly collisional solar wind plasma is governed by unknown kinetic mechanisms. Two candidates have been suggested to play an important role in the dissipation, collisionless damping via wave-particle interactions and dissipation in small-scale current sheets. High resolution spacecraft measurements of the turbulent magnetic energy spectrum provide important constraints on the dissipation mechanism. The limitations of popular fluid and hybrid numerical schemes for simulation of the dissipation of solar wind turbulence are discussed, and instead a three-dimensional kinetic approach is recommended. We present a three-dimensional nonlinear gyrokinetic simulation of solar wind turbulence at electron scales that quantitatively reproduces the exponential form of the turbulent magnetic energy spectrum measured in the solar wind. A weakened cascade model that accounts for nonlocal interactions and collisionless Landau damping also quantitatively agrees with the observed exponential form. These results establish that a turbulent cascade of kinetic Alfven waves that is terminated by collisionless Landau damping is sufficient to explain the observed magnetic energy spectrum in the dissipation range of solar wind turbulence.
IWA : an analysis program for isentropic wave measurements.
Ao, Tommy
2009-02-01T23:59:59.000Z
IWA (Isentropic Wave Analysis) is a program for analyzing velocity profiles of isentropic compression experiments. IWA applies incremental impedance matching correction to measured velocity profiles to obtain in-situ particle velocity profiles for Lagrangian wave analysis. From the in-situ velocity profiles, material properties such as wave velocities, stress, strain, strain rate, and strength are calculated. The program can be run in any current version of MATLAB (2008a or later) or as a Windows XP executable.
Turbulence and its effects upon neutrinos
Kneller, J. P.; McLaughlin, G. C.; Patton, K. M. [Department of Physics, North Carolina State University, Raleigh, North Carolina 27695 (United States)
2014-06-24T23:59:59.000Z
As a neutrino passes through turbulent matter, large amplitude transitions between its eigenstates can occur. These transitions can be modeled as like those of an irradiated polarized atom and we investigate this connection both analytically and numerically. We find a simple theory that makes use of the Rotating Wave Approximation can make predictions for the amplitudes and wavelengths of the transitions that agree very well with those from the numerical solutions.
Spark ignition of lifted turbulent jet flames
Ahmed, S.F.; Mastorakos, E. [Hopkinson Laboratory, Department of Engineering, University of Cambridge, Cambridge CB2 1PZ (United Kingdom)
2006-07-15T23:59:59.000Z
This paper presents experiments on ignition and subsequent edge flame propagation in turbulent nonpremixed methane jets in air. The spark position, energy, duration, electrode diameter and gap, and the jet velocity and air premixing of the fuel stream are examined to study their effects on the ignition probability defined as successful flame establishment. The flame is visualized by a high-speed camera and planar laser-induced fluorescence of OH. It was found that after an initially spherical shape, the flame took a cylindrical shape with a propagating edge upstream. The probability of successful ignition increases with high spark energy, thin electrode diameter and wide gap, but decreases with increasing dilution of the jet with air. The flame kernel growth rate is high when the ignition probability is high for all parameters, except for jet velocity. Increasing the jet velocity decreases the ignition probability at all locations. The average flame position as a function of time from the spark was measured and the data were used to estimate a net propagation speed, which then resulted in an estimate of the average edge flame speed relative to the incoming flow. This was about 3 to 6 laminar burning velocities of a stoichiometric mixture. The measurements can assist theoretical models for the probability of ignition of nonpremixed flames and for edge flame propagation in turbulent inhomogeneous mixtures, both of which determine the success of ignition in practical combustion systems. (author)
Che, H; Viñas, A F
2013-01-01T23:59:59.000Z
The observed sub-proton scale turbulence spectrum in the solar wind raises the question of how that turbulence originates. Observations of keV energetic electrons during solar quite-time suggest them as possible source of free energy to drive the turbulence. Using particle-in-cell simulations, we explore how free energy in energetic electrons, released by an electron two-stream instability drives Weibel-like electromagnetic waves that excite wave-wave interactions. Consequently, both kinetic Alfv\\'enic and whistler waves are excited that evolve through inverse and forward magnetic energy cascades.
Multipole seismoelectric logging while drilling (LWD) for acoustic velocity measurements
Zhu, Zhenya
2012-01-01T23:59:59.000Z
In seismoelectric well logging, an acoustic wave propagates along a borehole and induces electrical signals along the borehole wall. The apparent velocities of these seismoelectric signals are equal to the formation ...
Effective velocities in fractured media: a numerical study using the ...
2002-03-18T23:59:59.000Z
theories that predict the effective P- and S-wave velocities in fractured materials in ... can be treated only by numerical techniques because analyt- ... apply the rotated staggered grid (Saenger, Gold and Shapiro ..... (r ? 0:2) and for SH-
Sub-Alfvenic Non-Ideal MHD Turbulence Simulations with Ambipolar Diffusion: I. Turbulence Statistics
Klein, R I; Li, P S; McKee, C F; Fisher, R
2008-04-10T23:59:59.000Z
Most numerical investigations on the role of magnetic fields in turbulent molecular clouds (MCs) are based on ideal magneto-hydrodynamics (MHD). However, MCs are weakly ionized, so that the time scale required for the magnetic field to diffuse through the neutral component of the plasma by ambipolar diffusion (AD) can be comparable to the dynamical time scale. We have performed a series of 256{sup 3} and 512{sup 3} simulations on supersonic but sub-Alfvenic turbulent systems with AD using the Heavy-Ion Approximation developed in Li et al. (2006). Our calculations are based on the assumption that the number of ions is conserved, but we show that these results approximately apply to the case of time-dependent ionization in molecular clouds as well. Convergence studies allow us to determine the optimal value of the ionization mass fraction when using the heavy-ion approximation for low Mach number, sub-Alfvenic turbulent systems. We find that ambipolar diffusion steepens the velocity and magnetic power spectra compared to the ideal MHD case. Changes in the density PDF, total magnetic energy, and ionization fraction are determined as a function of the AD Reynolds number. The power spectra for the neutral gas properties of a strongly magnetized medium with a low AD Reynolds number are similar to those for a weakly magnetized medium; in particular, the power spectrum of the neutral velocity is close to that for Burgers turbulence.
Extreme wave impinging and overtopping
Ryu, Yong Uk
2009-06-02T23:59:59.000Z
This investigates the velocity fields of a plunging breaking wave impinging on a structure through measurements in a two-dimensional wave tank. As the wave breaks and overtops the structure, so-called green water is generated. The flow becomes multi-phased...
Flow characteristics of finite aspect ratio fences in turbulent shear flows
Matte, Joseph Rodney
1977-01-01T23:59:59.000Z
Profile as a Function of Surface Roughness for Fixed Aspect Ratio (x/h = 12, 16) 36 17 Velocity Profile as a Punction of Surface Roughness for Fixed Downstream Position (AR = 10, 5) 38 18 Velocity Profile as a Function of Surface Roughness for Fixed... Downstream Position (AR = ~, 20) 39 19 Turbulence Profile as a Function of Aspect Ratio Number I, IST OF FIGURES (Continued) Title Page 20 Turbulence Profile as a Function of a Downstream Fence 42 21 Turbulence Profile as a Function of an Upstream...
FliHy experimental facilities for studying open channel turbulent flows and heat transfer
Abdou, Mohamed
FliHy experimental facilities for studying open channel turbulent flows and heat transfer B. Freeze) facility was constructed at UCLA to study open channel turbulent flow and heat transfer of low supercritical flow regimes (Fr /1), in which the surface waves are amplified and heat transfer is enhanced due
Slinn, Donald
an improved understanding of oscillatory flow over sand ripples. [3] The wave bottom boundary layer (WBBL the ripple crest produce a continuously turbulent boundary layer, differing from results obtained processes; KEYWORDS: turbulent boundary layer, drag coefficient, dissipation rate Citation: Barr, B. C., D
Fine-Scale Zonal Flow Suppression of Electron Temperature Gradient Turbulence
Lin, Zhihong
as an explanation for the long time build up of the zonal flow in ETG turbulence and it is shown that the generationFine-Scale Zonal Flow Suppression of Electron Temperature Gradient Turbulence S.E. Parker , J continue to grow algebraically (proportional to time). These fine-scale zonal flows have a radial wave
On the origin of solar wind. Alfven waves induced jump of coronal temperature
T. M. Mishonov; M. V. Stoev; Y. G. Maneva
2007-06-06T23:59:59.000Z
Absorbtion of Alfven waves is considered to be the main mechanism of heating in the solar corona. It is concluded that the sharp increase of the plasma temperature by two orders of magnitude is related to a self-induced opacity with respect to Alfven waves. The maximal frequency for propagation of Alfven waves is determined by the strongly temperature dependent kinematic viscosity. In such a way the temperature jump is due to absorption of high frequency Alfven waves in a narrow layer above the solar surface. It is calculated that the power per unit area dissipated in this layer due to damping of Alfven waves blows up the plasma and gives birth to the solar wind. A model short wave-length (WKB) evaluation takes into account the 1/f^2 frequency dependance of the transversal magnetic field and velocity spectral densities. Such spectral densities agree with old magnetometric data taken by Voyager 1 and recent theoretical calculations in the framework of Langevin-Burgers MHD. The present theory predicts existence of intensive high frequency MHD Alfven waves in the cold layer beneath the corona. It is briefly discussed how this statement can be checked experimentally. It is demonstrated that the magnitude of the Alfven waves generating random noise and the solar wind velocity can be expressed only in terms of satellite experimental data. It is advocated that investigation of properties of the solar surface as a random driver by optical methods is an important task for future solar physics. Jets of accretion disks are speculated as a special case of the wind from magnetized turbulent plasma.
Power-law wrinkling turbulence-flame interaction model for astrophysical flames
Jackson, Aaron P. [Laboratories for Computational Physics and Fluid Dynamics, Naval Research Laboratory, Washington, DC (United States); Townsley, Dean M. [Department of Physics and Astronomy, The University of Alabama, Tuscaloosa, AL (United States); Calder, Alan C. [Department of Physics and Astronomy, The State University of New York - Stony Brook, Stony Brook, NY (United States)
2014-04-01T23:59:59.000Z
We extend a model for turbulence-flame interactions (TFI) to consider astrophysical flames with a particular focus on combustion in Type Ia supernovae. The inertial range of the turbulent cascade is nearly always under-resolved in simulations of astrophysical flows, requiring the use of a model in order to quantify the effects of subgrid-scale wrinkling of the flame surface. We provide implementation details to extend a well-tested TFI model to low-Prandtl number flames for use in the compressible hydrodynamics code FLASH. A local, instantaneous measure of the turbulent velocity is calibrated for FLASH and verification tests are performed. Particular care is taken to consider the relation between the subgrid rms turbulent velocity and the turbulent flame speed, especially for high-intensity turbulence where the turbulent flame speed is not expected to scale with the turbulent velocity. Finally, we explore the impact of different TFI models in full-star, three-dimensional simulations of Type Ia supernovae.
The response of anisotropic turbulence to rapid homogeneous one-dimensional compression
Mahesh, Krishnan
such as the interaction of turbulence with shock waves and the compression stroke of an internal combustion engine simulations8 show good agreement. "`Also with the Department of Aeronautics and Astronautics, Stanford
The interaction of high-speed turbulence with flames: Global properties and internal flame structure
Poludnenko, A.Y.; Oran, E.S. [Laboratory for Computational Physics and Fluid Dynamics, Naval Research Laboratory, Washington, DC 20375 (United States)
2010-05-15T23:59:59.000Z
We study the dynamics and properties of a turbulent flame, formed in the presence of subsonic, high-speed, homogeneous, isotropic Kolmogorov-type turbulence in an unconfined system. Direct numerical simulations are performed with Athena-RFX, a massively parallel, fully compressible, high-order, dimensionally unsplit, reactive flow code. A simplified reaction-diffusion model represents a stoichiometric H{sub 2}-air mixture. The system being modeled represents turbulent combustion with the Damkoehler number Da=0.05 and with the turbulent velocity at the energy injection scale 30 times larger than the laminar flame speed. The simulations show that flame interaction with high-speed turbulence forms a steadily propagating turbulent flame with a flame brush width approximately twice the energy injection scale and a speed four times the laminar flame speed. A method for reconstructing the internal flame structure is described and used to show that the turbulent flame consists of tightly folded flamelets. The reaction zone structure of these is virtually identical to that of the planar laminar flame, while the preheat zone is broadened by approximately a factor of two. Consequently, the system evolution represents turbulent combustion in the thin reaction zone regime. The turbulent cascade fails to penetrate the internal flame structure, and thus the action of small-scale turbulence is suppressed throughout most of the flame. Finally, our results suggest that for stoichiometric H{sub 2}-air mixtures, any substantial flame broadening by the action of turbulence cannot be expected in all subsonic regimes. (author)
Inertial range turbulence in kinetic plasmas
Howes, G G
2007-01-01T23:59:59.000Z
The transfer of turbulent energy through an inertial range from the driving scale to dissipative scales in a kinetic plasma followed by the conversion of this energy into heat is a fundamental plasma physics process. A theoretical foundation for the study of this process is constructed, but the details of the kinetic cascade are not well understood. Several important properties are identified: (a) the conservation of a generalized energy by the cascade; (b) the need for collisions to increase entropy and realize irreversible plasma heating; and (c) the key role played by the entropy cascade--a dual cascade of energy to small scales in both physical and velocity space--to convert ultimately the turbulent energy into heat. A strategy for nonlinear numerical simulations of kinetic turbulence is outlined. Initial numerical results are consistent with the operation of the entropy cascade. Inertial range turbulence arises in a broad range of space and astrophysical plasmas and may play an important role in the ther...
Inertial range turbulence in kinetic plasmas
G. G. Howes
2007-11-27T23:59:59.000Z
The transfer of turbulent energy through an inertial range from the driving scale to dissipative scales in a kinetic plasma followed by the conversion of this energy into heat is a fundamental plasma physics process. A theoretical foundation for the study of this process is constructed, but the details of the kinetic cascade are not well understood. Several important properties are identified: (a) the conservation of a generalized energy by the cascade; (b) the need for collisions to increase entropy and realize irreversible plasma heating; and (c) the key role played by the entropy cascade--a dual cascade of energy to small scales in both physical and velocity space--to convert ultimately the turbulent energy into heat. A strategy for nonlinear numerical simulations of kinetic turbulence is outlined. Initial numerical results are consistent with the operation of the entropy cascade. Inertial range turbulence arises in a broad range of space and astrophysical plasmas and may play an important role in the thermalization of fusion energy in burning plasmas.
Electron distributions observed with Langmuir waves in the plasma sheet boundary layer
Hwang, Junga [Solar and Space Weather Research Group, Korea Astronomy and Space Science Institute, Daejeon 305-348 (Korea, Republic of); Department of Astronomy and Space Science, University of Science and Technology, Daejeon (Korea, Republic of); Rha, Kicheol [Department of Physics, Pohang University of Science and Technology, Pohang 790-784 (Korea, Republic of); Seough, Jungjoon [Solar and Space Weather Research Group, Korea Astronomy and Space Science Institute, Daejeon 305-348 (Korea, Republic of); Yoon, Peter H. [School of Space Research, Kyung Hee University, Yongin-Si, Gyeonggi-Do 446-701 (Korea, Republic of); Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742 (United States)
2014-09-15T23:59:59.000Z
The present paper investigates the Langmuir turbulence driven by counter-streaming electron beams and its plausible association with observed features in the Earth's plasma sheet boundary layer region. A one-dimensional electrostatic particle-in-cell simulation code is employed in order to simulate broadband electrostatic waves with characteristic frequency in the vicinity of the electron plasma frequency ?/?{sub pe}?1.0. The present simulation confirms that the broadband electrostatic waves may indeed be generated by the counter-streaming electron beams. It is also found that the observed feature associated with low energy electrons, namely quasi-symmetric velocity space plateaus, are replicated according to the present simulation. However, the present investigation only partially succeeds in generating the suprathermal tails such that the origin of observed quasi power-law energetic population formation remains outstanding.
C. Peralta; A. Melatos; M. Giacobello; A. Ooi
2006-07-08T23:59:59.000Z
We investigate the global transition from a turbulent state of superfluid vorticity to a laminar state, and vice versa, in the outer core of a neutron star. By solving numerically the hydrodynamic Hall-Vinen-Bekarevich-Khalatnikov equations for a rotating superfluid in a differentially rotating spherical shell, we find that the meridional counterflow driven by Ekman pumping exceeds the Donnelly-Glaberson threshold throughout most of the outer core, exciting unstable Kelvin waves which disrupt the rectilinear vortex array, creating a vortex tangle. In the turbulent state, the torque exerted on the crust oscillates, and the crust-core coupling is weaker than in the laminar state. This leads to a new scenario for the rotational glitches observed in radio pulsars: a vortex tangle is sustained in the differentially rotating outer core by the meridional counterflow, a sudden spin-up event brings the crust and core into corotation, the vortex tangle relaxes back to a rectilinear vortex array, then the crust spins down electromagnetically until enough meridional counterflow builds up to reform a vortex tangle. The turbulent-laminar transition can occur uniformly or in patches; the associated time-scales are estimated from vortex filament theory. We calculate numerically the global structure of the flow with and without an inviscid superfluid component, for Hall-Vinen and Gorter-Mellink forms of the mutual friction. We also calculate the post-glitch evolution of the angular velocity of the crust and its time derivative, and compare the results with radio pulse timing data, predicting a correlation between glitch activity and Reynolds number.
Observational and Numerical Modeling Studies of Turbulence on the Texas-Louisiana Continental Shelf
Zhang, Zheng
2013-05-24T23:59:59.000Z
calculated from velocity measurements in the bot- tom boundary layer (BBL), using the Kolmogorov’s -5/3 law in the inertial subrange of energy spectra of vertical velocity fluctuations in each burst measurement. Four second-moment turbulence closure models...
Rahbarnia, Kian; Brown, Benjamin P.; Clark, Mike M.; Kaplan, Elliot J.; Nornberg, Mark D.; Rasmus, Alex M.; Taylor, Nicholas Zane; Forest, Cary B. [Department of Physics, University of Wisconsin-Madison, 1150 University Ave, Madison, WI 53706 (United States); Jenko, Frank; Limone, Angelo [Max-Planck-Institut fuer Plasmaphysik (IPP), EURATOM Association, D-85748 Garching (Germany); Pinton, Jean-Francois; Plihon, Nicolas; Verhille, Gautier, E-mail: kian.rahbarnia@ipp.mpg.de [Laboratoire de Physique de l'Ecole Normale Superieure de Lyon, CNRS and Universite de Lyon, F-69364 Lyon (France)
2012-11-10T23:59:59.000Z
For the first time, we have directly measured the transport of a vector magnetic field by isotropic turbulence in a high Reynolds number liquid metal flow. In analogy with direct measurements of the turbulent Reynolds stress (turbulent viscosity) that governs momentum transport, we have measured the turbulent electromotive force (emf) by simultaneously measuring three components of velocity and magnetic fields, and computed the correlations that lead to mean-field current generation. Furthermore, we show that this turbulent emf tends to oppose and cancel out the local current, acting to increase the effective resistivity of the medium, i.e., it acts as an enhanced magnetic diffusivity. This has important implications for turbulent transport in astrophysical objects, particularly in dynamos and accretion disks.
Turbulent regimes in the tokamak scrape-off layer
Mosetto, Annamaria; Halpern, Federico D.; Jolliet, Sébastien; Loizu, Joaquim; Ricci, Paolo [École Polytechnique Fédérale de Lausanne (EPFL), Centre de Recherches en Physique des Plasmas, Association Euratom-Confédération Suisse, CH-1015 Lausanne (Switzerland)] [École Polytechnique Fédérale de Lausanne (EPFL), Centre de Recherches en Physique des Plasmas, Association Euratom-Confédération Suisse, CH-1015 Lausanne (Switzerland)
2013-09-15T23:59:59.000Z
The non-linear turbulent regimes in the tokamak scrape-off layer (SOL) are identified according to the linear instability responsible for the perpendicular transport. Four regions of the SOL operational parameters are determined where turbulence is driven by the inertial or resistive branches of the ballooning mode or of drift waves. The analysis, based on the linear electrostatic drift-reduced Braginskii equations, evaluates the pressure scale length self-consistently from the balance between plasma losses at the vessel and perpendicular turbulent transport. The latter is estimated by assuming that turbulence saturation occurs due to a local flattening of the plasma gradients and associated removal of the linear instability drive; it is also shown that transport is led by the mode that maximizes the ratio of the linear growth to the poloidal wavenumber. The methodology used to identify the turbulent regimes is confirmed by the results of non-linear simulations of SOL turbulence. The identification of the turbulent regimes, the predicted pressure scale length, and the poloidal wavenumber of the leading mode are in reasonable agreement with non-linear simulation results.
Airborne observations and numerical modeling of fetch- limited waves in the Gulf of Tehuantepec
Romero, Leonel
2008-01-01T23:59:59.000Z
velocity scaling in wind wave generation. Boundary-Layerlinear theory of of wind wave generation applied to waveSource terms in a third-generation wind wave model. J. Phys.
Cosmic-ray pitch-angle scattering in imbalanced MHD turbulence simulations
Weidl, Martin S; Teaca, Bogdan; Schlickeiser, Reinhard
2015-01-01T23:59:59.000Z
Pitch-angle scattering rates for cosmic-ray particles in magnetohydrodynamic (MHD) simulations with imbalanced turbulence are calculated for fully evolving electromagnetic turbulence. We compare with theoretical predictions derived from the quasilinear theory of cosmic-ray diffusion for an idealized slab spectrum and demonstrate how cross helicity affects the shape of the pitch-angle diffusion coefficient. Additional simulations in evolving magnetic fields or static field configurations provide evidence that the scattering anisotropy in imbalanced turbulence is not primarily due to coherence with propagating Alfven waves, but an effect of the spatial structure of electric fields in cross-helical MHD turbulence.
Brian J. Smith; M. G. Raymer
2007-02-21T23:59:59.000Z
The position-representation wave function for multi-photon states and its equation of motion are introduced. A major strength of the theory is that it describes the complete evolution (including polarization and entanglement) of multi-photon states propagating through inhomogeneous media. As a demonstration of the two-photon wave function's use, we show how two photons in an orbital-angular-momentum entangled state decohere upon propagation through a turbulent atmosphere.
A. A. Schekochihin; S. C. Cowley; W. Dorland; G. W. Hammett; G. G. Howes; E. Quataert; T. Tatsuno
2009-05-09T23:59:59.000Z
We present a theoretical framework for plasma turbulence in astrophysical plasmas (solar wind, interstellar medium, galaxy clusters, accretion disks). The key assumptions are that the turbulence is anisotropic with respect to the mean magnetic field and frequencies are low compared to the ion cyclotron frequency. The energy injected at the outer scale scale has to be converted into heat, which ultimately cannot be done without collisions. A KINETIC CASCADE develops that brings the energy to collisional scales both in space and velocity. Its nature depends on the physics of plasma fluctuations. In each of the physically distinct scale ranges, the kinetic problem is systematically reduced to a more tractable set of equations. In the "inertial range" above the ion gyroscale, the kinetic cascade splits into a cascade of Alfvenic fluctuations, which are governed by the RMHD equations at both the collisional and collisionless scales, and a passive cascade of compressive fluctuations, which obey a linear kinetic equation along the moving field lines associated with the Alfvenic component. In the "dissipation range" between the ion and electron gyroscales, there are again two cascades: the kinetic-Alfven-wave (KAW) cascade governed by two fluid-like Electron RMHD equations and a passive phase-space cascade of ion entropy fluctuations. The latter cascade brings the energy of the inertial-range fluctuations that was damped by collisionless wave-particle interaction at the ion gyroscale to collisional scales in the phase space and leads to ion heating. The KAW energy is similarly damped at the electron gyroscale and converted into electron heat. Kolmogorov-style scaling relations are derived for these cascades. Astrophysical and space-physical applications are discussed in detail.
Modeling wind forcing in phase resolving simulation of nonlinear wind waves
Kalmikov, Alexander G
2010-01-01T23:59:59.000Z
Wind waves in the ocean are a product of complex interaction of turbulent air flow with gravity driven water surface. The coupling is strong and the waves are non-stationary, irregular and highly nonlinear, which restricts ...
Vortex Tubes of Turbulent Solar Convection
Kitiashvili, I N; Mansour, N N; Lele, S K; Wray, A A
2011-01-01T23:59:59.000Z
Investigation of turbulent properties of solar convection is extremely important for understanding of the multi-scale dynamics observed on the solar surface. In particular, recent high-resolution observations revealed ubiquitous vortical structures, and numerical simulations demonstrated links between the vortex tube dynamics and magnetic field organization, and also importance of vortex tube interactions in the mechanism of acoustic wave excitation on the Sun. In this paper we investigate mechanisms of formation of vortex tubes in highly-turbulent convective flows near the solar surface by using realistic radiative hydrodynamic LES simulations. Analysis of data, obtained by the simulations, indicates two basic processes of the vortex tube formation: 1) development of small-scale convective instability inside convective granules, and 2) a Kelvin-Helmholtz type instability of shearing flows in intergranular lanes. Our analysis shows that vortex stretching during these processes is a primary source of generatio...
Chiral Heat Wave and wave mixing in chiral media
Chernodub, M N
2015-01-01T23:59:59.000Z
We show that a hot rotating fluid of relativistic chiral fermions possesses a new gapless collective excitation associated with coherent propagation of energy density and chiral density waves along the axis of rotation. This excitation, which we call the Chiral Heat Wave, emerges due to a mixed gauge-gravitational anomaly. At finite density the Chiral Heat Wave couples to the Chiral Vortical Wave while in the presence of an external magnetic field it mixes with the Chiral Magnetic Wave. We find that the coupled waves - which are coherent fluctuations of the vector, axial and energy currents - have generally different velocities compared to the velocities of the individual waves. We also demonstrate that rotating chiral systems subjected to external magnetic field possess non-propagating metastable thermal excitations, the Dense Hot Spots.
Slow group velocity and Cherenkov radiation
I. Carusotto; M. Artoni; G. C. La Rocca; F. Bassani
2001-03-12T23:59:59.000Z
We theoretically study the effect of ultraslow group velocities on the emission of Vavilov-Cherenkov radiation in a coherently driven medium. We show that in this case the aperture of the group cone on which the intensity of the radiation peaks is much smaller than that of the usual wave cone associated with the Cherenkov coherence condition. We show that such a singular behaviour may be observed in a coherently driven ultracold atomic gas.
Modified definition of group velocity and electromagnetic energy conservation equation
Changbiao Wang
2015-05-11T23:59:59.000Z
The classical definition of group velocity has two flaws: (a) the group velocity can be greater than the phase velocity and break Fermat's principle in a non-dispersive, lossless, non-conducting, anisotropic uniform medium; (b) the definition is not consistent with the principle of relativity for a plane wave in a moving isotropic uniform medium. To remove the flaws, a modified definition is proposed. A criterion is set up to identify the justification of group velocity definition. A "superluminal power flow" is constructed to show that the electromagnetic energy conservation equation cannot uniquely define the power flow if the principle of Fermat is not taken into account.
The evaluation of a turbulent loads characterization system
Kelley, N.D.; McKenna, H.E. [National Renewable Energy Lab., Golden, CO (United States)
1996-01-01T23:59:59.000Z
In this paper we discuss an on-line turbulent load characterization system that has been designed to acquire loading spectra from turbines of the same design operating in several different environments and from different turbine designs operating in the same environment. This System simultaneously measures the rainflow-counted alternating and mean loading spectra and the hub-height turbulent mean shearing stress and atmospheric stability associated with the turbulent inflow. We discuss the theory behind the measurement configuration and the results of proof-of-concept testing recently performed at the National Wind Technology Center (NWTC) using a Bergey EXCEL-S 10-kW wind turbine. The on-line approach to characterizing the load spectra and the inflow turbulent scaling parameter produces results that are consistent with other measurements. The on-line approximation of the turbulent shear stress or friction velocity u* also is considered adequate. The system can be used to characterize turbulence loads during turbine deployment in a wide variety of environments. Using the WISPER protocol, we found that a wide-range, variable-speed turbine will accumulate a larger number of stress cycles in the low-cycle, high-amplitude (LCHA) region when compared with a constant speed rotor under similar inflow conditions.
Hietala, Vincent M. (Placitas, NM); Vawter, Gregory A. (Albuquerque, NM)
1993-01-01T23:59:59.000Z
The traveling-wave photodetector of the present invention combines an absorptive optical waveguide and an electrical transmission line, in which optical absorption in the waveguide results in a photocurrent at the electrodes of the electrical transmission line. The optical waveguide and electrical transmission line of the electrically distributed traveling-wave photodetector are designed to achieve matched velocities between the light in the optical waveguide and electrical signal generated on the transmission line. This velocity synchronization provides the traveling-wave photodetector with a large electrical bandwidth and a high quantum efficiency, because of the effective extended volume for optical absorption. The traveling-wave photodetector also provides large power dissipation, because of its large physical size.
Hietala, V.M.; Vawter, G.A.
1993-12-14T23:59:59.000Z
The traveling-wave photodetector of the present invention combines an absorptive optical waveguide and an electrical transmission line, in which optical absorption in the waveguide results in a photocurrent at the electrodes of the electrical transmission line. The optical waveguide and electrical transmission line of the electrically distributed traveling-wave photodetector are designed to achieve matched velocities between the light in the optical waveguide and electrical signal generated on the transmission line. This velocity synchronization provides the traveling-wave photodetector with a large electrical bandwidth and a high quantum efficiency, because of the effective extended volume for optical absorption. The traveling-wave photodetector also provides large power dissipation, because of its large physical size. 4 figures.
Acceleration of low energy charged particles by gravitational waves
G. Voyatzis; L. Vlahos; S. Ichtiaroglou; D. Papadopoulos
2005-12-07T23:59:59.000Z
The acceleration of charged particles in the presence of a magnetic field and gravitational waves is under consideration. It is shown that the weak gravitational waves can cause the acceleration of low energy particles under appropriate conditions. Such conditions may be satisfied close to the source of the gravitational waves if the magnetized plasma is in a turbulent state.
Multidimensional turbulence spectra -identifying properties of turbulent structures
Kevlahan, Nicholas
Sweden 2 Department of Mathematics and Statistics, McMaster University, Hamilton L8S 4K1, Canada * E turbulent structures are presented. Results from analysis of the turbulent kinetic energy in turbulent energy associated with a coherent vortex defined using different vortex identification methods
Quantum ghost imaging through turbulence
Dixon, P. Ben
We investigate the effect of turbulence on quantum ghost imaging. We use entangled photons and demonstrate that for a specific experimental configuration the effect of turbulence can be greatly diminished. By decoupling ...
Mapping the Gas Turbulence in the Coma Cluster: Predictions for Astro-H
ZuHone, J; Zhuravleva, I
2015-01-01T23:59:59.000Z
Astro-H will be able for the first time to map gas velocities and detect turbulence in galaxy clusters. One of the best targets for turbulence studies is the Coma cluster, due to its proximity, absence of a cool core, and lack of a central active galactic nucleus. To determine what constraints Astro-H will be able to place on the Coma velocity field, we construct simulated maps of the projected gas velocity and compute the second-order structure function, an analog of the velocity power spectrum. We vary the injection scale, dissipation scale, slope, and normalization of the turbulent power spectrum, and apply measurement errors and finite sampling to the velocity field. We find that even with sparse coverage of the cluster, Astro-H will be able to measure the Mach number and the injection scale of the turbulent power spectrum--the quantities determining the energy flux down the turbulent cascade and the diffusion rate for everything that is advected by the gas (metals, cosmic rays, etc). Astro-H will not be ...
J X Zheng-Johansson; P-I Johansson
2006-08-27T23:59:59.000Z
The electromagnetic component waves, comprising together with their generating oscillatory massless charge a material particle, will be Doppler shifted when the charge hence particle is in motion, with a velocity $v$, as a mere mechanical consequence of the source motion. We illustrate here that two such component waves generated in opposite directions and propagating at speed $c$ between walls in a one-dimensional box, superpose into a traveling beat wave of wavelength ${\\mit\\Lambda}_d$$=(\\frac{v}{c}){\\mit\\Lambda}$ and phase velocity $c^2/v+v$ which resembles directly L. de Broglie's hypothetic phase wave. This phase wave in terms of transporting the particle mass at the speed $v$ and angular frequency ${\\mit\\Omega}_d=2\\pi v /{\\mit\\Lambda}_d$, with ${\\mit\\Lambda}_d$ and ${\\mit\\Omega}_d$ obeying the de Broglie relations, represents a de Broglie wave. The standing-wave function of the de Broglie (phase) wave and its variables for particle dynamics in small geometries are equivalent to the eigen-state solutions to Schr\\"odinger equation of an identical system.
Numerical Simulation of the Wave Bottom Boundary Layer
Slinn, Donald
boundary layer. Oscillatory boundary layers are examined using a high-resolution time-dependent threeNumerical Simulation of the Wave Bottom Boundary Layer Over a Smooth Surface. Part 1: Three for turbulent boundary layers that occur over a smooth bottom. Results indicate that turbulence levels
Coherent structures in ion temperature gradient turbulence-zonal flow
Singh, Rameswar, E-mail: rameswar.singh@lpp.polytechnique.fr [Laboratoire de Physique des Plasmas, Ecole Polytechnique, Route de Saclay, 91128 Palaiseau Cedex (France); Institute for Plasma Research, Bhat, Gandhinagar 382 428 (India); Singh, R. [Institute for Plasma Research, Bhat, Gandhinagar 382 428 (India); WCI Center for Fusion Theory, National Fusion Research Institute, Daejeon 305-333 (Korea, Republic of); Kaw, P. [Institute for Plasma Research, Bhat, Gandhinagar 382 428 (India); Gürcan, Ö. D. [Laboratoire de Physique des Plasmas, Ecole Polytechnique, Route de Saclay, 91128 Palaiseau Cedex (France); Diamond, P. H. [WCI Center for Fusion Theory, National Fusion Research Institute, Daejeon 305-333 (Korea, Republic of); CMTFO and CASS, University of California, San Diego, California 92093 (United States)
2014-10-15T23:59:59.000Z
Nonlinear stationary structure formation in the coupled ion temperature gradient (ITG)-zonal flow system is investigated. The ITG turbulence is described by a wave-kinetic equation for the action density of the ITG mode, and the longer scale zonal mode is described by a dynamic equation for the m?=?n?=?0 component of the potential. Two populations of trapped and untrapped drift wave trajectories are shown to exist in a moving frame of reference. This novel effect leads to the formation of nonlinear stationary structures. It is shown that the ITG turbulence can self-consistently sustain coherent, radially propagating modulation envelope structures such as solitons, shocks, and nonlinear wave trains.
The interaction of high-speed turbulence with flames: Turbulent flame speed
Poludnenko, A.Y.; Oran, E.S. [Laboratory for Computational Physics and Fluid Dynamics, Naval Research Laboratory, Washington, DC 20375 (United States)
2011-02-15T23:59:59.000Z
Direct numerical simulations of the interaction of a premixed flame with driven, subsonic, homogeneous, isotropic, Kolmogorov-type turbulence in an unconfined system are used to study the mechanisms determining the turbulent flame speed, S{sub T}, in the thin reaction zone regime. High intensity turbulence is considered with the r.m.s. velocity 35 times the laminar flame speed, S{sub L}, resulting in the Damkoehler number Da=0.05. The simulations were performed with Athena-RFX, a massively parallel, fully compressible, high-order, dimensionally unsplit, reactive-flow code. A simplified reaction-diffusion model, based on the one-step Arrhenius kinetics, represents a stoichiometric H{sub 2}-air mixture under the assumption of the Lewis number Le=1. Global properties and the internal structure of the flame were analyzed in an earlier paper, which showed that this system represents turbulent combustion in the thin reaction zone regime. This paper demonstrates that: (1) The flame brush has a complex internal structure, in which the isosurfaces of higher fuel mass fractions are folded on progressively smaller scales. (2) Global properties of the turbulent flame are best represented by the structure of the region of peak reaction rate, which defines the flame surface. (3) In the thin reaction zone regime, S{sub T} is predominantly determined by the increase of the flame surface area, A{sub T}, caused by turbulence. (4) The observed increase of S{sub T} relative to S{sub L} exceeds the corresponding increase of A{sub T} relative to the surface area of the planar laminar flame, on average, by {approx}14%, varying from only a few percent to as high as {approx}30%. (5) This exaggerated response is the result of tight flame packing by turbulence, which causes frequent flame collisions and formation of regions of high flame curvature >or similar 1/{delta}{sub L}, or ''cusps,'' where {delta}{sub L} is the thermal width of the laminar flame. (6) The local flame speed in the cusps substantially exceeds its laminar value, which results in a disproportionately large contribution of cusps to S{sub T} compared with the flame surface area in them. (7) A criterion is established for transition to the regime significantly influenced by cusp formation. In particular, at Karlovitz numbers Ka >or similar 20, flame collisions provide an important mechanism controlling S{sub T}, in addition to the increase of A{sub T} by large-scale motions and the potential enhancement of diffusive transport by small-scale turbulence. (author)
Neutrino oscillations in a turbulent plasma
Mendonça, J. T. [Instituto de Física, Universidade de São Paulo, São Paulo, SP, CEP 05508-090 Brazil and IPFN, Instituto Superior Técnico, 1049-001 Lisboa (Portugal)] [Instituto de Física, Universidade de São Paulo, São Paulo, SP, CEP 05508-090 Brazil and IPFN, Instituto Superior Técnico, 1049-001 Lisboa (Portugal); Haas, F. [Departamento de Física, Universidade Federal do Paraná, Curitiba PR, CEP 81531-990 (Brazil)] [Departamento de Física, Universidade Federal do Paraná, Curitiba PR, CEP 81531-990 (Brazil)
2013-07-15T23:59:59.000Z
A new model for the joint neutrino flavor and plasma oscillations is introduced, in terms of the dynamics of the neutrino flavor polarization vector in a plasma background. Fundamental solutions are found for both time-invariant and time-dependent media, considering slow and fast variations of the electron plasma density. The model is shown to be described by a generalized Hamiltonian formalism. In the case of a broad spectrum of electron plasma waves, a statistical approach indicates the shift of both equilibrium value and frequency oscillation of flavor coherence, due to the existence of a turbulent plasma background.
Calculation of Extreme Wave Loads on Coastal Highway Bridges
Meng, Bo
2010-01-14T23:59:59.000Z
force on bridge decks. 2D Model is a linear wave model, which has the capability of calculating wave velocity potential components in time domain based on wave parameters such as wave height, wave period and water depth, and complex structural geometries...
Marsh, S.P.
1988-03-08T23:59:59.000Z
An explosive plane-wave air lens which enables a spherical wave form to be converted to a planar wave without the need to specially machine or shape explosive materials is described. A disc-shaped impactor having a greater thickness at its center than around its periphery is used to convert the spherical wave into a plane wave. When the wave reaches the impactor, the center of the impactor moves first because the spherical wave reaches the center of the impactor first. The wave strikes the impactor later in time as one moves radially along the impactor. Because the impactor is thinner as one moves radially outward, the velocity of the impactor is greater at the periphery than at the center. An acceptor explosive is positioned so that the impactor strikes the acceptor simultaneously. Consequently, a plane detonation wave is propagated through the acceptor explosive. 4 figs.
Marsh, S.P.
1987-03-12T23:59:59.000Z
An explosive plane-wave air lens which enables a spherical wave form to be converted to a planar wave without the need to specially machine or shape explosive materials is described. A disc-shaped impactor having a greater thickness at its center than around its periphery is used to convert the spherical wave into a plane wave. When the wave reaches the impactor, the center of the impactor moves first because the spherical wave reaches the center of the impactor first. The wave strikes the impactor later in time as one moves radially along the impactor. Because the impactor is thinner as one moves radially outward, the velocity of the impactor is greater at the periphery than at the center. An acceptor explosive is positioned so that the impactor strikes the acceptor simultaneously. Consequently, a plane detonation wave is propagated through the acceptor explosive. 3 figs., 3 tabs.
Particle dispersion in homogeneous turbulence using the one-dimensional turbulence model
Sun, Guangyuan, E-mail: gysungrad@gmail.com; Lignell, David O., E-mail: davidlignell@byu.edu [Chemical Engineering Department, Brigham Young University, Provo, Utah 84602 (United States); Hewson, John C., E-mail: jchewso@sandia.gov [Fire Science and Technology Department, Sandia National Laboratories, Albuquerque, New Mexico 87123 (United States); Gin, Craig R., E-mail: cgin@math.tamu.edu [Department of Mathematics, Texas A and M University, College Station, Texas 77843 (United States)
2014-10-15T23:59:59.000Z
Lagrangian particle dispersion is studied using the one-dimensional turbulence (ODT) model in homogeneous decaying turbulence configurations. The ODT model has been widely and successfully applied to a number of reacting and nonreacting flow configurations, but only limited application has been made to multiphase flows. Here, we present a version of the particle implementation and interaction with the stochastic and instantaneous ODT eddy events. The model is characterized by comparison to experimental data of particle dispersion for a range of intrinsic particle time scales and body forces. Particle dispersion, velocity, and integral time scale results are presented. The particle implementation introduces a single model parameter ?{sub p}, and sensitivity to this parameter and behavior of the model are discussed. Good agreement is found with experimental data and the ODT model is able to capture the particle inertial and trajectory crossing effects. These results serve as a validation case of the multiphase implementations of ODT for extensions to other flow configurations.
Tracking deep mantle reservoirs with ultra-low velocity zones Allen K. McNamara a,
Rhoads, James
Tracking deep mantle reservoirs with ultra-low velocity zones Allen K. McNamara a, , Edward J, that directly overlies the core-mantle boundary (CMB). These regions have been dubbed Ultra-Low Velocity Zones. Introduction For over 15 yrs seismologists have mapped regions of ultra-low P- and S-wave velocities
Velocity pump reaction turbine
House, Palmer A. (Walnut Creek, CA)
1982-01-01T23:59:59.000Z
An expanding hydraulic/two-phase velocity pump reaction turbine including a dual concentric rotor configuration with an inter-rotor annular flow channel in which the inner rotor is mechanically driven by the outer rotor. In another embodiment, the inner rotor is immobilized and provided with gas recovery ports on its outer surface by means of which gas in solution may be recovered. This velocity pump reaction turbine configuration is capable of potential energy conversion efficiencies of up to 70%, and is particularly suited for geothermal applications.
Velocity pump reaction turbine
House, Palmer A. (Walnut Creek, CA)
1984-01-01T23:59:59.000Z
An expanding hydraulic/two-phase velocity pump reaction turbine including a dual concentric rotor configuration with an inter-rotor annular flow channel in which the inner rotor is mechanically driven by the outer rotor. In another embodiment, the inner rotor is immobilized and provided with gas recovery ports on its outer surface by means of which gas in solution may be recovered. This velocity pump reaction turbine configuration is capable of potential energy conversion efficiencies of up to 70%, and is particularly suited for geothermal applications.
Multiscale nature of the dissipation range in solar wind turbulence
Told, D; TenBarge, J M; Howes, G G; Hammett, G W
2015-01-01T23:59:59.000Z
Nonlinear energy transfer and dissipation in Alfv\\'en wave turbulence are analyzed in the first gyrokinetic simulation spanning all scales from the tail of the MHD range to the electron gyroradius scale. For typical solar wind parameters at 1 AU, about 30% of the nonlinear energy transfer close to the electron gyroradius scale is mediated by modes in the tail of the MHD cascade. Collisional dissipation occurs across the entire kinetic range $k_\\perp\\rho_i\\gtrsim 1$. Both mechanisms thus act on multiple coupled scales, which have to be retained for a comprehensive picture of the dissipation range in Alfv\\'enic turbulence.
Cap Bubble Drift Velocity in a Confined Test Section
Xiaodong Sun; Seungjin Kim; Mamoru Ishii; Frank W. Lincoln; Stephen G. Beus
2002-10-09T23:59:59.000Z
In the two-group interfacial area transport equation, bubbles are categorized into two groups, i.e., spherical/distorted bubbles as group 1 and cap/slug/churn-turbulent bubbles as group 2. The bubble rise velocities for both groups of bubbles may be estimated by the drift flux model by applying different distribution parameters and drift velocities for both groups. However, the drift velocity for group 2 bubbles is not always applicable (when the wall effect becomes important) as in the current test loop of interest where the flow channel is confined by two parallel flat walls, with a dimension of 200-mm in width and 10-mm in gap. The previous experiments indicated that no stable slug flow existed in this test section, which was designed to permit visualization of the flow patterns and bubble characteristics without the distortion associated with curved surfaces. In fact, distorted cap bubbly and churn-turbulent flow was observed. Therefore, it is essential to developed a correlation for cap bubble drift velocity in this confined flow channel. Since the rise velocity of a cap bubble depends on its size, a high-speed movie camera is used to capture images of cap bubbles to obtain the bubble size information. Meanwhile, the rise velocity of cap and elongated bubbles (called cap bubbles hereafter) is investigated by examining the captured images frame by frame. As a result, the conventional correlation of drift velocity for slug bubbles is modified and acceptable agreements between the measurements and correlation estimation are achieved.
DRIVERS OF H I TURBULENCE IN DWARF GALAXIES
Stilp, Adrienne M.; Dalcanton, Julianne J. [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States); Skillman, Evan [Minnesota Institute for Astrophysics, University of Minnesota, 116 Church Street SE, Minneapolis, MN 55455 (United States); Warren, Steven R. [Department of Astronomy, University of Maryland, CSS Building, Room 1024, Stadium Drive, College Park, MD 20742-2421 (United States); Ott, Juergen [National Radio Astronomy Observatory, P.O. Box O, 1003 Lopezville Road, Socorro, NM 87801 (United States); Koribalski, Baerbel [Australia Telescope National Facility, CSIRO Astronomy and Space Science, P.O. Box 76, Epping, NSW 1710 (Australia)
2013-08-20T23:59:59.000Z
Neutral hydrogen (H I) velocity dispersions are believed to be set by turbulence in the interstellar medium (ISM). Although turbulence is widely believed to be driven by star formation, recent studies have shown that this driving mechanism may not be dominant in regions of low star formation surface density ({Sigma}{sub SFR}), such those as found in dwarf galaxies or the outer regions of spirals. We have generated average H I line profiles in a number of nearby dwarfs and low-mass spirals by co-adding H I spectra in subregions with either a common radius or {Sigma}{sub SFR}. We find that the individual spatially resolved ''superprofiles'' are composed of a central narrow peak ({approx}5-15 km s{sup -1}) with higher velocity wings to either side, similar to their global counterparts as calculated for the galaxy as a whole. Under the assumption that the central peak reflects the H I turbulent velocity dispersion, we compare measures of H I kinematics determined from the superprofiles to local ISM properties, including surface mass densities and measures of star formation. The shape of the wings of the superprofiles do not show any correlation with local ISM properties, which indicates that they may be an intrinsic feature of H I line-of-sight spectra. On the other hand, the H I velocity dispersion is correlated most strongly with baryonic and H I surface mass density, which points toward a gravitational origin for turbulence, but it is unclear which, if any, gravitational instabilities are able to operate efficiently in these systems. Star formation energy is typically produced at a level sufficient to drive H I turbulent motions at realistic coupling efficiencies in regimes where {Sigma}{sub SFR} {approx}> 10{sup -4} M{sub Sun} yr{sup -1} kpc{sup -2}, as is typically found in inner spiral disks. At low star formation intensities, on the other hand, star formation cannot supply enough energy to drive the observed turbulence, nor does it uniquely determine the turbulent velocity dispersion. Nevertheless, even at low intensity, star formation does appear to provide a lower threshold for H I velocity dispersions. We find a pronounced decrease in coupling efficiency with increasing {Sigma}{sub SFR}, which would be consistent with a picture where star formation couples to the ISM with constant efficiency, but that less of that energy is found in the neutral phase at higher {Sigma}{sub SFR}. We have examined a number of potential drivers of H I turbulence, including star formation, gravitational instabilities, the magneto-rotational instability, and accretion-driven turbulence, and found that, individually, none of these drivers is capable of driving the observed levels of turbulence in the low {Sigma}{sub SFR} regime. We discuss possible solutions to this conundrum.
Scaling Relations for Collision-less Dark Matter Turbulence
Akika Nakamichi; Masahiro Morikawa
2009-06-15T23:59:59.000Z
Many scaling relations are observed for self-gravitating systems in the universe. We explore the consistent understanding of them from a simple principle based on the proposal that the collision-less dark matter fluid terns into a turbulent state, i.e. dark turbulence, after crossing the caustic surface in the non-linear stage. The dark turbulence will not eddy dominant reflecting the collision-less property. After deriving Kolmogorov scaling laws from Navier-Stokes equation by the method similar to the one for Smoluchowski coagulation equation, we apply this to several observations such as the scale-dependent velocity dispersion, mass-luminosity ratio, magnetic fields, and mass-angular momentum relation, power spectrum of density fluctuations. They all point the concordant value for the constant energy flow per mass: $0.3 cm^2/sec^3$, which may be understood as the speed of the hierarchical coalescence process in the cosmic structure formation.
Compressible Turbulence in Galaxy Clusters: Physics and Stochastic Particle Re-acceleration
G. Brunetti; A. Lazarian
2007-03-22T23:59:59.000Z
We attempt to explain the non-thermal emission arising from galaxy clusters as a result of the re-acceleration of electrons by compressible turbulence induced by cluster mergers. In our model intracluster medium (ICM) is represented by a high beta plasma in which turbulent motions are driven at large scales. The corresponding injection velocities are higher than the Alfven velocity. As a result, the turbulence is approximately isotropic up to the scale at which the turbulent velocity gets comparable with the Alfven velocity. Under the hypothesis that turbulence in the ICM is highly super- Alfvenic the magnetic field is passively advected and the field lines are bended on scales smaller than that of the classical, unmagnetized, ion-ion mean free path. This affects ion diffusion and the strength of the effective viscosity. Under these conditions the bulk of turbulence in hot (5-10 keV temperature) galaxy clusters is likely to be dissipated at collisionless scales via resonant coupling with thermal and fast particles. We use collisionless physics to derive the amplitude of the different components of the energy of the compressible modes, and review and extend the treatment of plasma damping in the ICM. We calculate the acceleration of both protons and electrons taking into account both TTD acceleration and non-resonant acceleration by large scale compressions. We find that relativistic electrons can be re-accelerated in the ICM up to energies of several GeV provided that the rms velocity of the compressible turbulent-eddies is (V_L/c_s)^2~0.15-0.3. We find that under typical conditions ~ 2-5 % of the energy flux of the cascading of compressible motions injected at large scales goes into the acceleration of fast particles and that this may explain the observed non-thermal emission from merging galaxy clusters.
Perry, Russell W.; Farley, M. Jared; Hansen, Gabriel S. (US Geological Survey, Western Fisheries Research Center, Columbia River Research Laboratory, Cook, WA)
2005-07-01T23:59:59.000Z
Passage through dams is a major source of mortality of anadromous juvenile salmonids because some populations must negotiate up to eight dams in Columbia and Snake rivers. Dams cause direct mortality when fish pass through turbines, but dams may also cause indirect mortality by altering migration conditions in rivers. Forebays immediately upstream of dams have decreased the water velocity of rivers and may contribute substantially to the total migration delay of juvenile salmonids. Recently, Coutant (2001a) suggested that in addition to low water velocities, lack of natural turbulence may contribute to migration delay by causing fish to lose directional cues. Coutant (2001a) further hypothesized that restoring turbulence in dam forebays may reduce migration delay by providing directional cues that allow fish to find passage routes more quickly (Coutant 2001a). Although field experiments have yielded proof of the concept of using induced turbulence to guide fish to safe passage routes, little is known about mechanisms actually causing behavioral changes. To test hypotheses about how turbulence influences movement and behavior of migrating juvenile salmonids, we conducted two types of controlled experiments at Cowlitz Falls Dam, Washington. A common measure of migration delay is the elapsed time between arrival at, and passage through, a dam. Therefore, for the first set of experiments, we tested the effect of induced turbulence on the elapsed time needed for fish to traverse through a raceway and pass over a weir at its downstream end (time trial experiment). If turbulence helps guide fish to passage routes, then fish should pass through the raceway quicker in the presence of appropriately scaled and directed turbulent cues. Second, little is known about how the physical properties of water movement provide directional cues to migrating juvenile salmonids. To examine the feasibility of guiding fish with turbulence, we tested whether directed turbulence could guide fish into one of two channels in the raceway, and subsequently cause them to pass disproportionately over the weir where turbulent cues were aimed (guidance experiment). Last, we measured and mapped water velocity and turbulence during the experiments to understand water movement patterns and the spatial distribution of turbulence in the raceways.
Sanyal, Devashish [Department of Theoretical Physics, Indian Association for the Cultivation of Science, Jadavpur, Calcutta 700032 (India)]. E-mail: tpds@mahendra.iacs.res.in; Sen, Siddhartha [School of Mathematics, Trinity College, Dublin 2 (Ireland)]. E-mail: sen@maths.tcd.ie
2006-06-15T23:59:59.000Z
The present manuscript dealing with large occupation of states of a quantum system, extends the study to the case of quantum weak turbulence. The quasiparticle spectrum, calculated for such a system, using a Green's function approach, establishes the dissipative and inertial regimes, hence a Kolmogorov type of picture.
Kinematics of extreme waves in deep water John Grue*, Didier Clamond, Morten Huseby, Atle Jensen
Clamond, Didier
Kinematics of extreme waves in deep water John Grue*, Didier Clamond, Morten Huseby, Atle Jensen fluid velocity, e ffiffiffiffi g=k p is then defined. Deep water waves with a fluid velocity up to 75 2004 Abstract The velocity profiles under crest of a total of 62 different steep wave events in deep
Pradipta, Rezy
2012-01-01T23:59:59.000Z
In this thesis, we investigate the potential role played by large-scale anomalous heat sources (e.g. prolonged heat wave events) in generating acoustic-gravity waves (AGWs) that might trigger widespread plasma turbulence ...
Measurement of entropy production rate in compressible turbulence
M. M. Bandi; W. I. Goldburg; J. R. Cressman Jr
2006-10-22T23:59:59.000Z
The rate of change of entropy $\\dot S$ is measured for a system of particles floating on the surface of a fluid maintained in a turbulent steady state. The resulting coagulation of the floaters allows one to relate $\\dot S$ to the velocity divergence and to the Lyapunov exponents characterizing the behavior of this system. The quantities measured from experiments and simulations are found to agree well with the theoretical predictions.
Turbulent Von Karman Swirling Flows , R. Schiestel2
Paris-Sud XI, Université de
is often used for studying fundamental aspects of developed turbulence and especially of magneto-hydrodynamic-rotating disks (R = 92.5 mm) enclosed by a stationary cylinder (Rc = 100 mm) (Fig.1). The in- terdisk spacing H a volumic drag force in the equation of V the tangential velocity compo- nent: f = nCD(1,2r - V)|1,2r - V
aeroacoustics volume 8 number 4 2009 pages 337 354 337 Turbulence and sound-field POD analysis
Dabiri, John O.
and Applied Science California Institute of Technology colonius@caltech.edu ABSTRACT A Proper Orthogonal simulation database. Norms are defined based on near-field volume integrals of pressure, turbulence kinetic energy, streamwise velocity, and total enthalpy, two-dimensional integrals of streamswise velocity (to
Experimental study of turbulent flame kernel propagation
Mansour, Mohy [National Institute of Laser Enhanced Sciences, Cairo University, Giza (Egypt); Peters, Norbert; Schrader, Lars-Uve [Institute of Combustion Technology, Aachen (Germany)
2008-07-15T23:59:59.000Z
Flame kernels in spark ignited combustion systems dominate the flame propagation and combustion stability and performance. They are likely controlled by the spark energy, flow field and mixing field. The aim of the present work is to experimentally investigate the structure and propagation of the flame kernel in turbulent premixed methane flow using advanced laser-based techniques. The spark is generated using pulsed Nd:YAG laser with 20 mJ pulse energy in order to avoid the effect of the electrodes on the flame kernel structure and the variation of spark energy from shot-to-shot. Four flames have been investigated at equivalence ratios, {phi}{sub j}, of 0.8 and 1.0 and jet velocities, U{sub j}, of 6 and 12 m/s. A combined two-dimensional Rayleigh and LIPF-OH technique has been applied. The flame kernel structure has been collected at several time intervals from the laser ignition between 10 {mu}s and 2 ms. The data show that the flame kernel structure starts with spherical shape and changes gradually to peanut-like, then to mushroom-like and finally disturbed by the turbulence. The mushroom-like structure lasts longer in the stoichiometric and slower jet velocity. The growth rate of the average flame kernel radius is divided into two linear relations; the first one during the first 100 {mu}s is almost three times faster than that at the later stage between 100 and 2000 {mu}s. The flame propagation is slightly faster in leaner flames. The trends of the flame propagation, flame radius, flame cross-sectional area and mean flame temperature are related to the jet velocity and equivalence ratio. The relations obtained in the present work allow the prediction of any of these parameters at different conditions. (author)
MAGNETIC HELICITY IN THE DISSIPATION RANGE OF STRONG IMBALANCED TURBULENCE
Markovskii, S. A.; Vasquez, Bernard J., E-mail: sergei.markovskii@unh.edu, E-mail: bernie.vasquez@unh.edu [Space Science Center, University of New Hampshire, Durham, NH 03824 (United States)
2013-05-01T23:59:59.000Z
Hybrid numerical simulations of freely decaying two-dimensional turbulence are presented. The background magnetic field is perpendicular to the simulation plane, which eliminates linear kinetic Alfven waves from the system. The net magnetic helicity of the initial fluctuations at large scales is zero. The turbulence is set to be imbalanced in the sense that the net cross-helicity is not zero. As the turbulence evolves, it develops nonzero magnetic helicity at smaller scales, in the proton kinetic range. In the quasi-steady state of evolution, the magnetic helicity spectrum has a peak consistent with the solar wind observations. The peak position depends on the plasma beta and correlates with a sharp decline of the cross-helicity spectrum.
Turbulence transport modeling of the temporal outer heliosphere
Adhikari, L.; Zank, G. P.; Hu, Q. [Department of Space Science, University of Alabama in Huntsville, Huntsville, AL 35899 (United States); Dosch, A., E-mail: la0004@uah.edu [Center for Space Plasma and Aeronomic Research (CSPAR), University of Alabama in Huntsville, Huntsville, AL 35899 (United States)
2014-09-20T23:59:59.000Z
The solar wind can be regarded as a turbulent magnetofluid, evolving in an expanding solar wind and subject to turbulent driving by a variety of in situ sources. Furthermore, the solar wind and the drivers of turbulence are highly time-dependent and change with solar cycle. Turbulence transport models describing low-frequency magnetic and velocity fluctuations in the solar wind have so far neglected solar cycle effects. Here we consider the effects of solar cycle variability on a turbulence transport model developed by Zank et al. This model is appropriate for the solar wind beyond about 1 AU, and extensions have described the steady-state dependence of the magnetic energy density fluctuations, correlation length, and solar wind temperature throughout the outer heliosphere. We find that the temporal solar wind introduces a periodic variability, particularly beyond ?10 AU, in the magnetic energy density fluctuations, correlation length, and solar wind temperature. The variability is insufficient to account for the full observed variability in these quantities, but we find that the time-dependent solutions trace the steady-state solutions quite well, suggesting that the steady-state models are reasonable first approximations.
Numerical simulations of compressively driven interstellar turbulence: I. Isothermal gas
Schmidt, Wolfram; Hupp, Markus; Kern, Sebastian; Niemeyer, Jens C
2008-01-01T23:59:59.000Z
We performed numerical simulations of supersonic isothermal turbulence driven by mostly compressive large-scale forcing, using both a static grid and adaptive mesh refinement with an effective resolution N=768^3. After a transient phase dominated by shocks, turbulence evolves into a steady state with an RMS Mach number about 2.5, in which cloud-like structures of over-dense gas are surrounded by highly rarefied gas. The index of the turbulence energy spectrum function beta = 2.0 in the shock-dominated phase. As the flow approaches statistical equilibrium, the spectrum flattens, with beta = 1.9. For the scaling exponent of the root mean square velocity fluctuation, we obtain gamma = 0.43 from the velocity structure functions of second order. These results are well within the range of observed scaling properties for the velocity dispersion in molecular clouds. Calculating structure functions of order p=1,...,5, we find for all scaling exponents significant deviations from the Kolmogorov-Burgers model proposed b...
A primitive kinetic-fluid model for quasi-parallel propagating magnetohydrodynamic waves
Nariyuki, Y. [Faculty of Human Development, University of Toyama, 3190 Toyama City, Toyama 930-8555 (Japan)] [Faculty of Human Development, University of Toyama, 3190 Toyama City, Toyama 930-8555 (Japan); Saito, S. [Graduate School of Science, Nagoya University, Nagoya, Aichi 464-8601 (Japan)] [Graduate School of Science, Nagoya University, Nagoya, Aichi 464-8601 (Japan); Umeda, T. [Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya, Aichi 464-8601 (Japan)] [Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya, Aichi 464-8601 (Japan)
2013-07-15T23:59:59.000Z
The extension and limitation of the existing one-dimensional kinetic-fluid model (Vlasov-MHD (magnetohydrodynamic) model), which has been used to analyze parametric instabilities of parallel propagating Alfvén waves, are discussed. The inconsistency among the given velocity distribution functions in the past studies is resolved through the systematic derivation of the multi-dimensional Vlasov-MHD model. The linear dispersion analysis of the present model indicates that the collisionless damping of the slow modes is adequately evaluated in low beta plasmas, although the deviation between the present model and the full-Vlasov theory increases with increasing plasma beta and increasing propagation angle. This is because the transit-time damping is not correctly evaluated in the present model. It is also shown that the ponderomotive density fluctuations associated with the envelope-modulated quasi-parallel propagating Alfvén waves derived from the present model is not consistent with those derived from the other models such as the Landau-fluid model, except for low beta plasmas. The result indicates the present model would be useful to understand the linear and nonlinear development of the Alfvénic turbulence in the inner heliosphere, whose condition is relatively low beta, while the existing model and the present model are insufficient to discuss the parametric instabilities of Alfvén waves in high beta plasmas and the obliquely propagating waves.
Polymer Stretching by Turbulence
Chertkov, Michael
2000-05-15T23:59:59.000Z
The stretching of a polymer chain by a large-scale chaotic flow is considered. The steady state which emerges as a balance of the turbulent stretching and anharmonic resistance of the chain is quantitatively described, i.e., the dependency on the flow parameters (Lyapunov exponent statistics) and the chain characteristics (the number of beads and the interbead elastic potential) is made explicit. (c) 2000 The American Physical Society.
Discrimination of porosity and fluid saturation using seismic velocity analysis
Berryman, James G. (Danville, CA)
2001-01-01T23:59:59.000Z
The method of the invention is employed for determining the state of saturation in a subterranean formation using only seismic velocity measurements (e.g., shear and compressional wave velocity data). Seismic velocity data collected from a region of the formation of like solid material properties can provide relatively accurate partial saturation data derived from a well-defined triangle plotted in a (.rho./.mu., .lambda./.mu.)-plane. When the seismic velocity data are collected over a large region of a formation having both like and unlike materials, the method first distinguishes the like materials by initially plotting the seismic velocity data in a (.rho./.lambda., .mu./.lambda.)-plane to determine regions of the formation having like solid material properties and porosity.
Flavor evolution of supernova neutrinos in turbulent matter
Lund, Tina; Kneller, James P. [Department of Physics, North Carolina State University, 2401 Stinson Drive, Raleigh, NC 27695 (United States)
2014-01-01T23:59:59.000Z
The neutrino signal from the next galactic supernova carries with it an enormous amount of information on the explosion mechanism of a core-collapse supernova, as well as on the stellar progenitor and on the neutrinos themselves. In order to extract this information we need to know how the neutrino flavor evolves over time due to the interplay of neutrino self-interactions and matter effects. Additional turbulence in the supernova matter may impart its own signatures on the neutrino spectrum, and could partly obscure the imprints of collective and matter effects. We investigate the neutrino flavor evolution due to neutrino self-interactions, matter effects due to the shock wave propagation, and turbulence in three progenitors with masses of 8.8 M?, 10.8 M? and 18.0 M?. In the lightest progenitor we find that the impact of moderate turbulence of the order 10% is limited and occurs only briefly early on. This makes the signatures of collective and matter interactions relatively straightforward to interpret. Similarly, with moderate turbulence the two heavier progenitors exhibit only minor changes in the neutrino spectrum, and collective and matter signatures persists. However, when the turbulence is increased to 30% and 50% the high density matter resonance features in the neutrino spectrum get obscured, while new features arise in the low density resonance channel and in the non-resonant channels. We conclude that with moderate amounts of turbulence spectral features of collective and matter interactions survive in all three progenitors. For the larger amounts of turbulence in the 10.8 M? and 18.0 M? progenitor new features arise, as others disappear.
2D full wave modeling for a synthetic Doppler backscattering diagnostic
Hillesheim, J. C.; Schmitz, L.; Kubota, S.; Rhodes, T. L.; Carter, T. A. [Department of Physics and Astronomy, University of California, Los Angeles, California 90095 (United States); Holland, C. [University of California, San Diego, La Jolla, California 92093 (United States)
2012-10-15T23:59:59.000Z
Doppler backscattering (DBS) is a plasma diagnostic used in tokamaks and other magnetic confinement devices to measure the fluctuation level of intermediate wavenumber (k{sub {theta}}{rho}{sub s}{approx} 1) density fluctuations and the lab frame propagation velocity of turbulence. Here, a synthetic DBS diagnostic is described, which has been used for comparisons between measurements in the DIII-D tokamak and predictions from nonlinear gyrokinetic simulations. To estimate the wavenumber range to which a Gaussian beam would be sensitive, a ray tracing code and a 2D finite difference, time domain full wave code are used. Experimental density profiles and magnetic geometry are used along with the experimental antenna and beam characteristics. An example of the effect of the synthetic diagnostic on the output of a nonlinear gyrokinetic simulation is presented.
Excitation of kinetic geodesic acoustic modes by drift waves in nonuniform plasmas
Qiu, Z. [Inst. Fusion Theory and Simulation, Zhejiang Univ., Hangzhou 310027 (China)] [Inst. Fusion Theory and Simulation, Zhejiang Univ., Hangzhou 310027 (China); Chen, L. [Inst. Fusion Theory and Simulation, Zhejiang Univ., Hangzhou 310027 (China) [Inst. Fusion Theory and Simulation, Zhejiang Univ., Hangzhou 310027 (China); Dept. Physics and Astronomy, Univ. of California, Irvine, California 92697-4575 (United States); Zonca, F. [Inst. Fusion Theory and Simulation, Zhejiang Univ., Hangzhou 310027 (China) [Inst. Fusion Theory and Simulation, Zhejiang Univ., Hangzhou 310027 (China); Associazione Euratom-ENEA sulla Fusione, C.P. 65 - I-00044 - Frascati (Italy)
2014-02-15T23:59:59.000Z
Effects of system nonuniformities and kinetic dispersiveness on the spontaneous excitation of Geodesic Acoustic Mode (GAM) by Drift Wave (DW) turbulence are investigated based on nonlinear gyrokinetic theory. The coupled nonlinear equations describing parametric decay of DW into GAM and DW lower sideband are derived and then solved both analytically and numerically to investigate the effects on the parametric decay process due to system nonuniformities, such as nonuniform diamagnetic frequency, finite radial envelope of DW pump, and kinetic dispersiveness. It is found that the parametric decay process is a convective instability for typical tokamak parameters when finite group velocities of DW and GAM associated with kinetic dispersiveness and finite radial envelope are taken into account. When, however, nonuniformity of diamagnetic frequency is taken into account, the parametric decay process becomes, time asymptotically, a quasi-exponentially growing absolute instability.
Residual Energy Spectrum of Solar Wind Turbulence
Chen, C H K; Salem, C S; Maruca, B A
2013-01-01T23:59:59.000Z
It has long been known that the energy in velocity and magnetic field fluctuations in the solar wind is not in equipartition. In this paper, we present an analysis of 5 years of Wind data at 1 AU to investigate the reason for this. The residual energy (difference between energy in velocity and magnetic field fluctuations) was calculated using both the standard magnetohydrodynamic (MHD) normalization for the magnetic field and a kinetic version, which includes temperature anisotropies and drifts between particle species. It was found that with the kinetic normalization, the fluctuations are closer to equipartition, with a mean normalized residual energy of sigma_r = -0.19 and mean Alfven ratio of r_A = 0.71. The spectrum of residual energy, in the kinetic normalization, was found to be steeper than both the velocity and magnetic field spectra, consistent with some recent MHD turbulence predictions and numerical simulations, having a spectral index close to -1.9. The local properties of residual energy and cros...
Dark Matter Velocity Spectroscopy
Eric G. Speckhard; Kenny C. Y. Ng; John F. Beacom; Ranjan Laha
2015-07-31T23:59:59.000Z
Dark matter decays or annihilations that produce line-like spectra may be smoking-gun signals. However, even such distinctive signatures can be mimicked by astrophysical or instrumental causes. We show that velocity spectroscopy-the measurement of energy shifts induced by relative motion of source and observer-can separate these three causes with minimal theoretical uncertainties. The principal obstacle has been energy resolution, but upcoming experiments will reach the required 0.1% level. As an example, we show that the imminent Astro-H mission can use Milky Way observations to separate possible causes of the 3.5-keV line. We discuss other applications.
Resonance Van Hove Singularities in Wave Kinetics
Shi, Yi-Kang
2015-01-01T23:59:59.000Z
Wave kinetic theory has been developed to describe the statistical dynamics of weakly nonlinear, dispersive waves. However, we show that systems which are generally dispersive can have resonant sets of wave modes with identical group velocities, leading to a local breakdown of dispersivity. This shows up as a geometric singularity of the resonant manifold and possibly as an infinite phase measure in the collision integral. Such singularities occur widely for classical wave systems, including acoustical waves, Rossby waves, helical waves in rotating fluids, light waves in nonlinear optics and also in quantum transport, e.g. kinetics of electron-hole excitations (matter waves) in graphene. These singularities are the exact analogue of the critical points found by Van Hove in 1953 for phonon dispersion relations in crystals. The importance of these singularities in wave kinetics depends on the dimension of phase space $D=(N-2)d$ ($d$ physical space dimension, $N$ the number of waves in resonance) and the degree ...
Eddy fluxes in baroclinic turbulence
Thompson, Andrew F.
2006-01-01T23:59:59.000Z
cant dissipation of tidal energy in the deep ocean inferred2006: An estimate of tidal energy lost to turbulence at the
Turbulence models of gravitational clustering
Jose Gaite
2012-02-15T23:59:59.000Z
Large-scale structure formation can be modeled as a nonlinear process that transfers energy from the largest scales to successively smaller scales until it is dissipated, in analogy with Kolmogorov's cascade model of incompressible turbulence. However, cosmic turbulence is very compressible, and vorticity plays a secondary role in it. The simplest model of cosmic turbulence is the adhesion model, which can be studied perturbatively or adapting to it Kolmogorov's non-perturbative approach to incompressible turbulence. This approach leads to observationally testable predictions, e.g., to the power-law exponent of the matter density two-point correlation function.
The radial-velocity revolution
Griffin, R. (Cambridge Univ., Observatories (England))
1989-09-01T23:59:59.000Z
Instruments and techniques designed for registering the minute Doppler shifts arising from stellar radial velocity are examined. Particular attention is given to the photographic spectrographs, the high-dispersion spectrographs ('digital speedometers'), and the Palomar spectrometer. The principle of using radial-velocity masks is described, and the use of interferometers for radial-velocity measurements is discussed. Results are presented of radial velocity observations for HD 114762, HD 210647, and Epsilon Tauri, together with interpretations of these results.
Simulation of lean premixed turbulent combustion
2008-01-01T23:59:59.000Z
turbulent methane combustion. Proc. Combust. Inst. , 29:in premixed turbulent combustion. Proc. Combust. Inst. ,for zero Mach number combustion. Combust. Sci. Technol. ,
Advanced Computational Methods for Turbulence and Combustion...
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Advanced Computational Methods for Turbulence and Combustion Advanced Computational Methods for Turbulence and Combustion Bell.png Key Challenges: Development and application of...
Evidence for internal structures of spiral turbulence
2009-12-21T23:59:59.000Z
Dec 22, 2009 ... ary laminar-turbulent pattern in plane Couette flow. ... flow internal to the turbulent and laminar spirals, and unique ... 2 ( is the fluid density).
Ris-R-1188(EN) Turbulence and turbulence-
Risø-R-1188(EN) Turbulence and turbulence- generated structural loading in wind turbine clusters af den internationale standard for vindmøller, IEC61400-1 (2005). Også ekstrembelastninger under to ensure sufficient structural sustainability of the wind turbines exposed to "wind farm flow
Nonlinear three-wave interaction in marine sediments
Pushkina, N I
2015-01-01T23:59:59.000Z
Nonlinear interaction of three acoustic waves in a sandy sediment is studied in the frequency range where there is a considerable wave velocity dispersion. The possibility of an experimental observation of the generation of a sound wave by two pump waves propagating at an angle to each other is estimated.
Nonlinear three-wave interaction in marine sediments
N. I. Pushkina
2015-03-18T23:59:59.000Z
Nonlinear interaction of three acoustic waves in a sandy sediment is studied in the frequency range where there is a considerable wave velocity dispersion. The possibility of an experimental observation of the generation of a sound wave by two pump waves propagating at an angle to each other is estimated.
Numerical simulation of tsunami waves generated by deformable submarine landslides
Kirby, James T.
Numerical simulation of tsunami waves generated by deformable submarine landslides Gangfeng Ma a wave model Tsunami wave Numerical modeling a b s t r a c t This paper presents a new submarine of landslide motion and associated tsunami wave generation on parameters including sediment settling velocity
An electromagnetic analog of gravitational wave memory
Lydia Bieri; David Garfinkle
2013-09-10T23:59:59.000Z
We present an electromagnetic analog of gravitational wave memory. That is, we consider what change has occurred to a detector of electromagnetic radiation after the wave has passed. Rather than a distortion in the detector, as occurs in the gravitational wave case, we find a residual velocity (a "kick") to the charges in the detector. In analogy with the two types of gravitational wave memory ("ordinary" and "nonlinear") we find two types of electromagnetic kick.
White light velocity interferometer
Erskine, D.J.
1999-06-08T23:59:59.000Z
The invention is a technique that allows the use of broadband and incoherent illumination. Although denoted white light velocimetry, this principle can be applied to any wave phenomenon. For the first time, powerful, compact or inexpensive sources can be used for remote target velocimetry. These include flash and arc lamps, light from detonations, pulsed lasers, chirped frequency lasers, and lasers operating simultaneously in several wavelengths. The technique is demonstrated with white light from an incandescent source to measure a target moving at 16 m/s. 41 figs.
Turbulence production and turbulent pressure support in the intergalactic medium
Iapichino, L; Niemeyer, J C; Merklein, J
2011-01-01T23:59:59.000Z
The injection and evolution of turbulence in the intergalactic medium is studied by means of mesh-based hydrodynamical simulations, including a subgrid scale (SGS) model for small-scale unresolved turbulence. The simulations show that the production of turbulence has a different redshift dependence in the intracluster medium (ICM) and the warm-hot intergalactic medium (WHIM). We show that turbulence in the ICM is produced chiefly by merger-induced shear flows, whereas the production in the WHIM is dominated by shock interactions. Secondly, the effect of dynamical pressure support on the gravitational contraction has been studied. This turbulent support is stronger in the WHIM gas at baryon overdensities 1 < delta < 100, and less relevant for the ICM. Although the relative mass fraction of the gas with large vorticity is considerable (52% in the ICM), we find that for only about 10% in mass this is dynamically relevant, namely not associated to an equally large thermal pressure support. According to this...
A comparison of weak-turbulence and PIC simulations of weak electron-beam plasma interaction
Ratcliffe, Heather; Rozenan, Mohammed B Che; Nakariakov, Valery
2014-01-01T23:59:59.000Z
Quasilinear theory has long been used to treat the problem of a weak electron beam interacting with plasma and generating Langmuir waves. Its extension to weak-turbulence theory treats resonant interactions of these Langmuir waves with other plasma wave modes, in particular ion-sound waves. These are strongly damped in plasma of equal ion and electron temperatures, as sometimes seen in, for example, the solar corona and wind. Weak turbulence theory is derived in the weak damping limit, with a term describing ion-sound wave damping then added. In this paper we use the EPOCH particle-in-cell code to numerically test weak turbulence theory for a range of electron-ion temperature ratios. We find that in the cold ion limit the results agree well, but increasing ion temperature the three-wave resonance becomes broadened in proportion to the ion-sound wave damping rate. This may be important in, for example, the theory of solar radio bursts, where the spectrum of Langmuir waves is critical. Additionally we establish...
Unitaxial constant velocity microactuator
McIntyre, T.J.
1994-06-07T23:59:59.000Z
A uniaxial drive system or microactuator capable of operating in an ultra-high vacuum environment is disclosed. The mechanism includes a flexible coupling having a bore therethrough, and two clamp/pusher assemblies mounted in axial ends of the coupling. The clamp/pusher assemblies are energized by voltage-operated piezoelectrics therewithin to operatively engage the shaft and coupling causing the shaft to move along its rotational axis through the bore. The microactuator is capable of repeatably positioning to sub-nanometer accuracy while affording a scan range in excess of 5 centimeters. Moreover, the microactuator generates smooth, constant velocity motion profiles while producing a drive thrust of greater than 10 pounds. The system is remotely controlled and piezoelectrically driven, hence minimal thermal loading, vibrational excitation, or outgassing is introduced to the operating environment. 10 figs.
Unitaxial constant velocity microactuator
McIntyre, Timothy J. (Knoxville, TN)
1994-01-01T23:59:59.000Z
A uniaxial drive system or microactuator capable of operating in an ultra-high vacuum environment. The mechanism includes a flexible coupling having a bore therethrough, and two clamp/pusher assemblies mounted in axial ends of the coupling. The clamp/pusher assemblies are energized by voltage-operated piezoelectrics therewithin to operatively engage the shaft and coupling causing the shaft to move along its rotational axis through the bore. The microactuator is capable of repeatably positioning to sub-manometer accuracy while affording a scan range in excess of 5 centimeters. Moreover, the microactuator generates smooth, constant velocity motion profiles while producing a drive thrust of greater than 10 pounds. The system is remotely controlled and piezoelectrically driven, hence minimal thermal loading, vibrational excitation, or outgassing is introduced to the operating environment.
Wave-current interaction in water of finite depth
Huang, Zhenhua, 1967-
2004-01-01T23:59:59.000Z
In this thesis, the nonlinear interaction of waves and current in water of finite depth is studied. Wind is not included. In the first part, a 2D theory for the wave effect on a turbulent current over rough or smooth bottom ...
Radiosonde measurements of turbulence
Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)
AFDC Printable Version Share this resource Send a link to EERE: Alternative Fuels Data Center Home Page to someone by E-mail Share EERE: Alternative Fuels Data Center Home Page on Facebook Tweet about EERE: Alternative Fuels Data Center Home Page on Twitter Bookmark EERE:1 First Use of Energy for All Purposes (Fuel and Nonfuel), 2002; Level:5(Million Cubic Feet) Oregon (Including Vehicle Fuel) (Million Cubic Feet)setsManagementProtonQ1FY14 1 SummaryAOT: LANL RFRadiologicalTurbulence
Gravitational Radiation From Cosmological Turbulence
Arthur Kosowsky; Andrew Mack; Tinatin Kahniashvili
2002-06-27T23:59:59.000Z
An injection of energy into the early Universe on a given characteristic length scale will result in turbulent motions of the primordial plasma. We calculate the stochastic background of gravitational radiation arising from a period of cosmological turbulence, using a simple model of isotropic Kolmogoroff turbulence produced in a cosmological phase transition. We also derive the gravitational radiation generated by magnetic fields arising from a dynamo operating during the period of turbulence. The resulting gravitational radiation background has a maximum amplitude comparable to the radiation background from the collision of bubbles in a first-order phase transition, but at a lower frequency, while the radiation from the induced magnetic fields is always subdominant to that from the turbulence itself. We briefly discuss the detectability of such a signal.
Yutaka Fujita; Tomoaki Matsumoto; Keiichi Wada; Tae Furusho
2004-12-14T23:59:59.000Z
This is the first attempt to construct detailed X-ray spectra of clusters of galaxies from the results of high-resolution hydrodynamic simulations and simulate X-ray observations in order to study velocity fields of the intracluster medium (ICM). The hydrodynamic simulations are based on the recently proposed tsunami model, in which cluster cores are affected by bulk motions of the ICM and turbulence is produced. We note that most other solutions of the cooling flow problem also involve the generation of turbulence in cluster cores. From the mock X-ray observations with Astro-E2 XRS, we find that turbulent motion of the ICM in cluster cores could be detected with the satellite. The Doppler shifts of the metal lines could be used to discriminate among turbulence models. The gas velocities measured through the mock observations are consistent with the line-emission weighted values inferred directly from hydrodynamic simulations.
Trinity: A Unified Treatment of Turbulence, Transport, and Heating in Magnetized Plasmas
Barnes, Michael
2008-01-01T23:59:59.000Z
To faithfully simulate ITER and other modern fusion devices, one must resolve electron and ion fluctuation scales in a five-dimensional phase space and time. Simultaneously, one must account for the interaction of this turbulence with the slow evolution of the large-scale plasma profiles. Because of the enormous range of scales involved and the high dimensionality of the problem, resolved first-principles global simulations are very challenging using conventional (brute force) techniques. In this thesis, the problem of resolving turbulence is addressed by developing velocity space resolution diagnostics and an adaptive collisionality that allow for the confident simulation of velocity space dynamics using the approximate minimal necessary dissipation. With regard to the wide range of scales, a new approach has been developed in which turbulence calculations from multiple gyrokinetic flux tube simulations are coupled together using transport equations to obtain self-consistent, steady-state background profiles...
Understanding and modeling turbulent fluxes and entrainment in a gravity current
Odier, P; Ecke, R E
2015-01-01T23:59:59.000Z
We present an experimental study of the mixing processes in a gravity current flowing on an inclined plane. The turbulent transport of momentum and density can be described in a very direct and compact form by a Prandtl mixing length model: the turbulent vertical fluxes of momentum and density are found to scale quadratically with the vertical mean gradients of velocity and density. The scaling coefficient, the square of the mixing length, is approximately constant over the mixing zone of the stratified shear layer. We show how, in different flow configurations, this length can be related to the shear length of the flow ($\\epsilon$/$\\partial$ z u^3)^1/2. We also study the fluctuations of the momentum and density turbulent fluxes, showing how they relate to mixing and to the entrainment/detrainment balance. We suggest a quantitative measure of local entrainment and detrainment derived from observed conditional correlations of density flux and density or vertical velocity fluctuations.
PLASMA PHYSICS:Turbulence and Sheared Flow --Burrell 281 (5384): 1816 --Science q My Science
Lin, Zhihong
About the Journal Home > Science Magazine > 18 September 1998 > Burrell , pp. 1816 - 1817 Article Views with reduced turbulence and transport when an additional source of free energy is applied to it. Usually heating or fueling. Although there are a few cases where neutral fluids exhibit velocity shear
Non-Gaussian Invariant Measures for the Majda Model of Decaying Turbulent Transport
Van Den Eijnden, Eric
challenges for an even- tual statistical theory of hydrodynamic turbulence. In this context, many recent, the scalar can experience rare but very large fluctuations in amplitude, and its statistics can depart.1) in the large time limit in terms of the velocity field u and the initial Communications on Pure and Applied
Behavior of Turbulent Structures within a Mach 5 Mechanically Distorted Boundary Layer
Peltier, Scott Jacob
2013-08-05T23:59:59.000Z
High-resolution particle image velocimetry (PIV) is employed to resolve the velocity fields within a Mach 4.9 mechanically distorted turbulent boundary layer (Re? ? 40,000). The goal of this study is to directly observe the mechanisms responsible...
Diffusive radiation in one-dimensional Langmuir turbulence G. D. Fleishman1
-dimensional Langmuir turbulence which might be generated by a streaming instability in the plasma, in particular sensi- tively on the angle between the particle velocity and electric field direction. The radiation as gamma-ray bursts and collimated jets. DOI: 10.1103/PhysRevE.76.017401 PACS number s : 52.25.Os, 52.35.Ra
Premixed turbulent flame front structure investigation by Rayleigh scattering in the thin
Gülder, Ömer L.
in propane flames. The probability density function of curvature showed a Gaussian-like distribution at allair and propaneair stabilized on a bunsen type burner were studied using planar Rayleigh scattering and particle flames, and from 0.7 to stoichiometric for propane flames. The non-dimensional turbulence rms velocity, u
New near-wall two-equation model for turbulent heat transport
Torii, Shuichi [Kagoshima Univ. (Japan). Dept. of Mechanical Engineering; Yang, W.J. [Univ. of Michigan, Ann Arbor, MI (United States). Dept. of Mechanical Engineering and Applied Mechanics
1996-03-01T23:59:59.000Z
An anisotropic two-equation model is proposed to determine turbulent heat flux in a channel flow up to the wall. The turbulent heat fluxes are given in the form of an anisotropic eddy diffusivity representation in which both the isotropic and anisotropic eddy diffusivities of heat are expressed using the temperature variance {ovr t{sup 2}}, the dissipation rate of temperature fluctuations {var_epsilon}{sub t}, and the velocity gradient. The proposed model is tested through application to an incompressible, two-dimensional, turbulent channel flow with the neglect of buoyant heat transfer. Calculated results are compared with the direct numerical simulation data. It is disclosed from the study that the proposed anisotropic {ovr t{sup 2}}-{var_epsilon}{sub t} heat transfer model predicts reasonably well the distributions of the time-averaged temperature, normal and streamwise turbulent heat fluxes, temperature variance, dissipation rates, and these near-wall budgets.
Refined similarity hypotheses in shell models of turbulence
Emily S. C. Ching; H. Guo; T. S. Lo
2008-04-16T23:59:59.000Z
A major challenge in turbulence research is to understand from first principles the origin of anomalous scaling of the velocity fluctuations in high-Reynolds-number turbulent flows. One important idea was proposed by Kolmogorov [J. Fluid Mech. {\\bf 13}, 82 (1962)], which attributes the anomaly to the variations of the locally averaged energy dissipation rate. Kraichnan later pointed out [J. Fluid Mech. {\\bf 62}, 305 (1973)] that the locally averaged energy dissipation rate is not an inertial-range quantity and a proper inertial-range quantity would be the local energy transfer rate. As a result, Kraichnan's idea attributes the anomaly to the variations of the local energy transfer rate. These ideas, generally known as refined similarity hypotheses, can also be extended to study the anomalous scaling of fluctuations of an active scalar, like the temperature in turbulent convection. In this paper, we examine the validity of these refined similarity hypotheses and their extensions to an active scalar in shell models of turbulence. We find that Kraichnan's refined similarity hypothesis and its extension are valid.
STATISTICS OF TURBULENT FIELD VARIATIONS, NON-GAUSSIANITY AND INTERMITTENCY
Ragot, B. R
2009-05-10T23:59:59.000Z
Statistics of magnetic field and velocity variations are important to the study of turbulence. Their departure from Gaussianity on the short separation scales has long been recognized and ascribed to intermittency. Non-Gaussian log-normal statistics of field-line separations are now predicted, however, from simple nonfluctuating turbulence Fourier spectra that do not model any intermittency, and one may wonder how this result may impact our interpretation of the statistics of field variations. It is shown in this paper how the intermittency of the turbulence can be taken into account to estimate the distributions of field-line separations and of field variations from the simple Fourier-spectra calculations. The first accurate theory/modeling predictions for the observed in situ distributions of turbulent field variations are thereby made, free of parameter adjustment. Magnetic field data from Helios 2 and Wind are used for the validation. Because the field variations are measured between points of constant separation and not between real field lines, intermittency remains the main cause for the observed non-Gaussianity of the statistics of field variations on the short scales, even if spatial limitations and/or short-scale phase correlations could also contribute to the deviations from Gaussianity.
Relation between plasma plume density and gas flow velocity in atmospheric pressure plasma
Yambe, Kiyoyuki; Taka, Shogo; Ogura, Kazuo [Graduate School of Science and Technology, Niigata University, Niigata 950-2181 (Japan)] [Graduate School of Science and Technology, Niigata University, Niigata 950-2181 (Japan)
2014-04-15T23:59:59.000Z
We have studied atmospheric pressure plasma generated using a quartz tube, helium gas, and copper foil electrode by applying RF high voltage. The atmospheric pressure plasma in the form of a bullet is released as a plume into the atmosphere. To study the properties of the plasma plume, the plasma plume current is estimated from the difference in currents on the circuit, and the drift velocity is measured using a photodetector. The relation of the plasma plume density n{sub plu}, which is estimated from the current and the drift velocity, and the gas flow velocity v{sub gas} is examined. It is found that the dependence of the density on the gas flow velocity has relations of n{sub plu} ? log(v{sub gas}). However, the plasma plume density in the laminar flow is higher than that in the turbulent flow. Consequently, in the laminar flow, the density increases with increasing the gas flow velocity.
Turbulent flame speeds and NOx kinetics of HHC fuels with contaminants and high dilution levels
Petersen, Eric; Krejci, Michael; Mathieu, Olivier; Vissotski, Andrew; Ravi, Sankar; Plichta, Drew; Sikes, Travis; Levacque, Anthony; Aul, Christopher; Petersen, Eric
2012-09-30T23:59:59.000Z
This progress report documents the second year of the project, from October 1, 2011 through September 30, 2012. Characterization of the new turbulent flame speed vessel design was completed. Turbulence statistics of three impellers with different geometric features were measured using particle image velocimetry inside a Plexiglas model (~1:1 scale) of a cylindrical flame speed vessel (30.5 cm ID × 35.6 cm L). With four impellers arranged in a central-symmetric configuration, turbulence intensities between 1.2 and 1.7 m/s with negligible mean flow (0.1u´) were attained at the lowest fan speeds. Acceptable ranges for homogeneity and isotropy ratios of the velocity fields were set within a narrow bandwidth near unity (0.9-1.1). Homogeneity ratios were unaffected by changes to the impeller geometry, and the prototype with the higher number of blades caused the flow to become anisotropic. The integral length scale of the flow fields varied between 27 and 20 mm, which correlates well with those typically observed inside a gas turbine combustor. The mechanism to independently vary the intensity level and the integral length scale was established, where turbulence intensity level was dependent on the rotational speed of the fan, and the integral length scale decreased with increasing blade pitch angle. Ignition delay times of H?/O? mixtures highly diluted with Ar and doped with various amounts of N?O (100, 400, 1600, 3200 ppm) were measured in a shock tube behind reflected shock waves over a wide range of temperatures (940-1675 K). The pressure range investigated during this work (around 1.6, 13, and 30 atm) allows studying the effect of N?O on hydrogen ignition at pressure conditions that have never been heretofore investigated. Ignition delay times were decreased when N?O was added to the mixture only for the higher nitrous oxide concentrations, and some changes in the activation energy were also observed at 1.5 and 30 atm. When it occurred, the decrease in the ignition delay time was proportional to the amount of N?O added and depended on pressure and temperature conditions. A detailed chemical kinetics model was developed using kinetic mechanisms from the literature. This model predicts well the experimental data obtained during this study and from the literature. The chemical analysis using this model showed that the decrease in the ignition delay time was mainly due to the reaction N?O +M ? N? + O +M which provides O atoms to strengthen the channel O + H? ? OH + H. Ignition delay times have been measured behind reflected shock waves at 1.5, 12 and 30 atm for a mixture representative of a syngas produced from biomass (0.29659% CO / 0.29659% H? / 0.15748% CO? / 0.08924% CH? / 0.20997% H?O / 0.95013% O? in 98% Ar (mol.%)) and for the same biomass-derived syngas mixture doped with 200 ppm of NH?. The importance of the various constituents on the ignition delay time was investigated by comparing the results with data from various baseline mixtures (H?/O?/Ar, H?/CO/O?/Ar and H?/CO/O?/Ar with one of the other constituent of the syngas (i.e. CO?, H?O, CH? or NH?)). The equivalence ratio was set to 0.5 during this study. Several recent detailed kinetics mechanisms from the literature were computed against these data, with fair agreement. Results showed that the mixture composition can have an important effect on the ignition delay time, with most of the effect being due to CH? addition through the reaction CH?+OH?CH?+H?O. The ammonia impurity had very little effect on the ignition delay time over the range of conditions studied.
Compound cooling flow turbulator for turbine component
Lee, Ching-Pang; Jiang, Nan; Marra, John J; Rudolph, Ronald J
2014-11-25T23:59:59.000Z
Multi-scale turbulation features, including first turbulators (46, 48) on a cooling surface (44), and smaller turbulators (52, 54, 58, 62) on the first turbulators. The first turbulators may be formed between larger turbulators (50). The first turbulators may be alternating ridges (46) and valleys (48). The smaller turbulators may be concave surface features such as dimples (62) and grooves (54), and/or convex surface features such as bumps (58) and smaller ridges (52). An embodiment with convex turbulators (52, 58) in the valleys (48) and concave turbulators (54, 62) on the ridges (46) increases the cooling surface area, reduces boundary layer separation, avoids coolant shadowing and stagnation, and reduces component mass.
Broadband extended emission in gravitational waves from core-collapse supernovae
Levinson, Amir; Pick, Guy
2015-01-01T23:59:59.000Z
Black holes in core-collapse of massive stars are expected to surge in mass and angular momentum by hyper-accretion immediately following their formation. We here describe a general framework of extended emission in gravitational waves from non-axisymmetric accretion flows from fallback matter of the progenitor envelope. It shows (a) a maximum efficiency in conversion of accretion energy into gravitational waves at hyper-accretion rates exceeding a critical value set by the ratio of the quadrupole mass inhomogeneity and viscosity with (b) a peak characteristic strain amplitude at the frequency $f_b=\\Omega_b/\\pi$, where $\\Omega_b$ is the Keplerian angular velocity at which viscous torques equal angular momentum loss in gravitational radiation, with $h_{char}\\propto f^{1/6}$ at $ff_b$. Upcoming gravitational wave observations may probe this scaling by extracting broadband spectra using time-sliced matched filtering with chirp templates, recently developed for identifying turbulence in noisy time series.
A flowing plasma model to describe drift waves in a cylindrical helicon discharge
Chang, L.; Hole, M. J.; Corr, C. S. [Plasma Research Laboratory, Research School of Physics and Engineering, Australian National University, Canberra ACT 0200 (Australia)
2011-04-15T23:59:59.000Z
A two-fluid model developed originally to describe wave oscillations in the vacuum arc centrifuge, a cylindrical, rapidly rotating, low temperature, and confined plasma column, is applied to interpret plasma oscillations in a RF generated linear magnetized plasma [WOMBAT (waves on magnetized beams and turbulence)], with similar density and field strength. Compared to typical centrifuge plasmas, WOMBAT plasmas have slower normalized rotation frequency, lower temperature, and lower axial velocity. Despite these differences, the two-fluid model provides a consistent description of the WOMBAT plasma configuration and yields qualitative agreement between measured and predicted wave oscillation frequencies with axial field strength. In addition, the radial profile of the density perturbation predicted by this model is consistent with the data. Parameter scans show that the dispersion curve is sensitive to the axial field strength and the electron temperature, and the dependence of oscillation frequency with electron temperature matches the experiment. These results consolidate earlier claims that the density and floating potential oscillations are a resistive drift mode, driven by the density gradient. To our knowledge, this is the first detailed physics model of flowing plasmas in the diffusion region away from the RF source. Possible extensions to the model, including temperature nonuniformity and magnetic field oscillations, are also discussed.
Alfv'en Wave Solitons and Solar Intermediate Drift Bursts
Guedel, Manuel
propagate at velocities of the order of the Alfv'en veloc ity in a direction inclined to the magnetic field, the solar wind, and possibly accretion disks, and extra galactic jets. In such magnetized plasmas Alfv'en waves are easily excited by various processes. Linear waves propagate at the Alfv'en speed v
Velocity Dispersions Across Bulge Types
Fabricius, Maximilian; Bender, Ralf; Hopp, Ulrich [University Observatory of the Ludwig-Maximilians University (LMU) (Germany); Max-Planck Institute for Extraterrestrial Physics (MPE) (Germany); Saglia, Roberto; Drory, Niv [Max-Planck Institute for Extraterrestrial Physics (MPE) (Germany); Fisher, David [Department of Astronomy, University of Texas at Austin (United States)
2010-06-08T23:59:59.000Z
We present first results from a long-slit spectroscopic survey of bulge kinematics in local spiral galaxies. Our optical spectra were obtained at the Hobby-Eberly Telescope with the LRS spectrograph and have a velocity resolution of 45 km/s (sigma*), which allows us to resolve the velocity dispersions in the bulge regions of most objects in our sample. We find that the velocity dispersion profiles in morphological classical bulge galaxies are always centrally peaked while the velocity dispersion of morphologically disk-like bulges stays relatively flat towards the center--once strongly barred galaxies are discarded.
Is there Lower Limit to Velocity or Velocity Change?
B. N. Sreenath; Kenath Arun; C. Sivaram
2013-06-19T23:59:59.000Z
Here we explore the possibility of a lower limit to velocity or velocity change which is 20 orders of magnitude smaller than the speed of light and explore the various observable signatures including those in cosmic rays and gamma ray bursts.
Pore fluid effects on seismic velocity in anisotropic rocks
Mukerji, T.; Mavko, G. (Stanford Univ., CA (United States). Dept. of Geophysics)
1994-02-01T23:59:59.000Z
A simple new technique predicts the high- and low-frequency saturated velocities in anisotropic rocks entirely in terms of measurable dry rock properties without the need for idealized crack geometries. Measurements of dry velocity versus pressure and porosity versus pressure contain all of the necessary information for predicting the frequency-dependent effects of fluid saturation. Furthermore, these measurements automatically incorporate all pore interaction, so there is no limitation to low crack density. The velocities are found to depend on five key interrelated variables: frequency, the distribution of compliant crack-like porosity, the intrinsic or noncrack anisotropy, fluid viscosity and compressibility, and effective pressure. The sensitivity of velocities to saturation is generally greater at high frequencies than low frequencies. The magnitude of the differences from dry to saturated and from low frequency to high frequency is determined by the compliant or crack-like porosity. Predictions of saturated velocities based on dry data for sandstone and granite show that compressional velocities generally increase with saturation and with frequency. However, the degree of compressional wave anisotropy may either increase or decrease upon saturation depending on the crack distribution, the effective pressure, and the frequency at which the measurements are made. Shear-wave velocities can either increase or decrease with saturation, and the degree of anisotropy depends on the microstructure, pressure, and frequency. Consequently great care must be taken when interpreting observed velocity anisotropy for measurements at low frequencies, typical of in situ observations, will generally be different from those at high frequencies, typical of the laboratory.
Measurement of fast-changing low velocities by photonic Doppler velocimetry
Song Hongwei; Wu Xianqian; Huang Chenguang; Wei Yangpeng; Wang Xi [Key Laboratory for Hydrodynamics and Ocean Engineering, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190 (China)
2012-07-15T23:59:59.000Z
Despite the increasing popularity of photonic Doppler velocimetry (PDV) in shock wave experiments, its capability of capturing low particle velocities while changing rapidly is still questionable. The paper discusses the performance of short time Fourier transform (STFT) and continuous wavelet transform (CWT) in processing fringe signals of fast-changing low velocities measured by PDV. Two typical experiments are carried out to evaluate the performance. In the laser shock peening test, the CWT gives a better interpretation to the free surface velocity history, where the elastic precursor, main plastic wave, and elastic release wave can be clearly identified. The velocities of stress waves, Hugoniot elastic limit, and the amplitude of shock pressure induced by laser can be obtained from the measurement. In the Kolsky-bar based tests, both methods show validity of processing the longitudinal velocity signal of incident bar, whereas CWT improperly interprets the radial velocity of the shocked sample at the beginning period, indicating the sensitiveness of the CWT to the background noise. STFT is relatively robust in extracting waveforms of low signal-to-noise ratio. Data processing method greatly affects the temporal resolution and velocity resolution of a given fringe signal, usually CWT demonstrates a better local temporal resolution and velocity resolution, due to its adaptability to the local frequency, also due to the finer time-frequency product according to the uncertainty principle.
Kirchhoff prestack depth migration in velocity models with and without rotation of the tensor of
Cerveny, Vlastislav
Kirchhoff prestack depth migration in velocity models with and without rotation of the tensor-mail: bucha@seis.karlov.mff.cuni.cz Summary We use the Kirchhoff prestack depth migration to calculate is limited to P-waves. Keywords 3-D Kirchhoff prestack depth migration, anisotropic velocity model, rotation
Nonlinear closures for scale separation in supersonic magnetohydrodynamic turbulence
Grete, Philipp; Schmidt, Wolfram; Schleicher, Dominik R G; Federrath, Christoph
2015-01-01T23:59:59.000Z
Turbulence in compressible plasma plays a key role in many areas of astrophysics and engineering. The extreme plasma parameters in these environments, e.g. high Reynolds numbers, supersonic and super-Alfvenic flows, however, make direct numerical simulations computationally intractable even for the simplest treatment -- magnetohydrodynamics (MHD). To overcome this problem one can use subgrid-scale (SGS) closures -- models for the influence of unresolved, subgrid-scales on the resolved ones. In this work we propose and validate a set of constant coefficient closures for the resolved, compressible, ideal MHD equations. The subgrid-scale energies are modeled by Smagorinsky-like equilibrium closures. The turbulent stresses and the electromotive force (EMF) are described by expressions that are nonlinear in terms of large scale velocity and magnetic field gradients. To verify the closures we conduct a priori tests over 137 simulation snapshots from two different codes with varying ratios of thermal to magnetic pre...
Rotation Rate of Particle Pairs in Homogeneous Isotropic Turbulence
Daddi-Moussa-Ider, Abdallah
2015-01-01T23:59:59.000Z
Understanding the dynamics of particles in turbulent flow is important in many environmental and industrial applications. In this paper, the statistics of particle pair orientation is numerically studied in homogeneous isotropic turbulent flow, with Taylor microscale Rynolds number of 300. It is shown that the Kolmogorov scaling fails to predict the observed probability density functions (PDFs) of the pair rotation rate and the higher order moments accurately. Therefore, a multifractal formalism is derived in order to include the intermittent behavior that is neglected in the Kolmogorov picture. The PDFs of finding the pairs at a given angular velocity for small relative separations, reveals extreme events with stretched tails and high kurtosis values. Additionally, The PDFs are found to be less intermittent and follow a complementary error function distribution for larger separations.
Analogy between turbulence and quantum gravity: beyond Kolmogorov's 1941 theory
S. Succi
2011-11-14T23:59:59.000Z
Simple arguments based on the general properties of quantum fluctuations have been recently shown to imply that quantum fluctuations of spacetime obey the same scaling laws of the velocity fluctuations in a homogeneous incompressible turbulent flow, as described by Kolmogorov 1941 (K41) scaling theory. Less noted, however, is the fact that this analogy rules out the possibility of a fractal quantum spacetime, in contradiction with growing evidence in quantum gravity research. In this Note, we show that the notion of a fractal quantum spacetime can be restored by extending the analogy between turbulence and quantum gravity beyond the realm of K41 theory. In particular, it is shown that compatibility of a fractal quantum-space time with the recent Horava-Lifshitz scenario for quantum gravity, implies singular quantum wavefunctions. Finally, we propose an operational procedure, based on Extended Self-Similarity techniques, to inspect the (multi)-scaling properties of quantum gravitational fluctuations.
Mode-coupling and nonlinear Landau damping effects in auroral Farley-Buneman turbulence
Hamza, Abdelaziz M
2015-01-01T23:59:59.000Z
The fundamental problem of Farley-Buneman turbulence in the auroral $E$-region has been discussed and debated extensively in the past two decades. In the present paper we intend to clarify the different steps that the auroral $E$-region plasma has to undergo before reaching a steady state. The mode-coupling calculation, for Farley-Buneman turbulence, is developed in order to place it in perspective and to estimate its magnitude relative to the anomalous effects which arise through the nonlinear wave-particle interaction. This nonlinear effect, known as nonlinear ``Landau damping'' is due to the coupling of waves which produces other waves which in turn lose energy to the bulk of the particles by Landau damping. This leads to a decay of the wave energy and consequently a heating of the plasma. An equation governing the evolution of the field spectrum is derived and a physical interpration for each of its terms is provided.
Magnetic energy production by turbulence in binary neutron star mergers
Zrake, Jonathan
2013-01-01T23:59:59.000Z
The simultaneous detection of electromagnetic and gravitational wave emission from merging neutron star binaries would aid greatly in their discovery and interpretation. By studying turbulent amplification of magnetic fields in local high-resolution simulations of neutron star merger conditions, we demonstrate that magnetar-level (~10^16) G fields are present throughout the merger duration. We find that the small-scale turbulent dynamo converts 60% of the randomized kinetic energy into magnetic fields on a merger time scale. Since turbulent magnetic energy dissipates through reconnection events which accelerate relativistic electrons, turbulence may facilitate the conversion of orbital kinetic energy into radiation. If 10^-4 of the ~ 10^53 erg of orbital kinetic available gets processed through reconnection, and creates radiation in the 15-150 keV band, then the fluence at 200 Mpc would be 10^-7 erg/cm^2, potentially rendering most merging neutron stars in the advanced LIGO and Virgo detection volumes detecta...
Chemical Wave Packet Propagation, Reflection, and Spreading Lingfa Yang and Irving R. Epstein*
Epstein, Irving R.
or away from an initiating perturbation, are found in a reaction-diffusion model with a finite wave. The phase velocity, group velocity, and spreading velocity calculated by linear stability analysis packets in reaction-diffusion systems are rarely seen, even though wave packets have been intensively
Takase, Kazuyuki [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan)
1997-05-01T23:59:59.000Z
Thermal-hydraulic characteristics in a spacer-ribbed annular fuel channel for high-temperature gas-cooled reactors were analyzed numerically by three-dimensional computations under a fully developed turbulent flow. The two-equation {kappa}-{epsilon} turbulence model was applied in the present turbulent analysis, and the turbulence model constants for eddy viscosity and the turbulent Prandtl number were improved from the previous standard values to increase the accuracy of numerical simulations. Consequently, heat transfer coefficients and friction factors in the spacer-ribbed fuel channel were predicted with sufficient accuracy in the range of Reynolds number >3,000. It was clarified quantitatively that the main mechanism for heat transfer augmentation in the spacer-ribbed fuel channel was a combined effect of the turbulence promoter effect by the spacer rib and the velocity acceleration effect by a reduction in the channel cross section.
Energetic particle acceleration in a 3D magnetic field reconnection model: a role of MHD turbulence
Tomasz Kobak; Michal Ostrowski
2000-06-07T23:59:59.000Z
The role of MHD turbulence in the cosmic ray acceleration process in a volume with a reconnecting magnetic field is studied by means of Monte Carlo simulations. We performed modelling of proton acceleration with the 3D analytic model of stationary reconnection of Craig et al. (1995) providing the unperturbed background conditions. Perturbations of particle trajectories due to a turbulent magnetic field component were simulated using small-amplitude pitch-angle momentum scattering, enabling modelling of both small and large amplitude turbulence in a wide wave vector range. Within the approach, no second-order Fermi acceleration process is allowed. Comparison of the acceleration process in models involving particle trajectory perturbations to the unperturbed one reveals that the turbulence can substantially increase the acceleration efficiency, enabling much higher final particle energies and flat particle spectra.
A Novel Statistical Channel Model for Turbulence-Induced Fading in Free-Space Optical Systems
Aminikashani, Mohammadreza; Kavehrad, Mohsen
2015-01-01T23:59:59.000Z
In this paper, we propose a new probability distribution function which accurately describes turbulence-induced fading under a wide range of turbulence conditions. The proposed model, termed Double Generalized Gamma (Double GG), is based on a doubly stochastic theory of scintillation and developed via the product of two Generalized Gamma (GG) distributions. The proposed Double GG distribution generalizes many existing turbulence channel models and provides an excellent fit to the published plane and spherical waves simulation data. Using this new statistical channel model, we derive closed form expressions for the outage probability and the average bit error as well as corresponding asymptotic expressions of free-space optical communication systems over turbulence channels. We demonstrate that our derived expressions cover many existing results in the literature earlier reported for Gamma-Gamma, Double-Weibull and K channels as special cases.
A Novel Statistical Channel Model for Turbulence-Induced Fading in Free-Space Optical Systems
Mohammadreza Aminikashani; Murat Uysal; Mohsen Kavehrad
2015-02-02T23:59:59.000Z
In this paper, we propose a new probability distribution function which accurately describes turbulence-induced fading under a wide range of turbulence conditions. The proposed model, termed Double Generalized Gamma (Double GG), is based on a doubly stochastic theory of scintillation and developed via the product of two Generalized Gamma (GG) distributions. The proposed Double GG distribution generalizes many existing turbulence channel models and provides an excellent fit to the published plane and spherical waves simulation data. Using this new statistical channel model, we derive closed form expressions for the outage probability and the average bit error as well as corresponding asymptotic expressions of free-space optical communication systems over turbulence channels. We demonstrate that our derived expressions cover many existing results in the literature earlier reported for Gamma-Gamma, Double-Weibull and K channels as special cases.
Kinematics measurements of regular, irregular, and rogue waves by PIV/LDV
Choi, Hae-Jin
2007-04-25T23:59:59.000Z
waves. A series of experiments were conducted in a 2-D wave tank at Texas A&M University to measure wave velocities and accelerations using LDV and PIV systems. The wave crests of regular and rogue waves are the focus of this study. With the measured...
Analysis of the influence of external biasing on Texas Helimak turbulence
Toufen, D. L. [Institute of Physics, University of Sao Paulo, C.P. 66318, 05315-970 Sao Paulo, Sao Paulo (Brazil); Federal Institute of Education, Science and Technology of Sao Paulo-IFSP, 07115-000 Guarulhos, Sao Paulo (Brazil); Guimaraes-Filho, Z. O.; Caldas, I. L. [Institute of Physics, University of Sao Paulo, C.P. 66318, 05315-970 Sao Paulo, Sao Paulo (Brazil); Szezech, J. D. [Department of Physics, State University of Ponta Grossa, 84030-900 Parana (Brazil); Lopes, S.; Viana, R. L. [Department of Physics, Federal University of Parana, 81531-990 Curitiba, Parana (Brazil); Gentle, K. W. [Department of Physics and Institute for Fusion Studies, The University of Texas at Austin, Austin, Texas 78712 (United States)
2013-02-15T23:59:59.000Z
We analyze alterations on the electrostatic turbulence in experiments with imposed bias to control the plasma radial electric field in Texas Helimak (K. W. Gentle and H. He, Plasma Sci. Technol. 10, 284 (2008)), a toroidal plasma device with a one-dimensional equilibrium, magnetic curvature, and shear. Comparing discharges from different biased potentials, we identify, in a roughly uniform gradient region, a continuous variation from low turbulence level and narrower frequency spectra, for negative bias, to high turbulence level and broadband spectra for positive bias. Overall, we distinguish two kinds of perturbed turbulence, classified according to their intensity, spectral, statistical, and recurrence properties. When the bias is positive, the turbulence shows enhanced and broadband spectra with non Gaussian probability distribution functions having noticeable long tails (extreme events) similar to the turbulence in tokamak scrape-off layer. On the other hand, negative bias reduces the turbulence level and decreases the spectrum widths. Also for negative bias, we found large frequency widths whenever the coupling between drift waves and the sheared plasma flow is fast enough to allow the enhancement of sidebands modes.
Inversion Of Travel Time For Velocity
Willis, M.E.
1983-01-01T23:59:59.000Z
Common source velocities and borehole compensated (BC) estimates have been used to obtain formation velocity estimates from full waveform acoustic
Characterizing the convective velocity fields in massive stars
Chatzopoulos, Emmanouil; Graziani, Carlo; Couch, Sean M., E-mail: manolis@astro.as.utexas.edu [Department of Astronomy and Astrophysics, Flash Center for Computational Science, University of Chicago, Chicago, IL 60637 (United States)
2014-11-01T23:59:59.000Z
We apply the mathematical formalism of vector spherical harmonics decomposition to convective stellar velocity fields from multidimensional hydrodynamics simulations and show that the resulting power spectra furnish a robust and stable statistical description of stellar convective turbulence. Analysis of the power spectra helps identify key physical parameters of the convective process such as the dominant scale of the turbulent motions that influence the structure of massive evolved pre-supernova stars. We introduce the numerical method that can be used to calculate vector spherical harmonics power spectra from two-dimensional (2D) and three-dimensional (3D) convective shell simulation data. Using this method we study the properties of oxygen shell burning and convection for a 15 M {sub ?} star simulated by the hydrodynamics code FLASH in 2D and 3D. We discuss the importance of realistic initial conditions to achieving successful core-collapse supernova explosions in multidimensional simulations. We show that the calculated power spectra can be used to generate realizations of the velocity fields of presupernova convective shells. We find that the slope of the solenoidal mode power spectrum remains mostly constant throughout the evolution of convection in the oxygen shell in both 2D and 3D simulations. We also find that the characteristic radial scales of the convective elements are smaller in 3D than in 2D, while the angular scales are larger in 3D.
SOLAR WIND MAGNETOHYDRODYNAMICS TURBULENCE: ANOMALOUS SCALING AND ROLE OF INTERMITTENCY
Salem, C.; Bale, S. D. [Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States); Mangeney, A. [LESIA, Observatoire de Paris-Meudon, F-92195 Meudon (France); Veltri, P. [Dipartimento di Fisica, Universita della Calabria, Rende (Italy)], E-mail: salem@ssl.berkeley.edu
2009-09-01T23:59:59.000Z
In this paper, we present a study of the scaling properties and intermittency of solar wind MHD turbulence based on the use of wavelet transforms. More specifically, we use the Haar Wavelet transform on simultaneous 3 s resolution particle and magnetic field data from the Wind spacecraft, to investigate anomalous scaling and intermittency effects of both magnetic field and solar wind velocity fluctuations in the inertial range. For this purpose, we calculated spectra, structure functions, and probability distribution functions. We show that this powerful wavelet technique allows for a systematic elimination of intermittency effects on spectra and structure functions and thus for a clear determination of the actual scaling properties in the inertial range. The scaling of the magnetic field and the velocity fluctuations are found to be fundamentally different. Moreover, when the most intermittent structures superposed to the standard fluctuations are removed, simple statistics are recovered. The magnetic field and the velocity fluctuations exhibit a well-defined, although different, monofractal behavior, following a Kolmogorov -5/3 scaling and a Iroshnikov-Kraichnan -3/2 scaling, respectively. The multifractal properties of solar wind turbulence appear to be determined by the presence of those most intermittent structures. Finally, our wavelet technique also allows for a direct and systematic identification of the most active, singular structures responsible for the intermittency in the solar wind.
Particle acceleration in superluminal strong waves
Teraki, Yuto; Nagataki, Shigehiro
2015-01-01T23:59:59.000Z
We calculate the electron acceleration in random superluminal strong waves (SLSWs) and radiation from them by using numerical methods in the context of the termination shock of the pulsar wind nebulae. We pursue the electrons by solving the equation of motion in the analytically expressed electromagnetic turbulences. These consist of primary SLSW and isotropically distributed secondary electromagnetic waves. Under the dominance of the secondary waves, all electrons gain nearly equal energy. On the other hand, when the primary wave is dominant, selective acceleration occurs. The phase of the primary wave felt by the electrons moving nearly along the wavevector changes very slowly compared to the oscillation of the wave, which is called "phase locked", and such electrons are continuously accelerated. This acceleration by SLSWs may play a crucial role in the pre-acceleration for the shock acceleration. In general, the radiation from the phase-locked population is different from the synchro-Compton radiation. How...
Weijgaert, Rien van de
transitions in flow properties such as density, velocity and pressure; 2. In shocks the kinetic energy-flux conservation Energy-flux conservation 1 1 2 2n nV V 2 2 1 1 1 2 2 2n nV P V P 1 2t tV V 2 21 21 1 1 the various thermonuclear reactions Â· The sequence of thermonuclear reactions stops here: - formation
Observation of an Inverse Energy Cascade in Developed Acoustic Turbulence in Superfluid Helium
A. N. Ganshin; V. B. Efimov; G. V. Kolmakov; L. P. Mezhov-Deglin; P. V. E. McClintock
2009-01-27T23:59:59.000Z
We report observation of an inverse energy cascade in second sound acoustic turbulence in He II. Its onset occurs above a critical driving energy and it is accompanied by giant waves that constitute an acoustic analogue of the rogue waves that occasionally appear on the surface of the ocean. The theory of the phenomenon is developed and shown to be in good agreement with the experiments.
High Order Hybrid Numerical Simulations of Two Dimensional Detonation Waves
Cai, Wei
reaction time U1 = t + ux + vy contravariant velocity U2 = t + ux + vy contravariant velocity a0 = local. The detonation waves are assumed to un- dergo an irreversible, unimolecular reaction A B. Several cases T = temperature T = v u U = conservative variables in curvilinear (, ) coordinates 2 #12;u = flow x- velocity u
The impact of pedestal turbulence and electron inertia on edge-localized-mode crashes
Xi, P. W. [FSC and State Key Lab of Nuclear Physics and Technology, Department of Physics, Peking University, Beijing 100871 (China) [FSC and State Key Lab of Nuclear Physics and Technology, Department of Physics, Peking University, Beijing 100871 (China); Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Xu, X. Q. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)] [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Diamond, P. H. [WCI Center for Fusion Theory, National Fusion Research Institute, Daejeon (Korea, Republic of) [WCI Center for Fusion Theory, National Fusion Research Institute, Daejeon (Korea, Republic of); Center for Astrophysics and Space Sciences and Department of Physics, University of California San Diego, La Jolla, California 92093-0429 (United States)
2014-05-15T23:59:59.000Z
We demonstrate that the occurrence of Edge-Localized-Modes (ELM) crashes does not depend only on the linear peeling-ballooning threshold, but also relies on nonlinear processes. Wave-wave interaction constrains the growth time of a mode, thus inducing a shift in the criterion for triggering an ELM crash. An ELM crash requires the P-B growth rate to exceed a critical value ?>?{sub c}, where ?{sub c} is set by 1/?{sup ¯}{sub c}, and ?{sup ¯}{sub c} is the averaged mode phase coherence time. For 0turbulence develops but drives enhanced turbulent transport. We also show that electron inertia dramatically changes the instability threshold when density is low. However, P-B turbulence alone cannot generate enough current transport to allow fast reconnection during an ELM crash.
Selkowitz, Robert I
2007-01-01T23:59:59.000Z
We consider the dissipation by Fermi acceleration of magnetosonic turbulence in the Reynolds Layer of the interstellar medium. The scale in the cascade at which electron acceleration via stochastic Fermi acceleration (STFA) becomes comparable to further cascade of the turbulence defines the inner scale. For any magnetic turbulent spectra equal to or shallower than Goldreich-Sridhar this turns out to be $\\ge 10^{12}$cm, which is much larger than the shortest length scales observed in radio scintillation measurements. While STFA for such spectra then contradict models of scintillation which appeal directly to an extended, continuous turbulent cascade, such a separation of scales is consistent with the recent work of \\citet{Boldyrev2} and \\citet{Boldyrev3} suggesting that interstellar scintillation may result from the passage of radio waves through the galactic distribution of thin ionized boundary surfaces of HII regions, rather than density variations from cascading turbulence. The presence of STFA dissipation...
Imaging seismic velocity structure beneath the Iceland hot spot: A finite frequency approach
Shen, Yang
Imaging seismic velocity structure beneath the Iceland hot spot: A finite frequency approach Shu and S wave speeds extending from shallow mantle to 400 km depth beneath Iceland. In reality, seismic waves anomaly beneath Iceland and its geodynamic implications. We developed a tomographic method that utilizes
Velocity oscillations in the outer heliosphere: A signature of pickup ion temperature variability?
Richardson, John
unusual long-wavelength, low- frequency velocity oscillations in the solar wind with periods of $2.3 daysÃ?1 and characteristic length scales that range from 0.5 to 1 AU. The amplitudes of the waves these waves are seen can be attributed to their unusually long wavelength, since the only sources capable
Longshore sediment transport rate calculated incorporating wave orbital velocity fluctuations
Smith, Ernest Ray
2006-10-30T23:59:59.000Z
Laboratory experiments were performed to study and improve longshore sediment transport rate predictions. Measured total longshore transport in the laboratory was approximately three times greater for plunging breakers than spilling breakers. Three...
Fermi velocity renormalization and dynamical gap generation in graphene
C. Popovici; C. S. Fischer; L. von Smekal
2015-01-12T23:59:59.000Z
We study the renormalization of the Fermi velocity by the long-range Coulomb interactions between the charge carriers in the Dirac-cone approximation for the effective low-energy description of the electronic excitations in graphene at half filling. Solving the coupled system of Dyson-Schwinger equations for the dressing functions in the corresponding fermion propagator with various approximations for the particle-hole polarization we observe that Fermi velocity renormalization effects generally lead to a considerable increase of the critical coupling for dynamical gap generation and charge-density wave formation at the semimetal-insulator transition.
Maneva, Y G; Moya, Pablo S; Wicks, R; Poedts, S
2015-01-01T23:59:59.000Z
We perform 2.5D hybrid simulations with massless fluid electrons and kinetic particle-in-cell ions to study the temporal evolution of ion temperatures, temperature anisotropies and velocity distribution functions in relation to the dissipation and turbulent evolution of a broad-band spectrum of parallel and obliquely propagating Alfv\\'en-cyclotron waves. The purpose of this paper is to study the relative role of parallel versus oblique Alfv\\'en-cyclotron waves in the observed heating and acceleration of minor ions in the fast solar wind. We consider collisionless homogeneous multi-species plasma, consisting of isothermal electrons, isotropic protons and a minor component of drifting $\\alpha$ particles in a finite-$\\beta$ fast stream near the Earth. The kinetic ions are modeled by initially isotropic Maxwellian velocity distribution functions, which develop non-thermal features and temperature anisotropies when a broad-band spectrum of low-frequency non-resonant, $\\omega \\leq 0.34 \\Omega_p$, Alfv\\'en-cyclotron...
Geometric phases of water waves
Francesco Fedele
2014-08-08T23:59:59.000Z
Recently, Banner et al. (2014) highlighted a new fundamental property of open ocean wave groups, the so-called crest slowdown. For linear narrowband waves, this is related to the geometric and dynamical phase velocities $U_d$ and $U_g$ associated with the parallel transport through the principal fiber bundle of the wave motion with $\\mathit{U}(1)$ symmetry. The theoretical predictions are shown to be in fair agreement with ocean field observations, from which the average crest speed $c=U_d+U_g$ with $c/U_d\\approx0.8$ and $U_{g}/U_d\\approx-0.2$.
Fast Computation Algorithm for Discrete Resonances among Gravity Waves
Elena Kartashova
2006-05-25T23:59:59.000Z
Traditionally resonant interactions among short waves, with large real wave-numbers, were described statistically and only a small domain in spectral space with integer wave-numbers, discrete resonances, had to be studied separately in resonators. Numerical simulations of the last few years showed unambiguously the existence of some discrete effects in the short-waves part of the wave spectrum. Newly presented model of laminated turbulence explains theoretically appearance of these effects thus putting a novel problem - construction of fast algorithms for computation of solutions of resonance conditions with integer wave-numbers of order $10^3$ and more. Example of such an algorithm for 4-waves interactions of gravity waves is given. Its generalization on the different types of waves is briefly discussed.
Time-resolved heat transfer in the oscillating turbulent flow of a pulse-combustor tail pipe
Dec, J.E.
1988-01-01T23:59:59.000Z
The need for efficient combustion systems has led to active research in pulse combustion. One advantage of pulse combustor heating systems is a high rate of heat transfer in the tail pipe. These high heat transfer rates result from large velocity oscillations, which occur in the tailpipe as a result of the acoustic resonance of the pulse combustor. Past research on the effects of flow oscillations on heat transfer rates is inconclusive; however, some oscillating turbulent flows have been shown to have Nusselt numbers, which are much higher than those to steady turbulent flow at the same mean Reynolds number. An experimental study of the heat transfer rates and convective transport processes in a pulse combustor tail pipe was conducted. A test combustor was used, in which the oscillation frequencies could be varied from 54 to 101 Hz, with peak-to-peak velocity oscillations from zero (steady flow) to 10 times the mean velocity, and mean Reynolds numbers from 3100 to 4750. Nusselt numbers in the tail pipe are enhanced by the oscillations up to a factor of 2.5 times the expected value for steady turbulent flow. The Nusselt number enhancement increases with both oscillation frequency and velocity oscillation amplitude. Increases in the mean Reynolds number decreased the enhancement. Possible causes for the heat-transfer enhancement in oscillating flows are discussed. The data indicate that the heat transfer enhancement results from a combination of increased turbulence intensity and transverse flows generated during the streamwise velocity reversals.
Dissipation-Scale Turbulence in the Solar Wind
Gregory G. Howes; Steven C. Cowley; William Dorland; Gregory W. Hammett; Eliot Quataert; Alexander A. Schekochihin
2007-07-20T23:59:59.000Z
We present a cascade model for turbulence in weakly collisional plasmas that follows the nonlinear cascade of energy from the large scales of driving in the MHD regime to the small scales of the kinetic Alfven wave regime where the turbulence is dissipated by kinetic processes. Steady-state solutions of the model for the slow solar wind yield three conclusions: (1) beyond the observed break in the magnetic energy spectrum, one expects an exponential cut-off; (2) the widely held interpretation that this dissipation range obeys power-law behavior is an artifact of instrumental sensitivity limitations; and, (3) over the range of parameters relevant to the solar wind, the observed variation of dissipation range spectral indices from -2 to -4 is naturally explained by the varying effectiveness of Landau damping, from an undamped prediction of -7/3 to a strongly damped index around -4.
Universal statistics of density of inertial particles sedimenting in turbulence
Itzhak Fouxon; Yongnam Park; Roei Harduf; Changhoon Lee
2014-10-30T23:59:59.000Z
We solve the problem of spatial distribution of inertial particles that sediment in Navier-Stokes turbulence with small ratio $Fr$ of acceleration of fluid particles to acceleration of gravity $g$. The particles are driven by linear drag and have arbitrary inertia. We demonstrate that independently of the particles' size or density the particles distribute over fractal set with log-normal statistics determined completely by the Kaplan-Yorke dimension $D_{KY}$. When inertia is not small $D_{KY}$ is proportional to the ratio of integral of spectrum of turbulence multiplied by wave-number and $g$. This ratio is independent of properties of particles so that the particles concentrate on fractal with universal, particles-independent statistics. We find Lyapunov exponents and confirm predictions numerically. The considered case includes typical situation of water droplets in clouds.
Numerical Simulations of MHD Turbulence in Accretion Disks
Steven A. Balbus; John F. Hawley
2002-03-20T23:59:59.000Z
We review numerical simulations of MHD turbulence. The last decade has witnessed fundamental advances both in the technical capabilities of direct numerical simulation, and in our understanding of key physical processes. Magnetic fields tap directly into the free energy sources in a sufficiently ionized gas. The result is that adverse angular velocity and adverse temperature gradients, not the classical angular momentum and entropy gradients, destabilize laminar and stratified flow. This has profound consequences for astrophysical accretion flows, and has opened the door to a new era of numerical simulation experiments.}
Thakur, S. C., E-mail: saikat@ucsd.edu; Tynan, G. R. [Center for Momentum Transport and Flow Organization, San Diego, California 92093 (United States); Center for Energy Research, University of California at San Diego, San Diego, California 92093 (United States); Brandt, C.; Cui, L.; Gosselin, J. J. [Center for Energy Research, University of California at San Diego, San Diego, California 92093 (United States); Light, A. [Center for Integrated Plasma Studies, Department of Physics, University of Colorado at Boulder, Boulder, Colorado 80309-0390 (United States)
2014-11-15T23:59:59.000Z
We use multiple-tip Langmuir probes and fast imaging to unambiguously identify and study the dynamics of underlying instabilities during the controlled route to fully-developed plasma turbulence in a linear magnetized helicon plasma device. Langmuir probes measure radial profiles of electron temperature, plasma density and potential; from which we compute linear growth rates of instabilities, cross-phase between density and potential fluctuations, Reynold's stress, particle flux, vorticity, time-delay estimated velocity, etc. Fast imaging complements the 1D probe measurements by providing temporally and spatially resolved 2D details of plasma structures associated with the instabilities. We find that three radially separated plasma instabilities exist simultaneously. Density gradient driven resistive drift waves propagating in the electron diamagnetic drift direction separate the plasma into an edge region dominated by strong, velocity shear driven Kelvin-Helmholtz instabilities and a central core region which shows coherent Rayleigh-Taylor modes propagating in the ion diamagnetic drift direction. The simultaneous, complementary use of both probes and camera was crucial to identify the instabilities and understand the details of the very rich plasma dynamics.
Quantitative imaging of turbulent and reacting flows
Paul, P.H. [Sandia National Laboratories, Livermore, CA (United States)
1993-12-01T23:59:59.000Z
Quantitative digital imaging, using planar laser light scattering techniques is being developed for the analysis of turbulent and reacting flows. Quantitative image data, implying both a direct relation to flowfield variables as well as sufficient signal and spatial dynamic range, can be readily processed to yield two-dimensional distributions of flowfield scalars and in turn two-dimensional images of gradients and turbulence scales. Much of the development of imaging techniques to date has concentrated on understanding the requisite molecular spectroscopy and collision dynamics to be able to determine how flowfield variable information is encoded into the measured signal. From this standpoint the image is seen as a collection of single point measurements. The present effort aims at realizing necessary improvements in signal and spatial dynamic range, signal-to-noise ratio and spatial resolution in the imaging system as well as developing excitation/detection strategies which provide for a quantitative measure of particular flowfield scalars. The standard camera used for the study is an intensified CCD array operated in a conventional video format. The design of the system was based on detailed modeling of signal and image transfer properties of fast UV imaging lenses, image intensifiers and CCD detector arrays. While this system is suitable for direct scalar imaging, derived quantities (e.g. temperature or velocity images) require an exceptionally wide dynamic range imaging detector. To apply these diagnostics to reacting flows also requires a very fast shuttered camera. The authors have developed and successfully tested a new type of gated low-light level detector. This system relies on fast switching of proximity focused image-diode which is direct fiber-optic coupled to a cooled CCD array. Tests on this new detector show significant improvements in detection limit, dynamic range and spatial resolution as compared to microchannel plate intensified arrays.
Burkert, A.; Naab, T. [University Observatory Munich (USM), Scheinerstrasse 1, 81679 Munich (Germany); Genzel, R.; Bouche, N.; Cresci, G.; Khochfar, S.; Schreiber, N. Foerster; Tacconi, L.; Hicks, E.; Lutz, D.; Davies, R.; Buschkamp, P.; Genel, S. [Max-Planck-Institut fuer extraterrestrische Physik (MPE), Giessenbachstr. 1, 85748 Garching (Germany); Sommer-Larsen, J. [Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Marie Vej 30, 2100 Copenhagen (Denmark); Sternberg, A. [School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978 (Israel); Shapiro, K., E-mail: burkert@usm.uni-muenchen.d, E-mail: genzel@mpe.mpg.d [Department of Astronomy, Campbell Hall, University of California, Berkeley, CA 94720 (United States)
2010-12-20T23:59:59.000Z
The structure of a sample of high-redshift (z {approx} 2), rotating galaxies with high star formation rates and turbulent gas velocities of {sigma} {approx} 40-80 km s{sup -1} is investigated. Fitting the observed disk rotational velocities and radii with a Mo et al. (MMW) model requires unusually large disk spin parameters {lambda}{sub d}>0.1 and disk-to-dark halo mass fractions of m{sub d} {approx} 0.2, close to the cosmic baryon fraction. The galaxies segregate into dispersion-dominated systems with 1 {<=} v{sub max}/{sigma} {<=} 3, maximum rotational velocities v{sub max{<=}} 200 km s{sup -1}, and disk half-light radii r{sub 1/2{approx}} 1-3 kpc, and rotation-dominated systems with v{sub max}> 200 km s{sup -1}, v{sub max}/{sigma}>3, and r{sub 1/2{approx}} 4-8 kpc. For the dispersion-dominated sample, radial pressure gradients partly compensate the gravitational force, reducing the rotational velocities. Including this pressure effect in the MMW model, dispersion-dominated galaxies can be fitted well with spin parameters of {lambda}{sub d} = 0.03-0.05 for high disk mass fractions of m{sub d} {approx} 0.2 and with {lambda}{sub d} = 0.01-0.03 for m{sub d} {approx} 0.05. These values are in good agreement with cosmological expectations. For the rotation-dominated sample, however, pressure effects are small and better agreement with theoretically expected disk spin parameters can only be achieved if the dark halo mass contribution in the visible disk regime (2-3 x r{sub 1/2}) is smaller than predicted by the MMW model. We argue that these galaxies can still be embedded in standard cold dark matter halos if the halos do not contract adiabatically in response to disk formation. In this case, the data favor models with small disk mass fractions of m{sub d} = 0.05 and disk spin parameters of {lambda}{sub d} {approx} 0.035. It is shown that the observed high turbulent gas motions of the galaxies are consistent with a Toomre instability parameter Q = 1 which is equal to the critical value, expected for gravitational disk instability to be the major driver of turbulence. The dominant energy source of turbulence is then the potential energy of the gas in the disk.
Benjamin D. G. Chandran
2003-11-13T23:59:59.000Z
Energetic particles that undergo strong pitch-angle scattering and diffuse through a plasma containing strong compressible MHD turbulence undergo diffusion in momentum space with diffusion coefficient Dp. In this paper, the contribution of slow modes to Dp is calculated assuming the rms turbulent velocity is of order the Alfven speed. The energy spectrum of accelerated particles is derived assuming slow modes make the dominant contribution to Dp, taking into account Coulomb losses and particle escape from the acceleration region with an energy-independent escape time. The results are applied to solar flares.
An investigation into the spectral evolution of turbulent mixing by Rayleigh-Taylor Instability
Wilson, Peter Nixon
1998-01-01T23:59:59.000Z
?dx ?dx, dx, (2-2) The mass-weighted average of the velocity vector separates as u, = u, + u, ", defined as, p" i u p (2-3) and the relationship, pu, " = 0, is shown from the following: 14 pu, " = p(u, ? u, ) = piu, ? =' = pu, ? pu, = 0. p (2-4... TABLE OF CONTENTS, LIST OF FIGURES . . LIST OF TABLES. . xn1 NOMENCLATURE . 1. INTRODUCTION. xtv 1. 1 Description of Turbulence. 1. 2 Motivation for Research. 1. 3 Previous Investigations Into Vanable-Density Turbulence. . . . 1. 4 Spectral...
Numerical analysis of turbulent heat transfer in a nuclear reactor coolant channel
Garrard, Clarence William
1965-01-01T23:59:59.000Z
paragraphs. The method of' approach will be to numerically solve the energy ecuation using expressions ="or the veloc-'ty distribution ano the turbulent dif'f'usivity for heat that have 'seen def'ined by previous investigators (9) CHAPTER III NETHOD... of tne tem- per . urc prof'le. 'i(ith the aid of the energy equa, sion for . he tu bale;. ' neat transfer the solution for the tempera- ". ure profile is avails. ole. T' he energy ecuation for a. turbulent flowing fluid 1n a circular tube may...
Velocity and attenuation in partially molten rocks
Mavko, G.M.
1980-10-10T23:59:59.000Z
Interpretation of seismic velocity and attenuation in partially molten rocks has been limited, with few exceptions, to models that assume the melt to be distributed either as spheres or as thin films. However, other melt phase geometries, such as interconnected tubes along grain edges, might equally well account for seismic observations if there is a much larger fraction of melt. Seismic velocity and attenuation are estimated in rocks in which the melt phase has the tube geometry, and the results are compared with results expected for the more familiar film model under similar conditions. For a given melt fraction, tubes are found to give moduli intermediate between moduli for rigid spherical inclusions and compliant films. For example, in polycrystalline olivine at 20 kbar the model predicts a decrease in V/sub s/ of 10% and a decrease in V/sub p/ of 5% at 0.05 melt fraction, without considering inelastic relaxation. Shear attenuation appears to be dominated by viscous flow of melt between the tubes and/or films. For olivine the tube model predicts the increment of relaxation due to melt, ..delta mu../..mu.., to be 0.01 at 0.05 melt fraction. Relaxation of the bulk modulus is dominated by flow between melt pockets of different shape, heat flow, and solid-melt phase change. If melt is present, considerable bulk attenuation is expected, although the relaxation may be observable only at long periods, outside the seismic body wave band.
L. Iapichino; J. C. Niemeyer
2008-07-01T23:59:59.000Z
The development of turbulent gas flows in the intra-cluster medium and in the core of a galaxy cluster is studied by means of adaptive mesh refinement (AMR) cosmological simulations. A series of six runs was performed, employing identical simulation parameters but different criteria for triggering the mesh refinement. In particular, two different AMR strategies were followed, based on the regional variability of control variables of the flow and on the overdensity of subclumps, respectively. We show that both approaches, albeit with different results, are useful to get an improved resolution of the turbulent flow in the ICM. The vorticity is used as a diagnostic for turbulence, showing that the turbulent flow is not highly volume-filling but has a large area-covering factor, in agreement with previous theoretical expectations. The measured turbulent velocity in the cluster core is larger than 200 km/s, and the level of turbulent pressure contribution to the cluster hydrostatic equilibrium is increased by using the improved AMR criteria.
GMTI radar minimum detectable velocity.
Richards, John Alfred
2011-04-01T23:59:59.000Z
Minimum detectable velocity (MDV) is a fundamental consideration for the design, implementation, and exploitation of ground moving-target indication (GMTI) radar imaging modes. All single-phase-center air-to-ground radars are characterized by an MDV, or a minimum radial velocity below which motion of a discrete nonstationary target is indistinguishable from the relative motion between the platform and the ground. Targets with radial velocities less than MDV are typically overwhelmed by endoclutter ground returns, and are thus not generally detectable. Targets with radial velocities greater than MDV typically produce distinct returns falling outside of the endoclutter ground returns, and are thus generally discernible using straightforward detection algorithms. This document provides a straightforward derivation of MDV for an air-to-ground single-phase-center GMTI radar operating in an arbitrary geometry.
Fundamental Statistical Descriptions of Plasma Turbulence in Magnetic Fields
John A. Krommes
2001-02-16T23:59:59.000Z
A pedagogical review of the historical development and current status (as of early 2000) of systematic statistical theories of plasma turbulence is undertaken. Emphasis is on conceptual foundations and methodology, not practical applications. Particular attention is paid to equations and formalism appropriate to strongly magnetized, fully ionized plasmas. Extensive reference to the literature on neutral-fluid turbulence is made, but the unique properties and problems of plasmas are emphasized throughout. Discussions are given of quasilinear theory, weak-turbulence theory, resonance-broadening theory, and the clump algorithm. Those are developed independently, then shown to be special cases of the direct-interaction approximation (DIA), which provides a central focus for the article. Various methods of renormalized perturbation theory are described, then unified with the aid of the generating-functional formalism of Martin, Siggia, and Rose. A general expression for the renormalized dielectric function is deduced and discussed in detail. Modern approaches such as decimation and PDF methods are described. Derivations of DIA-based Markovian closures are discussed. The eddy-damped quasinormal Markovian closure is shown to be nonrealizable in the presence of waves, and a new realizable Markovian closure is presented. The test-field model and a realizable modification thereof are also summarized. Numerical solutions of various closures for some plasma-physics paradigms are reviewed. The variational approach to bounds on transport is developed. Miscellaneous topics include Onsager symmetries for turbulence, the interpretation of entropy balances for both kinetic and fluid descriptions, self-organized criticality, statistical interactions between disparate scales, and the roles of both mean and random shear. Appendices are provided on Fourier transform conventions, dimensional and scaling analysis, the derivations of nonlinear gyrokinetic and gyrofluid equations, stochasticity criteria for quasilinear theory, formal aspects of resonance-broadening theory, Novikov's theorem, the treatment of weak inhomogeneity, the derivation of the Vlasov weak-turbulence wave kinetic equation from a fully renormalized description, some features of a code for solving the direct-interaction approximation and related Markovian closures, the details of the solution of the EDQNM closure for a solvable three-wave model, and the notation used in the article.
Inwardly Rotating Spiral Waves in a Reaction-Diffusion System
Epstein, Irving R.
in an autocatalytic reaction. The local curvature near the open wave ends is high, making the velocity of the endInwardly Rotating Spiral Waves in a Reaction-Diffusion System Vladimir K. Vanag and Irving R in the spatially extended Belousov-Zhabotinsky (BZ) reaction. Since then, rotating spirals and target waves have
On the terminal velocity of sedimenting particles in a flowing fluid
Marco Martins Afonso
2008-06-11T23:59:59.000Z
The influence of an underlying carrier flow on the terminal velocity of sedimenting particles is investigated both analytically and numerically. Our theoretical framework works for a general class of (laminar or turbulent) velocity fields and, by means of an ordinary perturbation expansion at small Stokes number, leads to closed partial differential equations (PDE) whose solutions contain all relevant information on the sedimentation process. The set of PDE's are solved by means of direct numerical simulations for a class of 2D cellular flows (static and time dependent) and the resulting phenomenology is analysed and discussed.
Predicted Impacts of Proton Temperature Anisotropy on Solar Wind Turbulence
Klein, Kristopher G
2015-01-01T23:59:59.000Z
Particle velocity distributions measured in the weakly collisional solar wind are frequently found to be non-Maxwellian, but how these non-Maxwellian distributions impact the physics of plasma turbulence in the solar wind remains unanswered. Using numerical solutions of the linear dispersion relation for a collisionless plasma with a bi-Maxwellian proton velocity distribution, we present a unified framework for the four proton temperature anisotropy instabilities, identifying the associated stable eigenmodes, highlighting the unstable region of wavevector space, and presenting the properties of the growing eigenfunctions. Based on physical intuition gained from this framework, we address how the proton temperature anisotropy impacts the nonlinear dynamics of the \\Alfvenic fluctuations underlying the dominant cascade of energy from large to small scales and how the fluctuations driven by proton temperature anisotropy instabilities interact nonlinearly with each other and with the fluctuations of the large-scal...
LDV measurements of the velocity field within a ribbed internal duct flow
Huckle, E.; Pantelic, D.; Hu, K.; Jones, S.; Travkin, V.; Catton, I.
1999-07-01T23:59:59.000Z
Laser Doppler velocimetry (LDV) has been used to measure the velocity field in an internal duct flow of air with regular rib roughness. The experiments were conducted to study the effect regular wall obstacles have on the flow velocity field. The instantaneous u and v velocities were measured in both a smooth and rough rectangular duct. For the smooth channel the wind tunnel Reynolds number capability was first investigated and was shown to be linear with blower shaft frequency, having a range of 13,000--42,000. Next, the turbulent velocity profiles were measured in the smooth channel for 6 different blower speeds (Reynolds numbers), and the results greatly resembled those found in previous literature. Twenty sets of rectangular, 6.35 mm x 6.35 mm ribs were then mounted to the top and bottom of the channel with a spacing of 75 mm (P/H = 11.8). A grid of nodes were selected and the turbulent velocities were measured for a given Reynolds number, and are presented and discussed. Valuable insight was gained which will aid in future studies intended to measure the Reynolds stress and other closure terms.
Particle Acceleration by MHD Turbulence
Jungyeon Cho; A. Lazarian
2005-10-21T23:59:59.000Z
Recent advances in understanding of magnetohydrodynamic (MHD) turbulence call for revisions in the picture of particle acceleration. We make use of the recently established scaling of slow and fast MHD modes in strong and weak MHD turbulence to provide a systematic study of particle acceleration in magnetic pressure (low-$\\beta$) and gaseous pressure (high-$\\beta$) dominated plasmas. We consider the acceleration by large scale compressions in both slow and fast particle diffusion limits. We compare the results with the acceleration rate that arises from resonance scattering and Transit-Time Damping (TTD). We establish that fast modes accelerate particles more efficiently than slow modes. We find that particle acceleration by pitch-angle scattering and TTD dominates acceleration by slow or fast modes when the spatial diffusion rate is small. When the rate of spatial diffusion of particles is high, we establish an enhancement of the efficiency of particle acceleration by slow and fast modes in weak turbulence. We show that highly supersonic turbulence is an efficient agent for particle acceleration. We find that even incompressible turbulence can accelerate particles on the scales comparable with the particle mean free path.
Effect of Finite-rate Chemical Reactions on Turbulence in Hypersonic Turbulent Boundary Layers
Martín, Pino
Effect of Finite-rate Chemical Reactions on Turbulence in Hypersonic Turbulent Boundary Layers Lian reaction. The influence of chemical reactions on temperature fluctuation variance, Reynolds stresses that the recombination reaction enhances turbulence, while the dissociation reaction damps turbulence. Chemical reactions
Title of dissertation: EXPERIMENTAL CHARACTERIZATION OF TURBULENT
Lathrop, Daniel P.
ABSTRACT Title of dissertation: EXPERIMENTAL CHARACTERIZATION OF TURBULENT SUPERFLUID HELIUM Matthew S. Paoletti, Doctor of Philosophy, 2010 Dissertation directed by: Professor Daniel Lathrop. #12;EXPERIMENTAL CHARACTERIZATION OF TURBULENT SUPERFLUID HELIUM by Matthew S. Paoletti Dissertation
Linearly Organized Turbulence Structures Observed Over a Suburban Area by Dual-Doppler Lidar
Newsom, Rob K.; Calhoun, Ron; Ligon, David; Allwine, K Jerry
2008-04-01T23:59:59.000Z
Dual-Doppler lidar observations are used to investigate the structure and evolution of surface layer flow over a suburban area. The observations were made during the Joint Urban 2003 (JU2003) field experiment in Oklahoma City in the summer of 2003. This study focuses specifically on a 10-hour sequence of scan data beginning shortly after noon local time on July 7, 2003. During this period two coherent Doppler lidars performed overlapping low elevation angle sector scans upwind and south of Oklahoma City’s central business district (CBD). Radial velocity data from the two lidars are processed to reveal the structure and evolution of the horizontal velocity field in the surface layer throughout the afternoon and evening transition periods. The retrieved velocity fields clearly show a tendency for turbulence structures to be elongated in the direction of the mean flow throughout the entire 10-hour study period. As the stratification changed from unstable to weakly stable the turbulence structures became increasingly more linearly organized, and the cross-stream separation between high- and low-speed regoins decreased. The spatially resolved velocity fields are used to estimate streamwise and cross-stream turbulence length scales as functions of stability.
Helical mode interactions and spectral transfer processes in magnetohydrodynamic turbulence
Moritz F. Linkmann; Arjun Berera; Mairi E. McKay; Julia Jäger
2015-08-22T23:59:59.000Z
Spectral transfer processes in magnetohydrodynamic (MHD) turbulence are investigated analytically by decomposition of the velocity and magnetic fields in Fourier space into helical modes. Steady solutions of the dynamical system which governs the evolution of the helical modes are determined, and a stability analysis of these solutions is carried out. The interpretation of the analysis is that unstable solutions lead to energy transfer between the interacting modes while stable solutions do not. From this, a dependence of possible interscale energy and helicity transfers on the helicities of the interacting modes is derived. As expected from the inverse cascade of magnetic helicity in 3D MHD turbulence, mode interactions with like helicities lead to transfer of energy and magnetic helicity to smaller wavenumbers. However, some interactions of modes with unlike helicities also contribute to an inverse energy transfer. As such, an inverse energy cascade for nonhelical magnetic fields is shown to be possible. Furthermore, it is found that high values of the cross-helicity may have an asymmetric effect on forward and reverse transfer of energy, where forward transfer is more quenched in regions of high cross-helicity than reverse transfer. This conforms with recent observations of solar wind turbulence. For specific helical interactions the relation to dynamo action is established.
Anisotropic Formation of Magnetized Cores in Turbulent Clouds
Chen, Che-Yu
2015-01-01T23:59:59.000Z
In giant molecular clouds (GMCs), shocks driven by converging turbulent flows create high-density, strongly-magnetized regions that are locally sheetlike. In previous work, we showed that within these layers, dense filaments and embedded self-gravitating cores form by gathering material along the magnetic field lines. Here, we extend the parameter space of our three-dimensional, turbulent MHD core formation simulations. We confirm the anisotropic core formation model we previously proposed, and quantify the dependence of median core properties on the pre-shock inflow velocity and upstream magnetic field strength. Our results suggest that bound core properties are set by the total dynamic pressure (dominated by large-scale turbulence) and thermal sound speed c_s in GMCs, independent of magnetic field strength. For models with Mach number between 5 and 20, the median core masses and radii are comparable to the critical Bonnor-Ebert mass and radius defined using the dynamic pressure for P_ext. Our results corres...
Magnetohydrodynamic turbulent cascade of coronal loop magnetic fields
Rappazzo, A. F. [Instituto de Astrofisica de Canarias, E-38200 La Laguna, Tenerife (Spain); Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109 (United States); Bartol Research Institute, Department of Physics and Astronomy, University of Delaware, Delaware 19716 (United States); Velli, M. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109 (United States)
2011-06-15T23:59:59.000Z
The Parker model for coronal heating is investigated through a high resolution simulation. An inertial range is resolved where fluctuating magnetic energy E{sub M}(k{sub perpendicular}){proportional_to}k{sub perpendicular}{sup -2.7} exceeds kinetic energy E{sub K}(k{sub perpendicular}){proportional_to}k{sub perpendicular}{sup -0.6}. Increments scale as {delta}b{sub l}{approx_equal}l{sup -0.85}and {delta}u{sub l}{approx_equal}l{sup +0.2} with velocity increasing at small scales, indicating that magnetic reconnection plays a prime role in this turbulent system. We show that spectral energy transport is akin to standard magnetohydrodynamic (MHD) turbulence even for a system of reconnecting current sheets sustained by the boundary. In this new MHD turbulent cascade, kinetic energy flows are negligible while cross-field flows are enhanced, and through a series of ''reflections'' between the two fields, cascade more than half of the total spectral energy flow.
Mixing at the external boundary of a submerged turbulent jet
A. Eidelman; T. Elperin; N. Kleeorin; G. Hazak; I. Rogachevskii; O. Sadot; I. Sapir-Katiraie
2009-05-11T23:59:59.000Z
We study experimentally and theoretically mixing at the external boundary of a submerged turbulent jet. In the experimental study we use Particle Image Velocimetry and an Image Processing Technique based on the analysis of the intensity of the Mie scattering to determine the spatial distribution of tracer particles. An air jet is seeded with the incense smoke particles which are characterized by large Schmidt number and small Stokes number. We determine the spatial distributions of the jet fluid characterized by a high concentration of the particles and of the ambient fluid characterized by a low concentration of the tracer particles. In the data analysis we use two approaches, whereby one approach is based on the measured phase function for the study of the mixed state of two fluids. The other approach is based on the analysis of the two-point second-order correlation function of the particle number density fluctuations generated by tangling of the gradient of the mean particle number density by the turbulent velocity field. This gradient is formed at the external boundary of a submerged turbulent jet. We demonstrate that PDF of the phase function of a jet fluid penetrating into an external flow and the two-point second-order correlation function of the particle number density do not have universal scaling and cannot be described by a power-law function. The theoretical predictions made in this study are in a qualitative agreement with the obtained experimental results.
Helical mode interactions and spectral transfer processes in magnetohydrodynamic turbulence
Moritz F. Linkmann; Arjun Berera; Mairi E. McKay; Julia Jäger
2015-09-01T23:59:59.000Z
Spectral transfer processes in magnetohydrodynamic (MHD) turbulence are investigated analytically by decomposition of the velocity and magnetic fields in Fourier space into helical modes. Steady solutions of the dynamical system which governs the evolution of the helical modes are determined, and a stability analysis of these solutions is carried out. The interpretation of the analysis is that unstable solutions lead to energy transfer between the interacting modes while stable solutions do not. From this, a dependence of possible interscale energy and helicity transfers on the helicities of the interacting modes is derived. As expected from the inverse cascade of magnetic helicity in 3D MHD turbulence, mode interactions with like helicities lead to transfer of energy and magnetic helicity to smaller wavenumbers. However, some interactions of modes with unlike helicities also contribute to an inverse energy transfer. As such, an inverse energy cascade for nonhelical magnetic fields is shown to be possible. Furthermore, it is found that high values of the cross-helicity may have an asymmetric effect on forward and reverse transfer of energy, where forward transfer is more quenched in regions of high cross-helicity than reverse transfer. This conforms with recent observations of solar wind turbulence. For specific helical interactions the relation to dynamo action is established.
Turbulent breakage of ductile aggregates
Marchioli, Cristian
2015-01-01T23:59:59.000Z
In this paper we study breakage rate statistics of small colloidal aggregates in non-homogeneous anisotropic turbulence. We use pseudo-spectral direct numerical simulation of turbulent channel flow and Lagrangian tracking to follow the motion of the aggregates, modelled as sub-Kolmogorov massless particles. We focus specifically on the effects produced by ductile rupture: This rupture is initially activated when fluctuating hydrodynamic stresses exceed a critical value, $\\sigma>\\sigma_{cr}$, and is brought to completion when the energy absorbed by the aggregate meets the critical breakage value. We show that ductile rupture breakage rates are significantly reduced with respect to the case of instantaneous brittle rupture (i.e. breakage occurs as soon as $\\sigma>\\sigma_{cr}$). These discrepancies are due to the different energy values at play as well as to the statistical features of energy distribution in the anisotropic turbulence case examined.
Turbulence patterns and neutrino flavor transitions in high-resolution supernova models
Borriello, Enrico; Mirizzi, Alessandro [II. Institut für Theoretische Physik, Universität Hamburg, Luruper Chaussee 149, D-22761 Hamburg (Germany); Chakraborty, Sovan [Max-Planck-Institut für Physik (Werner-Heisenberg-Institut), Föhringer Ring 6, D-80805 München (Germany); Janka, Hans-Thomas [Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85748 Garching (Germany); Lisi, Eligio, E-mail: enrico.borriello@desy.de, E-mail: sovan@mppmu.mpg.de, E-mail: thj@mpa-garching.mpg.de, E-mail: eligio.lisi@ba.infn.it, E-mail: alessandro.mirizzi@desy.de [INFN—Sezione di Bari, Via Orabona 4, 70126 Bari (Italy)
2014-11-01T23:59:59.000Z
During the shock-wave propagation in a core-collapse supernova (SN), matter turbulence may affect neutrino flavor conversion probabilities. Such effects have been usually studied by adding parametrized small-scale random fluctuations (with arbitrary amplitude) on top of coarse, spherically symmetric matter density profiles. Recently, however, two-dimensional (2D) SN models have reached a space resolution high enough to directly trace anisotropic density profiles, down to scales smaller than the typical neutrino oscillation length. In this context, we analyze the statistical properties of a large set of SN matter density profiles obtained in a high-resolution 2D simulation, focusing on a post-bounce time (2 s) suited to study shock-wave effects on neutrino propagation on scales as small as O(100) km and possibly below. We clearly find the imprint of a broken (Kolmogorov-Kraichnan) power-law structure, as generically expected in 2D turbulence spectra. We then compute the flavor evolution of SN neutrinos along representative realizations of the turbulent matter density profiles, and observe no or modest damping of the neutrino crossing probabilities on their way through the shock wave. In order to check the effect of possibly unresolved fluctuations at scales below O(100) km, we also apply a randomization procedure anchored to the power spectrum calculated from the simulation, and find consistent results within ± 1? fluctuations. These results show the importance of anchoring turbulence effects on SN neutrinos to realistic, fine-grained SN models.
G. Pavlovski; M. D. Smith; M. -M. Mac Low
2006-02-17T23:59:59.000Z
A roughly constant temperature over a wide range of densities is maintained in molecular clouds through radiative heating and cooling. An isothermal equation of state is therefore frequently employed in molecular cloud simulations. However, the dynamical processes in molecular clouds include shock waves, expansion waves, cooling induced collapse and baroclinic vorticity, all incompatible with the assumption of a purely isothermal flow. Here, we incorporate an energy equation including all the important heating and cooling rates and a simple chemical network into simulations of three-dimensional, hydrodynamic, decaying turbulence. This allows us to test the accuracy of the isothermal assumption by directly comparing a model run with the modified energy equation to an isothermal model. We compute an extreme case in which the initial turbulence is sufficiently strong to dissociate much of the gas and alter the specific heat ratio. The molecules then reform as the turbulence weakens. We track the true specific heat ratio as well as its effective value. We analyse power spectra, vorticity and shock structures, and discuss scaling laws for decaying turbulence. We derive some limitations to the isothermal approximation for simulations of the interstellar medium using simple projection techniques. Overall, even given the extreme conditions, we find that an isothermal flow provides an adequate physical and observational description of many properties. The main exceptions revealed here concern behaviour directly related to the high temperature zones behind the shock waves.
Saturation of radiation-induced parametric instabilities by excitation of Langmuir turbulence
Dubois, D.F.; Rose, H.A. [Los Alamos National Lab., NM (United States); Russell, D. [Lodestar Research Inc., Boulder, CO (United States)
1995-12-01T23:59:59.000Z
Progress made in the last few years in the calculation of the saturation spectra of parametric instabilities which involve Langmuir daughter waves will be reviewed. These instabilities include the ion acoustic decay instability, the two plasmon decay instability (TPDI), and stimulated Raman scattering (SRS). In particular I will emphasize spectral signatures which can be directly compared with experiment. The calculations are based on reduced models of driven Laugmuir turbulence. Thomson scattering from hf-induced Langmuir turbulence in the unpreconditioned ionosphere has resulted in detailed agreement between theory and experiment at early times. Strong turbulence signatures dominate in this regime where the weak turbulence approximation fails completely. Recent experimental studies of the TPDI have measured the Fourier spectra of Langmuir waves as well as the angular and frequency, spectra of light emitted near 3/2 of the pump frequency again permitting some detailed comparisons with theory. The experiments on SRS are less detailed but by Thomson scattering the secondary decay of the daughter Langmuir wave has been observed. Scaling laws derived from a local model of SRS saturation are compared with full simulations and recent Nova experiments.
The effects of a magnetic field on planetary migration in laminar and turbulent discs
Comins, M L; Koldoba, A V; Ustyugova, G V; Lovelace, R V E
2015-01-01T23:59:59.000Z
We investigate the migration of low-mass planets ($5 M_{\\oplus}$ and $20 M_{\\oplus}$) in accretion discs threaded with a magnetic field using 2D MHD code in polar coordinates. We observed that, in the case of a strong azimuthal magnetic field where the plasma parameter is $\\beta\\sim 1-2$, density waves at the magnetic resonances exert a positive torque on the planet and may slow down or reverse its migration. However, when the magnetic field is weaker (i.e., the plasma parameter $\\beta$ is relatively large), then non-axisymmetric density waves excited by the planet lead to growth of the radial component of the field and, subsequently, to development of the magneto-rotational instability, such that the disc becomes turbulent. Migration in a turbulent disc is stochastic, and the migration direction may change as such. To understand migration in a turbulent disc, both the interaction between a planet and individual turbulent cells, as well as the interaction between a planet and ordered density waves, have been ...
Development of Interfacial Structure in a Confined Air-Water Cap-Turbulent and Churn-Turbulent Flow
Xiaodong Sun; Seungjin Kim; Ling Cheng; Mamoru Ishii [Purdue University, West Lafayette, IN 47907 (United States); Beus, Stephen G. [Bechtel Bettis, Inc., Bettis Atomic Power Laboratory, Post Office Box 79, West Mifflin, PA 15122-0079 (United States)
2002-07-01T23:59:59.000Z
The objective of the present work is to study and model the interfacial structure development of air-water two-phase flow in a confined test section. Experiments of a total of 9 flow conditions in cap-turbulent and churn-turbulent flow regimes are carried out in a vertical air-water upward two-phase flow experimental loop with a test section of 200-mm in width and 10-mm in gap. Miniaturized four-sensor conductivity probes are used to measure local two-phase parameters at three different elevations for each flow condition. The bubbles captured by the probes are categorized into two groups in view of the two-group interfacial area transport equation, i.e., spherical/distorted bubbles as Group 1 and cap/churn-turbulent bubbles as Group 2. The acquired parameters are time-averaged local void fraction, interfacial velocity, bubble number frequency, interfacial area concentration, and bubble Sauter mean diameter for both groups of bubbles. Also, the line-averaged and area-averaged data are presented and discussed. The comparisons of these parameters at different elevations demonstrate the development of interfacial structure along the flow direction due to bubble interactions. (authors)
Development of Interfacial Structure in a Confined Air-Water Cap-Turbulent and Churn-Turbulent Flow
X. Sun; S. Kim; L. Cheng; M. Ishii; S.G. Beus
2001-10-31T23:59:59.000Z
The objective of the present work is to study and model the interfacial structure development of air-water two-phase flow in a confined test section. Experiments of a total of 9 flow conditions in a cap-turbulent and churn-turbulent flow regimes are carried out in a vertical air-water upward two-phase flow experimental loop with a test section of 20-cm in width and 1-cm in gap. The miniaturized four-sensor conductivity probes are used to measure local two-phase parameters at three different elevations for each flow condition. The bubbles captured by the probes are categorized into two groups in view of the two-group interfacial area transport equation, i.e., spherical/distorted bubbles as Group 1 and cap/churn-turbulent bubbles as Group 2. The acquired parameters are time-averaged local void fraction, interfacial velocity, bubble number frequency, interfacial area concentration, and bubble Sauter mean diameter for both groups of bubbles. Also, the line-averaged and area-averaged data are presented and discussed. The comparisons of these parameters at different elevations demonstrate the development of interfacial structure along the flow direction due to bubble interactions.
Velocity requirements for causality violation
Giovanni Modanese
2015-01-18T23:59:59.000Z
We re-examine the "Regge-Tolman paradox" with reference to some recent experimental results. It is straightforward to find a formula for the velocity v of the moving system required to produce causality violation. This formula typically yields a velocity very close to the speed of light (for instance, v/c > 0.97 for X-shaped microwaves), which raises some doubts about the real physical observability of the violations. We then compute the velocity requirement introducing a delay between the reception of the primary signal and the emission of the secondary. It turns out that in principle for any delay it is possible to find moving observers able to produce active causal violation. This is mathematically due to the singularity of the Lorentz transformations for beta to 1. For a realistic delay due to the propagation of a luminal precursor, we find that causality violations in the reported experiments are still more unlikely (v/c > 0.989), and even in the hypothesis that the superluminal propagation velocity goes to infinity, the velocity requirement is bounded by v/c > 0.62. We also prove that if two macroscopic bodies exchange energy and momentum through superluminal signals, then the swap of signal source and target is incompatible with the Lorentz transformations; therefore it is not possible to distinguish between source and target, even with reference to a definite reference frame.
Homogeneous isotropic turbulence in dilute polymers: scale by scale budget
E. De Angelis; C. M. Casciola; R. Benzi; R. Piva
2002-08-09T23:59:59.000Z
The turbulent energy cascade in dilute polymers solution is addressed here by considering a direct numerical simulation of homogeneous isotropic turbulence of a FENE-P fluid in a triply periodic box. On the basis of the DNS data, a scale by scale analysis is provided by using the proper extension to visco-elastic fluids of the Karman-Howarth equation for the velocity. For the microstructure, an equation, analogous to the Yaglom equation for scalars, is proposed for the free-energy density associated to the elastic behavior of the material. Two mechanisms of energy removal from the scale of the forcing are identified, namely the classical non-linear transfer term of the standard Navier-Stokes equations and the coupling between macroscopic velocity and microstructure. The latter, on average, drains kinetic energy to feed the dynamics of the microstructure. The cross-over scale between the two corresponding energy fluxes is identified, with the flux associated with the microstructure dominating at small separations to become sub-leading above the cross-over scale, which is the equivalent of the elastic limit scale defined by De Gennes-Tabor on the basis of phenomenological assumptions.
Elasto-viscoplastic wave propagation in single crystallographic silicon thin structure
Liu, Li
2006-08-16T23:59:59.000Z
wavelet transform scheme was also employed for the extraction of wafer thermal and geometric information from exploring wave attenuation and dispersion. Researched results concluded that wave group velocity is a nonlinear function of temperature...
Quantitative imaging of the air-water flow fields formed by unsteady breaking waves
Belden, Jesse (Jesse Levi)
2009-01-01T23:59:59.000Z
An experimental method for simultaneously measuring the velocity fields on the air and water side of unsteady breaking waves is presented. The method is applied to breaking waves to investigate the physics of the air and ...
Mahesh, Krishnan
simulation of turbulent jets in crossflow Suman Muppidi and Krishnan Mahesh University of Minnesota crossflow. The velocity ratio of the jet to that of the crossflow is 5.7 and the Reynolds number based agreement. I. Introduction A jet in crossflow is defined as the flow field where a jet of fluid enters
Evolution and lifetimes of flow topology in a turbulent boundary layer G. E. Elsinga and I. Marusic
Marusic, Ivan
Evolution and lifetimes of flow topology in a turbulent boundary layer G. E. Elsinga and I. Marusic of Physics. Related Articles Lagrangian evolution of the invariants of the velocity gradient tensor subject to AIP license or copyright; see http://pof.aip.org/about/rights_and_permissions #12;Evolution
Multi-Scale Gradient Expansion of the Turbulent Stress Tensor
Gregory L. Eyink
2005-12-10T23:59:59.000Z
We develop an expansion of the turbulent stress tensor into a double series of contributions from different scales of motion and different orders of space-derivatives of velocity, a Multi-Scale Gradient (MSG) expansion. The expansion is proved to converge to the exact stress, as a consequence of the locality of cascade both in scale and in space. Simple estimates show, however, that the convergence rate may be slow for the expansion in spatial gradients of very small scales. Therefore, we develop an approximate expansion, based upon an assumption that similar or `coherent' contributions to turbulent stress are obtained from disjoint subgrid regions. This Coherent-Subregions Approximation (CSA) yields an MSG expansion that can be proved to converge rapidly at all scales and is hopefully still reasonably accurate. As an application, we consider the cascades of energy and helicity in three-dimensional turbulence. To first order in velocity-gradients, the stress has three contributions: a tensile stress along principal directions of strain, a contractile stress along vortex lines, and a shear stress proportional to `skew-strain.' While vortex-stretching plays the major role in energy cascade, there is a second, less scale-local contribution from `skew-strain'. For helicity cascade the situation is reversed, and it arises scale-locally from `skew-strain' while the stress along vortex-lines gives a secondary, less scale-local contribution. These conclusions are illustrated with simple exact solutions of 3D Euler equations. In the first, energy cascade occurs by Taylor's mechanism of stretching and spin-up of small-scale vortices due to large-scale strain. In the second, helicity cascade occurs by `twisting' of small-scale vortex filaments due to a large-scale screw.
Scale-selective turbulence reduction in H-mode plasmas in the TJ-II stellarator
Happel, T.; Conway, G. D.; Stroth, U. [Max-Planck-Institut fuer Plasmaphysik, Association Euratom-IPP, 85748 Garching (Germany); Estrada, T.; Blanco, E.; Hidalgo, C.; Collaboration: TJ-II Team
2011-10-15T23:59:59.000Z
Wavenumber spectra of density turbulence in L- and H-mode plasmas have been measured in the TJ-II stellarator by means of Doppler reflectometry. A pronounced suppression of the density fluctuation level is observed in H-mode close to the radial position of maximum radial electric field (E{sub r}) shear. Furthermore, intermediate scale density turbulence is reduced preferentially. This effect can be interpreted within the framework of vortex stretching feeding energy through Reynolds stress into zonal flows, while shear decorrelation of turbulent structures might not play a central role in TJ-II. Moreover, it is shown that in both L- and H-mode, the phase velocity of density fluctuations does not depend on the structure scale.
Gore, R.A. (Los Alamos National Lab., NM (USA)); Crowe, C.T. (Washington State Univ., Pullman, WA (USA). Dept. of Mechanical and Materials Engineering); Bejan, A. (Duke Univ., Durham, NC (USA). Dept. of Mechanical Engineering and Materials Science)
1990-01-01T23:59:59.000Z
Experiments performed demonstrate the transition to turbulent flow of water jets discharging coaxially into a stream confined in a round duct. The critical Reynolds number is shown to be a strong function of velocity ratio. From the flow visualization it is shown that a proportionality between the laminar length of the jet (L) and the wavelength ({lambda}) can be seen in the region of transition to turbulence. The proportionality coincides with similar observations concerning the transition to turbulence in various other flows. A brief argument based on scale analysis is presented for the confined coaxial jet and round plume. The apparent universality of the L/{lambda} {approximately} O(10) scaling law supports the conclusion that the laminar sections of all naturally progressing boundary layer-type flows are geometrically similar. 21 refs., 8 figs.
Collision-dependent power law scalings in two dimensional gyrokinetic turbulence
Cerri, S. S., E-mail: silvio.sergio.cerri@ipp.mpg.de; Bañón Navarro, A.; Told, D. [Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, D-85748 Garching (Germany); Jenko, F. [Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, D-85748 Garching (Germany); Max-Planck/Princeton Center for Plasma Physics (Germany)
2014-08-15T23:59:59.000Z
Nonlinear gyrokinetics provides a suitable framework to describe short-wavelength turbulence in magnetized laboratory and astrophysical plasmas. In the electrostatic limit, this system is known to exhibit a free energy cascade towards small scales in (perpendicular) real and/or velocity space. The dissipation of free energy is always due to collisions (no matter how weak the collisionality), but may be spread out across a wide range of scales. Here, we focus on freely decaying two dimensional electrostatic turbulence on sub-ion-gyroradius scales. An existing scaling theory for the turbulent cascade in the weakly collisional limit is generalized to the moderately collisional regime. In this context, non-universal power law scalings due to multiscale dissipation are predicted, and this prediction is confirmed by means of direct numerical simulations.
Smith, Jerome A.
be sampled every second or less, with under 2 cm/s rms velocity error per sample. Radial velocity estimates. Free waves, bound harmonics, finite-amplitude effects, Doppler shifting by currents, etc., can systems are described that use sound to probe the velocity field over finite areas, "Phased-Array Doppler
Compressible Turbulence and Interactions with Shock Waves and Material
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Turbulence and internal waves in tidal flow over topography
Gayen, Bishakhdatta
2012-01-01T23:59:59.000Z
structures in oscillatory boundary layers. J. Fluid. Mech.structures in oscillatory boundary layers. J. Fluid Mech.zero time-mean oscillatory boundary layer based on the value
Turbulence and internal waves in tidal flow over topography
Gayen, Bishakhdatta
2012-01-01T23:59:59.000Z
the semidiurnal kinetic and potential energies, phasethe baroclinic kinetic and potential energy, respectively.both the kinetic and the potential energy start dropping
Gyrokinetic Particle Simulation of Compressible Electromagnetic Turbulence in High-? Plasmas
Lin, Zhihong
2014-03-13T23:59:59.000Z
Supported by this award, the PI and his research group at the University of California, Irvine (UCI) have carried out computational and theoretical studies of instability, turbulence, and transport in laboratory and space plasmas. Several massively parallel, gyrokinetic particle simulation codes have been developed to study electromagnetic turbulence in space and laboratory plasmas. In space plasma projects, the simulation codes have been successfully applied to study the spectral cascade and plasma heating in kinetic Alfven wave turbulence, the linear and nonlinear properties of compressible modes including mirror instability and drift compressional mode, and the stability of the current sheet instabilities with finite guide field in the context of collisionless magnetic reconnection. The research results have been published in 25 journal papers and presented at many national and international conferences. Reprints of publications, source codes, and other research-related information are also available to general public on the PI’s webpage (http://phoenix.ps.uci.edu/zlin/). Two PhD theses in space plasma physics are highlighted in this report.
Vorticity dynamics after the shock–turbulence interaction
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Livescu, Daniel; Ryu, Jaiyoung
2015-07-23T23:59:59.000Z
The interaction of a shock wave with quasi-vortical isotropic turbulence (IT) represents a basic problem for studying some of the phenomena associated with high speed flows, such as hypersonic flight, supersonic combustion and Inertial Confinement Fusion (ICF). In general, in practical applications, the shock width is much smaller than the turbulence scales and the upstream turbulent Mach number is modest. In this case, recent high resolution shock-resolved Direct Numerical Simulations (DNS) (Ryu and Livescu, J Fluid Mech 756:R1, 2014) show that the interaction can be described by the Linear Interaction Approximation (LIA). Using LIA to alleviate the need to resolvemore »the shock, DNS post-shock data can be generated at much higher Reynolds numbers than previously possible. Here, such results with Taylor Reynolds number approximately 180 are used to investigate the changes in the vortical structure as a function of the shock Mach number, Ms, up to Ms = 10. It is shown that, as Ms increases, the shock interaction induces a tendency towards a local axisymmetric state perpendicular to the shock front, which has a profound influence on the vortex-stretching mechanism and divergence of the Lamb vector and, ultimately, on the flow evolution away from the shock.« less
3D Velocity from 3D Doppler Radial Velocity J. L. Barron,1
Barron, John
to compute local 3D velocity (local 3D optical flow). Radial velocity (measured by the Doppler effect3D Velocity from 3D Doppler Radial Velocity J. L. Barron,1 R. E. Mercer,1 X. Chen,1 P. Joe2 1 velocity data and qualitatively on real radial velocity data, obtained from the Doppler radar at Kurnell
Fort, James A.; Pfund, David M.; Sheen, David M.; Pappas, Richard A.; Morgen, Gerald P.
2007-04-01T23:59:59.000Z
The MFDRC was formed in 1998 to advance the state-of-the-art in simulating multiphase turbulent flows by developing advanced computational models for gas-solid flows that are experimentally validated over a wide range of industrially relevant conditions. The goal was to transfer the resulting validated models to interested US commercial CFD software vendors, who would then propagate the models as part of new code versions to their customers in the US chemical industry. Since the lack of detailed data sets at industrially relevant conditions is the major roadblock to developing and validating multiphase turbulence models, a significant component of the work involved flow measurements on an industrial-scale riser contributed by Westinghouse, which was subsequently installed at SNL. Model comparisons were performed against these datasets by LANL. A parallel Office of Industrial Technology (OIT) project within the consortium made similar comparisons between riser measurements and models at NETL. Measured flow quantities of interest included volume fraction, velocity, and velocity-fluctuation profiles for both gas and solid phases at various locations in the riser. Some additional techniques were required for these measurements beyond what was currently available. PNNL’s role on the project was to work with the SNL experimental team to develop and test two new measurement techniques, acoustic tomography and millimeter-wave velocimetry. Acoustic tomography is a promising technique for gas-solid flow measurements in risers and PNNL has substantial related experience in this area. PNNL is also active in developing millimeter wave imaging techniques, and this technology presents an additional approach to make desired measurements. PNNL supported the advanced diagnostics development part of this project by evaluating these techniques and then by adapting and developing the selected technology to bulk gas-solids flows and by implementing them for testing in the SNL riser testbed.
The Nature of Running Penumbral Waves Revealed
D. Shaun Bloomfield; Andreas Lagg; Sami K. Solanki
2007-09-24T23:59:59.000Z
We seek to clarify the nature of running penumbral (RP) waves: are they chromospheric trans-sunspot waves or a visual pattern of upward-propagating waves? Full Stokes spectropolarimetric time series of the photospheric Si I 10827 \\AA line and the chromospheric He I 10830 \\AA multiplet were inverted using a Milne-Eddington atmosphere. Spatial pixels were paired between the outer umbral/inner penumbral photosphere and the penumbral chromosphere using inclinations retrieved by the inversion and the dual-height pairings of line-of-sight velocity time series were studied for signatures of wave propagation using a Fourier phase difference analysis. The dispersion relation for radiatively cooling acoustic waves, modified to incorporate an inclined propagation direction, fits well the observed phase differences between the pairs of photospheric and chromospheric pixels. We have thus demonstrated that RP waves are in effect low-beta slow-mode waves propagating along the magnetic field.
The Numerical Simulation of Turbulence
W. Schmidt
2007-12-06T23:59:59.000Z
In this contribution, I give an overview of the various approaches toward the numerical modelling of turbulence, particularly, in the interstellar medium. The discussion is placed in a physical context, i. e. computational problems are motivated from basic physical considerations. Presenting selected examples for solutions to these problems, I introduce the basic ideas of the most commonly used numerical methods.
Scour around a circular pile due to oscillatory wave motion
Wells, Donald Raymond
1970-01-01T23:59:59.000Z
( COLEMAN ) 10 authors. In general the committee on sedimentation has found many inconsistencies in critical velocities necessary for incipient motion and have concluded that when studying incipient motion critical shear stresses should be the governing...- city of the paddle arm on the flywheel. The period is varied through a variable rheostat that controls the speed of the flywheel. The rocker arms can be varied so as to vary the wave from a deep water wave to a shallow water wave. Wave heights...
Random Vortex-Street Model for a Self-Similar Plane Turbulent Jet
Victor L'vov; Anna Pomyalov; Itamar Procaccia; Rama Govindarajan
2008-03-18T23:59:59.000Z
We ask what determines the (small) angle of turbulent jets. To answer this question we first construct a deterministic vortex-street model representing the large scale structure in a self-similar plane turbulent jet. Without adjustable parameters the model reproduces the mean velocity profiles and the transverse positions of the large scale structures, including their mean sweeping velocities, in a quantitative agreement with experiments. Nevertheless the exact self similar arrangement of the vortices (or any other deterministic model) necessarily leads to a collapse of the jet angle. The observed (small) angle results from a competition between vortex sweeping tending to strongly collapse the jet and randomness in the vortex structure, with the latter resulting in a weak spreading of the jet.
On the Two-point Correlation of Potential Vorticity in Rotating and Stratified Turbulence
Susan Kurien; Leslie M. Smith; Beth Wingate
2006-03-15T23:59:59.000Z
A framework is developed to describe the two-point statistics of potential vorticity in rotating and stratified turbulence as described by the Boussinesq equations. The Karman-Howarth equation for the dynamics of the two-point correlation function of potential vorticity reveals the possibility of inertial-range dynamics in certain regimes in the Rossby, Froude, Prandtl and Reynolds number parameters. For the case of large Rossby and Froude numbers, and for the case of quasi-geostrophic dynamics, a linear scaling law with 2/3 prefactor is derived for the third-order mixed correlation between potential vorticity and velocity, a result that is analogous to the Kolmogorov 4/5-law for the third-order velocity structure function in turbulence theory.
Small-scale Interaction of Turbulence with Thermonuclear Flames in Type Ia Supernovae
J. C. Niemeyer; W. K. Bushe; G. R. Ruetsch
1999-05-07T23:59:59.000Z
Microscopic turbulence-flame interactions of thermonuclear fusion flames occuring in Type Ia Supernovae were studied by means of incompressible direct numerical simulations with a highly simplified flame description. The flame is treated as a single diffusive scalar field with a nonlinear source term. It is characterized by its Prandtl number, Pr << 1, and laminar flame speed, S_L. We find that if S_L ~ u', where u' is the rms amplitude of turbulent velocity fluctuations, the local flame propagation speed does not significantly deviate from S_L even in the presence of velocity fluctuations on scales below the laminar flame thickness. This result is interpreted in the context of subgrid-scale modeling of supernova explosions and the mechanism for deflagration-detonation-transitions.
A Molecular Dynamics Simulation of the Turbulent Couette Minimal Flow Unit
Smith, E R
2015-01-01T23:59:59.000Z
A molecular dynamics (MD) simulation of planar Couette flow is presented for the minimal channel in which turbulence structures can be sustained. Evolution over a single breakdown and regeneration cycle is compared to computational fluid dynamics (CFD) simulations. Qualitative similar structures are observed and turbulent statistics show excellent quantitative agreement. The molecular scale law of the wall is presented in which stick-slip molecular wall-fluid interactions replace the no-slip conditions. The impact of grid resolution is explored and the observed structures are seen to be dependant on averaging time and length scales. The kinetic energy spectra show a range of scales are present in the molecular system and that spectral content is dependent on the grid resolution employed. The subgrid velocity of the molecules is compared to spatial averaged velocity using joint probability density functions. Molecular trajectories, diffusions and Lagrangian statistics are presented. The importance of sub-grid ...
Sedimentation of finite-size spheres in quiescent and turbulent environments
Fornari, Walter; Brandt, Luca
2015-01-01T23:59:59.000Z
Sedimentation of a solid phase is widely encountered in applications and environmental flows, yet little is known about the behavior of finite-size particles in homogeneous isotropic turbulence. To fill this gap, we perform Direct Numerical Simulations of sedimentation in quiescent and turbulent environments using an Immersed Boundary Method to account for the dispersed rigid spherical particles. The solid volume fractions considered are 0.5-1%, while the solid to fluid density ratio is 1.02. The particle radius is chosen to be approximately 6 Komlogorov lengthscales. The results show that the mean settling velocity is lower in an already turbulent flow than in a still fluid. The reduction with respect to a single particle in quiescent fluid is about 12% and 14% for the two volume fractions investigated. The probability density function of the particle velocity is almost Gaussian in a turbulent flow, whereas it displays large positive tails in still fluid. These tails are associated to the rare fast sedimenta...
Turbulence in Global Simulations of Magnetized Thin Accretion Disks
Kris Beckwith; Philip J. Armitage; Jacob B. Simon
2011-05-09T23:59:59.000Z
We use a global magnetohydrodynamic simulation of a geometrically thin accretion disk to investigate the locality and detailed structure of turbulence driven by the magnetorotational instability (MRI). The model disk has an aspect ratio $H / R \\simeq 0.07$, and is computed using a higher-order Godunov MHD scheme with accurate fluxes. We focus the analysis on late times after the system has lost direct memory of its initial magnetic flux state. The disk enters a saturated turbulent state in which the fastest growing modes of the MRI are well-resolved, with a relatively high efficiency of angular momentum transport $ > \\approx 2.5 \\times 10^{-2}$. The accretion stress peaks at the disk midplane, above and below which exists a moderately magnetized corona with patches of superthermal field. By analyzing the spatial and temporal correlations of the turbulent fields, we find that the spatial structure of the magnetic and kinetic energy is moderately well-localized (with correlation lengths along the major axis of $2.5H$ and $1.5H$ respectively), and generally consistent with that expected from homogenous incompressible turbulence. The density field, conversely, exhibits both a longer correlation length and a long correlation time, results which we ascribe to the importance of spiral density waves within the flow. Consistent with prior results, we show that the mean local stress displays a well-defined correlation with the local vertical flux, and that this relation is apparently causal (in the sense of the flux stimulating the stress) during portions of a global dynamo cycle. We argue that the observed flux-stress relation supports dynamo models in which the structure of coronal magnetic fields plays a central role in determining the dynamics of thin-disk accretion.
Statistically Steady Turbulence in Soap Films: Direct Numerical Simulations with Ekman Friction
Prasad Perlekar; Rahul Pandit
2008-11-09T23:59:59.000Z
We present a detailed direct numerical simulation (DNS) designed to investigate the combined effects of walls and Ekman friction on turbulence in forced soap films. We concentrate on the forward-cascade regime and show how to extract the isotropic parts of velocity and vorticity structure functions and thence the ratios of multiscaling exponents. We find that velocity structure functions display simple scaling whereas their vorticity counterparts show multiscaling; and the probability distribution function of the Weiss parameter $\\Lambda$, which distinguishes between regions with centers and saddles, is in quantitative agreement with experiments.
Time-resolved gas temperatures in the oscillating turbulent flow of a pulse combustor tail pipe
Dec, J.E. (Michigan Univ., Ann Arbor, MI (USA)); Keller, J.O. (Sandia National Labs., Livermore, CA (USA). Combustion Research Faclity)
1990-06-01T23:59:59.000Z
This paper reports the cyclic behavior of the gas temperature in the oscillating turbulent flow in a pulse combustor tail pipe studied using two-line atomic fluorescence. In this flow, the oscillations result from an acoustic resonance, and have amplitudes of up to 5 times the mean velocity. Oscillation frequencies were varied from 67 to 101 Hz. Spatially resolved temperature measurements were made to within 400 {mu}m of the wall, providing cycle-resolved profiles of the temperature and the random temperature fluctuations. The combustor-cycle phase relationships among the gas temperature, random-temperature-fluctuation intensity, velocity, and combustion chamber pressure, are compared.
Test of the Fluctuation Relation in lagrangian turbulence on a free surface
M. M. Bandi; J. R. Cressman Jr.; W. I. Goldburg
2007-03-07T23:59:59.000Z
The statistics of lagrangian velocity divergence are studied for an assembly of particles in compressible turbulence on a free surface. Under an appropriate definition of entropy, the two-dimensional lagrangian velocity divergence of a particle trajectory represents the local entropy rate, a random variable. The statistics of this rate are shown to be in agreement with the fluctuation relation (FR) over a limited range. The probability distribution functions (PDFs) obtained in this analysis exhibit features different from those observed in previous experimental tests.
Statistical evidence for the existence of Alfvénic turbulence in solar coronal loops
Liu, Jiajia [Earth and Space Science School, University of Science and Technology of China, No. 96, JinZhai Road, Hefei (China); McIntosh, Scott W.; Bethge, Christian [High Altitude Observatory, National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307 (United States); De Moortel, Ineke; Threlfall, James, E-mail: ljj128@mail.ustc.edu.cn [School of Mathematics and Statistics, University of St Andrews, St Andrews, Fife KY16 9SS (United Kingdom)
2014-12-10T23:59:59.000Z
Recent observations have demonstrated that waves capable of carrying large amounts of energy are ubiquitous throughout the solar corona. However, the question of how this wave energy is dissipated (on which timescales and length scales) and released into the plasma remains largely unanswered. Both analytic and numerical models have previously shown that Alfvénic turbulence may play a key role not only in the generation of the fast solar wind, but in the heating of coronal loops. In an effort to bridge the gap between theory and observations, we expand on a recent study by analyzing 37 clearly isolated coronal loops using data from the Coronal Multi-channel Polarimeter instrument. We observe Alfvénic perturbations with phase speeds which range from 250 to 750 km s{sup –1} and periods from 140 to 270 s for the chosen loops. While excesses of high-frequency wave power are observed near the apex of some loops (tentatively supporting the onset of Alfvénic turbulence), we show that this excess depends on loop length and the wavelength of the observed oscillations. In deriving a proportional relationship between the loop length/wavelength ratio and the enhanced wave power at the loop apex, and from the analysis of the line widths associated with these loops, our findings are supportive of the existence of Alfvénic turbulence in coronal loops.
Contents lists available at ScienceDirect. Wave Motion .... The mudstone layers are fully saturated with water and their properties are frequency independent.
Energy spectra of the ocean's internal wave field: theory and observations
Yuri V. Lvov; Kurt L. Polzin; Esteban G. Tabak
2003-12-30T23:59:59.000Z
The high-frequency limit of the Garrett and Munk spectrum of internal waves in the ocean and the observed deviations from it are shown to form a pattern consistent with the predictions of wave turbulence theory. In particular, the high frequency limit of the Garrett and Munk spectrum constitutes an {\\it exact} steady state solution of the corresponding kinetic equation.
Effects of shock topology on temperature field in compressible turbulence
Ni, Qionglin
2015-01-01T23:59:59.000Z
Effects of two types of shock topology, namely, small-scale shocklet and large-scale shock wave, on the statistics of temperature in compressible turbulence were investigated by simulations. The shocklet and shock wave are caused by the solenoidal and compressive modes of driven forces, respectively. Hereafter, the related two flows are called as SFT and CFT, respectively. It shows that in SFT the temperature spectrum follows the k^-5/3 power law, and the temperature field has "ramp-cliff" structures. By contrast, in CFT the temperature spectrum obeys the k^-2 power law, and the temperature field is dominated by large-scale rarefaction and compression. The power-law exponents for the p.d.f. of large negative dilatation are -2.5 in SFT and -3.5 in CFT, close to theoretical values. For the isentropic assumption of thermodynamic variables, the derivation in SFT grows with the turbulent Mach number (Mt), and for same Mt, the variables in CFT are more anisentropic. The angle statistics shows that the temperature g...
Deep-water gravity waves: theoretical estimating of wave parameters
Mindlin, Ilia M
2014-01-01T23:59:59.000Z
This paper addresses deep-water gravity waves of finite amplitude generated by an initial disturbance to the water. It is assumed that the horizontal dimensions of the initially disturbed body of the water are much larger than the magnitude of the free surface displacement in the origin of the waves. Initially the free surface has not yet been displaced from its equilibrium position, but the velocity field has already become different from zero. This means that the water at rest initially is set in motion suddenly by an impulse. Duration of formation of the wave origin and the maximum water elevation in the origin are estimated using the arrival times of the waves and the maximum wave-heights at certain locations obtained from gauge records at the locations, and the distances between the centre of the origin and each of the locations. For points situated at a long distance from the wave origin, forecast is made for the travel time and wave height at the points. The forecast is based on the data recorded by th...
Léonie Canet; Bertrand Delamotte; Nicolás Wschebor
2014-11-28T23:59:59.000Z
We investigate the regime of fully developed homogeneous turbulence of the Navier-Stokes (NS) equation in the presence of a stochastic forcing. Using the nonperturbative (functional) version of the renormalization group (NPRG), we avoid all the difficulties that plague standard RG approaches to NS turbulence and have hindered real progress in the calculation of multi-scaling. We obtain the fixed point solution of the NPRG flow equations, which corresponds to fully developed turbulence, in $d=2$ and $d=3$ dimensions. The striking feature of this fixed point is that it does not entail the usual scale invariance, because of the absence of a regular limit when the integral scale (the typical length scale of energy injection) tends to infinity. We indeed show, on the basis of exact flow equations in the large wave-number limit, how violations to the Kolmogorov scaling can emerge, leaving the accurate determination of the ensuing intermittent exponents for future work.
Double Kelvin Wave Cascade in Superfluid Helium
G. Boffetta; A. Celani; D. Dezzani; J. Laurie; S. Nazarenko
2008-10-20T23:59:59.000Z
We study the double cascade of energy and wave action in a local model of superfluid vortex filaments. The model is obtained from a truncated expansion of the 2D Local Induction Approximation and it is shown to support six-wave interactions. We argue that, because of the uncertainty in the vortex core profile, this model has the same status of validity as the traditionally used Biot-Savart model with cutoff, but it has advantage of being much simpler. Our minimal model leads to a wave kinetic equation for which we predict existence of two distinct power-law scaling in the spectrum, corresponding to a direct cascade of energy and an inverse one of wave action. Direct numerical simulations confirm the theoretical predictions in the weak turbulence regime.
Active control for turbulent premixed flame simulations
Bell, John B.; Day, Marcus S.; Grcar, Joseph F.; Lijewski, Michael J.
2004-03-26T23:59:59.000Z
Many turbulent premixed flames of practical interest are statistically stationary. They occur in combustors that have anchoring mechanisms to prevent blow-off and flashback. The stabilization devices often introduce a level of geometric complexity that is prohibitive for detailed computational studies of turbulent flame dynamics. As a result, typical detailed simulations are performed in simplified model configurations such as decaying isotropic turbulence or inflowing turbulence. In these configurations, the turbulence seen by the flame either decays or, in the latter case, increases as the flame accelerates toward the turbulent inflow. This limits the duration of the eddy evolutions experienced by the flame at a given level of turbulent intensity, so that statistically valid observations cannot be made. In this paper, we apply a feedback control to computationally stabilize an otherwise unstable turbulent premixed flame in two dimensions. For the simulations, we specify turbulent in flow conditions and dynamically adjust the integrated fueling rate to control the mean location of the flame in the domain. We outline the numerical procedure, and illustrate the behavior of the control algorithm. We use the simulations to study the propagation and the local chemical variability of turbulent flame chemistry.