Turbulent diffusion and turbulent thermal diffusion of aerosols in stratified atmospheric flows
Elperin, Tov
Turbulent diffusion and turbulent thermal diffusion of aerosols in stratified atmospheric flows M to the turbulent diffusion, and its potential impact on aerosol distribution. This phenomenon was predicted a nondiffusive flux of aerosols in the direction of the heat flux and results in formation of long-living aerosol
Forced turbulence in thermally bistable gas: A parameter study
Seifried, D; Niemeyer, J C
2010-01-01T23:59:59.000Z
Context: The thermal instability is one of the dynamical agents for turbulence in the diffuse interstellar medium, where both, turbulence and thermal instability interact in a highly non-linear manner. Aims: We study basic properties of turbulence in thermally bistable gas for variable simulation parameters. The resulting cold gas fractions can be applied as parameterisation in simulations on galactic scales. Methods: Turbulent flow is induced on large scales by means of compressive stochastic forcing in a periodic box. The compressible Euler equations with constant UV heating and a parameterised cooling function are solved on uniform grids. We investigate several values of the mean density of the gas and different magnitudes of the forcing. For comparison with other numerical studies, solenoidal forcing is applied as well. Results: After a transient phase, we observe that a state of statistically stationary turbulence is approached. Compressive forcing generally produces a two-phase medium, with a decreasing...
Thermal Instability-Induced Interstellar Turbulence 1 Alexei Kritsuk
Kritsuk, Alexei
Thermal Instability-Induced Interstellar Turbulence 1 Alexei Kritsuk University of California, San Diego, USA Saint Petersburg State University, Russia In collaboration with Mike Norman, UCSD http://akpc.ucsd.edu/Thermal conditions: periodic box Parameters: box size L, 0, T0, heating rate , = 5 3 , metallicity Z = Z Thermal
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...
Progress in Simulating Turbulent Electron Thermal Transport in NSTX
Guttenfelder, Walter; Kaye, S. M.; Ren, Y.; Bell, R. E.; Hammett, G. W.; LeBlanc, B. P.; Mikkelsen, D. R. [Princeton Plasma Physics Lab., Princeton, NJ (United States); Peterson, J. L.; Nevins, W. M. [Lawrence Livermore National Lab., Livermore, CA (United States); Candy, J. [General Atomics, San Diego, CA (United States); Yuh, H. [Nova Photonics, Princeton, NJ (United States)
2013-07-17T23:59:59.000Z
Nonlinear simulations based on multiple NSTX discharge scenarios have progressed to help differentiate unique instability mechanisms and to validate with experimental turbulence and transport data. First nonlinear gyrokinetic simulations of microtearing (MT) turbulence in a high-beta NSTX H-mode discharge predict experimental levels of electron thermal transport that are dominated by magnetic flutter and increase with collisionality, roughly consistent with energy confinement times in dimensionless collisionality scaling experiments. Electron temperature gradient (ETG) simulations predict significant electron thermal transport in some low and high beta discharges when ion scales are suppressed by E x B shear. Although the predicted transport in H-modes is insensitive to variation in collisionality (inconsistent with confinement scaling), it is sensitive to variations in other parameters, particularly density gradient stabilization. In reversed shear (RS) Lmode discharges that exhibit electron internal transport barriers, ETG transport has also been shown to be suppressed nonlinearly by strong negative magnetic shear, s<<0. In many high beta plasmas, instabilities which exhibit a stiff beta dependence characteristic of kinetic ballooning modes (KBM) are sometimes found in the core region. However, they do not have a distinct finite beta threshold, instead transitioning gradually to a trapped electron mode (TEM) as beta is reduced to zero. Nonlinear simulations of this "hybrid" TEM/KBM predict significant transport in all channels, with substantial contributions from compressional magnetic perturbations. As multiple instabilities are often unstable simultaneously in the same plasma discharge, even on the same flux surface, unique parametric dependencies are discussed which may be useful for distinguishing the different mechanisms experimentally.
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.
Transition from thermal to turbulent equilibrium with a resulting electromagnetic spectrum
Ziebell, L. F., E-mail: luiz.ziebell@ufrgs.br [Instituto de Física, UFRGS, Porto Alegre, RS (Brazil); Yoon, P. H. [Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742 (United States) [Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742 (United States); School of Space Research, Kyung Hee University, Yongin, Gyeonggi 446-701 (Korea, Republic of); Gaelzer, R. [Instituto de Física, UFRGS, Porto Alegre, RS (Brazil) [Instituto de Física, UFRGS, Porto Alegre, RS (Brazil); Instituto de Física e Matemática, UFPel, Pelotas, RS (Brazil); Pavan, J. [Instituto de Física e Matemática, UFPel, Pelotas, RS (Brazil)] [Instituto de Física e Matemática, UFPel, Pelotas, RS (Brazil)
2014-01-15T23:59:59.000Z
A recent paper [Ziebell et al., Phys. Plasmas 21, 010701 (2014)] discusses a new type of radiation emission process for plasmas in a state of quasi-equilibrium between the particles and enhanced Langmuir turbulence. Such a system may be an example of the so-called “turbulent quasi-equilibrium.” In the present paper, it is shown on the basis of electromagnetic weak turbulence theory that an initial thermal equilibrium state (i.e., only electrostatic fluctuations and Maxwellian particle distributions) transitions toward the turbulent quasi-equilibrium state with enhanced electromagnetic radiation spectrum, thus demonstrating that the turbulent quasi-equilibrium discussed in the above paper correctly describes the weakly turbulent plasma dynamically interacting with electromagnetic fluctuations, while maintaining a dynamical steady-state in the average sense.
Regulation of thermal conductivity in hot galaxy clusters by MHD turbulence
Steven A. Balbus; Christopher S. Reynolds
2008-06-05T23:59:59.000Z
The role of thermal conduction in regulating the thermal behavior of cooling flows in galaxy clusters is reexamined. Recent investigations have shown that the anisotropic Coulomb heat flux caused by a magnetic field in a dilute plasma drives a dynamical instability. A long standing problem of cooling flow theory has been to understand how thermal conduction can offset radiative core losses without completely preventing them. In this Letter we propose that magnetohydrodynamic turbulence driven by the heat flux instability regulates field-line insulation and drives a reverse convective thermal flux, both of which may mediate the stabilization of the cooling cores of hot clusters. This model suggests that turbulent mixing should accompany strong thermal gradients in cooling flows. This prediction seems to be supported by the spatial distribution of metals in the central galaxies of clusters, which shows a much stronger correlation with the ambient hot gas temperature gradient than with the parent stellar population.
Optimal thermalization in a shell model of homogeneous turbulence
Thalabard, Simon
2015-01-01T23:59:59.000Z
We investigate the turbulence-induced dissipation of the large scales in a statistically homogeneous flow using an "optimal closure," which one of us (BT) has recently exposed in the context of Hamiltonian dynamics. This statistical closure employs a Gaussian model for the turbulent scales, with corresponding vanishing third cumulant, and yet it captures an intrinsic damping. The key to this apparent paradox lies in a clear distinction between true ensemble averages and their proxies, most easily grasped when one works directly with the Liouville equation rather than the cumulant hierarchy. We focus on a simple problem for which the optimal closure can be fully and exactly worked out: the relaxation arbitrarily far-from-equilibrium of a single energy shell towards Gibbs equilibrium in an inviscid shell model of 3D turbulence. The predictions of the optimal closure are validated against DNS and contrasted with those derived from EDQNM closure.
Logarithmic corrections to scaling in turbulent thermal convection
B. Dubrulle
2001-01-04T23:59:59.000Z
We use an analytic toy model of turbulent convection to show that most of the scaling regimes are spoiled by logarithmic corrections, in a way consistent with the most accurate experimental measurements available nowadays. This sets a need for the search of new measurable quantities which are less prone to dimensional theories.
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
Turbulent thermalization process in high-energy heavy-ion collisions
Jürgen Berges; Björn Schenke; Sören Schlichting; Raju Venugopalan
2014-09-05T23:59:59.000Z
We discuss the onset of the thermalization process in high-energy heavy-ion collisions from a weak coupling perspective, using classical-statistical real-time lattice simulations as a first principles tool to study the pre-equilibrium dynamics. Most remarkably, we find that the thermalization process is governed by a universal attractor, where the space-time evolution of the plasma becomes independent of the initial conditions and exhibits the self-similar dynamics characteristic of wave turbulence. We discuss the consequences of our weak coupling results for the thermalization process in heavy-ion experiments and briefly comment on the use of weak coupling techniques at larger values of the coupling.
Turbulent thermalization process in heavy-ion collisions at ultrarelativistic energies
J. Berges; K. Boguslavski; S. Schlichting; R. Venugopalan
2014-03-02T23:59:59.000Z
The non-equilibrium evolution of heavy-ion collisions is studied in the limit of weak coupling at very high energy employing lattice simulations of the classical Yang-Mills equations. Performing the largest classical-statistical simulations to date, we find that the dynamics of the longitudinally expanding plasma becomes independent of the details of the initial conditions. After a transient regime dominated by plasma instabilities and free streaming, the subsequent space-time evolution is governed by a nonthermal fixed point, where the system exhibits the self-similar dynamics characteristic of wave turbulence. This allows us to distinguish between different kinetic scenarios in the classical regime. Within the accuracy of our simulations, the scaling behavior found is consistent with the ``bottom-up" thermalization scenario.
Ando, Yasutaka; Tobe, Shogo [Ashikaga Institute of Technology, 268-1 Omae, Ashikaga, Tochigi 326-8558 (Japan); Tahara, Hirokazu [Osaka Institute of Technology, 5-16-1 Omiya, Asahi-Ku, Osaka 535-8585 (Japan)
2008-02-21T23:59:59.000Z
In this study, to provide continuous plasma atmosphere on the substrate surface in the case of atmospheric thermal plasma CVD, TiO{sub 2} film deposition by thermal plasma CVD using laminar plasma jet was carried out. For comparison, the film deposition using turbulence plasma jet was conducted as well. Consequently, transition of the plasma jet from laminar to turbulent occurred on the condition of over 3.5 1/min in Ar working gas flow rate and the plasma jet became turbulent on the condition of over 10 1/min. In the case of the turbulent plasma jet use, anatase rich titanium oxide film could be obtained though plasma jet could not contact with the surface of the substrate continuously even on the condition that feedstock material was injected into the plasma jet. On the other hand,, in the case of laminar gas flow rate, the plasma jet could contact with the substrate continuously without melt down of the substrate during film deposition. Besides, titanium oxide film could be obtained even in the case of the laminar plasma jet use. From these results, this technique was thought to have high potential for atmospheric thermal plasma CVD.
Polymer heat transport enhancement in thermal convection: the case of Rayleigh-Taylor turbulence
G. Boffetta; A. Mazzino; S. Musacchio; L. Vozella
2010-01-19T23:59:59.000Z
We study the effects of polymer additives on turbulence generated by the ubiquitous Rayleigh-Taylor instability. Numerical simulations of complete viscoelastic models provide clear evidence that the heat transport is enhanced up to 50% with respect to the Newtonian case. This phenomenon is accompanied by a speed up of the mixing layer growth. We give a phenomenological interpretation of these results based on small-scale turbulent reduction induced by polymers.
Isolation of Metals from Liquid Wastes: Reactive Scavenging in Turbulent Thermal Reactors
Jost O.L. Wendt; Alan R. Kerstein; Alexander Scheeline; Arne Pearlstein; William Linak
2003-08-06T23:59:59.000Z
The Overall project demonstrated that toxic metals (cesium Cs and strontium Sr) in aqueous and organic wastes can be isolated from the environment through reaction with kaolinite based sorbent substrates in high temperature reactor environments. In addition, a state-of-the art laser diagnostic tool to measure droplet characteristic in practical 'dirty' laboratory environments was developed, and was featured on the cover of a recent edition of the scientific journal ''applied Spectroscopy''. Furthermore, great strides have been made in developing a theoretical model that has the potential to allow prediction of the position and life history of every particle of waste in a high temperature, turbulent flow field, a very challenging problem involving as it does, the fundamentals of two phase turbulence and of particle drag physics.
Large-eddy simulations of isolated disc galaxies with thermal and turbulent feedback
Braun, Harald; Niemeyer, Jens C; Almgren, Ann S
2014-01-01T23:59:59.000Z
We present a subgrid-scale model for the Multi-phase Interstellar medium, Star formation, and Turbulence (MIST) and explore its behaviour in high-resolution large-eddy simulations of isolated disc galaxies. MIST follows the evolution of a clumpy cold and a diffuse warm component of the gas within a volume element which exchange mass and energy via various cooling, heating and mixing processes. The star formation rate is dynamically computed from the state of the gas in the cold phase. An important feature of MIST is the treatment of unresolved turbulence in the two phases and its interaction with star formation and feedback by supernovae. This makes MIST a particularly suitable model for the interstellar medium in galaxy simulations. We carried out a suite of simulations varying fundamental parameters of our feedback implementation. Several observational properties of galactic star formation are reproduced in our simulations, such as an average star formation efficiency ~1%, a typical velocity dispersion arou...
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Eiamsa-ard, Smith [Department of Mechanical Engineering, Faculty of Engineering, Mahanakorn University of Technology, Bangkok 10530 (Thailand); Seemawute, Panida [Department of Civil Engineering, Faculty of Engineering, Mahanakorn University of Technology, Bangkok 10530 (Thailand); Wongcharee, Khwanchit [Department of Chemical Engineering, Faculty of Engineering, Mahanakorn University of Technology, Bangkok 10530 (Thailand)
2010-09-15T23:59:59.000Z
Effects of peripherally-cut twisted tape insert on heat transfer, friction loss and thermal performance factor characteristics in a round tube were investigated. Nine different peripherally-cut twisted tapes with constant twist ratio (y/W = 3.0) and different three tape depth ratios (DR = d/W = 0.11, 0.22 and 0.33), each with three different tape width ratios (WR = w/W = 0.11, 0.22 and 0.33) were tested. Besides, one typical twisted tape was also tested for comparison. The measurement of heat transfer rate was conducted under uniform heat flux condition while that of friction factor was performed under isothermal condition. Tests were performed with Reynolds number in a range from 1000 to 20,000, using water as a working fluid. The experimental results revealed that both heat transfer rate and friction factor in the tube equipped with the peripherally-cut twisted tapes were significantly higher than those in the tube fitted with the typical twisted tape and plain tube, especially in the laminar flow regime. The higher turbulence intensity of fluid in the vicinity of the tube wall generated by the peripherally-cut twisted tape compared to that induced by the typical twisted tape is referred as the main reason for achieved results. The obtained results also demonstrated that as the depth ratio increased and width ratio decreased, the heat transfer enhancement increased. Over the range investigated, the peripherally-cut twisted tape enhanced heat transfer rates in term of Nusselt numbers up to 2.6 times (turbulent regime) and 12.8 times (laminar regime) of that in the plain tube. These corresponded to the maximum performance factors of 1.29 (turbulent regime) and 4.88 (laminar regime). (author)
Turbulent electron transport in edge pedestal by electron temperature gradient turbulence
Singh, R. [WCI Center for Fusion Theory, National Fusion Research Institute, Daejeon 305-333 (Korea, Republic of) [WCI Center for Fusion Theory, National Fusion Research Institute, Daejeon 305-333 (Korea, Republic of); Institute for Plasma Research, Bhat Gandhinagar, Gujarat 2382 428 (India); Jhang, Hogun [WCI Center for Fusion Theory, National Fusion Research Institute, Daejeon 305-333 (Korea, Republic of)] [WCI Center for Fusion Theory, National Fusion Research Institute, Daejeon 305-333 (Korea, Republic of); Diamond, P. H. [WCI Center for Fusion Theory, National Fusion Research Institute, Daejeon 305-333 (Korea, Republic of) [WCI Center for Fusion Theory, National Fusion Research Institute, Daejeon 305-333 (Korea, Republic of); CMTFO and CASS, University of California, San Diego 92093-0424, California (United States)
2013-11-15T23:59:59.000Z
We present a model for turbulent electron thermal transport at the edge pedestal in high (H)-mode plasmas based on electron temperature gradient (ETG) turbulence. A quasi-linear analysis of electrostatic toroidal ETG modes shows that both turbulent electron thermal diffusivity and hyper-resistivity exhibits the Ohkawa scaling in which the radial correlation length of turbulence becomes the order of electron skin depth. Combination of the Ohkawa scales and the plasma current dependence results in a novel confinement scaling inside the pedestal region. It is also shown that ETG turbulence induces a thermoelectric pinch, which may accelerate the density pedestal formation.
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...
Solar Wind Electrons and Langmuir Turbulence , D.E. Larson
California at Berkeley, University of
electron VDFs contain high-energy tail [9] which is typically described as thermal core plus superthermal are in dynamical equilibrium with quasi-thermal noise turbulence. Customary theories of superthermal electrons
TURBULENT FRBRNNING MVK130 Turbulent Combustion
TURBULENT FÖRBRÄNNING MVK130 Turbulent Combustion Poäng: 3.0 Betygskala: TH Valfri för: M4 to combustion, McGraw-Hill 1996. #12;
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.
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
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.
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...
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.
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.
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.
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.
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.
Literature Review of Airflow Fluid Characteristics and their Impact on Human Thermal Comfort
Zhao, R.; Zhang, Y.; Yu, N.; Di, H.
2006-01-01T23:59:59.000Z
Airflow dynamics significantly impact indoor thermal environment and human thermal comfort. Studies on the effects of airflow fluctuations on thermal comfort mainly focus on the effects of turbulence intensity and fluctuation frequency...
Contribution to the numerical study of turbulence in high intensity discharge lamps
Kaziz, S.; Ben Ahmed, R.; Helali, H.; Gazzah, H.; Charrada, K. [Unite d'Etude des Milieux Ionises et Reactifs, IPEIM, 5019 route de Kairouan Monastir (Tunisia)
2011-07-15T23:59:59.000Z
We present in this paper a comparison between results obtained with a laminar and turbulent models for high-pressure mercury arc. The two models are based on the resolution of bidimensional time-dependent equations by a semi-implicit finite-element code. The numerical computation of turbulent model is solved with large eddy simulation model; this approach takes into account the various scales of turbulence by a filtering method on each scale. The results show the quantitative influence of turbulence on the flow fields and also the difference between laminar and turbulent effects on the dynamic thermal behaviour and on the characteristics of the discharge.
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.
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.
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
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.
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
Center for Turbulence Research Annual Research Briefs 2008
Prinz, Friedrich B.
combustion instability, and unsteady high temperature streaks at the combustor exit cause thermal failure of turbulent combustion in a gas turbine engine combustor By D. You, F. Ham AND P. Moin 1. Motivation to a significant change in mass flow rate; separation of compressor wakes in the combustor pre-diffuser can induce
Turbulent heating of the corona and solar wind: the heliospheric
Turbulent heating of the corona and solar wind: the heliospheric dark energy problem Stuart D. Bale and Solar Wind · There are very few collisions in the solar wind · Not in thermal equilibrium · Large' Photospheric blackbody ~5000-6000K Sunspots and `active regions' #12;Impulsive Solar Activity - `Carrington
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 ...
Jia, S.; Chung, B.T.F. [Univ. of Akron, OH (United States). Dept. of Mechanical Engineering
1996-12-31T23:59:59.000Z
Based on a previously proposed non-linear turbulence model, a turbulent heat transfer model is formulated in the present study using the concept of Generalized Gradient Diffusion (GGD) hypothesis. Under this hypothesis, an anisotropic thermal diffusivity can be obtained through the proposed non-linear turbulent model which is applied to the turbulent flow and heat transfer in a sudden expansion pipe with a constant heat flux through the pipe wall. The numerical results are compared with the available experimental data for both turbulent and thermal quantities, with an emphasis on the non-linear heat transfer predictions. The improved results are obtained for the bulk temperature distribution showing that the present non-linear heat transfer model is capable of predicting the anisotropic turbulent heat transfer for the pipe expansion flow. Some limits of the proposed model are also identified and discussed.
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.
PLASMA EMISSION BY WEAK TURBULENCE PROCESSES
Ziebell, L. F.; Gaelzer, R. [Instituto de Física, UFRGS, Porto Alegre, RS (Brazil); Yoon, P. H. [Institute for Physical Science and Technology, University of Maryland, College Park, MD (United States); Pavan, J., E-mail: luiz.ziebell@ufrgs.br, E-mail: rudi.gaelzer@ufrgs.br, E-mail: yoonp@umd.edu, E-mail: joel.pavan@ufpel.edu.br [Instituto de Física e Matemática, UFPel, Pelotas, RS (Brazil)
2014-11-10T23:59:59.000Z
The plasma emission is the radiation mechanism responsible for solar type II and type III radio bursts. The first theory of plasma emission was put forth in the 1950s, but the rigorous demonstration of the process based upon first principles had been lacking. The present Letter reports the first complete numerical solution of electromagnetic weak turbulence equations. It is shown that the fundamental emission is dominant and unless the beam speed is substantially higher than the electron thermal speed, the harmonic emission is not likely to be generated. The present findings may be useful for validating reduced models and for interpreting particle-in-cell simulations.
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)
Muradoglu, Metin
and pollution are directly related to the conversion of chemical energy into thermal energy via combustion Available online 10 September 2014 Keywords: PDF methods Consistent hybrid method Turbulent combustion Bluff rights reserved. 1. Introduction Turbulent combustion continues to be a key technology in energy
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.
Magnetic turbulent electron transport in a reversed field pinch
Schoenberg, K.; Moses, R.
1990-01-01T23:59:59.000Z
A model of magnetic turbulent electron transport is presented. The model, based on the thermal conduction theory of Rechester and Rosenbluth, entails a Boltzmann description of electron dynamics in the long mean-free-path limit and quantitatively describes the salient features of superthermal electron measurements in the RFP edge plasma. Included are predictions of the mean superthermal electron energy, current density, and power flux asymmetry. A discussion of the transport model, the assumptions implicit in the model, and the relevance of this work to more general issue of magnetic turbulent transport in toroidal systems is presented. 32 refs., 3 figs.
A Critical "Dimension" in a Shell Model for Turbulence
Paolo Giuliani; Mogens H. Jensen; Victor Yakhot
2001-02-08T23:59:59.000Z
We investigate the GOY shell model within the scenario of a critical dimension in fully developed turbulence. By changing the conserved quantities, one can continuously vary an ``effective dimension'' between $d=2$ and $d=3$. We identify a critical point between these two situations where the flux of energy changes sign and the helicity flux diverges. Close to the critical point the energy spectrum exhibits a turbulent scaling regime followed by a plateau of thermal equilibrium. We identify scaling laws and perform a rescaling argument to derive a relation between the critical exponents. We further discuss the distribution function of the energy flux.
Hall MHD Stability and Turbulence in Magnetically Accelerated Plasmas
H. R. Strauss
2012-11-27T23:59:59.000Z
The object of the research was to develop theory and carry out simulations of the Z pinch and plasma opening switch (POS), and compare with experimental results. In the case of the Z pinch, there was experimental evidence of ion kinetic energy greatly in excess of the ion thermal energy. It was thought that this was perhaps due to fine scale turbulence. The simulations showed that the ion energy was predominantly laminar, not turbulent. Preliminary studies of a new Z pinch experiment with an axial magnetic field were carried out. The axial magnetic is relevant to magneto - inertial fusion. These studies indicate the axial magnetic field makes the Z pinch more turbulent. Results were also obtained on Hall magnetohydrodynamic instability of the POS.
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.
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.
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.
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)
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...
Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)
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
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.
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.
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.
Thermal-hydraulic analysis of cross-shaped spiral fuel in high power density BWRs
Conboy, Thomas M
2007-01-01T23:59:59.000Z
Preliminary analysis of the cross-shaped spiral (CSS) fuel assembly suggests great thermal-hydraulic upside. According to computational models, the increase in rod surface area, combined with an increase in coolant turbulence ...
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.
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.
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...
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.
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
Karnes, T.E.; Trupin, R.J.
1984-01-03T23:59:59.000Z
A thermal engine utilizing a strip of nitinol material or other thermally responsive shape memory effect material to drive a reciprocating output shaft, said strip of material forming a common wall between two different alternating temperature sources which thermally cycle the material.
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.
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
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.
Elementary Vortex Processes in Thermal Superfluid Turbulence
Kivotides, Demosthenes; Wilkin, S. Louise
2009-01-01T23:59:59.000Z
a complex system of vortex tubes has only (a vigorouslyIn this context, the vortex tube model (VTM) of Kivotidesstraight normal ?uid vortex tube, suggested an explicit
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.
Georgi Pavlovski; Michael D. Smith; Mordecai-Mark Mac Low; Alexander Rosen
2002-08-15T23:59:59.000Z
We present the results from three dimensional hydrodynamical simulations of decaying high-speed turbulence in dense molecular clouds. We compare our results, which include a detailed cooling function, molecular hydrogen chemistry and a limited C and O chemistry, to those previously obtained for decaying isothermal turbulence. After an initial phase of shock formation, power-law decay regimes are uncovered, as in the isothermal case. We find that the turbulence decays faster than in the isothermal case because the average Mach number remains higher, due to the radiative cooling. The total thermal energy, initially raised by the introduction of turbulence, decays only a little slower than the kinetic energy. We discover that molecule reformation, as the fast turbulence decays, is several times faster than that predicted for a non-turbulent medium. This is caused by moderate speed shocks which sweep through a large fraction of the volume, compressing the gas and dust. Through reformation, the molecular density and molecular column appear as complex patterns of filaments, clumps and some diffuse structure. In contrast, the molecular fraction has a wider distribution of highly distorted clumps and copious diffuse structure, so that density and molecular density are almost identically distributed during the reformation phase. We conclude that molecules form in swept-up clumps but effectively mix throughout via subsequent expansions and compressions.
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
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
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.
Magnetic shear-driven instability and turbulent mixing in magnetized protostellar disks
Bonanno, Alfio
2008-01-01T23:59:59.000Z
Observations of protostellar disks indicate the presence of the magnetic field of thermal (or superthermal) strength. In such a strong magnetic field, many MHD instabilities responsible for turbulent transport of the angular momentum are suppressed. We consider the shear-driven instability that can occur in protostellar disks even if the field is superthermal. This instability is caused by the combined influence of shear and compressibility in a magnetized gas and can be an efficient mechanism to generate turbulence in disks. The typical growth time is of the order of several rotation periods.
Magnetic shear-driven instability and turbulent mixing in magnetized protostellar disks
Alfio Bonanno; Vadim Urpin
2008-01-13T23:59:59.000Z
Observations of protostellar disks indicate the presence of the magnetic field of thermal (or superthermal) strength. In such a strong magnetic field, many MHD instabilities responsible for turbulent transport of the angular momentum are suppressed. We consider the shear-driven instability that can occur in protostellar disks even if the field is superthermal. This instability is caused by the combined influence of shear and compressibility in a magnetized gas and can be an efficient mechanism to generate turbulence in disks. The typical growth time is of the order of several rotation periods.
The high-energy-density counterpropagating shear experiment and turbulent self-heating
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Doss, F. W.; Fincke, J. R.; Loomis, E. N.; Welser-Sherrill, L.; Flippo, K. A.
2013-12-06T23:59:59.000Z
The counterpropagating shear experiment has previously demonstrated the ability to create regions of shockdriven shear, balanced symmetrically in pressure and experiencing minimal net drift. This allows for the creation of a high-Mach-number high-energy-density shear environment. New data from the counterpropagating shear campaign is presented, and both hydrocode modeling and theoretical analysis in the context of a Reynolds-averaged-Navier-Stokes model suggest turbulent dissipation of energy from the supersonic flow bounding the layer is a significant driver in its expansion. A theoretical minimum shear flow Mach number threshold is suggested for substantial thermal-turbulence coupling.
Turbulence Modelling and Stirring Mechanisms in the Cosmological Large-scale Structure
Iapichino, L; Niemeyer, J C; Merklein, J
2011-01-01T23:59:59.000Z
FEARLESS (Fluid mEchanics with Adaptively Refined Large Eddy SimulationS) is a numerical scheme for modelling subgrid-scale turbulence in cosmological adaptive mesh refinement simulations. In this contribution, the main features of this tool will be outlined. We discuss the application of this method to cosmological simulations of the large-scale structure. The simulations show that the production of turbulence has a different redshift dependence in the intra-cluster medium and the warm-hot intergalactic medium, caused by the distinct stirring mechanisms (mergers and shock interactions) acting in them. Some properties of the non-thermal pressure support in the two baryon phases are also described.
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...
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 ...
Kandlikar, Satish
rates in the presence of thermal convection should have been nearly the same as those measured under iso in the Interfacial Boundary Layer Measured in an Open Tank of Water in Turbulent Free Convection," J. Fluid Meek Vol
Wind reversals in turbulent Rayleigh-Benard convection
Francisco Fontenele Araujo; S. Grossmann; D. Lohse
2005-08-29T23:59:59.000Z
The phenomenon of irregular cessation and subsequent reversal of the large-scale circulation in turbulent Rayleigh-B\\'enard convection is theoretically analysed. The force and thermal balance on a single plume detached from the thermal boundary layer yields a set of coupled nonlinear equations, whose dynamics is related to the Lorenz equations. For Prandtl and Rayleigh numbers in the range $10^{-2} \\leq \\Pr \\leq 10^{3}$ and $10^{7} \\leq \\Ra \\leq 10^{12}$, the model has the following features: (i) chaotic reversals may be exhibited at Ra $\\geq 10^{7}$; (ii) the Reynolds number based on the root mean square velocity scales as $\\Re_{rms} \\sim \\Ra^{[0.41 ... 0.47]}$ (depending on Pr), and as $\\Re_{rms} \\sim \\Pr^{-[0.66 ... 0.76]}$ (depending on Ra); and (iii) the mean reversal frequency follows an effective scaling law $\\omega / (\
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.
Reprocessing of Ices in Turbulent Protoplanetary Disks: Carbon and Nitrogen Chemistry
Furuya, Kenji
2014-01-01T23:59:59.000Z
We study the influence of the turbulent transport on ice chemistry in protoplanetary disks, focusing on carbon and nitrogen bearing molecules. Chemical rate equations are solved with the diffusion term, mimicking the turbulent mixing in the vertical direction. Turbulence can bring ice-coated dust grains from the midplane to the warm irradiated disk surface, and the ice mantles are reprocessed by photoreactions, thermal desorption, and surface reactions. The upward transport decreases the abundance of methanol and ammonia ices at r reprocessing could explain the smaller abundances of carbon and nitrogen bearing molecules in cometary coma than those in low-mass protostellar envelopes. We also show the effect of mixing on the synthesis of complex organic molecules (COMs) are two ways: (1) transport of ices from the midplane to the disk surface and (2) transport of atomic hydrogen from the surface to the midplane. The fo...
Improved detection of atmospheric turbulence with SLODAR
Michael Goodwin; Charles Jenkins; Andrew Lambert
2007-06-19T23:59:59.000Z
We discuss several improvements in the detection of atmospheric turbulence using SLOpe Detection And Ranging (SLODAR). Frequently, SLODAR observations have shown strong ground-layer turbulence, which is beneficial to adaptive optics. We show that current methods which neglect atmospheric propagation effects can underestimate the strength of high altitude turbulence by up to ~ 30%. We show that mirror and dome seeing turbulence can be a significant fraction of measured ground-layer turbulence, some cases up to ~ 50%. We also demonstrate a novel technique to improve the nominal height resolution, by a factor of 3, called Generalized SLODAR. This can be applied when sampling high-altitude turbulence, where the nominal height resolution is the poorest, or for resolving details in the important ground-layer.
Quantifying Turbulence for Tidal Power Applications
Thomson, Jim; Richmond, Marshall C.; Polagye, Brian; Durgesh, Vibhav
2010-08-01T23:59:59.000Z
Using newly collected data from a tidal power site in Puget Sound, WA, metrics for turbulence quantification are assessed and discussed. The quality of raw ping Acoustic Doppler Current Profiler (ADCP) data for turbulence studies is evaluated against Acoustic Doppler Velocimeter (ADV) data at a point. Removal of Doppler noise from the raw ping data is shown to be a crucial step in turbulence quantification. Excluding periods of slack tide, the turbulent intensity estimates at a height of 4.6 m above the seabed are 8% and 11% from the ADCP and ADV, respectively. Estimates of the turbulent dissipation rate are more variable, from 10e-3 to 10e-1 W/m^3. An example analysis of coherent Turbulent Kinetic Energy (TKE) is presented.
Turbulent heat transfer and friction in a square channel with discrete rib turbulators
McMillin, Robert Dale
1989-01-01T23:59:59.000Z
TURBULENT HEAT TRANSFER AND FRICTION IN A SQUARE CHANNEL WITH DISCRETE RIB TURBULATORS A Thesis by ROBERT DALE iXIGMILLIN Subniitted to the Office of Graduate Studies of Texas AK. M L niversrty in partial fulfillment of the requirements... for the degree of MASTER OF SGIE IGE Deceinber 1989 Major Subject' Mechanical Engineering TURBULENT HEAT TRANSFER AND FRICTION IN A SQUARE CHANNEL WITH DISCRETE RIB TURBULATORS A Thesrs by ROBERT DALE MCMILLI'V Approverl as to style and content...
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.
Turbulent Supersonic Channel Flow: Direct Numerical Simulation and Modeling
Heinz, Stefan
modeling: the turbulence frequency production mechanism, wall damping effects on turbulence model frequency production mechanisms and wall damping effects may be explained very well on the basis, Chik w = wall viscosity = kinematic viscosity, = T = turbulent kinematic viscosity, Ck d = pressure
Massively Parallel Simulations of Solar Flares and Plasma Turbulence
Grauer, Rainer
Massively Parallel Simulations of Solar Flares and Plasma Turbulence Lukas Arnold, Christoph Beetz in space- and astrophysical plasmasystems include solar flares and hydro- or magnetohydrodynamic turbulence of solar flares and Lagrangian statistics of compressible and incompress- ible turbulent flows
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...
Assessment of Combustion and Turbulence Models for the Simulation...
Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site
Combustion and Turbulence Models for the Simulation of Combustion Processes in a DI Diesel Engine Assessment of Combustion and Turbulence Models for the Simulation of Combustion...
Consider Installing Turbulators on Two- and Three-Pass Firetube...
Broader source: Energy.gov (indexed) [DOE]
turbulators on firetube boilers as part of optimized steam systems. STEAM TIP SHEET 25 Consider Installing Turbulators on Two- and Three-Pass Firetube Boilers (January 2012) More...
Turbulence-Flame Interactions in Type Ia Supernovae
Aspden, Andrew J; Lawrence Berkeley National Laboratory, 1 Cyclotron Road, MS 50A-1148, Berkeley, CA 94720 (Authors 1, 2 & 3); Department of Astronomy and Astrophysics, University of California at Santa Cruz, Santa Cruz, CA 95064 (Author 4); Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794 (Author 5)
2008-01-01T23:59:59.000Z
dynamics of turbulent thermonuclear ?ames are essential tostudy of turbulent thermonuclear ? ames that explores aadapted to the study of thermonuclear ?ames, as described in
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)
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
turbulent heat International Journal of Numerical
Lin, Wen-Wei
flow behavior in a rectangular channel with streamwise-periodic ribs mounted on one of the principal. Nomenclature De = hydraulic diameter h = rib height H = channel height k = turbulent kinetic energy Nu = local June 1999 Accepted September 1999 Computation of enhanced turbulent heat transfer in a channel
Fifteen Lectures on Laminar and Turbulent Combustion
Peters, Norbert
Fifteen Lectures on Laminar and Turbulent Combustion N. Peters RWTH Aachen Ercoftac Summer School in Combustion Systems 1 Lecture 2: Calculation of Adiabatic Flame Temperatures and Chemical Equilibria 20: Laminar Diffusion Flames: Different Flow Geometries 156 Lecture 11: Turbulent Combustion: Introduction
Stochastic models for turbulent reacting flows
Kerstein, A. [Sandia National Laboratories, Livermore, CA (United States)
1993-12-01T23:59:59.000Z
The goal of this program is to develop and apply stochastic models of various processes occurring within turbulent reacting flows in order to identify the fundamental mechanisms governing these flows, to support experimental studies of these flows, and to further the development of comprehensive turbulent reacting flow models.
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.
Turbulence of a Unidirectional Flow Bjorn Birnir
Birnir, Björn
-flying aircraft. Turbulent drag also prevents the design of more fuel-efficient cars and aircrafts. Turbulence plays a role in the heat trans- fer in nuclear reactors, causes drag in oil pipelines and influence and intrigued people for centuries. Five centuries ago a fluid engineer by the name of Leonardo da Vinci tackled
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...
Meso-scale turbulence in living fluids
Wensink, Henricus H; Heidenreich, Sebastian; Drescher, Knut; Goldstein, Raymond E; Löwen, Hartmut; Yeomans, Julia M
2012-01-01T23:59:59.000Z
Turbulence is ubiquitous, from oceanic currents to small-scale biological and quantum systems. Self-sustained turbulent motion in microbial suspensions presents an intriguing example of collective dynamical behavior amongst the simplest forms of life, and is important for fluid mixing and molecular transport on the microscale. The mathematical characterization of turbulence phenomena in active non-equilibrium fluids proves even more difficult than for conventional liquids or gases. It is not known which features of turbulent phases in living matter are universal or system-specific, or which generalizations of the Navier-Stokes equations are able to describe them adequately. Here, we combine experiments, particle simulations, and continuum theory to identify the statistical properties of self-sustained meso-scale turbulence in active systems. To study how dimensionality and boundary conditions affect collective bacterial dynamics, we measured energy spectra and structure functions in dense Bacillus subtilis su...
Flame front configuration of turbulent premixed flames
Furukawa, Junichi [Tokyo Metropolitan Technical Coll. (Japan). Dept. of Mechanical Engineering] [Tokyo Metropolitan Technical Coll. (Japan). Dept. of Mechanical Engineering; Maruta, Kaoru [Tohoku Univ., Sendai (Japan). Inst. of Fluid Science] [Tohoku Univ., Sendai (Japan). Inst. of Fluid Science; Hirano, Toshisuke [Univ. of Tokyo (Japan). Dept. of Chemical System Engineering] [Univ. of Tokyo (Japan). Dept. of Chemical System Engineering
1998-02-01T23:59:59.000Z
The present study is performed to explore dependence of the wrinkle scale of propane-air turbulent premixed flames on the characteristics of turbulence in the nonreacting flow, burner size, and mixture ratio. The wrinkle scales are examined and expressed in the frequency distribution of the radii of flame front curvatures. The average wrinkle scale depends not only on the characteristics of turbulence in the nonreacting flow but also on burner diameter and mixture ratio. The average wrinkle scale of a lean propane-air flame is larger than those of the near stoichiometric and rich flames. The smallest wrinkle scale of turbulent premixed flame is in the range of 0.75--1.0 mm, which is much larger than the Kolmogorov scale of turbulence in the nonreacting flow.
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
Great Plains Turbulence Environment: Its Origins, Impact, and Simulation
Kelley, N. D.; Jonkman, B. J.; Scott, G. N.
2006-12-01T23:59:59.000Z
This paper summarizes the known impacts of nocturnal turbulence on wind turbine performance and operations.
Thermal hydraulics development for CASL
Lowrie, Robert B [Los Alamos National Laboratory
2010-12-07T23:59:59.000Z
This talk will describe the technical direction of the Thermal-Hydraulics (T-H) Project within the Consortium for Advanced Simulation of Light Water Reactors (CASL) Department of Energy Innovation Hub. CASL is focused on developing a 'virtual reactor', that will simulate the physical processes that occur within a light-water reactor. These simulations will address several challenge problems, defined by laboratory, university, and industrial partners that make up CASL. CASL's T-H efforts are encompassed in two sub-projects: (1) Computational Fluid Dynamics (CFD), (2) Interface Treatment Methods (ITM). The CFD subproject will develop non-proprietary, scalable, verified and validated macroscale CFD simulation tools. These tools typically require closures for their turbulence and boiling models, which will be provided by the ITM sub-project, via experiments and microscale (such as DNS) simulation results. The near-term milestones and longer term plans of these two sub-projects will be discussed.
Gauge turbulence, topological defect dynamics, and condensation in Higgs models
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Gasenzer, Thomas [Universitat Heidelberg, Institut fur Theoretische Physik, Heidelberg (Germany); GSI, ExtreMe Matter Institute EMMI, Darmstadt (Germany); McLerran, Larry [Brookhaven National Laboratory, Physics Department, RIKEN BNL Research Center Upton NY (United States); China Central Normal University, Physics Department, Wuhan (China); Pawlowski, Jan M [Universitat Heidelberg, Institut fur Theoretische Physik, Heidelberg (Germany); GSI, ExtreMe Matter Institute EMMI, Darmstadt (Germany); Sexty, Denes [Universitat Heidelberg, Institut fur Theoretische Physik, Heidelberg (Germany); GSI, ExtreMe Matter Institute EMMI, Darmstadt (Germany)
2014-10-01T23:59:59.000Z
The real-time dynamics of topological defects and turbulent configurations of gauge fields for electric and magnetic confinement are studied numerically within a 2+1D Abelian Higgs model. It is shown that confinement is appearing in such systems equilibrating after a strong initial quench such as the overpopulation of the infrared modes. While the final equilibrium state does not support confinement, metastable vortex defect configurations appearing in the gauge field are found to be closely related to the appearance of physically observable confined electric and magnetic charges. These phenomena are seen to be intimately related to the approach of a non-thermal fixed point of the far-from-equilibrium dynamical evolution, signaled by universal scaling in the gauge-invariant correlation function of the Higgs field. Even when the parameters of the Higgs action do not support condensate formation in the vacuum, during this approach, transient Higgs condensation is observed. We discuss implications of these results for the far-from-equilibrium dynamics of Yang–Mills fields and potential mechanisms of how confinement and condensation in non-Abelian gauge fields can be understood in terms of the dynamics of Higgs models. These suggest that there is an interesting new class of dynamics of strong coherent turbulent gauge fields with condensates.
Gauge turbulence, topological defect dynamics, and condensation in Higgs models
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Gasenzer, Thomas; McLerran, Larry; Pawlowski, Jan M.; Sexty, Dénes
2014-10-01T23:59:59.000Z
The real-time dynamics of topological defects and turbulent configurations of gauge fields for electric and magnetic confinement are studied numerically within a 2+1D Abelian Higgs model. It is shown that confinement is appearing in such systems equilibrating after a strong initial quench such as the overpopulation of the infrared modes. While the final equilibrium state does not support confinement, metastable vortex defect configurations appearing in the gauge field are found to be closely related to the appearance of physically observable confined electric and magnetic charges. These phenomena are seen to be intimately related to the approach of a non-thermal fixedmore »point of the far-from-equilibrium dynamical evolution, signaled by universal scaling in the gauge-invariant correlation function of the Higgs field. Even when the parameters of the Higgs action do not support condensate formation in the vacuum, during this approach, transient Higgs condensation is observed. We discuss implications of these results for the far-from-equilibrium dynamics of Yang–Mills fields and potential mechanisms of how confinement and condensation in non-Abelian gauge fields can be understood in terms of the dynamics of Higgs models. These suggest that there is an interesting new class of dynamics of strong coherent turbulent gauge fields with condensates.« less
Wind turbulence characterization for wind energy development
Wendell, L.L.; Gower, G.L.; Morris, V.R.; Tomich, S.D.
1991-09-01T23:59:59.000Z
As part of its support of the US Department of Energy's (DOE's) Federal Wind Energy Program, the Pacific Northwest Laboratory (PNL) has initiated an effort to work jointly with the wind energy community to characterize wind turbulence in a variety of complex terrains at existing or potential sites of wind turbine installation. Five turbulence characterization systems were assembled and installed at four sites in the Tehachapi Pass in California, and one in the Green Mountains near Manchester, Vermont. Data processing and analyses techniques were developed to allow observational analyses of the turbulent structure; this analysis complements the more traditional statistical and spectral analyses. Preliminary results of the observational analyses, in the rotating framework or a wind turbine blade, show that the turbulence at a site can have two major components: (1) engulfing eddies larger than the rotor, and (2) fluctuating shear due to eddies smaller than the rotor disk. Comparison of the time series depicting these quantities at two sites showed that the turbulence intensity (the commonly used descriptor of turbulence) did not adequately characterize the turbulence at these sites. 9 refs., 10 figs.,
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.
Turbulence-chemistry interactions in reacting flows
Barlow, R.S.; Carter, C.D. [Sandia National Laboratories, Livermore, CA (United States)
1993-12-01T23:59:59.000Z
Interactions between turbulence and chemistry in nonpremixed flames are investigated through multiscalar measurements. Simultaneous point measurements of major species, NO, OH, temperature, and mixture fraction are obtained by combining spontaneous Raman scattering, Rayleigh scattering, and laser-induced fluorescence (LIF). NO and OH fluorescence signals are converted to quantitative concentrations by applying shot-to-shot corrections for local variations of the Boltzmann fraction and collisional quenching rate. These measurements of instantaneous thermochemical states in turbulent flames provide insights into the fundamental nature of turbulence-chemistry interactions. The measurements also constitute a unique data base for evaluation and refinement of turbulent combustion models. Experimental work during the past year has focused on three areas: (1) investigation of the effects of differential molecular diffusion in turbulent combustion: (2) experiments on the effects of Halon CF{sub 3}Br, a fire retardant, on the structure of turbulent flames of CH{sub 4} and CO/H{sub 2}/N{sub 2}; and (3) experiments on NO formation in turbulent hydrogen jet flames.
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) (MillionStructural Basis of WntSupportBRAP-focused topics 13538
AQUIFER THERMAL ENERGY STORAGE
Tsang, C.-F.
2011-01-01T23:59:59.000Z
varying solar energy inputs and thermal or power demands. Itusing aquifers for thermal energy storage. Problems outlinedmatical Modeling of Thermal Energy Storage in Aquifers,"
Solar Thermal Powered Evaporators
Moe, Christian Robert
2015-01-01T23:59:59.000Z
of solar collectors and thermal energy storage in solaraided or powered by solar thermal energy. A section is alsobesides MVC require thermal energy as their primary energy
AQUIFER THERMAL ENERGY STORAGE
Tsang, C.-F.
2011-01-01T23:59:59.000Z
aquifers for thermal energy storage. Problems outlined aboveModeling of Thermal Energy Storage in Aquifers," Proceed-ings of Aquifer Thermal Energy Storage Workshop, Lawrence
Solar Thermal Powered Evaporators
Moe, Christian Robert
2015-01-01T23:59:59.000Z
15] O. A. Hamed, "THERMAL PERFORMANCE OF MULTISTAGE FLASHdesa4.aspx. [18] Encon, "Thermal Evaporators," June 2013. [http://www.evaporator.com/thermal-evaporator. [19] Y. Tian
AQUIFER THERMAL ENERGY STORAGE
Tsang, C.-F.
2011-01-01T23:59:59.000Z
of such an aquifer thermal storage system were studied andusing aquifers for thermal energy storage. Problems outlinedmatical Modeling of Thermal Energy Storage in Aquifers,"
Solar Thermal Powered Evaporators
Moe, Christian Robert
2015-01-01T23:59:59.000Z
This requires no thermal storage tanks, but can have athe need for large thermal storage equipment, the evaporatorinclude analysis of thermal storage. A way of keeping the
THERMAL HYDRAULICS KEYWORDS: thermal hydraulics,
Smith, Barton L.
-fluid modeling of nuclear reactor systems. Thermal-hydraulic analysis codes such as RELAP5-3D ~Ref. 1! and FLICA regions of the system. In fact, the CFD code FLUENT has previously been coupled to RELAP5-3D ~Refs. 3
Spontaneous emission of electromagnetic radiation in turbulent plasmas
Ziebell, L. F., E-mail: luiz.ziebell@ufrgs.br [Instituto de Física, UFRGS, Porto Alegre, Rio Grande do Sul (Brazil); Yoon, P. H., E-mail: yoonp@umd.edu [School of Space Research, Kyung Hee University, Yongin, Gyeonggi 446-701, South Korea and University of Maryland, College Park, Maryland 20742 (United States); Simões, F. J. R.; Pavan, J. [Instituto de Física e Matemática, UFPel, Pelotas, Rio Grande do Sul (Brazil)] [Instituto de Física e Matemática, UFPel, Pelotas, Rio Grande do Sul (Brazil); Gaelzer, R. [Instituto de Física, UFRGS, Porto Alegre, Rio Grande do Sul (Brazil) [Instituto de Física, UFRGS, Porto Alegre, Rio Grande do Sul (Brazil); Instituto de Física e Matemática, UFPel, Pelotas, Rio Grande do Sul (Brazil)
2014-01-15T23:59:59.000Z
Known radiation emission mechanisms in plasmas include bremmstrahlung (or free-free emission), gyro- and synchrotron radiation, cyclotron maser, and plasma emission. For unmagnetized plasmas, only bremmstrahlung and plasma emissions are viable. Of these, bremmstrahlung becomes inoperative in the absence of collisions, and the plasma emission requires the presence of electron beam, followed by various scattering and conversion processes. The present Letter proposes a new type of radiation emission process for plasmas in a state of thermodynamic quasi-equilibrium between particles and enhanced Langmuir turbulence. The radiation emission mechanism proposed in the present Letter is not predicted by the linear theory of thermal plasmas, but it relies on nonlinear wave-particle resonance processes. The electromagnetic particle-in-cell numerical simulation supports the new mechanism.
Universal turbulence on branes in holography
Koji Hashimoto; Mitsuhiro Nishida; Akihiko Sonoda
2015-05-19T23:59:59.000Z
At a meson melting transition in holographic QCD, a weak turbulence of mesons was found with critical embeddings of probe D-branes in gravity duals. The turbulent mesons have a power-law energy distribution $\\varepsilon_n \\propto (\\omega_n)^\\alpha$ where $\\omega_n$ is the mass of the $n$-th excited resonance of the meson tower. In this paper, we find that the turbulence power $\\alpha$ is universal, irrespective of how the transition is driven, by numerically calculating the power in various static brane setups at criticality. We also find that the power $\\alpha$ depends only on the cone dimensions of the probe D-branes.
Universal turbulence on branes in holography
Hashimoto, Koji; Sonoda, Akihiko
2015-01-01T23:59:59.000Z
At a meson melting transition in holographic QCD, a weak turbulence of mesons was found with critical embeddings of probe D-branes in gravity duals. The turbulent mesons have a power-law energy distribution $\\varepsilon_n \\propto (\\omega_n)^\\alpha$ where $\\omega_n$ is the mass of the $n$-th excited resonance of the meson tower. In this paper, we find that the turbulence power $\\alpha$ is universal, irrespective of how the transition is driven, by numerically calculating the power in various static brane setups at criticality. We also find that the power $\\alpha$ depends only on the cone dimensions of the probe D-branes.
Non-thermal Plasma Chemistry Non-thermal Thermal
Greifswald, Ernst-Moritz-Arndt-Universität
Non-thermal Plasma Chemistry #12;Non-thermal Thermal (non-equilibr.) (equilibr.) Ti T 300 ... 103 eV): ,,Kinetic temperature" Te: 1eV about 10 000 K 1 eV / Molekül = 23 kcal / mol #12;Non-thermal;Leuchtstoffröhre Plasma-Bildschirm Energiesparlampe #12;electrical engineering light sources textile industry
Mechanical Engineering & Thermal Group
Mojzsis, Stephen J.
Mechanical Engineering & Thermal Group The Mechanical Engineering (ME) & Thermal Group at LASP has · STOP (Structural, Thermal, and Optical Performance) analyses of optical systems Thermal engineers lead evolved with the complexity of instrument design demands, LASP mechanical engineers develop advanced
Thermal Transport in Nanoporous Materials for Energy Applications
Fang, Jin
2012-01-01T23:59:59.000Z
Thermal Conductivity Measurement . . . . . . . . . . . . .Thermal ConductivityThermal Conductivity . . . . . . . . . . . . . . . .Thermal
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...
Equilibration of an atmosphere by geostrophic turbulence
Jansen, Malte F. (Malte Friedrich)
2013-01-01T23:59:59.000Z
A major question for climate studies is to quantify the role of turbulent eddy fluxes in maintaining the observed atmospheric mean state. It has been argued that eddy fluxes keep the mid-latitude atmosphere in a state that ...
TIDAL TURBULENCE SPECTRA FROM A COMPLIANT MOORING
Thomson, Jim; Kilcher, Levi; Richmond, Marshall C.; Talbert, Joe; deKlerk, Alex; Polagye, Brian; Guerra, Maricarmen; Cienfuegos, Rodrigo
2013-06-13T23:59:59.000Z
A compliant mooring to collect high frequency turbulence data at a tidal energy site is evaluated in a series of short demon- stration deployments. The Tidal Turbulence Mooring (TTM) improves upon recent bottom-mounted approaches by suspend- ing Acoustic Doppler Velocimeters (ADVs) at mid-water depths (which are more relevant to tidal turbines). The ADV turbulence data are superior to Acoustic Doppler Current Profiler (ADCP) data, but are subject to motion contamination when suspended on a mooring in strong currents. In this demonstration, passive stabilization is shown to be sufficient for acquiring bulk statistics of the turbulence, without motion correction. With motion cor- rection (post-processing), data quality is further improved; the relative merits of direct and spectral motion correction are dis- cussed.
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.
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.
Quantum light in the turbulent atmosphere
A. A. Semenov; W. Vogel
2009-08-12T23:59:59.000Z
Nonclassical properties of light propagating through the turbulent atmosphere are studied. We demonstrate by numerical simulation that the probability distribution of the transmission coefficient, which characterizes the effects of the atmosphere on the quantum state of light, can be reconstructed by homodyne detection. Nonclassical photon-statistics and, more generally, nonclassical Glauber-Sudarshan functions appear to be more robust against turbulence for weak light fields rather than for bright ones.
Direct numerical simulation of turbulent reacting flows
Chen, J.H. [Sandia National Laboratories, Livermore, CA (United States)
1993-12-01T23:59:59.000Z
The development of turbulent combustion models that reflect some of the most important characteristics of turbulent reacting flows requires knowledge about the behavior of key quantities in well defined combustion regimes. In turbulent flames, the coupling between the turbulence and the chemistry is so strong in certain regimes that is is very difficult to isolate the role played by one individual phenomenon. Direct numerical simulation (DNS) is an extremely useful tool to study in detail the turbulence-chemistry interactions in certain well defined regimes. Globally, non-premixed flames are controlled by two limiting cases: the fast chemistry limit, where the turbulent fluctuations. In between these two limits, finite-rate chemical effects are important and the turbulence interacts strongly with the chemical processes. This regime is important because industrial burners operate in regimes in which, locally the flame undergoes extinction, or is at least in some nonequilibrium condition. Furthermore, these nonequilibrium conditions strongly influence the production of pollutants. To quantify the finite-rate chemistry effect, direct numerical simulations are performed to study the interaction between an initially laminar non-premixed flame and a three-dimensional field of homogeneous isotropic decaying turbulence. Emphasis is placed on the dynamics of extinction and on transient effects on the fine scale mixing process. Differential molecular diffusion among species is also examined with this approach, both for nonreacting and reacting situations. To address the problem of large-scale mixing and to examine the effects of mean shear, efforts are underway to perform large eddy simulations of round three-dimensional jets.
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.
Reaction and diffusion in turbulent combustion
Pope, S.B. [Mechanical and Aerospace Engineering, Ithaca, NY (United States)
1993-12-01T23:59:59.000Z
The motivation for this project is the need to obtain a better quantitative understanding of the technologically-important phenomenon of turbulent combustion. In nearly all applications in which fuel is burned-for example, fossil-fuel power plants, furnaces, gas-turbines and internal-combustion engines-the combustion takes place in a turbulent flow. Designers continually demand more quantitative information about this phenomenon-in the form of turbulent combustion models-so that they can design equipment with increased efficiency and decreased environmental impact. For some time the PI has been developing a class of turbulent combustion models known as PDF methods. These methods have the important virtue that both convection and reaction can be treated without turbulence-modelling assumptions. However, a mixing model is required to account for the effects of molecular diffusion. Currently, the available mixing models are known to have some significant defects. The major motivation of the project is to seek a better understanding of molecular diffusion in turbulent reactive flows, and hence to develop a better mixing model.
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.
Meso-scale turbulence in living fluids
Henricus H. Wensink; Jörn Dunkel; Sebastian Heidenreich; Knut Drescher; Raymond E. Goldstein; Hartmut Löwen; Julia M. Yeomans
2012-08-21T23:59:59.000Z
Turbulence is ubiquitous, from oceanic currents to small-scale biological and quantum systems. Self-sustained turbulent motion in microbial suspensions presents an intriguing example of collective dynamical behavior amongst the simplest forms of life, and is important for fluid mixing and molecular transport on the microscale. The mathematical characterization of turbulence phenomena in active non-equilibrium fluids proves even more difficult than for conventional liquids or gases. It is not known which features of turbulent phases in living matter are universal or system-specific, or which generalizations of the Navier-Stokes equations are able to describe them adequately. Here, we combine experiments, particle simulations, and continuum theory to identify the statistical properties of self-sustained meso-scale turbulence in active systems. To study how dimensionality and boundary conditions affect collective bacterial dynamics, we measured energy spectra and structure functions in dense Bacillus subtilis suspensions in quasi-2D and 3D geometries. Our experimental results for the bacterial flow statistics agree well with predictions from a minimal model for self-propelled rods, suggesting that at high concentrations the collective motion of the bacteria is dominated by short-range interactions. To provide a basis for future theoretical studies, we propose a minimal continuum model for incompressible bacterial flow. A detailed numerical analysis of the 2D case shows that this theory can reproduce many of the experimentally observed features of self-sustained active turbulence.
Uzdensky, Dmitri A., E-mail: uzdensky@colorado.edu [Center for Integrated Plasma Studies, Physics Department, University of Colorado, Boulder, CO 80309 (United States)
2013-10-01T23:59:59.000Z
In this paper, we consider two outstanding intertwined problems in modern high-energy astrophysics: (1) the vertical-thermal structure of an optically thick accretion disk heated by the dissipation of magnetohydrodynamic turbulence driven by the magnetorotational instability (MRI), and (2) determining the fraction of the accretion power released in the corona above the disk. For simplicity, we consider a gas-pressure-dominated disk and assume a constant opacity. We argue that the local turbulent dissipation rate due to the disruption of the MRI channel flows by secondary parasitic instabilities should be uniform across most of the disk, almost up to the disk photosphere. We then obtain a self-consistent analytical solution for the vertical thermal structure of the disk, governed by the balance between the heating by MRI turbulence and the cooling by radiative diffusion. Next, we argue that the coronal power fraction is determined by the competition between the Parker instability, viewed as a parasitic instability feeding off of MRI channel flows, and other parasitic instabilities. We show that the Parker instability inevitably becomes important near the disk surface, leading to a certain lower limit on the coronal power. While most of the analysis in this paper focuses on the case of a disk threaded by an externally imposed vertical magnetic field, we also discuss the zero net flux case, in which the magnetic field is produced by the MRI dynamo itself, and show that most of our arguments and conclusions should be valid in this case as well.
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
Accepted, Nuclear Fusion, 1999 Turbulent Transport and Turbulence in Radiative I-Mode Plasmas in
California at San Diego, University of
Accepted, Nuclear Fusion, 1999 Turbulent Transport and Turbulence in Radiative I-Mode Plasmas vs. radiated fraction suggests a common underlying suppression mechanism. #12;Accepted, Nuclear of Physics University of Alberta Edmonton, Alberta Canada, T6G 2J1 1/4/00 17:25 PM #12;Accepted, Nuclear
The Nature of Subproton Scale Turbulence in the Solar Wind
Chen, C H K; Xia, Q; Perez, J C
2013-01-01T23:59:59.000Z
The nature of subproton scale fluctuations in the solar wind is an open question, partly because two similar types of electromagnetic turbulence can occur: kinetic Alfven turbulence and whistler turbulence. These two possibilities, however, have one key qualitative difference: whistler turbulence, unlike kinetic Alfven turbulence, has negligible power in density fluctuations. In this Letter, we present new observational data, as well as analytical and numerical results, to investigate this difference. The results show, for the first time, that the fluctuations well below the proton scale are predominantly kinetic Alfven turbulence, and, if present at all, the whistler fluctuations make up only a small fraction of the total energy.
Numerical Investigation of Scaling Properties of Turbulent Premixed Flames
J. C. Niemeyer; A. R. Kerstein
1997-07-09T23:59:59.000Z
Gibson scaling and related properties of flame-surface geometry in turbulent premixed combustion are demonstrated using a novel computational model, Deterministic Turbulent Mixing (DTM). In DTM, turbulent advection is represented by a sequence of maps applied to the computational domain. The structure of the mapping sequence incorporates pertinent scaling properties of the turbulent cascade. Here, combustion in Kolmogorov turbulence (kinetic-energy cascade) and in Bolgiano-Obukhov convective turbulence (potential-energy cascade) is simulated. Implications with regard to chemical flames and astrophysical (thermonuclear) flames are noted.
Magnetic Turbulence and Thermodynamics in the Inner Region of Protoplanetary Discs
Hirose, Shigenobu
2015-01-01T23:59:59.000Z
Using radiation magnetohydrodynamics simulations with realistic opacities and equation of state, and zero net magnetic flux, we have explored thermodynamics in the inner part of protoplanetary discs where magnetic turbulence is expected. The thermal equilibrium curve consists of the upper, lower, and middle branches. The upper (lower) branch corresponds to hot (cool) and optically very (moderately) thick discs, respectively, while the middle branch is characterized by convective energy transport near the midplane. Convection is also the major energy transport process near the low surface density end of the upper branch. There, convective motion is fast with Mach numbers reaching $\\gtrsim 0.01$, and enhances both magnetic turbulence and cooling, raising the ratio of vertically-integrated shear stress to vertically-integrated pressure by a factor of several. This convectively enhanced ratio seems a robust feature in accretion discs having an ionization transition. We have also examined causes of the S-shaped th...
Application of an EASM model for turbulent convective heat transfer in ribbed duct
Saidi, A.; Sunden, B.
1999-07-01T23:59:59.000Z
A numerical investigation is performed to predict local and mean thermal-hydraulic characteristics in rib-roughened ducts. The Navier-Stokes and energy equations, and a low-Re number {kappa}-{epsilon} turbulence model are solved with two methods for determination of the Reynolds stresses, eddy viscosity model (EVM) and explicit algebraic stress model (EASM). The numerical solution procedure uses a collocated grid, and the pressure-velocity coupling is handled by the SIMPLEC algorithm. The assumption of fully developed periodic conditions is applied. The calculated mean and local heat transfer enhancement values are compared with experimental data and fairly good agreement on mean Nu numbers is achieved. The prediction capabilities of the two turbulence models (EVM and EASM) are discussed. Both models have similar ability to predict the mean Nusselt numbers but the EASM model is superior in description of the flow field structure.
Robert I Selkowitz; Eric G. Blackman
2007-07-31T23:59:59.000Z
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 also provides a mechanism for the non-ionizing heat source observed in the Reynolds Layer of the interstellar medium \\citep{Reynolds}. STFA accommodates the proper heating power, and the input energy is rapidly thermalized within the low density Reynolds layer plasma.
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.
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.
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.
NO concentration imaging in turbulent nonpremixed flames
Schefer, R.W. [Sandia National Laboratories, Livermore, CA (United States)
1993-12-01T23:59:59.000Z
The importance of NO as a pollutant species is well known. An understanding of the formation characteristics of NO in turbulent hydrocarbon flames is important to both the desired reduction of pollutant emissions and the validation of proposed models for turbulent reacting flows. Of particular interest is the relationship between NO formation and the local flame zone, in which the fuel is oxidized and primary heat release occurs. Planar imaging of NO provides the multipoint statistics needed to relate NO formation to the both the flame zone and the local turbulence characteristics. Planar imaging of NO has been demonstrated in turbulent flames where NO was seeded into the flow at high concentrations (2000 ppm) to determine the gas temperature distribution. The NO concentrations in these experiments were significantly higher than those expected in typical hydrocarbon-air flames, which require a much lower detectability limit for NO measurements. An imaging technique based on laser-induced fluorescence with sufficient sensitivity to study the NO formation mechanism in the stabilization region of turbulent lifted-jet methane flames.
Biophysical coupling between turbulence, veliger behavior, and larval supply
Fuchs, Heidi L
2005-01-01T23:59:59.000Z
The goals of this thesis were to quantify the behavior of gastropod larvae (mud snails Ilyanassa obsoleta) in turbulence, and to investigate how that behavior affects larval supply in a turbulent coastal inlet. Gastropod ...
Drag, turbulence, and diffusion in flow through emergent vegetation
Nepf, Heidi
Aquatic plants convert mean kinetic energy into turbulent kinetic energy at the scale of the plant stems and branches. This energy transfer, linked to wake generation, affects vegetative drag and turbulence intensity. ...
Examining A Hypersonic Turbulent Boundary Layer at Low Reynolds Number
Semper, Michael Thomas
2013-05-15T23:59:59.000Z
The purpose of the current study was to answer several questions related to hypersonic, low Reynolds number, turbulent boundary layers, of which available data related to turbulence quantities is scarce. To that end, a unique research facility...
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
Assessment of reduced mechanisms using One Dimensional Stochastic Turbulence model
Chien, Li-Chun
2010-01-01T23:59:59.000Z
turbulence model for a syngas jet flame. Proceeding of FallKerstein 2002), a turbulent syngas (CO/H2/NO) jet flame wasand DNS results of the syngas jet flame was recently done
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)
Evolution of an initially turbulent stratified shear layer
Brucker, Kyle A.; Sarkar, Sutanu
2007-01-01T23:59:59.000Z
the turbulent kinetic energy and potential energy are givenbe- tween potential and kinetic energy, is not positive de?kinetic energy that may be trans- ferred to turbulent potential energy.
High Temperature Thermal Array for Next Generation Solar Thermal...
Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site
High Temperature Thermal Array for Next Generation Solar Thermal Power Production High Temperature Thermal Array for Next Generation Solar Thermal Power Production This...
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.
Multigrid solution of incompressible turbulent flows by using two-equation turbulence models
Zheng, X.; Liu, C. [Front Range Scientific Computations, Inc., Denver, CO (United States); Sung, C.H. [David Taylor Model Basin, Bethesda, MD (United States)
1996-12-31T23:59:59.000Z
Most of practical flows are turbulent. From the interest of engineering applications, simulation of realistic flows is usually done through solution of Reynolds-averaged Navier-Stokes equations and turbulence model equations. It has been widely accepted that turbulence modeling plays a very important role in numerical simulation of practical flow problem, particularly when the accuracy is of great concern. Among the most used turbulence models today, two-equation models appear to be favored for the reason that they are more general than algebraic models and affordable with current available computer resources. However, investigators using two-equation models seem to have been more concerned with the solution of N-S equations. Less attention is paid to the solution method for the turbulence model equations. In most cases, the turbulence model equations are loosely coupled with N-S equations, multigrid acceleration is only applied to the solution of N-S equations due to perhaps the fact the turbulence model equations are source-term dominant and very stiff in sublayer region.
A signature for turbulence driven magnetic islands
Agullo, O.; Muraglia, M.; Benkadda, S. [Aix-Marseille Université, CNRS, PIIM, UMR 7345 Marseille (France); France-Japan Magnetic Fusion Laboratory, LIA 336 CNRS, Marseille (France); Poyé, A. [Univ. Bordeaux, CNRS, CEA, CELIA (Centre Lasers Intenses et Applications), UMR 5107, F-33405 Talence (France); Yagi, M. [Plasma Theory and Simulation Gr., JAEA, Rokkasho (Japan); Garbet, X. [IRFM, CEA, St-Paul-Lez-Durance 13108 (France); Sen, A. [Institute for Plasma Research, Bhat, Gandhinagar 382428 (India)
2014-09-15T23:59:59.000Z
We investigate the properties of magnetic islands arising from tearing instabilities that are driven by an interchange turbulence. We find that such islands possess a specific signature that permits an identification of their origin. We demonstrate that the persistence of a small scale turbulence maintains a mean pressure profile, whose characteristics makes it possible to discriminate between turbulence driven islands from those arising due to an unfavourable plasma current density gradient. We also find that the island poloidal turnover time, in the steady state, is independent of the levels of the interchange and tearing energy sources. Finally, we show that a mixing length approach is adequate to make theoretical predictions concerning island flattening in the island rotation frame.
Boundary Plasma Turbulence Simulations for Tokamaks
Xu, X; Umansky, M; Dudson, B; Snyder, P
2008-05-15T23:59:59.000Z
The boundary plasma turbulence code BOUT models tokamak boundary-plasma turbulence in a realistic divertor geometry using modified Braginskii equations for plasma vorticity, density (ni), electron and ion temperature (T{sub e}; T{sub i}) and parallel momenta. The BOUT code solves for the plasma fluid equations in a three dimensional (3D) toroidal segment (or a toroidal wedge), including the region somewhat inside the separatrix and extending into the scrape-off layer; the private flux region is also included. In this paper, a description is given of the sophisticated physical models, innovative numerical algorithms, and modern software design used to simulate edge-plasmas in magnetic fusion energy devices. The BOUT code's unique capabilities and functionality are exemplified via simulations of the impact of plasma density on tokamak edge turbulence and blob dynamics.
Closure models for turbulent reacting flows
Dutta, A.; Tarbell, J.M. (Pennsylvania State Univ., University Park, PA (USA). Dept. of Chemical Engineering)
1989-12-01T23:59:59.000Z
In this paper, a simple procedure based on fast and slow reaction asymptotics has been employed to drive first-order closure models for the nonlinear reaction terms in turbulent mass balances from mechanistic models of turbulent mixing and reaction. The coalescence-redispersion (CRD) model, the interaction by exchange with the mean (IEM) model, the three-environment (3E) model, and the four-environment (4E) model have been used to develop closure equations. The closure models have been tested extensively against experimental data for both single and multiple reactions. The closures based on slow asymptotics for the CRD, 3E and 4E models provide very good predictions of all of the experimental data, while other models available either in the literature or derived here are not adequate. The simple new closure equations developed in this paper may be useful in modeling systems involving turbulent mixing and complex chemical reactions.
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...
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...
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 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.
The First Galaxies: Assembly, Cooling and the Onset of Turbulence
Thomas H. Greif; Jarrett L. Johnson; Ralf S. Klessen; Volker Bromm
2009-10-20T23:59:59.000Z
We investigate the properties of the first galaxies at z > 10 with highly resolved numerical simulations, starting from cosmological initial conditions and taking into account all relevant primordial chemistry and cooling. A first galaxy is characterized by the onset of atomic hydrogen cooling, once the virial temperature exceeds 10^4 K, and its ability to retain photoheated gas. We follow the complex accretion and star formation history of a 5*10^7 M_sun system by means of a detailed merger tree and derive an upper limit on the number of Population III (Pop III) stars formed prior to its assembly. We investigate the thermal and chemical evolution of infalling gas and find that partial ionization at temperatures > 10^4 K catalyses the formation of H2 and hydrogen deuteride, allowing the gas to cool to the temperature of the cosmic microwave background. Depending on the strength of radiative and chemical feedback, primordial star formation might be dominated by intermediate-mass Pop III stars formed during the assembly of the first galaxies. Accretion on to the nascent galaxy begins with hot accretion, where gas is accreted directly from the intergalactic medium and shock-heated to the virial temperature, but is quickly accompanied by a phase of cold accretion, where the gas cools in filaments before flowing into the parent halo with high velocities. The latter drives supersonic turbulence at the centre of the galaxy and could lead to very efficient chemical mixing. The onset of turbulence in the first galaxies thus likely marks the transition to Pop II star formation.
Turbulent Wind Fields for Gaseous Phenomena Eugene Fiume 0
Toronto, University of
Turbulent Wind Fields for Gaseous Phenomena Jos Stam Eugene Fiume 0 Department of Computer Science of smoke, steam, mist and water re acting to a turbulent field such as wind is an attractive, and realistic illumina tion. We present a model for turbulent wind flow having a deterministic component
Spectrally condensed turbulence in thin layers and G. Falkovich2
Falkovich, Gregory
on the underlying turbulence; it generates stronger non-Gaussianity and reduces the efficiency of the inverse energy School of Physics and Engineering, The Australian National University, Canberra ACT 0200, Australia 2 turbulence, the effects of the bottom friction and of the spectral condensation of the turbulence energy
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.
Effects of thermal fluctuations on thermal inflation
Takashi Hiramatsu; Yuhei Miyamoto; Jun'ichi Yokoyama
2014-12-25T23:59:59.000Z
The mechanism of thermal inflation, a relatively short period of accelerated expansion after primordial inflation, is a desirable ingredient for a certain class of particle physics models if they are not to be in contention with the cosmology of the early Universe. Though thermal inflation is most simply described in terms of a thermal effective potential, a thermal environment also gives rise to thermal fluctuations that must be taken into account. We numerically study the effects of these thermal fluctuations using lattice simulations. We conclude that though they do not ruin the thermal inflation scenario, the phase transition at the end of thermal inflation proceeds through phase mixing and is therefore not accompanied by the formations of bubbles nor appreciable amplitude of gravitational waves.
Solar Thermal Powered Evaporators
Moe, Christian Robert
2015-01-01T23:59:59.000Z
and thermal energy storage in solar thermal applications,"Solar infrastructure should include analysis of thermal storage.storage equipment, the evaporator can be integrated into the current solar
A note on dissipation in helical turbulence
P. D. Ditlevsen; P. Giuliani
2001-04-04T23:59:59.000Z
In helical turbulence a linear cascade of helicity accompanying the energy cascade has been suggested. Since energy and helicity have different dimensionality we suggest the existence of a characteristic inner scale, $\\xi=k_H^{-1}$, for helicity dissipation in a regime of hydrodynamic fully developed turbulence and estimate it on dimensional grounds. This scale is always larger than the Kolmogorov scale, $\\eta=k_E^{-1}$, and their ratio $\\eta / \\xi $ vanishes in the high Reynolds number limit, so the flow will always be helicity free in the small scales.
Turbulence model of the cosmic structure
Jose Gaite
2012-02-14T23:59:59.000Z
The Kolmogorov approach to turbulence is applied to the Burgers turbulence in the stochastic adhesion model of large-scale structure formation. As the perturbative approach to this model is unreliable, here is proposed a new, non-perturbative approach, based on a suitable formulation of Kolmogorov's scaling laws. This approach suggests that the power-law exponent of the matter density two-point correlation function is in the range 1--1.33, but it also suggests that the adhesion model neglects important aspects of the gravitational dynamics.
Computational aspects of astrophysical MHD and turbulence
Axel Brandenburg
2001-09-27T23:59:59.000Z
The advantages of high-order finite difference scheme for astrophysical MHD and turbulence simulations are highlighted. A number of one-dimensional test cases are presented ranging from various shock tests to Parker-type wind solutions. Applications to magnetized accretion discs and their associated outflows are discussed. Particular emphasis is placed on the possibility of dynamo action in three-dimensional turbulent convection and shear flows, which is relevant to stars and astrophysical discs. The generation of large scale fields is discussed in terms of an inverse magnetic cascade and the consequences imposed by magnetic helicity conservation are reviewed with particular emphasis on the issue of alpha-quenching.
Feedback Trading and Intermittent Market Turbulence
Tambakis, Demosthenes N
the market progressively becomes stressed and turbulent. Returns and ab- solute returns persistence are found to display power-law features, and episodes of turbulence are intermittent. Keywords: Feedback trading, Price impact, Financial stability... of T = 500 trading periods (ticks)13 b?n = 1 + T " TX t=1 log µ xtn xnmin ¶#?1 (8) where xnmin is the minimum obervation in returns vector n that could be consistent with a power-law distribution. The power-law exponent estimator in (8) is always greater than...
Solar Thermal Powered Evaporators
Moe, Christian Robert
2015-01-01T23:59:59.000Z
and C. Y. Zhao, "A review of solar collectors and thermalenergy storage in solar thermal applications," Appliedon photovoltaic/thermal hybrid solar technology," Applied
Thermal Control & System Integration
Broader source: Energy.gov [DOE]
The thermal control and system integration activity focuses on issues such as the integration of motor and power control technologies and the development of advanced thermal control technologies....
Raizada, Manish N.
® Peltier Thermal Cycler PTC-0200 DNA Engine Cycler Operations Manual Version 4.0 #12;ii Tech Support: 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .vi The DNA Engine® Peltier Thermal Cycler Introduction
Helton, Donald McLean
2002-01-01T23:59:59.000Z
The premise of the work presented here is to use a common analytical tool, Computational Fluid Dynamics (CFD), along with a prevalent turbulence model, Large Eddy Simulation (LES), to study the flow past rectangular cylinders. In an attempt to use...
Gilmore, Mark A. [University of New Mexico
2013-06-27T23:59:59.000Z
Final Report for grant DE-FG02-06ER54898. The dynamics and generation of intermittent plasma turbulent structures, widely known as "blobs" have been studied in the presence of sheared plasma flows in a controlled laboratory experiment.
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.
Pressure atomizer having multiple orifices and turbulent generation feature
VanBrocklin, Paul G. (Pittsford, NY); Geiger, Gail E. (Caledonia, NY); Moran, Donald James (Rochester, NY); Fournier, Stephane (Rochester, NY)
2002-01-01T23:59:59.000Z
A pressure atomizer includes a silicon plate having a top surface and a bottom surface. A portion of the top surface defines a turbulent chamber. The turbulent chamber is peripherally bounded by the top surface of the plate. The turbulent chamber is recessed a predetermined depth relative to the top surface. The silicon plate further defines at least one flow orifice. Each flow orifice extends from the bottom surface of the silicon plate to intersect with and open into the turbulent chamber. Each flow orifice is in fluid communication with the turbulent chamber.
He, Yanping
On-line supplement: The Turbulence Parameterization Scheme The turbulence scheme used in this work-gradient turbulent transfer processes for cloud-free conditions. Throughout this supplement w denotes vertical
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}})\
6 Scalar Turbulence within the Canopy Sublayer
Katul, Gabriel
Engineering, University of Brasilia, Brazil 4 Department of Hydraulics, Transport and Civil Infrastructure changes in turbulent kinetic energy dissipation rate inside canopies, the relative importance of ejections that leads to scalar ramps is briefly discussed. The work draws upon a large number of flume, wind tunnel
Energy Spectrum of Quasi-Geostrophic Turbulence
Peter Constantin
2002-07-24T23:59:59.000Z
We consider the energy spectrum of a quasi-geostrophic model of forced, rotating turbulent flow. We provide a rigorous a priori bound E(k) energy spectrum that is expected in a two-dimensional Navier-Stokes inverse cascade. Our bound provides theoretical support for the k^{-2} spectrum observed in recent experiments.
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...
Interplay between confinement, turbulence and magnetic topology
Basse, Nils Plesner
Alcator C-Mod Interplay between confinement, turbulence and magnetic topology Nils P. Basse, S. Zoletnik1, W. L. Rowan2 et al. MIT Plasma Science and Fusion Center 1KFKI-RMKI, Euratom Association, Budapest, Hungary 2Fusion Research Center, University of Texas at Austin This idea originates from density
Optical monitor for observing turbulent flow
Albrecht, Georg F. (Livermore, CA); Moore, Thomas R. (Rochester, NY)
1992-01-01T23:59:59.000Z
The present invention provides an apparatus and method for non-invasively monitoring turbulent fluid flows including anisotropic flows. The present invention uses an optical technique to filter out the rays travelling in a straight line, while transmitting rays with turbulence induced fluctuations in time. The output is two dimensional, and can provide data regarding the spectral intensity distribution, or a view of the turbulence in real time. The optical monitor of the present invention comprises a laser that produces a coherent output beam that is directed through a fluid flow, which phase-modulates the beam. The beam is applied to a temporal filter that filters out the rays in the beam that are straight, while substantially transmitting the fluctuating, turbulence-induced rays. The temporal filter includes a lens and a photorefractive crystal such as BaTiO.sub.3 that is positioned in the converging section of the beam near the focal plane. An imaging system is used to observe the filtered beam. The imaging system may take a photograph, or it may include a real time camera that is connected to a computer. The present invention may be used for many purposes including research and design in aeronautics, hydrodynamics, and combustion.
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...
Shear Turbulence: Onset and Structure Fabian Waleffe
Lebovitz, Norman
filament in laminar flow (a), and the rapid mixing of the dye and water when the Reynolds number is larger and reproduces the seminal experiments of Osborne Reynolds [24] on the transition from laminar to turbulent flow in a pipe, illustrated in Fig. 1. The 2011 Annual Review 1 #12;of Fluid Mechanics article by Tom Mullin [21
OF HEALTH CARE IN TURBULENT TIMES
Feschotte, Cedric
FIXING THE FLOW OF HEALTH CARE IN TURBULENT TIMES INNOVATION REPORT 2014 #12;Since 2012, Algorithms facing health care today. We believe there's an unprecedented opportunity to invent a new vision for health care, and academic medicine is poised to lead the way. Algorithms for Innovations is designed
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
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.
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...
Testing neoclassical and turbulent effects on poloidal rotation in the core of DIII-D
Chrystal, C. [University of California San Diego, 9500 Gilman Dr., La Jolla, California 92093-0417 (United States); Burrell, K. H.; Staebler, G. M.; Kinsey, J. E.; Lao, L. L.; Grassie, J. S. de [General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States); Grierson, B. A.; Solomon, W. M.; Wang, W. X. [Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543-0451 (United States); Rhodes, T. L.; Schmitz, L. [University of California Los Angeles, P.O. Box 957099, Los Angeles, California 90095-7099 (United States); Mordijck, S. [College of William and Mary, P.O. Box 8795, Williamsburg, Virginia 23187-8795 (United States); Meneghini, O. [Oak Ridge Associated Universities, 1299 Bethel Valley Rd, Bldg SC-200, Oak Ridge, Tennessee 37830 (United States)
2014-07-15T23:59:59.000Z
Experimental tests of ion poloidal rotation theories have been performed on DIII-D using a novel impurity poloidal rotation diagnostic. These tests show significant disagreements with theoretical predictions in various conditions, including L-mode plasmas with internal transport barriers (ITB), H-mode plasmas, and QH-mode plasmas. The theories tested include standard neoclassical theory, turbulence driven Reynolds stress, and fast-ion friction on the thermal ions. Poloidal rotation is observed to spin up at the formation of an ITB and makes a significant contribution to the measurement of the E{sup ?}×B{sup ?} shear that forms the ITB. In ITB cases, neoclassical theory agrees quantitatively with the experimental measurements only in the steep gradient region. Significant quantitative disagreement with neoclassical predictions is seen in the cores of ITB, QH-, and H-mode plasmas, demonstrating that neoclassical theory is an incomplete description of poloidal rotation. The addition of turbulence driven Reynolds stress does not remedy this disagreement; linear stability calculations and Doppler backscattering measurements show that disagreement increases as turbulence levels decline. Furthermore, the effect of fast-ion friction, by itself, does not lead to improved agreement; in QH-mode plasmas, neoclassical predictions are closest to experimental results in plasmas with the largest fast ion friction. Predictions from a new model that combines all three effects show somewhat better agreement in the H-mode case, but discrepancies well outside the experimental error bars remain.
Numerical simulation of turbulent heat transfer in an annular fuel channel augmented by spacer ribs
Takase, Kazuyuki; Akino, Norio [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Dept. of High Temperature Engineering
1995-12-31T23:59:59.000Z
Thermal-hydraulic characteristics of fuel channels with three dimensional trapezoidal spacer ribs for high temperature gas-cooled reactors were investigated under the same coolant conditions as the reactor operation, maximum fuel channel outlet temperature of 1,000 C and pressure of 4 MPa, and analytically by numerical simulations using the {kappa}-{var_epsilon} turbulence model. The turbulent heat transfer coefficients in the spacer ribbed fuel channel were 20 to 100% higher than those in a concentric smooth annulus for a region of Reynolds number exceeding 2,000. Furthermore, the predicted Nusselt number in the spacer ribbed fuel channel was in good agreement with the empirical correlation obtained from the present experimental data within an error of 10% with Reynolds number of more than 5000. On the other hand, the friction factors in the spacer ribbed fuel channel were higher than those in the smooth duct in the turbulent region, and also they could be predicted with sufficient accuracy. In addition, the present numerical simulation could clarify quantitatively the effects of the heat transfer augmentation due to the spacer ribs and the axial velocity increase due to a reduction in the annular channel cross-section.
Accretion Disc Turbulence and the X-Ray Power Spectra of Black Hole High States
Michael A. Nowak; Robert V. Wagoner
1994-10-06T23:59:59.000Z
The high state of black hole candidates is characterized by a quasi- thermal emission component at $kT \\sim 1$ keV. In addition, this state tends to have very low variability which indicates that it is relatively stable, at least on {\\it short} time scales. Most models of the high state imply that the bulk of the emission comes from an optically thick accretion disc; therefore, this state may be an excellent laboratory for testing our ideas about the physics of accretion discs. In this work we consider the implications of assuming that accretion disc viscosity arises from some form of turbulence. Specifically, we consider the simple case of three dimensional hydrodynamic turbulence. It is found that the coupling of such turbulence to acoustic modes in the disc can alter the disc emission. We calculate the amplitude and frequencies of this modulation, and we express our results in terms of the X-ray power spectral density. We compare our calculations with observations of the black hole candidate GS 1124-683, and show that for certain parameters we can reproduce some of the high frequency power. We then briefly explore mechanisms for producing the low frequency power, and note the difficulty that a single variability mechanism has in reproducing the full range of observed variability. In addition, we outline ways in which future spacecraft missions -- such as USA and XTE -- can further constrain our model, especially at frequencies above $\\sim 10^2$ Hz.
Convection Heat Transfer in Three-Dimensional Turbulent Separated/Reattached Flow
Bassem F. Armaly
2007-10-31T23:59:59.000Z
The measurements and the simulation of convective heat transfer in separated flow have been a challenge to researchers for many years. Measurements have been limited to two-dimensional flow and simulations failed to predict accurately turbulent heat transfer in the separated and reattached flow region (prediction are higher than measurements by more than 50%). A coordinated experimental and numerical effort has been initiated under this grant for examining the momentum and thermal transport in three-dimensional separated and reattached flow in an effort to provide new measurements that can be used for benchmarking and for improving the simulation capabilities of 3-D convection in separated/reattached flow regime. High-resolution and non-invasive measurements techniques are developed and employed in this study to quantify the magnitude and the behavior of the three velocity components and the resulting convective heat transfer. In addition, simulation capabilities are developed and employed for improving the simulation of 3-D convective separated/reattached flow. Such basic measurements and simulation capabilities are needed for improving the design and performance evaluation of complex (3-D) heat exchanging equipment. Three-dimensional (3-D) convective air flow adjacent to backward-facing step in rectangular channel is selected for the experimental component of this study. This geometry is simple but it exhibits all the complexities that appear in any other separated/reattached flow, thus making the results generated in this study applicable to any other separated and reattached flow. Boundary conditions, inflow, outflow, and wall thermal treatment in this geometry can be well measured and controlled. The geometry can be constructed with optical access for non-intrusive measurements of the flow and thermal fields. A three-component laser Doppler velocimeter (LDV) is employed to measure simultaneously the three-velocity components and their turbulent fluctuations. Infrared thermography is utilized to measure the wall temperature and that information is used to determine the local convective heat transfer coefficient. FLUENT – CFD code is used as the platform in the simulation effort and User Defined Functions are developed for incorporating advanced turbulence models into this simulation code. Predictions of 3-D turbulent convection in separated flow, using the developed simulation capabilities under this grant, compared well with measured results. Results from the above research can be found in the seventeen refereed journal articles, and thirteen refereed publications and presentations in conference proceedings that have been published by the PI during the this grant period. The research effort is still going on and several publications are being prepared for reporting recent results.
Locality and stability of the cascades of two-dimensional turbulence.
Gkioulekas, Eleftherios - Department of Mathematics, University of Texas
chemical combustion Stabilize plasma in a nuclear fusion reactor Propagation of laser through turbulence;Outline Why study turbulence? Brief overview of K41 theory (3D turbulence) Frisch reformulation of K41 theory. KLB theory (2D turbulence). My reformulation of Frisch to address 2D turbulence Locality
Photoionisation Feedback in a Self-Gravitating, Magnetised, Turbulent Cloud
Geen, Sam; Tremblin, Pascal; Rosdahl, Joakim
2015-01-01T23:59:59.000Z
We present a new set of analytic models for the expansion of HII regions powered by UV photoionisation from massive stars and compare them to a new suite of radiative magnetohydrodynamic simulations of self-gravitating molecular clouds. To perform these simulations we use RAMSES-RT, an Eulerian adaptive mesh magnetohydrodynamics code with radiative transfer of UV photons. We find two models that fit the simulation results well, and give a physically-motivated criterion for determining which of the models should be used. In one model, the ionisation front is only resisted by the ram pressure from the external medium, which we model as a spherically symmetric power law model. In the other, the front stalls at an equilibrium radius at which the ram pressure from accretion or turbulence in the cloud is balanced by the thermal pressure of the photoionised gas. If this stalling radius is larger than the radius of the cloud, the ionisation front can escape the cloud and expand freely in most directions. Otherwise, t...
Physics of Intrinsic Rotation in Flux-Driven ITG Turbulence
Ku, S; Dimond, P H; Dif-Pradalier, G; Kwon, J M; Sarazin, Y; Hahm, T S; Garbet, X; Chang, C S; Latu, G; Yoon, E S; Ghendrih, Ph; Yi, S; Strugarek, A; Solomon, W
2012-02-23T23:59:59.000Z
Global, heat flux-driven ITG gyrokinetic simulations which manifest the formation of macroscopic, mean toroidal flow profiles with peak thermal Mach number 0.05, are reported. Both a particle-in-cell (XGC1p) and a semi-Lagrangian (GYSELA) approach are utilized without a priori assumptions of scale-separation between turbulence and mean fields. Flux-driven ITG simulations with different edge flow boundary conditions show in both approaches the development of net unidirectional intrinsic rotation in the co-current direction. Intrinsic torque is shown to scale approximately linearly with the inverse scale length of the ion temperature gradient. External momentum input is shown to effectively cancel the intrinsic rotation profile, thus confirming the existence of a local residual stress and intrinsic torque. Fluctuation intensity, intrinsic torque and mean flow are demonstrated to develop inwards from the boundary. The measured correlations between residual stress and two fluctuation spectrum symmetry breakers, namely E x B shear and intensity gradient, are similar. Avalanches of (positive) heat flux, which propagate either outwards or inwards, are correlated with avalanches of (negative) parallel momentum flux, so that outward transport of heat and inward transport of parallel momentum are correlated and mediated by avalanches. The probability distribution functions of the outward heat flux and the inward momentum flux show strong structural similarity
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.
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...
Refined critical balance in strong Alfvenic turbulence
A. Mallet; A. A. Schekochihin; B. D. G. Chandran
2015-08-24T23:59:59.000Z
We present numerical evidence that in strong Alfvenic turbulence, the critical balance principle---equality of the nonlinear decorrelation and linear propagation times---is scale invariant, in the sense that the probability distribution of the ratio of these times is independent of scale. This result only holds if the local alignment of the Elsasser fields is taken into account in calculating the nonlinear time. At any given scale, the degree of alignment is found to increase with fluctuation amplitude, supporting the idea that the cause of alignment is mutual dynamical shearing of Elsasser fields. The scale-invariance of critical balance (while all other quantities of interest are strongly intermittent, i.e., have scale-dependent distributions) suggests that it is the most robust of the scaling principles used to describe Alfvenic turbulence. The quality afforded by situ fluctuation measurements in the solar wind allows for direct verification of this fundamental principle.
None
2012-01-01T23:59:59.000Z
HEATS Project: The 15 projects that make up ARPA-E’s HEATS program, short for “High Energy Advanced Thermal Storage,” seek to develop revolutionary, cost-effective ways to store thermal energy. HEATS focuses on 3 specific areas: 1) developing high-temperature solar thermal energy storage capable of cost-effectively delivering electricity around the clock and thermal energy storage for nuclear power plants capable of cost-effectively meeting peak demand, 2) creating synthetic fuel efficiently from sunlight by converting sunlight into heat, and 3) using thermal energy storage to improve the driving range of electric vehicles (EVs) and also enable thermal management of internal combustion engine vehicles.
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.
Simulation of spherically expanding turbulent premixed flames
Ahmed, I.; Swaminathan, N.
2013-09-16T23:59:59.000Z
canonically im- portant configuration and its investigation is helpful to understand combustion in prac- tical devices such as the spark ignited internal combustion engine, modern stratified charge engines and accidental explosions of fuel vapour cloud... Simulation of spherically expanding turbulent premixed flames I. Ahmed, N. Swaminathan? Department of Engineering, Cambridge University, Cambridge, CB2 1PZ, UK. ?Corresponding author: Department of Engineering, Cambridge University, Trumpington...
Hindered energy cascade in highly helical isotropic turbulence
Stepanov, Rodion; Frick, Peter; Shestakov, Alexander
2015-01-01T23:59:59.000Z
The conventional approach to the turbulent energy cascade, based on Richardson-Kolmogorov phenomenology, ignores the topology of emerging vortices, which is related to the helicity of the turbulent flow. It is generally believed that helicity can play a significant role in turbulent systems, e.g., supporting the generation of large-scale magnetic fields, but its impact on the energy cascade to small scales has never been observed. We suggest for the first time a generalized phenomenology for isotropic turbulence with an arbitrary spectral distribution of the helicity. We discuss various scenarios of direct turbulent cascades with new helicity effect, which can be interpreted as a hindering of the spectral energy transfer. Therefore the energy is accumulated and redistributed so that the efficiency of non-linear interactions will be sufficient to provide a constant energy flux. We confirm our phenomenology by high Reynolds number numerical simulations based on a shell model of helical turbulence. The energy in...
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.
AN OBSERVED CORRELATION BETWEEN THERMAL AND NON-THERMAL EMISSION...
Office of Scientific and Technical Information (OSTI)
AN OBSERVED CORRELATION BETWEEN THERMAL AND NON-THERMAL EMISSION IN GAMMA-RAY BURSTS Citation Details In-Document Search Title: AN OBSERVED CORRELATION BETWEEN THERMAL AND...
Forecasting Turbulent Modes with Nonparametric Diffusion Models
Tyrus Berry; John Harlim
2015-01-27T23:59:59.000Z
This paper presents a nonparametric diffusion modeling approach for forecasting partially observed noisy turbulent modes. The proposed forecast model uses a basis of smooth functions (constructed with the diffusion maps algorithm) to represent probability densities, so that the forecast model becomes a linear map in this basis. We estimate this linear map by exploiting a previously established rigorous connection between the discrete time shift map and the semi-group solution associated to the backward Kolmogorov equation. In order to smooth the noisy data, we apply diffusion maps to a delay embedding of the noisy data, which also helps to account for the interactions between the observed and unobserved modes. We show that this delay embedding biases the geometry of the data in a way which extracts the most predictable component of the dynamics. The resulting model approximates the semigroup solutions of the generator of the underlying dynamics in the limit of large data and in the observation noise limit. We will show numerical examples on a wide-range of well-studied turbulent modes, including the Fourier modes of the energy conserving Truncated Burgers-Hopf (TBH) model, the Lorenz-96 model in weakly chaotic to fully turbulent regimes, and the barotropic modes of a quasi-geostrophic model with baroclinic instabilities. In these examples, forecasting skills of the nonparametric diffusion model are compared to a wide-range of stochastic parametric modeling approaches, which account for the nonlinear interactions between the observed and unobserved modes with white and colored noises.
Vortices within vortices: hierarchical nature of vortex tubes in turbulence
Bürger, Kai; Westermann, Rüdiger; Werner, Suzanne; Lalescu, Cristian C; Szalay, Alexander; Meneveau, Charles; Eyink, Gregory L
2012-01-01T23:59:59.000Z
The JHU turbulence database [1] can be used with a state of the art visualisation tool [2] to generate high quality fluid dynamics videos. In this work we investigate the classical idea that smaller structures in turbulent flows, while engaged in their own internal dynamics, are advected by the larger structures. They are not advected undistorted, however. We see instead that the small scale structures are sheared and twisted by the larger scales. This illuminates the basic mechanisms of the turbulent cascade.
Space-time correlations in turbulent flow: A review
Wallace, James M
2015-01-01T23:59:59.000Z
This paper reviews some of the principal uses, over almost seven decades, of correlations, in both Eulerian and Lagrangian frames of reference, of properties of turbulent flows at variable spatial locations and variable time instants. Commonly called space--time correlations, they have been fundamental to theories and models of turbulence as well as for the analyses of experimental and direct numerical simulation turbulence data.
Thermal and Electrical Transport in Oxide Heterostructures
Ravichandran, Jayakanth
2011-01-01T23:59:59.000Z
of thermal conductivity . . . . . . . . . . . . . . . .4.4 Thermal transport in2.3.2 Thermal transport . . . . . . . . . . . . . . . .
Non-premixed flame-turbulence interaction in compressible turbulent flow
Livescu, D. (Daniel); Madnia, C. K.
2002-01-01T23:59:59.000Z
Nonpremixed turbulent reacting flows are intrinsically difficult to model due to the strong coupling between turbulent motions and reaction. The large amount of heat released by a typical hydrocarbon flame leads to significant modifications of the thermodynamic variables and the molecular transport coefficients and thus alters the fluid dynamics. Additionally, in nonpremixed combustion, the flame has a complex spatial structure. Localized expansions and contractions occur, enhancing the dilatational motions. Therefore, the compressibility of the flow and the heat release are intimately related. However, fundamental studies of the role of compressibility on the scalar mixing and reaction are scarce. In this paper they present results concerning the fundamental aspects of the interaction between non-premixed flame and compressible turbulence.
Massively Parallel Spectral Element Large Eddy Simulation of a Turbulent Channel Using Wall Models
Rabau, Joshua I
2013-05-01T23:59:59.000Z
Wall-bounded turbulent flows are prevalent in engineering and industrial applications. Walls greatly affect turbulent characteristics in many ways including production and propagation of turbulent stresses. While computational ...
Boehringer, Hans
8. Particle Diffusion and Acceleration #12; #12; Proceedings of the Workshop: ``Diffuse Thermal. Feretti & P. Schuecker, MPE Report 271, pp. 249253 Turbulent Particle Acceleration in the Diffuse Cluster Abstract. In situ particle acceleration is probably occur ing in cluster radio haloes. This is suggested
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.
DNS/LES of Complex Turbulent Flows | Argonne Leadership Computing...
Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)
hot oxygen. The green isocontours illustrate the turbulent structures in the fuel, the blue isocontours show the HO2 radical (an important precursor to autoignition), and the...
TURBULENT CONVECTION IN STELLAR INTERIORS. III. MEAN-FIELD ANALYSIS...
Office of Scientific and Technical Information (OSTI)
STARS; RESOLUTION; REYNOLDS NUMBER; SHELL MODELS; STAR EVOLUTION; STRATIFICATION; SUPERNOVAE; THREE-DIMENSIONAL CALCULATIONS; TURBULENCE Word Cloud More Like This Full Text...
Magnetostrophic balance as the optimal state for turbulent magnetoconvection
King, EM; Aurnou, JM
2015-01-01T23:59:59.000Z
that the magnetostrophic balance is no longer attained (Magnetostrophic balance as the optimal state for turbulentLorentz and Coriolis forces balance. One can estimate the
Gyrokinetic simulations of turbulent transport in fusion plasmas
Rogers, Barrett Neil [Dartmouth] [Dartmouth
2013-05-30T23:59:59.000Z
This is the final report for a DOE award that was targeted at understanding and simulating turbulence and transport in plasma fusion devices such as tokamaks.
Sandia Energy - The CRF's Turbulent Combustion Lab (TCL) Captures...
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CRF's Turbulent Combustion Lab (TCL) Captures the Moment of Hydrogen Ignition Home Energy Transportation Energy CRF Facilities News News & Events Research & Capabilities The CRF's...
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.
Sandia Energy - Measuring Inflow and Wake Flow Turbulence Using...
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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...
ASCR Workshop on Turbulent Flow Simulations at the Exascale:...
Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site
experts in turbulent- flow simulation, computational mathematics, and high-performance computing. Building upon previous ASCR workshops on exascale computing, participants...
Advanced Turbulence Measurements and Signal Processing for Hydropower Flow Characterization
Advanced Turbulence Measurements and Signal Processing for Hydropower Flow Characterization and flow characterization within full scale conventional hydropower systems, at marine and hydrokinetic
Hot Particle and Turbulent Transport Effects on Resistive Instabilities
Brennan, Dylan P.
2012-10-16T23:59:59.000Z
This research project included two main thrusts; energetic particle effects on resistive MHD modes in tokamaks, and turbulence interactions with tearing modes in simplified geometry.
Cylindrical thermal contact conductance
Ayers, George Harold
2004-09-30T23:59:59.000Z
Thermal contact conductance is highly important in a wide variety of applications, from the cooling of electronic chips to the thermal management of spacecraft. The demand for increased efficiency means that components ...
Rutberg, Michael; Hastbacka, Mildred; Cooperman, Alissa; Bouza, Antonio
2013-06-05T23:59:59.000Z
The article discusses thermal energy storage technologies. This article addresses benefits of TES at both the building site and the electricity generation source. The energy savings and market potential of thermal energy store are reviewed as well.
Thermal Management of Solar Cells
Saadah, Mohammed Ahmed
2013-01-01T23:59:59.000Z
phonon transmission and interface thermal conductance acrossF. Miao, et al. , "Superior Thermal Conductivity of Single-Advanced Materials for Thermal Management of Electronic
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.
Thermal Performance Benchmarking (Presentation)
Moreno, G.
2014-11-01T23:59:59.000Z
This project will benchmark the thermal characteristics of automotive power electronics and electric motor thermal management systems. Recent vehicle systems will be benchmarked to establish baseline metrics, evaluate advantages and disadvantages of different thermal management systems, and identify areas of improvement to advance the state-of-the-art.
Thermal neutron detection system
Peurrung, Anthony J. (Richland, WA); Stromswold, David C. (West Richland, WA)
2000-01-01T23:59:59.000Z
According to the present invention, a system for measuring a thermal neutron emission from a neutron source, has a reflector/moderator proximate the neutron source that reflects and moderates neutrons from the neutron source. The reflector/moderator further directs thermal neutrons toward an unmoderated thermal neutron detector.
Multiwavelength Thermal Emission
California at Santa Cruz, University of
Multiwavelength Astronomy NASA #12;Thermal Emission #12;Thermal Emission Non-thermal p-p collisions Optical IR Radio/ Microwave sources of emission massive stars, WHIM, Ly many dust, cool objects-ray ~GeV Gamma-ray ~TeV sources of emission AGN, clusters, SNR, binaries, stars AGN (obscured), shocks
Adaptive LES Methodology for Turbulent Flow Simulations
Oleg V. Vasilyev
2008-06-12T23:59:59.000Z
Although turbulent flows are common in the world around us, a solution to the fundamental equations that govern turbulence still eludes the scientific community. Turbulence has often been called one of the last unsolved problem in classical physics, yet it is clear that the need to accurately predict the effect of turbulent flows impacts virtually every field of science and engineering. As an example, a critical step in making modern computational tools useful in designing aircraft is to be able to accurately predict the lift, drag, and other aerodynamic characteristics in numerical simulations in a reasonable amount of time. Simulations that take months to years to complete are much less useful to the design cycle. Much work has been done toward this goal (Lee-Rausch et al. 2003, Jameson 2003) and as cost effective accurate tools for simulating turbulent flows evolve, we will all benefit from new scientific and engineering breakthroughs. The problem of simulating high Reynolds number (Re) turbulent flows of engineering and scientific interest would have been solved with the advent of Direct Numerical Simulation (DNS) techniques if unlimited computing power, memory, and time could be applied to each particular problem. Yet, given the current and near future computational resources that exist and a reasonable limit on the amount of time an engineer or scientist can wait for a result, the DNS technique will not be useful for more than 'unit' problems for the foreseeable future (Moin & Kim 1997, Jimenez & Moin 1991). The high computational cost for the DNS of three dimensional turbulent flows results from the fact that they have eddies of significant energy in a range of scales from the characteristic length scale of the flow all the way down to the Kolmogorov length scale. The actual cost of doing a three dimensional DNS scales as Re{sup 9/4} due to the large disparity in scales that need to be fully resolved. State-of-the-art DNS calculations of isotropic turbulence have recently been completed at the Japanese Earth Simulator (Yokokawa et al. 2002, Kaneda et al. 2003) using a resolution of 40963 (approximately 10{sup 11}) grid points with a Taylor-scale Reynolds number of 1217 (Re {approx} 10{sup 6}). Impressive as these calculations are, performed on one of the world's fastest super computers, more brute computational power would be needed to simulate the flow over the fuselage of a commercial aircraft at cruising speed. Such a calculation would require on the order of 10{sup 16} grid points and would have a Reynolds number in the range of 108. Such a calculation would take several thousand years to simulate one minute of flight time on today's fastest super computers (Moin & Kim 1997). Even using state-of-the-art zonal approaches, which allow DNS calculations that resolve the necessary range of scales within predefined 'zones' in the flow domain, this calculation would take far too long for the result to be of engineering interest when it is finally obtained. Since computing power, memory, and time are all scarce resources, the problem of simulating turbulent flows has become one of how to abstract or simplify the complexity of the physics represented in the full Navier-Stokes (NS) equations in such a way that the 'important' physics of the problem is captured at a lower cost. To do this, a portion of the modes of the turbulent flow field needs to be approximated by a low order model that is cheaper than the full NS calculation. This model can then be used along with a numerical simulation of the 'important' modes of the problem that cannot be well represented by the model. The decision of what part of the physics to model and what kind of model to use has to be based on what physical properties are considered 'important' for the problem. It should be noted that 'nothing is free', so any use of a low order model will by definition lose some information about the original flow.
Thermal Regimes of Northeast Streams
Thermal Regimes of Northeast Streams February 17, 2011 Jennifer M. Jacobs Environmental Research Urbanization Drivers #12;Overview Regime Urbanization Drivers Thermal Regime Significance Pictures Credit: NJ Thermal Loading (USGS) Stormwater and Streams Optimizing Stormwater Management to Protect the Thermal
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.
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
Evolution of isolated turbulent trailing vortices Karthik Duraisamy1,a
Alonso, Juan J.
Evolution of isolated turbulent trailing vortices Karthik Duraisamy1,a and Sanjiva K. Lele2,b 1 evolution of a low swirl-number turbulent Batchelor vortex is studied using pseudospectral direct numerical application of boundary conditions. The physics of the evolution is investigated with an emphasis
Center for Turbulence Research Annual Research Briefs 2008
Prinz, Friedrich B.
in a supersonic turbulent crossflow By S. Kawai AND S. K. Lele 1. Motivation and objectives Important recent load, etc. Jet mixing in a supersonic crossflow (JISC) is a type of flow where compressible LES can, the enhancement of supersonic turbulent mixing of jet fuel and crossflow air is a critical issue in developing
Taming turbulence in magnetized plasmas: from fusion energy to
occurs (fusion of particle beams will not work...) Thermonuclear fusion in a confined plasma (T~10 keTaming turbulence in magnetized plasmas: from fusion energy to black hole accretion disks Troy?: In fusion plasmas turbulent leakage of heat and particles is a key issue. Sheared flow can suppress
Center for Turbulence Research Proceedings of the Summer Program 2012
Wang, Wei
-to-cycle variations in internal combustion engines (Richard et al. 2007). The unresolved flame/turbulence in models for turbulent premixed combustion By D. Veynante, T. Schmitt, M. Boileau AND V. Moureau Very few attempts have been made to implement dynamic combustion models in large eddy simulations, whereas
Center for Turbulence Research Annual Research Briefs 2012
Wang, Wei
in an internal combustion engine By D. Kah, V. Mittal, Shashank AND H. Pitsch 1. Motivation and objectives, in the turbulent reactive flows occurring in Internal Combustion (IC) engines, the mixing of the reactants enablingCenter for Turbulence Research Annual Research Briefs 2012 43 LES of spray and combustion
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
Center for Turbulence Research Proceedings of the Summer Program 2012
Wang, Wei
streaks which are observed to breakdown into turbulent spots are differentiated from innocuous events the conventionally reported values of urms. Furthermore the streaks responsible for breakdown to turbulence have instability analysis of Vaughan & Zaki (2011). Regardless of the mechanism which leads to breakdown
Turbulence, Transport and the Density Limit in Magnetic Fusion Experiments
Greenwald, Martin
Turbulence, Transport and the Density Limit in Magnetic Fusion Experiments Martin Greenwald - MIT AND MAGNETIC CONFINEMENT· · · · THE DENSITY LIMIT PROBLEM INTERLUDE ON TRANSPORT AND TURBULENCE TOWARDS OF THE FUSION REACTION AND FOR ELASTIC SCATTERING LEAD US DIRECTLY TO THE STUDY OF CONFINED PLASMAS · · imes
Growth of Cloud Droplets in a Turbulent Environment
Wang, Lian-Ping
Growth of Cloud Droplets in a Turbulent Environment Wojciech W. Grabowski1 and Lian-Ping Wang2 1 Keywords condensational growth, turbulent collision-coalescence, particle-laden flow, cloud microphysical concerning the growth of cloud droplets by water-vapor diffu- sion and by collision
Modeling of combustion noise spectrum from turbulent premixed flames
Paris-Sud XI, Université de
Modeling of combustion noise spectrum from turbulent premixed flames Y. Liu, A. P. Dowling, T. D, Nantes, France 2321 #12;Turbulent combustion processes generate sound radiation due to temporal changes, this temporal correlation and its role in the modeling of combustion noise spectrum are studied by analyzing
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
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
TURBULENT-LAMINAR PATTERNS IN PLANE COUETTE Dwight Barkley
Barkley, Dwight
@limsi.fr Abstract Regular patterns of turbulent and laminar fluid motion arise in plane Couette flow near the lowest and is the kinematic viscosity of the fluid. See figure 1. For all val- ues of ¡£¢ , laminar Couette flow at an angle to the streamwise direction. Fluid flows exhibiting coexisting turbulent and laminar regions have
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
Skin friction and pressure: the "footprints" of turbulence
Protas, Bartosz
been a flurry of activity in controlling both laminar and turbulent flows in certain idealized settings, and to begin to shed light on how to control fluid flow in practical engineering applications with modelSkin friction and pressure: the "footprints" of turbulence Thomas R. Bewley and Bartosz Protas Flow
Assessment of turbulence by high-order statistics. Offshore example.
Peinke, Joachim
Assessment of turbulence by high-order statistics. Offshore example. Allan Morales Joachim Peinke ForWind - Center for Wind Energy Research University of Oldenburg, Germany 1 Summary Offshore. Keywords: Offshore turbulence. Intermittency. Tur- bulence Intensity. Log-Normal distributions. 2 Data sets
Numerical simulation of turbulent jet primary breakup in Diesel engines
Helluy, Philippe
Numerical simulation of turbulent jet primary breakup in Diesel engines Peng Zeng1 Marcus Herrmann" IRMA Strasbourg, 23.Jan.2008 #12;Introduction DNS of Primary Breakup in Diesel Injection Phase Transition Modeling Turbulence Modeling Summary Outline 1 Introduction 2 DNS of Primary Breakup in Diesel
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
Transition to turbulence in particulate pipe flow
Matas, J P; Guazzelli, E; Matas, Jean-Philippe; Morris, Jeffrey F.; Guazzelli, Elisabeth
2003-01-01T23:59:59.000Z
We investigate experimentally the influence of suspended particles on the transition to turbulence. The particles are monodisperse and neutrally-buoyant with the liquid. The role of the particles on the transition depends both upon the pipe to particle diameter ratios and the concentration. For large pipe-to-particle diameter ratios the transition is delayed while it is lowered for small ratios. A scaling is proposed to collapse the departure from the critical Reynolds number for pure fluid as a function of concentration into a single master curve.
Acceleration statistics of heavy particles in turbulence
J. Bec; L. Biferale; G. Boffetta; A. Celani; M. Cencini; A. Lanotte; S. Musacchio; F. Toschi
2005-12-09T23:59:59.000Z
We present the results of direct numerical simulations of heavy particle transport in homogeneous, isotropic, fully developed turbulence, up to resolution $512^3$ ($R_\\lambda\\approx 185$). Following the trajectories of up to 120 million particles with Stokes numbers, $St$, in the range from 0.16 to 3.5 we are able to characterize in full detail the statistics of particle acceleration. We show that: ({\\it i}) The root-mean-squared acceleration $a_{\\rm rms}$ sharply falls off from the fluid tracer value already at quite small Stokes numbers; ({\\it ii}) At a given $St$ the normalised acceleration $a_{\\rm rms}/(\\epsilon^3/\
Selected problems in turbulence theory and modeling
Jeong, Eun-Hwan
2004-09-30T23:59:59.000Z
: E QR dt dQ ?23 ??= ; E RQ dt dR ?3 2 3 2 ?= ; E D dt dD ?6?= . (2.12) This is also an autonomous dynamical system of equations that can be solved knowing the initial conditions. This system has one attracting fixed point at the origin (Q=0... are assigned from DNS data14. Depending on the quantity of interest, 3,000 to 30,000 fluid elements are used in the model calculations. The results are summarized in the next section. 2.4 RESULT AND DISCUSSION We will now investigate the turbulence small...
Lyapunov exponents of heavy particles in turbulence
Jeremie Bec; Luca Biferale; Guido Boffetta; Massimo Cencini; Stefano Musacchio; Federico Toschi
2006-06-08T23:59:59.000Z
Lyapunov exponents of heavy particles and tracers advected by homogeneous and isotropic turbulent flows are investigated by means of direct numerical simulations. For large values of the Stokes number, the main effect of inertia is to reduce the chaoticity with respect to fluid tracers. Conversely, for small inertia, a counter-intuitive increase of the first Lyapunov exponent is observed. The flow intermittency is found to induce a Reynolds number dependency for the statistics of the finite time Lyapunov exponents of tracers. Such intermittency effects are found to persist at increasing inertia.
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.
Gyrokinetic Simulation of Global Turbulent Transport Properties in Tokamak Experiments
Wang, W.X.; Lin, Z.; Tang, W.M.; Lee, W.W.; Ethier, S.; Lewandowski, J.L.V.; Rewoldt, G.; Hahm, T.S.; Manickam, J.
2006-01-01T23:59:59.000Z
A general geometry gyro-kinetic model for particle simulation of plasma turbulence in tokamak experiments is described. It incorporates the comprehensive influence of noncircular cross section, realistic plasma profiles, plasma rotation, neoclassical (equilibrium) electric fields, and Coulomb collisions. An interesting result of global turbulence development in a shaped tokamak plasma is presented with regard to nonlinear turbulence spreading into the linearly stable region. The mutual interaction between turbulence and zonal flows in collisionless plasmas is studied with a focus on identifying possible nonlinear saturation mechanisms for zonal flows. A bursting temporal behavior with a period longer than the geodesic acoustic oscillation period is observed even in a collisionless system. Our simulation results suggest that the zonal flows can drive turbulence. However, this process is too weak to be an effective zonal flow saturation mechanism.
The energetic coupling of scales in gyrokinetic plasma turbulence
Teaca, Bogdan, E-mail: bogdan.teaca@coventry.ac.uk [Applied Mathematics Research Centre, Coventry University, Coventry CV1 5FB (United Kingdom); Max-Planck für Sonnensystemforschung, Justus-von-Liebig-Weg 3, D-37077 Göttingen (Germany); Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, D-85748 Garching (Germany); Max-Planck/Princeton Center for Plasma Physics (Germany); Navarro, Alejandro Bañón, E-mail: alejandro.banon.navarro@ipp.mpg.de [Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, D-85748 Garching (Germany); Jenko, Frank, E-mail: frank.jenko@ipp.mpg.de [Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, D-85748 Garching (Germany); Max-Planck/Princeton Center for Plasma Physics (Germany)
2014-07-15T23:59:59.000Z
In magnetized plasma turbulence, the couplings of perpendicular spatial scales that arise due to the nonlinear interactions are analyzed from the perspective of the free-energy exchanges. The plasmas considered here, with appropriate ion or electron adiabatic electro-neutrality responses, are described by the gyrokinetic formalism in a toroidal magnetic geometry. Turbulence develops due to the electrostatic fluctuations driven by temperature gradient instabilities, either ion temperature gradient (ITG) or electron temperature gradient (ETG). The analysis consists in decomposing the system into a series of scale structures, while accounting separately for contributions made by modes possessing special symmetries (e.g., the zonal flow modes). The interaction of these scales is analyzed using the energy transfer functions, including a forward and backward decomposition, scale fluxes, and locality functions. The comparison between the ITG and ETG cases shows that ETG turbulence has a more pronounced classical turbulent behavior, exhibiting a stronger energy cascade, with implications for gyrokinetic turbulence modeling.
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.
Scale invariance at the onset of turbulence in Couette flow
Shi, Liang; Hof, Bjoern
2013-01-01T23:59:59.000Z
Laminar-turbulent intermittency is intrinsic to the transitional regime of a wide range of fluid flows including pipe, channel, boundary layer and Couette flow. In the latter turbulent spots can grow and form continuous stripes, yet in the stripe-normal direction they remain interspersed by laminar fluid. We carry out direct numerical simulations in a long narrow domain and observe that individual turbulent stripes are transient. In agreement with recent observations in pipe flow we find that turbulence becomes sustained at a distinct critical point once the spatial proliferation outweighs the inherent decaying process. By resolving the asymptotic size distributions close to criticality we can for the first time demonstrate scale invariance at the onset of turbulence.
Reconnection events in two-dimensional Hall magnetohydrodynamic turbulence
Donato, S.; Servidio, S.; Carbone, V. [Dipartimento di Fisica, Universita della Calabria, I-87036 Cosenza (Italy); Dmitruk, P. [Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires and Instituto de Fisica de Buenos Aires, CONICET, Buenos Aires (Argentina); Shay, M. A.; Matthaeus, W. H. [Bartol Research Institute and Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716 (United States); Cassak, P. A. [Department of Physics, West Virginia University, Morgantown, West Virginia 26506 (United States)
2012-09-15T23:59:59.000Z
The statistical study of magnetic reconnection events in two-dimensional turbulence has been performed by comparing numerical simulations of magnetohydrodynamics (MHD) and Hall magnetohydrodynamics (HMHD). The analysis reveals that the Hall term plays an important role in turbulence, in which magnetic islands simultaneously reconnect in a complex way. In particular, an increase of the Hall parameter, the ratio of ion skin depth to system size, broadens the distribution of reconnection rates relative to the MHD case. Moreover, in HMHD the local geometry of the reconnection region changes, manifesting bifurcated current sheets and quadrupolar magnetic field structures in analogy to laminar studies, leading locally to faster reconnection processes in this case of reconnection embedded in turbulence. This study supports the idea that the global rate of energy dissipation is controlled by the large scale turbulence, but suggests that the distribution of the reconnection rates within the turbulent system is sensitive to the microphysics at the reconnection sites.
Gupta, Kamlesh G.; Echekki, Tarek [Department of Mechanical and Aerospace Engineering, North Carolina State University, NC (United States)
2011-02-15T23:59:59.000Z
The autoignition of hydrogen/carbon monoxide in a turbulent jet with preheated co-flow air is studied using the one-dimensional turbulence (ODT) model. The simulations are performed at atmospheric pressure based on varying the jet Reynolds number and the oxidizer preheat temperature for two compositions corresponding to varying the ratios of H{sub 2} and CO in the fuel stream. Moreover, simulations for homogeneous autoignition are implemented for similar mixture conditions for comparison with the turbulent jet results. The results identify the key effects of differential diffusion and turbulence on the onset and eventual progress of autoignition in the turbulent jets. The differential diffusion of hydrogen fuels results in a reduction of the ignition delay relative to similar conditions of homogeneous autoignition. Turbulence may play an important role in delaying ignition at high-turbulence conditions, a process countered by the differential diffusion of hydrogen relative to carbon monoxide; however, when ignition is established, turbulence enhances the overall rates of combustion of the non-premixed flame downstream of the ignition point. (author)
Moncrieff, John B.
to the creation of emerging TEAL structures to the power passing down the Richardson cascade in the outer layer-Obukhov similarity, self-organizing systems 1. Introduction In convective boundary layers the structureTurbulence structure of the surface layer Boun 2247-03D TURBULENCE STRUCTURE OF THE UNSTABLE
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)
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.
Optimal lengthscale for a turbulent dynamo
Sadek, Mira; Fauve, Stephan
2015-01-01T23:59:59.000Z
We demonstrate that there is an optimal forcing length scale for low Prandtl number dynamo flows, that can significantly reduce the required energy injection rate. The investigation is based on simulations of the induction equation in a periodic box of size $2\\pi L$. The flows considered are turbulent ABC flows forced at different forcing wavenumbers $k_f$ simulated using a subgrid turbulent model. The critical magnetic Reynolds number $Rm_c^T$ decreases as the forcing wavenumber $k_f$ increases from the smallest allowed $k_{min}=1/L$. At large $k_f$ on the other hand, $Rm_c^T$ increases with the forcing wavenumber as $Rm_c^T \\propto \\sqrt{ k_f}$ in agreement with mean-field scaling prediction. At $k_f L\\simeq 4$ an optimal wavenumber is reached where $Rm_c^T$ obtains its minimum value. At this optimal wavenumber $Rm_c^T$ is smaller by more than a factor of ten than the case forced in $k_f=1$. This leads to a reduction of the energy injection rate by three orders of magnitude when compared to the case that th...
Catalytic thermal barrier coatings
Kulkarni, Anand A. (Orlando, FL); Campbell, Christian X. (Orlando, FL); Subramanian, Ramesh (Oviedo, FL)
2009-06-02T23:59:59.000Z
A catalyst element (30) for high temperature applications such as a gas turbine engine. The catalyst element includes a metal substrate such as a tube (32) having a layer of ceramic thermal barrier coating material (34) disposed on the substrate for thermally insulating the metal substrate from a high temperature fuel/air mixture. The ceramic thermal barrier coating material is formed of a crystal structure populated with base elements but with selected sites of the crystal structure being populated by substitute ions selected to allow the ceramic thermal barrier coating material to catalytically react the fuel-air mixture at a higher rate than would the base compound without the ionic substitutions. Precious metal crystallites may be disposed within the crystal structure to allow the ceramic thermal barrier coating material to catalytically react the fuel-air mixture at a lower light-off temperature than would the ceramic thermal barrier coating material without the precious metal crystallites.
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.
Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site
Potential Thermal Control Technologies Advanced Vehicle Systems Technology Transfer Jet Cooling Alternative Coolants TIM Low R Structure Phase Change Spray Cooling Air Cooling...
AQUIFER THERMAL ENERGY STORAGE
Tsang, C.-F.
2011-01-01T23:59:59.000Z
aquifers for thermal energy storage. Problems outlined abovean Aquifer Used for Hot Water Storage: Digital Simulation ofof Aquifer Systems for Cyclic Storage of Water," of the Fall
Solar Thermal Powered Evaporators
Moe, Christian Robert
2015-01-01T23:59:59.000Z
pp. 67-73, 2003. [17] "Energy Requirements of Desalinationof solar collectors and thermal energy storage in solarapplications," Applied Energy, pp. 538-553, 2013. [20] P. G.
Solar Thermal Powered Evaporators
Moe, Christian Robert
2015-01-01T23:59:59.000Z
C. Y. Zhao, "A review of solar collectors and thermal energya Passive Flat-Plate Solar Collector," International Journalof Flat Plate Solar Collector Equipped with Rectangular Cell
Saffman, Mark
turbulence A. V. Mamaev* and M. Saffman Department of Optics and Fluid Dynamics, Riso" National Laboratory
Turbulence-Flame Interactions in Type Ia Supernovae A. J. Aspden1
Bell, John B.
. INTRODUCTION The complex small-scale dynamics of turbulent thermonuclear flames are essential to understanding
Turbulent Oxygen Flames in Type Ia Supernovae A. J. Aspden1
Bell, John B.
ABSTRACT In previous studies, we examined turbulence-flame interactions in carbon- burning thermonuclear
High-performance Computation and Visualization of Plasma Turbulence on Graphics Processors
Varshney, Amitabh
thermonuclear fusion devices. Turbulence in plasma can lead to energy losses and various catastrophic events
Laminar-Turbulent Transition: Calculation of Minimum Critical Reynolds Number in Channel Flow
Laminar-Turbulent Transition: Calculation of Minimum Critical Reynolds Number in Channel Flow) for laminar-turbulent transition in pipe and channel flows. For pipe flow, the minimum critical Reynolds laminar to turbulent flow Rc2 Rc from turbulent to laminar flow Rc(min) minimum Rc Re Reynolds number = UH
Variable pressure thermal insulating jacket
Nelson, P.A.; Malecha, R.F.; Chilenskas, A.A.
1994-09-20T23:59:59.000Z
A device for controlled insulation of a thermal device is disclosed. The device includes a thermal jacket with a closed volume able to be evacuated to form an insulating jacket around the thermal source. A getter material is in communication with the closed volume of the thermal jacket. The getter material can absorb and desorb a control gas to control gas pressure in the volume of the thermal jacket to control thermal conductivity in the thermal jacket. 10 figs.
Global NOx Measurements in Turbulent Nitrogen-Diluted Hydrogen Jet Flames
Weiland, N.T.; Strakey, P.A.
2007-03-01T23:59:59.000Z
Turbulent hydrogen diffusion flames diluted with nitrogen are currently being studied to assess their ability to achieve the DOE Turbine Program’s aggressive emissions goal of 2 ppm NOx in a hydrogen-fueled IGCC gas turbine combustor. Since the unstrained adiabatic flame temperatures of these diluted flames are not low enough to eliminate thermal NOx formation the focus of the current work is to study how the effects of flame residence time and global flame strain can be used to help achieve the stated NOx emissions goal. Dry NOx measurements are presented as a function of jet diameter nitrogen dilution and jet velocity for a turbulent hydrogen/nitrogen jet issuing from a thin-lipped tube in an atmospheric pressure combustor. The NOx emission indices from these experiments are normalized by the flame residence time to ascertain the effects of global flame strain and fuel Lewis Number on the NOx emissions. In addition dilute hydrogen diffusion flame experiments were performed in a high-pressure combustor at 2 4 and 8 atm. The NOx emission data from these experiments are discussed as well as the results from a Computational Fluid Dynamics modeling effort currently underway to help explain the experimental data.
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.
An h-adaptive finite element method for turbulent heat transfer
Carriington, David B [Los Alamos National Laboratory
2009-01-01T23:59:59.000Z
A two-equation turbulence closure model (k-{omega}) using an h-adaptive grid technique and finite element method (FEM) has been developed to simulate low Mach flow and heat transfer. These flows are applicable to many flows in engineering and environmental sciences. Of particular interest in the engineering modeling areas are: combustion, solidification, and heat exchanger design. Flows for indoor air quality modeling and atmospheric pollution transport are typical types of environmental flows modeled with this method. The numerical method is based on a hybrid finite element model using an equal-order projection process. The model includes thermal and species transport, localized mesh refinement (h-adaptive) and Petrov-Galerkin weighting for the stabilizing the advection. This work develops the continuum model of a two-equation turbulence closure method. The fractional step solution method is stated along with the h-adaptive grid method (Carrington and Pepper, 2002). Solutions are presented for 2d flow over a backward-facing step.
Large-eddy simulations of turbulent flow for grid-to-rod fretting in nuclear reactors
Bakosi, J; Lowrie, R B; Pritchett-Sheats, L A; Nourgaliev, R R
2013-01-01T23:59:59.000Z
The grid-to-rod fretting (GTRF) problem in pressurized water reactors is a flow-induced vibration problem that results in wear and failure of the fuel rods in nuclear assemblies. In order to understand the fluid dynamics of GTRF and to build an archival database of turbulence statistics for various configurations, implicit large-eddy simulations of time-dependent single-phase turbulent flow have been performed in 3x3 and 5x5 rod bundles with a single grid spacer. To assess the computational mesh and resolution requirements, a method for quantitative assessment of unstructured meshes with no-slip walls is described. The calculations have been carried out using Hydra-TH, a thermal-hydraulics code developed at Los Alamos for the Consortium for Advanced Simulation of Light water reactors, a United States Department of Energy Innovation Hub. Hydra-TH uses a second-order implicit incremental projection method to solve the single-phase incompressible Navier-Stokes equations. The simulations explicitly resolve the la...
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.
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.
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.
Simulations of drift resistive ballooning L-mode turbulence in the edge plasma of the DIII-D tokamak
Cohen, B. I.; Umansky, M. V.; Nevins, W. M.; Makowski, M. A. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)] [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Boedo, J. A.; Rudakov, D. L. [University of California, San Diego, San Diego, California 92093 (United States)] [University of California, San Diego, San Diego, California 92093 (United States); McKee, G. R.; Yan, Z. [University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)] [University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States); Groebner, R. J. [General Atomics, P.O. Box 85608, San Diego, California 92186 (United States)] [General Atomics, P.O. Box 85608, San Diego, California 92186 (United States)
2013-05-15T23:59:59.000Z
Results from simulations of electromagnetic drift-resistive ballooning turbulence for tokamak edge turbulence in realistic single-null geometry are reported. The calculations are undertaken with the BOUT three-dimensional fluid code that solves Braginskii-based fluid equations [X. Q. Xu and R. H. Cohen, Contrib. Plasma Phys. 36, 158 (1998)]. The simulation setup models L-mode edge plasma parameters in the actual magnetic geometry of the DIII-D tokamak [J. L. Luxon et al., Fusion Sci. Technol. 48, 807 (2002)]. The computations track the development of drift-resistive ballooning turbulence in the edge region to saturation. Fluctuation amplitudes, fluctuation spectra, and particle and thermal fluxes are compared to experimental data near the outer midplane from Langmuir probe and beam-emission-spectroscopy for a few well-characterized L-mode discharges in DIII-D. The simulations are comprised of a suite of runs in which the physics model is varied to include more fluid fields and physics terms. The simulations yield results for fluctuation amplitudes, correlation lengths, particle and energy fluxes, and diffusivities that agree with measurements within an order of magnitude and within factors of 2 or better for some of the data. The agreement of the simulations with the experimental measurements varies with respect to including more physics in the model equations within the suite of models investigated. The simulations show stabilizing effects of sheared E × B poloidal rotation (imposed zonal flow) and of lower edge electron temperature and density.
Bryant, Duncan Burnette
2011-08-08T23:59:59.000Z
Akker 1999), and ocean CO2 sequestration (Adams and Wannamaker 2005; Adams and Wannamaker 2006). In particular, ocean CO2 sequestration has been noted by the Intergovernmental Panel on Climate Change in its 2005 special report on Carbon Dioxide... for direct carbon sequestration in the oceans have been considered as a means to mitigate the effects on global warming of burning fossil fuels. While the concept of CO2 sequestration is promising, the turbulent structures in multiphase plumes...
Testing ASTRO-H Measurements of Bulk and Turbulent Gas Motions in Galaxy Clusters
Ota, Naomi; Lau, Erwin T
2015-01-01T23:59:59.000Z
Gas motions in galaxy clusters play important roles in determining the properties of the intracluster medium (ICM) and constraining cosmological parameters using X-ray and Sunyaev-Zel'dovich effect observations of galaxy clusters. The upcoming ASTRO-H mission, equipped with high-resolution X-ray spectrometer, will make the first direct measurements of gas motions in galaxy clusters through measurements of Doppler shifting and broadening of emission lines. However, the physical interpretation of the data will be challenging due to the complex thermal and velocity structures of the ICM. In this work, we investigate how well we can measure bulk and turbulent gas motions in the ICM with ASTRO-H, by analyzing mock ASTRO-H simulations of galaxy clusters extracted from cosmological hydrodynamic simulations. We assess how photon counts, spectral fitting methods, multiphase ICM structure, deprojections, and region selection affect the measurements of gas motions. We show that while ASTRO-H is capable of recovering the...
Kolmogorov Dispersion for Turbulence in Porous Media: A Conjecture
Bikas K. Chakrabarti
2006-12-26T23:59:59.000Z
We will utilise the self-avoiding walk (SAW) mapping of the vortex line conformations in turbulence to get the Kolmogorov scale dependence of energy dispersion from SAW statistics, and the knowledge of the disordered fractal geometries on the SAW statistics. These will give us the Kolmogorov energy dispersion exponent value for turbulence in porous media in terms of the size exponent for polymers in the same. We argue that the exponent value will be somewhat less than 5/3 for turbulence in porous media.
Forecasting stratospheric clear-air turbulence by discriminant analysis
Cox, Robert Earl
1973-01-01T23:59:59.000Z
by Discriminant Analysis. (December lg73) Robert Earl Cox, A. B. , Dartmouth College Directed by: Dr. Jam s R. Scoggins The appllca'bili. ty of the statis! ical method of discriminart sna1ysis Lo the prediction of clear-air turbulence over the western Unixed... turbulent and non-turbulent: regions of the stratosphere. The results show that the predictive periormance of most discriminant functions i. s optimized between 45, 000 and 55, 000 ft. The four best discriminant functions of the dependent sample (XB-70...
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.
Large scale properties in turbulent spherically symmetric accretion
Arnab K. Ray; J. K. Bhattacharjee
2005-10-05T23:59:59.000Z
The role of turbulence in a spherically symmetric accreting system has been studied on very large spatial scales of the system. This is also a highly subsonic flow region and here the accreting fluid has been treated as nearly incompressible. It has been shown here that the coupling of the mean flow and the turbulent fluctuations, gives rise to a scaling relation for an effective "turbulent viscosity". This in turn leads to a dynamic scaling for sound propagation in the accretion process. As a consequence of this scaling, the sonic horizon of the transonic inflow solution is shifted inwards, in comparison with the inviscid flow.
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.
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.
Bennett, Gloria A. (Los Alamos, NM); Elder, Michael G. (Los Alamos, NM); Kemme, Joseph E. (Albuquerque, NM)
1985-01-01T23:59:59.000Z
An apparatus which thermally protects sensitive components in tools used in a geothermal borehole. The apparatus comprises a Dewar within a housing. The Dewar contains heat pipes such as brass heat pipes for thermally conducting heat from heat sensitive components to a heat sink such as ice.
Bennett, G.A.; Elder, M.G.; Kemme, J.E.
1984-03-20T23:59:59.000Z
The disclosure is directed to an apparatus for thermally protecting sensitive components in tools used in a geothermal borehole. The apparatus comprises a Dewar within a housing. The Dewar contains heat pipes such as brass heat pipes for thermally conducting heat from heat sensitive components such as electronics to a heat sink such as ice.
Thermal radiation Ron Zevenhoven
Zevenhoven, Ron
.00032, similarly for 2·T = 0.7·2500 = 1750 µmK4 this gives f0-2 = 0.03392. Thus for 0.4 - 0.7 µm, f1-2 = 0Thermal radiation revisited Ron Zevenhoven Åbo Akademi University Thermal and Flow Engineering Laboratory / Värme- och strömningsteknik tel. 3223 ; ron.zevenhoven@abo.fi Process Engineering
Bennett, Charles L. (Livermore, CA)
2007-09-18T23:59:59.000Z
A solar thermal powered aircraft powered by heat energy from the sun. A heat engine, such as a Stirling engine, is carried by the aircraft body for producing power for a propulsion mechanism, such as a propeller. The heat engine has a thermal battery in thermal contact with it so that heat is supplied from the thermal battery. A solar concentrator, such as reflective parabolic trough, is movably connected to an optically transparent section of the aircraft body for receiving and concentrating solar energy from within the aircraft. Concentrated solar energy is collected by a heat collection and transport conduit, and heat transported to the thermal battery. A solar tracker includes a heliostat for determining optimal alignment with the sun, and a drive motor actuating the solar concentrator into optimal alignment with the sun based on a determination by the heliostat.
Aines, Roger D. (Livermore, CA); Newmark, Robin L. (Livermore, CA); Knauss, Kevin G. (Livermore, CA)
2000-01-01T23:59:59.000Z
A thermal treatment wall emplaced to perform in-situ destruction of contaminants in groundwater. Thermal destruction of specific contaminants occurs by hydrous pyrolysis/oxidation at temperatures achievable by existing thermal remediation techniques (electrical heating or steam injection) in the presence of oxygen or soil mineral oxidants, such as MnO.sub.2. The thermal treatment wall can be installed in a variety of configurations depending on the specific objectives, and can be used for groundwater cleanup, wherein in-situ destruction of contaminants is carried out rather than extracting contaminated fluids to the surface, where they are to be cleaned. In addition, the thermal treatment wall can be used for both plume interdiction and near-wellhead in-situ groundwater treatment. Thus, this technique can be utilized for a variety of groundwater contamination problems.
Chang, Chih-Wei; Majumdar, Arunava; Zettl, Alexander K.
2014-07-15T23:59:59.000Z
Disclosed is a device whereby the thermal conductance of a multiwalled nanostructure such as a multiwalled carbon nanotube (MWCNT) can be controllably and reversibly tuned by sliding one or more outer shells with respect to the inner core. As one example, the thermal conductance of an MWCNT dropped to 15% of the original value after extending the length of the MWCNT by 190 nm. The thermal conductivity returned when the tube was contracted. The device may comprise numbers of multiwalled nanotubes or other graphitic layers connected to a heat source and a heat drain and various means for tuning the overall thermal conductance for applications in structure heat management, heat flow in nanoscale or microscale devices and thermal logic devices.
Collective neutrino oscillations in turbulent backgrounds
Reid, Giles; Adams, Jenni; Seunarine, Suruj [University of Canterbury, Christchurch (New Zealand); University of the West Indies, Bridgetown (Barbados)
2011-10-15T23:59:59.000Z
Using a Kolmogorov turbulence model, we investigate the effects of fluctuations in matter and neutrino density in the region near a supernova core on the flavor oscillations of neutrinos emitted in the core collapse in a single-angle, two-flavor approximation. Deviation from a smooth background neutrino density causes significant alterations in the final flavor state of the neutrino ensemble after 400 km, but even very large fluctuations in the matter density do not strongly affect the state of the neutrinos after the collective phase. In both cases, there is a strong effect on the neutrino flavor evolution at intermediate radii, with the flavor evolution becoming much more chaotic. The effect of fluctuations also depends strongly on the initial neutrino spectra. We conclude that the true neutrino fluxes arriving at Earth from core-collapse supernova could differ considerably from predictions of neutrino fluxes based on approximate models with smoothly decreasing matter and neutrino densities.
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.
MAGNETIC FIELD LINE RANDOM WALK IN ISOTROPIC TURBULENCE WITH ZERO MEAN FIELD
Sonsrettee, W.; Ruffolo, D.; Snodin, A. P.; Wongpan, P. [Department of Physics, Faculty of Science, Mahidol University, Bangkok 10400 (Thailand); Subedi, P.; Matthaeus, W. H. [Bartol Research Institute, University of Delaware, Newark, DE 19716 (United States); Chuychai, P., E-mail: bturbulence@gmail.com, E-mail: david.ruf@mahidol.ac.th, E-mail: andrew.snodin@gmail.com, E-mail: pat.wongpan@postgrad.otago.ac.nz, E-mail: piyanate@gmail.com, E-mail: prasub@udel.edu, E-mail: whm@udel.edu [Thailand Center of Excellence in Physics, CHE, Ministry of Education, Bangkok 10400 (Thailand)
2015-01-01T23:59:59.000Z
In astrophysical plasmas, magnetic field lines often guide the motions of thermal and non-thermal particles. The field line random walk (FLRW) is typically considered to depend on the Kubo number R = (b/B {sub 0})(?{sub ?}/? ) for rms magnetic fluctuation b, large-scale mean field B {sub 0}, and parallel and perpendicular coherence scales ?{sub ?} and ? , respectively. Here we examine the FLRW when R ? ? by taking B {sub 0} ? 0 for finite b{sub z} (fluctuation component along B {sub 0}), which differs from the well-studied route with b{sub z} = 0 or b{sub z} << B {sub 0} as the turbulence becomes quasi-two-dimensional (quasi-2D). Fluctuations with B {sub 0} = 0 are typically isotropic, which serves as a reasonable model of interstellar turbulence. We use a non-perturbative analytic framework based on Corrsin's hypothesis to determine closed-form solutions for the asymptotic field line diffusion coefficient for three versions of the theory, which are directly related to the k {sup –1} or k {sup –2} moment of the power spectrum. We test these theories by performing computer simulations of the FLRW, obtaining the ratio of diffusion coefficients for two different parameterizations of a field line. Comparing this with theoretical ratios, the random ballistic decorrelation version of the theory agrees well with the simulations. All results exhibit an analog to Bohm diffusion. In the quasi-2D limit, previous works have shown that Corrsin-based theories deviate substantially from simulation results, but here we find that as B {sub 0} ? 0, they remain in reasonable agreement. We conclude that their applicability is limited not by large R, but rather by quasi-two-dimensionality.
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.
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.
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)
Thermally-related safety issues associated with thermal batteries.
Guidotti, Ronald Armand
2006-06-01T23:59:59.000Z
Thermal batteries can experience thermal runaway under certain usage conditions. This can lead to safety issues for personnel and cause damage to associated test equipment if the battery thermally self destructs. This report discusses a number of thermal and design related issues that can lead to catastrophic destruction of thermal batteries under certain conditions. Contributing factors are identified and mitigating actions are presented to minimize or prevent undesirable thermal runaway.
Understanding and predicting soot generation in turbulent non-premixed jet flames.
Wang, Hai (University of Southern California, Los Angeles, CA); Kook, Sanghoon; Doom, Jeffrey; Oefelein, Joseph Charles; Zhang, Jiayao; Shaddix, Christopher R.; Schefer, Robert W.; Pickett, Lyle M.
2010-10-01T23:59:59.000Z
This report documents the results of a project funded by DoD's Strategic Environmental Research and Development Program (SERDP) on the science behind development of predictive models for soot emission from gas turbine engines. Measurements of soot formation were performed in laminar flat premixed flames and turbulent non-premixed jet flames at 1 atm pressure and in turbulent liquid spray flames under representative conditions for takeoff in a gas turbine engine. The laminar flames and open jet flames used both ethylene and a prevaporized JP-8 surrogate fuel composed of n-dodecane and m-xylene. The pressurized turbulent jet flame measurements used the JP-8 surrogate fuel and compared its combustion and sooting characteristics to a world-average JP-8 fuel sample. The pressurized jet flame measurements demonstrated that the surrogate was representative of JP-8, with a somewhat higher tendency to soot formation. The premixed flame measurements revealed that flame temperature has a strong impact on the rate of soot nucleation and particle coagulation, but little sensitivity in the overall trends was found with different fuels. An extensive array of non-intrusive optical and laser-based measurements was performed in turbulent non-premixed jet flames established on specially designed piloted burners. Soot concentration data was collected throughout the flames, together with instantaneous images showing the relationship between soot and the OH radical and soot and PAH. A detailed chemical kinetic mechanism for ethylene combustion, including fuel-rich chemistry and benzene formation steps, was compiled, validated, and reduced. The reduced ethylene mechanism was incorporated into a high-fidelity LES code, together with a moment-based soot model and models for thermal radiation, to evaluate the ability of the chemistry and soot models to predict soot formation in the jet diffusion flame. The LES results highlight the importance of including an optically-thick radiation model to accurately predict gas temperatures and thus soot formation rates. When including such a radiation model, the LES model predicts mean soot concentrations within 30% in the ethylene jet flame.
Offner, S R; Krumholz, M R; Klein, R I; McKee, C F
2008-04-18T23:59:59.000Z
In this study we investigate the formation and properties of prestellar and protostellar cores using hydrodynamic, self-gravitating Adaptive Mesh Refinement simulations, comparing the cases where turbulence is continually driven and where it is allowed to decay. We model observations of these cores in the C{sup 18}O(2 {yields} 1), NH{sub 3}(1,1), and N{sub 2}H{sup +} (1 {yields} 0) lines, and from the simulated observations we measure the linewidths of individual cores, the linewidths of the surrounding gas, and the motions of the cores relative to one another. Some of these distributions are significantly different in the driven and decaying runs, making them potential diagnostics for determining whether the turbulence in observed star-forming clouds is driven or decaying. Comparing our simulations with observed cores in the Perseus and {rho} Ophiuchus clouds shows reasonably good agreement between the observed and simulated core-to-core velocity dispersions for both the driven and decaying cases. However, we find that the linewidths through protostellar cores in both simulations are too large compared to the observations. The disagreement is noticeably worse for the decaying simulation, in which cores show highly supersonic infall signatures in their centers that decrease toward their edges, a pattern not seen in the observed regions. This result gives some support to the use of driven turbulence for modeling regions of star formation, but reaching a firm conclusion on the relative merits of driven or decaying turbulence will require more complete data on a larger sample of clouds as well as simulations that include magnetic fields, outflows, and thermal feedback from the protostars.
Turbulent Transport and the Scrape-off-layer Width
Myra, J. R. [Lodestar Research Corporation; Russell, D. A. [Lodestar Research Corporation; Ahn, J.W. [Oak Ridge National Laboratory (ORNL); D'Ippolito, D. A. [Lodestar Research Corporation; Maingi, Rajesh [ORNL; Maqueda, R. J. [Nova Photonics, Princeton, NJ; Lundberg, D. P. [Princeton Plasma Physics Laboratory (PPPL); Stotler, D. P. [Princeton Plasma Physics Laboratory (PPPL); Zweben, S. J. [Princeton Plasma Physics Laboratory (PPPL); Umansky, M. [Lawrence Livermore National Laboratory (LLNL)
2011-01-01T23:59:59.000Z
The two-dimensional fluid turbulence code SOLT is employed to study the role of midplane turbulence on the scrape-off-layer (SOL) heat flux width of tokamak plasmas. The physics simulated includes curvature-driven-interchange modes, sheath losses, and perpendicular turbulent diffusive and convective (blob) transport. Midplane SOL profiles of density, temperature and parallel heat flux are obtained from the simulation and compared with experimental results from the National Spherical Torus Experiment (NSTX) to study the scaling of the heat flux width with power and plasma current. It is concluded that midplane turbulence is the main contributor to the SOL width for the low power ELM-free H-mode discharges studied, while additional physics is required to explain the plasma current scaling of the SOL width observed experimentally in higher power discharges. Additional simulations predict a transition to a convectively-dominated SOL at critical values of power and connection length.
Title of dissertation: HYDROMAGNETIC TURBULENT INSTABILITY IN LIQUID SODIUM
Lathrop, Daniel P.
ABSTRACT Title of dissertation: HYDROMAGNETIC TURBULENT INSTABILITY IN LIQUID SODIUM EXPERIMENTS Daniel R. Sisan, Doctor of Philosophy, 2004 Dissertation directed by: Professor Daniel P. Lathrop Department of Physics This dissertation describes the observation of magnetically-induced instabil- ities
Title of dissertation: TURBULENT SHEAR FLOW IN A RAPIDLY ROTATING
Lathrop, Daniel P.
ABSTRACT Title of dissertation: TURBULENT SHEAR FLOW IN A RAPIDLY ROTATING SPHERICAL ANNULUS Daniel S. Zimmerman, Doctor of Philosophy, 2010 Dissertation directed by: Professor Daniel P. Lathrop Department of Physics This dissertation presents experimental measurements of torque, wall shear stress
Magnetohydrodynamic lattice Boltzmann simulations of turbulence and rectangular jet flow
Riley, Benjamin Matthew
2009-05-15T23:59:59.000Z
-rate tensor are evaluated to assess the key physical MHD turbulence mechanisms. The magnetic and kinetic energies interact and exchange through the influence of the Lorentz force work. An initial random fluctuating magnetic field increases the vortex...
ccsd00001826, Impurity Transport in Plasma Edge Turbulence
,Martin Priego Wood, and Jens Juul Rasmussen Association EURATOM Risø National Laboratory Optics and Plasma Research, OPL 128 DK 4000 Roskilde, Denmark October 14, 2004 The turbulent transport of minority
Experimental Signatures of Critically Balanced Turbulence in MAST
Ghim, Y.-c.
Beam emission spectroscopy (BES) measurements of ion-scale density fluctuations in the MAST tokamak are used to show that the turbulence correlation time, the drift time associated with ion temperature or density gradients, ...
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...
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 ...
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...
Turbulence and Transport The Secrets of Magnetic Confinement
Greenwald, Martin
Turbulence and Transport The Secrets of Magnetic Confinement Presented by Martin Greenwald MIT statement of the requirements for good confinement and high temperature. In steady state, Fusion Power = Loss Power (Scientific Breakeven) FUSION REQUIRES HIGH CONFINEMENT, DENSITY AND TEMPERATURE
NUMERICAL MODELING OF TURBULENT FLOW IN A COMBUSTION TUNNEL
Ghoniem, A.F.
2013-01-01T23:59:59.000Z
1VJcDona·ld, H. (1979) Combustion r 1 iodeJ·ing in Two and1979) Practical Turbulent-Combustion Interaction Models forInternation on Combustors. Combustion The 17th Symposium
Behavior of buoyant moist plumes in turbulent atmospheres
Hamza, Redouane
1981-01-01T23:59:59.000Z
A widely applicable computational model of buoyant moist plumes in turbulent atmospheres has been constructed. To achieve this a one dimensional Planetary Boundary Layer (P.B.L.) model has been developed to account for ...
Modulation of homogeneous turbulence seeded with finite size ...
"K. Yeo; S. Dong; E. Climent; M.R. Maxey"
2010-01-30T23:59:59.000Z
Nov 10, 2009 ... Modulation of homogeneous turbulence seeded with finite size bubbles or particles. K. Yeo a, S. Dong a,1, E. Climent b, M.R. Maxey a,*.
Recent results on analytical plasma turbulence theory: Realizability, intermittency, submarginal
Recent results on analytical plasma turbulence theory: Realizability, intermittency, submarginal Phys. Control. Fusion 1. Introduction Two fundamental challenges in the systematic analytical theory as f . = # # f # for n = 1, where . = denotes definition and #. . .# denotes an ensemble average) #12
Turbulence-induced persistence in laser beam wandering
Zunino, Luciano; Funes, Gustavo; Pérez, Darío G
2015-01-01T23:59:59.000Z
We have experimentally confirmed the presence of long-memory correlations in the wandering of a thin Gaussian laser beam over a screen after propagating through a turbulent medium. A laboratory-controlled experiment was conducted in which coordinate fluctuations of the laser beam were recorded at a sufficiently high sampling rate for a wide range of turbulent conditions. Horizontal and vertical displacements of the laser beam centroid were subsequently analyzed by implementing detrended fluctuation analysis. This is a very well-known and widely used methodology to unveil memory effects from time series. Results obtained from this experimental analysis allow us to confirm that both coordinates behave as highly persistent signals for strong turbulent intensities. This finding is relevant for a better comprehension and modeling of the turbulence effects in free-space optical communication systems and other applications related to propagation of optical signals in the atmosphere.
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, ...
Center for Turbulence Research Proceedings of the Summer Program 2008
Prinz, Friedrich B.
channel flow and turbulent boundary-layer separation, have demonstrated the good perfor that stabilizing under- resolved simulations by upwind or non-oscillatory schemes is insufficient for accurately
Temporal coherence of individual turbulent patterns in atmospheric seeing
Dimotakis, Paul E.
by turbulent mixing of volumes of air with different indices of refraction. Adaptive optics sys- tems designed, under the conditions described above. In this paper we de- scribe a measurement of this coherence time
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...
Diapycnal advection by double diffusion and turbulence in the ocean
St. Laurent, Louis C
1999-01-01T23:59:59.000Z
Observations of diapycnal mixing rates are examined and related to diapycnal advection for both double-diffusive and turbulent regimes. The role of double-diffusive mixing at the site of the North Atlantic Tracer Release ...
Armas, Jay; Obers, Niels A; Orselli, Marta; Pedersen, Andreas Vigand
2012-01-01T23:59:59.000Z
We study the giant graviton solution as the AdS_5 X S^5 background is heated up to finite temperature. The analysis employs the thermal brane probe technique based on the blackfold approach. We focus mainly on the thermal giant graviton corresponding to a thermal D3-brane probe wrapped on an S^3 moving on the S^5 of the background at finite temperature. We find several interesting new effects, including that the thermal giant graviton has a minimal possible value for the angular momentum and correspondingly also a minimal possible radius of the S^3. We compute the free energy of the thermal giant graviton in the low temperature regime, which potentially could be compared to that of a thermal state on the gauge theory side. Moreover, we analyze the space of solutions and stability of the thermal giant graviton and find that, in parallel with the extremal case, there are two available solutions for a given temperature and angular momentum, one stable and one unstable. In order to write down the equations of mot...
Turbulent Flame Propagation Characteristics of High Hydrogen Content Fuels
Seitzman, Jerry [Georgia Inst. of Technology, Atlanta, GA (United States); Lieuwen, Timothy [Georgia Inst. of Technology, Atlanta, GA (United States)
2014-09-30T23:59:59.000Z
This final report describes the results of an effort to better understand turbulent flame propagation, especially at conditions relevant to gas turbines employing fuels with syngas or hydrogen mixtures. Turbulent flame speeds were measured for a variety of hydrogen/carbon monoxide (H2/CO) and hydrogen/methane (H2/CH4) fuel mixtures with air as the oxidizer. The measurements include global consumption speeds (ST,GC) acquired in a turbulent jet flame at pressures of 1-10 atm and local displacement speeds (ST,LD) acquired in a low-swirl burner at atmospheric pressure. The results verify the importance of fuel composition in determining turbulent flame speeds. For example, different fuel-air mixtures having the same unstretched laminar flame speed (SL,0) but different fuel compositions resulted in significantly different ST,GC for the same turbulence levels (u'). This demonstrates the weakness of turbulent flame speed correlations based simply on u'/SL,0. The results were analyzed using a steady-steady leading points concept to explain the sensitivity of turbulent burning rates to fuel (and oxidizer) composition. Leading point theories suggest that the premixed turbulent flame speed is controlled by the flame front characteristics at the flame brush leading edge, or, in other words, by the flamelets that advance farthest into the unburned mixture (the so-called leading points). For negative Markstein length mixtures, this is assumed to be close to the maximum stretched laminar flame speed (SL,max) for the given fuel-oxidizer mixture. For the ST,GC measurements, the data at a given pressure were well-correlated with an SL,max scaling. However the variation with pressure was not captured, which may be due to non-quasi-steady effects that are not included in the current model. For the ST,LD data, the leading points model again faithfully captured the variation of turbulent flame speed over a wide range of fuel-compositions and turbulence intensities. These results provide evidence that the leading points model can provide useful predictions of turbulent flame speed over a wide range of operating conditions and flow geometries.
Multilayer thermal barrier coating systems
Vance, Steven J. (Orlando, FL); Goedjen, John G. (Oviedo, FL); Sabol, Stephen M. (Orlando, FL); Sloan, Kelly M. (Longwood, FL)
2000-01-01T23:59:59.000Z
The present invention generally describes multilayer thermal barrier coating systems and methods of making the multilayer thermal barrier coating systems. The thermal barrier coating systems comprise a first ceramic layer, a second ceramic layer, a thermally grown oxide layer, a metallic bond coating layer and a substrate. The thermal barrier coating systems have improved high temperature thermal and chemical stability for use in gas turbine applications.
On the Physics of Kinetic-Alfven Turbulence
Boldyrev, Stanislav
2013-01-01T23:59:59.000Z
Observations reveal nearly power-law spectra of magnetic and density plasma fluctuations at subproton scales in the solar wind, which indicates the presence of a turbulent cascade. We discuss the three-field and two-field models for micro-scale plasma fluctuations, and then present the results of numerical simulations of a two-field model of kinetic-Alfven turbulence, which models plasma motion at sub-proton scales.
Low-altitude atmospheric turbulence around an airport
Cass, Stanley Dale
1972-01-01T23:59:59.000Z
speed and the average wind speed computed over an entire run (approximately 1 hr). iv Profiles of wind speed were approximately logarithmic, but profiles of turbulent energy showed a large increase in the wake of large obstructions. Spectra of wind... from u 30-sec averages 56 57 28 Spectra of accelerometer and wind data for same period 59 LIST OF SYMBOLS Symbol Definition Exchange coefficient for momentum Height Time Kinetic energy Average kinetic energy of turbulence u' + v'2 + w' (' 2...
Turbulent transport across shear layers in magnetically confined plasmas
Nold, B.; Ramisch, M. [Institut für Grenzflächenverfahrenstechnik und Plasmatechnologie, Universität Stuttgart, D-70569 Stuttgart (Germany); Manz, P.; Birkenmeier, G. [Physik-Department E28, Technische Universität München, James-Franck-Str.1, D-85748 Garching (Germany); Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, D-85748 Garching (Germany); Ribeiro, T. T.; Müller, H. W.; Scott, B. D. [Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, D-85748 Garching (Germany); Fuchert, G. [IJL, Université de Lorraine, CNRS (UMR 7198), BP 40239 Vandoeuvre-lès-Nancy (France); Stroth, U. [Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, D-85748 Garching (Germany); Physik-Department E28, Technische Universität München, James-Franck-Str.1, D-85748 Garching (Germany)
2014-10-15T23:59:59.000Z
Shear layers modify the turbulence in diverse ways and do not only suppress it. A spatial-temporal investigation of gyrofluid simulations in comparison with experiments allows to identify further details of the transport process across shear layers. Blobs in and outside a shear layer merge, thereby exchange particles and heat and subsequently break up. Via this mechanism particles and heat are transported radially across shear layers. Turbulence spreading is the immanent mechanism behind this process.
Computations of turbulent premixed flames using conditional moment closure
Amzin, Shokri
2012-06-12T23:59:59.000Z
- combustible renewable energy such as solar, wind and hydro power. However, ac- cording to European Commission statistics, renewable energy sources accounted for 8.4 % of the EUs consumption in 2008 [10]. Certainly, it is highly unlikely to replace fossil fuel... from turbulent combustion in simple geometries or flows. In LES, the energy con- taining scales of turbulence are captured explicitly using approximate governing equations. Since chemical reactions occur at small scales, some sort of models are required...
Supersonic turbulent boundary layers with periodic mechanical non-equilibrium
Ekoto, Isaac Wesley
2007-04-25T23:59:59.000Z
is essential. Turbulence reduction has applications for reentry vehicles. On their undersurface they have a heat shield that is composed of uniformly shaped materials (e.g. tiles, ablative materiel, etc.). Shape selection that can reduce turbulent heat... of the literature reveals roughness elements with sharp leading edges have not been explored. Much could be revealed by an investigation into a these type of roughness elements. The thought is that the blunt shaped roughness elements used in the past (e.g. square...
Tong, Penger
indicates that the vertical direction is special and buoy- ancy is important even at the center is within the inertial range. Experimental measurements confirm the power-law behavior but indicate
Three-dimensional flow structures and dynamics of turbulent thermal convection in a cylindrical cell
Tong, Penger
, such as the mean velocity profile in the LSC plane, the boundary layer thickness and its scaling with Ra and Pr and organize their motions spatially between the top and bottom plates, leading to an oscillatory motion
Isolation of Metals from Liquid Wastes: Reactive Scavenging in Turbulent Thermal Reactors
William Linak
2004-12-16T23:59:59.000Z
Sorption of cesium and strontium on kaolinite powders was investigated as a means to minimize the emissions of these metals during certain high temperature processes currently being developed to isolate and dispose of radiological and mixed wastes. In this work, non-radioactive aqueous cesium acetate or strontium acetate was atomized down the center of a natural gas flame supported on a variable-swirl burner in a refractory-lined laboratory-scale combustion facility. Kaolinite powder was injected at a post-flame location in the combustor. Cesium readily vaporizes in the high temperature regions of the combustor, but was reactively scavenged onto dispersed kaolinite. Global sorption mechanisms of cesium vapor on kaolinite were quantified, and are related to those available in the literature for sodium and lead. Both metal adsorption and substrate deactivation steps are important, and so there is an optimum temperature, between 1400 and 1500 K, at which maximum sorption occurs. The presence of chlorine inhibits cesium sorption. In contrast to cesium, and in the absence of chlorine, strontium was only partially vaporized and was, therefore, only partially scavengeable. The strontium data did not allow quantification of global kinetic mechanisms of interaction, although equilibrium arguments provided insight into the effects of chlorine on strontium sorption. These results have implications for the use of sorbents to control cesium and strontium emissions during high temperature waste processing including incineration and vitrification.
Kreith, F.; Meyer, R. T.
1982-11-01T23:59:59.000Z
The thermal conversion process of solar energy is based on well-known phenomena of heat transfer (Kreith 1976). In all thermal conversion processes, solar radiation is absorbed at the surface of a receiver, which contains or is in contact with flow passages through which a working fluid passes. As the receiver heats up, heat is transferred to the working fluid which may be air, water, oil, or a molten salt. The upper temperature that can be achieved in solar thermal conversion depends on the insolation, the degree to which the sunlight is concentrated, and the measures taken to reduce heat losses from the working fluid.
Thermal insulations using vacuum panels
Glicksman, Leon R. (Lynnfield, MA); Burke, Melissa S. (Pittsburgh, PA)
1991-07-16T23:59:59.000Z
Thermal insulation vacuum panels are formed of an inner core of compressed low thermal conductivity powders enclosed by a ceramic/glass envelope evaluated to a low pressure.
GYROKINETIC PARTICLE SIMULATION OF TURBULENT TRANSPORT IN BURNING PLASMAS
Horton, Claude Wendell
2014-06-10T23:59:59.000Z
The SciDAC project at the IFS advanced the state of high performance computing for turbulent structures and turbulent transport. The team project with Prof Zhihong Lin [PI] at Univ California Irvine produced new understanding of the turbulent electron transport. The simulations were performed at the Texas Advanced Computer Center TACC and the NERSC facility by Wendell Horton, Lee Leonard and the IFS Graduate Students working in that group. The research included a Validation of the electron turbulent transport code using the data from a steady state university experiment at the University of Columbia in which detailed probe measurements of the turbulence in steady state were used for wide range of temperature gradients to compare with the simulation data. These results were published in a joint paper with Texas graduate student Dr. Xiangrong Fu using the work in his PhD dissertation. X.R. Fu, W. Horton, Y. Xiao, Z. Lin, A.K. Sen and V. Sokolov, “Validation of electron Temperature gradient turbulence in the Columbia Linear Machine, Phys. Plasmas 19, 032303 (2012).
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.
A Model for the Saturation of the Turbulent Dynamo
Schober, Jennifer; Federrath, Christoph; Bovino, Stefano; Klessen, Ralf S
2015-01-01T23:59:59.000Z
The origin of strong magnetic fields in the Universe can be explained by amplifying weak seed fields via turbulent motions on small spatial scales and subsequently transporting the magnetic energy to larger scales. This process is known as the turbulent dynamo and depends on the properties of turbulence, i.e. on the hydrodynamical Reynolds number and the compressibility of the gas, and on the magnetic diffusivity. While we know the growth rate the magnetic energy in the linear regime, the saturation level, i.e. the ratio of magnetic energy to turbulent kinetic energy that can be reached, is not known from analytical calculations. In this paper we present the first scale-dependent saturation model based on an effective turbulent resistivity which is determined by the turnover timescale of turbulent eddies and the magnetic energy density. The magnetic resistivity increases compared to the Spitzer value and the effective scale on which the magnetic energy spectrum is at its maximum moves to larger spatial scales...
Turbulent Angular Momentum Transport in Weakly-Ionized Accretion Disks
Bryan Mark Johnson
2005-09-13T23:59:59.000Z
Understanding the mechanism that drives accretion has been the primary challenge in accretion disk theory. Turbulence provides a natural means of dissipation and the removal of angular momentum, but firmly establishing its presence in disks proved for many years to be difficult. The realization in the 1990s that a weak magnetic field will destabilize a disk and result in a vigorous turbulent transport of angular momentum has revolutionized the field. Much of accretion disk research now focuses on understanding the implications of this mechanism for astrophysical observations. At the same time, the success of this mechanism depends upon a sufficient ionization level in the disk for the flow to be well-coupled to the magnetic field. Many disks, such as disks around young stars and disks in binary systems that are in quiescence, are too cold to be sufficiently ionized, and so efforts to establish the presence of turbulence in these disks continues. This dissertation focuses on several possible mechanisms for the turbulent transport of angular momentum in weakly-ionized accretion disks: gravitational instability, radial convection and vortices driving compressive motions. It appears that none of these mechanisms are very robust in driving accretion. A discussion is given, based on these results, as to the most promising directions to take in the search for a turbulent transport mechanism that does not require magnetic fields. Also discussed are the implications of assuming that no turbulent transport mechanism exists for weakly-ionized disks.
Magnetic Discontinuities in Magnetohydrodynamic Turbulence and in the Solar Wind
Vladimir Zhdankin; Stanislav Boldyrev; Joanne Mason; Jean Carlos Perez
2012-04-19T23:59:59.000Z
Recent measurements of solar wind turbulence report the presence of intermittent, exponentially distributed angular discontinuities in the magnetic field. In this Letter, we study whether such discontinuities can be produced by magnetohydrodynamic (MHD) turbulence. We detect the discontinuities by measuring the fluctuations of the magnetic field direction, Delta theta, across fixed spatial increments Delta x in direct numerical simulations of MHD turbulence with an imposed uniform guide field B_0. A large region of the probability density function (pdf) for Delta theta is found to follow an exponential decay, proportional to exp(-Delta theta/theta_*), with characteristic angle theta_* ~ (14 deg) (b_rms/B_0)^0.65 for a broad range of guide-field strengths. We find that discontinuities observed in the solar wind can be reproduced by MHD turbulence with reasonable ratios of b_rms/B_0. We also observe an excess of small angular discontinuities when Delta x becomes small, possibly indicating an increasing statistical significance of dissipation-scale structures. The structure of the pdf in this case closely resembles the two-population pdf seen in the solar wind. We thus propose that strong discontinuities are associated with inertial-range MHD turbulence, while weak discontinuities emerge from near-dissipation-range turbulence. In addition, we find that the structure functions of the magnetic field direction exhibit anomalous scaling exponents, which indicates the existence of intermittent structures.
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.
Caughey, David
2010-10-08T23:59:59.000Z
A Symposium on Turbulence and Combustion was held at Cornell University on August 3-4, 2009. The overall goal of the Symposium was to promote future advances in the study of turbulence and combustion, through an unique forum intended to foster interactions between leading members of these two research communities. The Symposium program consisted of twelve invited lectures given by world-class experts in these fields, two poster sessions consisting of nearly 50 presentations, an open forum, and other informal activities designed to foster discussion. Topics covered in the lectures included turbulent dispersion, wall-bounded flows, mixing, finite-rate chemistry, and others, using experiment, modeling, and computations, and included perspectives from an international community of leading researchers from academia, national laboratories, and industry.
Schmidt, Aaron Jerome, 1979-
2004-01-01T23:59:59.000Z
Contact thermal lithography is a method for fabricating microscale patterns using heat transfer. In contrast to photolithography, where the minimum achievable feature size is proportional to the wavelength of light used ...
Stanley, T. F.
1982-01-01T23:59:59.000Z
Thermal insulation systems are receiving a high degree of attention in view of increasing energy cost. Industrial, commercial and residential energy users are all well aware of energy cost increases and great emphasis is being directed to energy...
Manipulation of Thermal Phonons
Hsu, Chung-Hao
2013-03-28T23:59:59.000Z
in silicon nanofabrication techniques, this makes tungsten/silicon phononic crystal a particularly attractive platform for manipulating thermal phonons. Phononic crystal makes use of the fundamental properties of waves to create band gap over which there can...
Nelken, Haim
1987-01-01T23:59:59.000Z
Several problems connected by the theme of thermal forcing are addressed herein. The main topic is the stratification and flow field resulting from imposing a specified heat flux on a fluid that is otherwise confined to a ...
Manipulation of Thermal Phonons
Hsu, Chung-Hao
2013-03-28T23:59:59.000Z
in silicon nanofabrication techniques, this makes tungsten/silicon phononic crystal a particularly attractive platform for manipulating thermal phonons. Phononic crystal makes use of the fundamental properties of waves to create band gap over which there can...
Photovoltaic-thermal collectors
Cox, III, Charles H. (Carlisle, MA)
1984-04-24T23:59:59.000Z
A photovoltaic-thermal solar cell including a semiconductor body having antireflective top and bottom surfaces and coated on each said surface with a patterned electrode covering less than 10% of the surface area. A thermal-absorbing surface is spaced apart from the bottom surface of the semiconductor and a heat-exchange fluid is passed between the bottom surface and the heat-absorbing surface.
Bao-Guo Dong
2015-07-07T23:59:59.000Z
We first show a possible mechanism to create a new type of nuclear fusion, thermal resonance fusion, i.e. low energy nuclear fusion with thermal resonance of light nuclei or atoms, such as deuterium or tritium. The fusion of two light nuclei has to overcome the Coulomb barrier between these two nuclei to reach up to the interacting region of nuclear force. We found nuclear fusion could be realized with thermal vibrations of crystal lattice atoms coupling with light atoms at low energy by resonance to overcome this Coulomb barrier. Thermal resonances combining with tunnel effects can greatly enhance the probability of the deuterium fusion to the detectable level. Our low energy nuclear fusion mechanism research - thermal resonance fusion mechanism results demonstrate how these light nuclei or atoms, such as deuterium, can be fused in the crystal of metal, such as Ni or alloy, with synthetic thermal vibrations and resonances at different modes and energies experimentally. The probability of tunnel effect at different resonance energy given by the WKB method is shown that indicates the thermal resonance fusion mode, especially combined with the tunnel effect, is possible and feasible. But the penetrating probability decreases very sharply when the input resonance energy decreases less than 3 keV, so for thermal resonance fusion, the key point is to increase the resonance peak or make the resonance sharp enough to the acceptable energy level by the suitable compound catalysts, and it is better to reach up more than 3 keV to make the penetrating probability larger than 10^{-10}.
Coral Thermal Tolerance: Tuning Gene Expression to Resist Thermal Stress
Coral Thermal Tolerance: Tuning Gene Expression to Resist Thermal Stress Anthony J. Bellantuono1 thermal tolerance in the scleractinian coral Acropora millepora, corals preconditioned to a sub under which non-preconditioned corals bleached and preconditioned corals (thermal-tolerant) maintained
Dong, Bao-Guo
2015-01-01T23:59:59.000Z
We first show a possible mechanism to create a new type of nuclear fusion, thermal resonance fusion, i.e. low energy nuclear fusion with thermal resonance of light nuclei or atoms, such as deuterium or tritium. The fusion of two light nuclei has to overcome the Coulomb barrier between these two nuclei to reach up to the interacting region of nuclear force. We found nuclear fusion could be realized with thermal vibrations of crystal lattice atoms coupling with light atoms at low energy by resonance to overcome this Coulomb barrier. Thermal resonances combining with tunnel effects can greatly enhance the probability of the deuterium fusion to the detectable level. Our low energy nuclear fusion mechanism research - thermal resonance fusion mechanism results demonstrate how these light nuclei or atoms, such as deuterium, can be fused in the crystal of metal, such as Ni or alloy, with synthetic thermal vibrations and resonances at different modes and energies experimentally. The probability of tunnel effect at dif...
Bryant, Duncan Burnette
2011-08-08T23:59:59.000Z
stream_source_info BRYANT-DISSERTATION.pdf.txt stream_content_type text/plain stream_size 163756 Content-Encoding ISO-8859-1 stream_name BRYANT-DISSERTATION.pdf.txt Content-Type text/plain; charset=ISO-8859..., the turbulent energy spectra in inertial particle plumes followed the same modulation as the bubble plumes. PIV experiments from the tidal starting-jet vortices detail the influence of a finite channel length using identified vortice. The results show...
Ovchinnikov, K. N.; Uryupin, S. A., E-mail: uryupin@sci.lebedev.ru [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation)
2013-09-15T23:59:59.000Z
Specific features of the interaction of a relatively weak electromagnetic pulse with a nonisothermal current-carrying plasma in which the electron drift velocity is much higher than the ion-acoustic velocity, but lower than the electron thermal velocity, are studied. If the state of the plasma with ion-acoustic turbulence does not change during the pulse action, the field penetrates into the plasma in the ordinary diffusion regime, but the diffusion coefficient in this case is inversely proportional to the anomalous conductivity. If, during the pulse action, the particle temperatures and the current-driving field change due to turbulent heating, the field penetrates into the plasma in the subdiffusion regime. It is shown how the presence of subdiffusion can be detected by measuring the reflected field.
Turbulent resuspension of small nondeformable particles
Lazaridis, M.; Drossinos, Y. [European Commission, Ispra (Italy). Joint Research Centre] [European Commission, Ispra (Italy). Joint Research Centre; Georgopoulos, P.G. [Rutgers-the State Univ., Piscataway, NJ (United States). Environmental and Occupational Health Sciences Inst.] [Rutgers-the State Univ., Piscataway, NJ (United States). Environmental and Occupational Health Sciences Inst.; [Univ. of Medicine and Dentistry of New Jersey, Piscataway, NJ (United States)
1998-08-01T23:59:59.000Z
An energy-balance resuspension model is modified and applied to the resuspension of a monolayer of nondeformable spherical particles. The particle-surface adhesive force is calculated from a microscopic model based on the Lennard-Jones intermolecular potential. Pairwise additivity of intermolecular interactions is assumed and elastic flattening of the particles is neglected. From the resulting particle-surface interaction potential the natural frequency of vibration of a particle on a surface and the depth of the potential well are calculated. The particle resuspension rate is calculated using the results of a previously developed energy-balance model, where the influence of fluid flow on the bound particle motion is recognized. The effect of surface roughness is included by introducing an effective particle radius that results in log-normally distributed adhesive forces. The predictions of the model are compared with experimental results for the resuspension of Al{sub 2}O{sub 3} particles from stainless steel surfaces. Particle resuspension due to turbulent fluid flow is important in the interaction of the atmosphere with various surfaces and in numerous industrial processes. For example, in the nuclear industry, fission-product aerosols released during a postulated severe accident in a Light Water Reactor may deposit and resuspend repeatedly in the vessel circuit and containment.
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...
Thermal Lens Spectroscopy Mladen Franko
Reid, Scott A.
Thermal Lens Spectroscopy Mladen Franko Laboratory of Environmental Research, University of Nova-beam Instruments 5 3.3 Differential Thermal Lens Instruments 7 3.4 Multiwavelength and Tunable Thermal Lens Spectrometers 8 3.5 Circular Dichroism TLS Instruments 9 3.6 Miniaturization of Thermal Lens Instruments 9 4
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.
Article for thermal energy storage
Salyer, Ival O. (Dayton, OH)
2000-06-27T23:59:59.000Z
A thermal energy storage composition is provided which is in the form of a gel. The composition includes a phase change material and silica particles, where the phase change material may comprise a linear alkyl hydrocarbon, water/urea, or water. The thermal energy storage composition has a high thermal conductivity, high thermal energy storage, and may be used in a variety of applications such as in thermal shipping containers and gel packs.
Holographic thermalization in noncommutative geometry
Xiao-Xiong Zeng; Xian-Ming Liu; Wen-Biao Liu
2015-05-02T23:59:59.000Z
Gravitational collapse of a shell of dust in noncommutative geometry is probed by the renormalized geodesic length, which is dual to probe the thermalization by the two-point correlation function in the dual conformal field theory. We find that larger the noncommutative parameter is, longer the thermalization time is, which implies that the large noncommutative parameter delays the thermalization process. We also investigate how the noncommutative parameter affects the thermalization velocity and thermalization acceleration.
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.
A spray-suppression model for turbulent combustion
DESJARDIN,PAUL E.; TIESZEN,SHELDON R.; GRITZO,LOUIS A.
2000-02-14T23:59:59.000Z
A spray-suppression model that captures the effects of liquid suppressant on a turbulent combusting flow is developed and applied to a turbulent diffusion flame with water spray suppression. The spray submodel is based on a stochastic separated flow approach that accounts for the transport and evaporation of liquid droplets. Flame extinguishment is accounted for by using a perfectly stirred reactor (PSR) submodel of turbulent combustion. PSR pre-calculations of flame extinction times are determined using CHEMKIN and are compared to local turbulent time scales of the flow to determine if local flame extinguishment has occurred. The PSR flame extinguishment and spray submodels are incorporated into Sandia's flow fire simulation code, VULCAN, and cases are run for the water spray suppression studies of McCaffrey for turbulent hydrogen-air jet diffusion flames. Predictions of flame temperature decrease and suppression efficiency are compared to experimental data as a function of water mass loading using three assumed values of drop sizes. The results show that the suppression efficiency is highly dependent on the initial droplet size for a given mass loading. A predicted optimal suppression efficiency was observed for the smallest class of droplets while the larger drops show increasing suppression efficiency with increasing mass loading for the range of mass loadings considered. Qualitative agreement to the experiment of suppression efficiency is encouraging, however quantitative agreement is limited due to the uncertainties in the boundary conditions of the experimental data for the water spray.
GRAVITATIONALLY UNSTABLE FLAMES: RAYLEIGH-TAYLOR STRETCHING VERSUS TURBULENT WRINKLING
Hicks, E. P. [Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and the Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208 (United States); Rosner, R., E-mail: eph2001@columbia.edu [Computation Institute, University of Chicago, 5735 S. Ellis Ave., Chicago, IL 60637 (United States)
2013-07-10T23:59:59.000Z
In this paper, we provide support for the Rayleigh-Taylor-(RT)-based subgrid model used in full-star simulations of deflagrations in Type Ia supernovae explosions. We use the results of a parameter study of two-dimensional direct numerical simulations of an RT unstable model flame to distinguish between the two main types of subgrid models (RT or turbulence dominated) in the flamelet regime. First, we give scalings for the turbulent flame speed, the Reynolds number, the viscous scale, and the size of the burning region as the non-dimensional gravity (G) is varied. The flame speed is well predicted by an RT-based flame speed model. Next, the above scalings are used to calculate the Karlovitz number (Ka) and to discuss appropriate combustion regimes. No transition to thin reaction zones is seen at Ka = 1, although such a transition is expected by turbulence-dominated subgrid models. Finally, we confirm a basic physical premise of the RT subgrid model, namely, that the flame is fractal, and thus self-similar. By modeling the turbulent flame speed, we demonstrate that it is affected more by large-scale RT stretching than by small-scale turbulent wrinkling. In this way, the RT instability controls the flame directly from the large scales. Overall, these results support the RT subgrid model.
Thermal insulated glazing unit
Selkowitz, S.E.; Arasteh, D.K.; Hartmann, J.L.
1988-04-05T23:59:59.000Z
An improved insulated glazing unit is provided which can attain about R5 to about R10 thermal performance at the center of the glass while having dimensions about the same as those of a conventional double glazed insulated glazing unit. An outer glazing and inner glazing are sealed to a spacer to form a gas impermeable space. One or more rigid, non-structural glazings are attached to the inside of the spacer to divide the space between the inner and outer glazings to provide insulating gaps between glazings of from about 0.20 inches to about 0.40 inches. One or more glazing surfaces facing each thermal gap are coated with a low emissivity coating. Finally, the thermal gaps are filled with a low conductance gas such as krypton gas. 2 figs.
Bazydola, Sarah; Ghiu, Camil-Daniel; Harrison, Robert; Jeswani, Anil
2013-11-19T23:59:59.000Z
A luminaire with a thermal pathway to reduce the junction temperature of the luminaire's light source, and methods for so doing, are disclosed. The luminaire includes a can, a light engine, and a trim, that define a substantially continuous thermal pathway from the light engine to a surrounding environment. The can defines a can cavity and includes a can end region. The light engine is within the can cavity and includes a light source and a heat sink, including a heat sink end region, coupled thereto. The trim is at least partially disposed within the can cavity and includes a first trim end region coupled to the heat sink end region and a second trim end region coupled to the can end region. Thermal interface material may be located between: the heat sink and the trim, the trim and the can, and/or the heat sink and the light source.
Thermal insulated glazing unit
Selkowitz, Stephen E. (Piedmont, CA); Arasteh, Dariush K. (Oakland, CA); Hartmann, John L. (Seattle, WA)
1991-01-01T23:59:59.000Z
An improved insulated glazing unit is provided which can attain about R5 to about R10 thermal performance at the center of the glass while having dimensions about the same as those of a conventional double glazed insulated glazing unit. An outer glazing and inner glazing are sealed to a spacer to form a gas impermeable space. One or more rigid, non-structural glazings are attached to the inside of the spacer to divide the space between the inner and outer glazings to provide insulating gaps between glazings of from about 0.20 inches to about 0.40 inches. One or more glazing surfaces facing each thermal gap are coated with a low emissivity coating. Finally, the thermal gaps are filled with a low conductance gas such as krypton gas.
Thermal noise driven computing
Laszlo B. Kish
2006-10-28T23:59:59.000Z
The possibility of a new type of computing, where thermal noise is the information carrier and the clock in a computer, is studied. The information channel capacity and the lower limit of energy requirement/dissipation are studied in a simple digital system with zero threshold voltage, for the case of error probability close to 0.5, when the thermal noise is equal to or greater than the digital signal. In a simple hypothetical realization of a thermal noise driven gate, the lower limit of energy needed to generate the digital signal is 1.1*kT/bit. The arrangement has potentially improved energy efficiency and it is free of leakage current, crosstalk and ground plane electromagnetic interference problems. Disadvantage is the large number of redundancy elements needed for low-error operation.
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...
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
Thermal ignition combustion system
Kamo, R.; Kakwani, R.M.; Valdmanis, E.; Woods, M.E.
1988-04-19T23:59:59.000Z
The thermal ignition combustion system comprises means for providing walls defining an ignition chamber, the walls being made of a material having a thermal conductivity greater than 20 W/m C and a specific heat greater than 480 J/kg C with the ignition chamber being in constant communication with the main combustion chamber, means for maintaining the temperature of the walls above a threshold temperature capable of causing ignition of a fuel, and means for conducting fuel to the ignition chamber. 8 figs.
Koski, J.A.; Keltner, N.R.; Sobolik, K.B.
1993-02-01T23:59:59.000Z
Shipping containers for radioactive materials must be qualified to meet a thermal accident environment specified in regulations, such at Title 10, Code of Federal Regulations, Part 71. Aimed primarily at the shipping container design, this report discusses the thermal testing options available for meeting the regulatory requirements, and states the advantages and disadvantages of each approach. The principal options considered are testing with radiant heat, furnaces, and open pool fires. The report also identifies some of the facilities available and current contacts. Finally, the report makes some recommendations on the appropriate use of these different testing methods.
Thermal ignition combustion system
Kamo, Roy (Columbus, IN); Kakwani, Ramesh M. (Columbus, IN); Valdmanis, Edgars (Columbus, IN); Woods, Melvins E. (Columbus, IN)
1988-01-01T23:59:59.000Z
The thermal ignition combustion system comprises means for providing walls defining an ignition chamber, the walls being made of a material having a thermal conductivity greater than 20 W/m.degree. C. and a specific heat greater than 480 J/kg.degree. C. with the ignition chamber being in constant communication with the main combustion chamber, means for maintaining the temperature of the walls above a threshold temperature capable of causing ignition of a fuel, and means for conducting fuel to the ignition chamber.
INTERCHANGE RECONNECTION IN A TURBULENT CORONA
Rappazzo, A. F.; Matthaeus, W. H. [Bartol Research Institute, Department of Physics and Astronomy, University of Delaware, Newark, DE 19716 (United States); Ruffolo, D. [Department of Physics, Faculty of Science, Mahidol University, Bangkok 10400 (Thailand); Servidio, S. [Dipartimento di Fisica, Universita della Calabria, I-87036 Cosenza (Italy); Velli, M., E-mail: rappazzo@udel.edu [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)
2012-10-10T23:59:59.000Z
Magnetic reconnection at the interface between coronal holes and loops, the so-called interchange reconnection, can release the hotter, denser plasma from magnetically confined regions into the heliosphere, contributing to the formation of the highly variable slow solar wind. The interchange process is often thought to develop at the apex of streamers or pseudo-streamers, near Y- and X-type neutral points, but slow streams with loop composition have been recently observed along fanlike open field lines adjacent to closed regions, far from the apex. However, coronal heating models, with magnetic field lines shuffled by convective motions, show that reconnection can occur continuously in unipolar magnetic field regions with no neutral points: photospheric motions induce a magnetohydrodynamic turbulent cascade in the coronal field that creates the necessary small scales, where a sheared magnetic field component orthogonal to the strong axial field is created locally and can reconnect. We propose that a similar mechanism operates near and around boundaries between open and closed regions inducing a continual stochastic rearrangement of connectivity. We examine a reduced magnetohydrodynamic model of a simplified interface region between open and closed corona threaded by a strong unipolar magnetic field. This boundary is not stationary, becomes fractal, and field lines change connectivity continuously, becoming alternatively open and closed. This model suggests that slow wind may originate everywhere along loop-coronal-hole boundary regions and can account naturally and simply for outflows at and adjacent to such boundaries and for the observed diffusion of slow wind around the heliospheric current sheet.
Studies of turbulence and flows in the DIII-D tokamak
Hillesheim, Jon Clark
2012-01-01T23:59:59.000Z
The DIII-D tokamak . . . . . . . . . . . . . . . .2 Turbulence in tokamaks: background and review of existingscale instabilities in tokamaks . . . . . . . . . . . .
Phase Change Materials for Thermal Energy Storage in Concentrated Solar Thermal Power Plants
Hardin, Corey Lee
2011-01-01T23:59:59.000Z
and Background Solar thermal energy collection is anCHANGE THERMAL ENERGY STORAGE FOR CONCENTRATING SOLAR POWERfor Thermal Energy Storage in Concentrated Solar Thermal
Phase Change Materials for Thermal Energy Storage in Concentrated Solar Thermal Power Plants
Hardin, Corey Lee
2011-01-01T23:59:59.000Z
ENERGY STORAGE FOR CONCENTRATING SOLAR POWER PLANTS,”Thermal Energy Storage in Concentrated Solar Thermal PowerThermal Energy Storage in Concentrated Solar Thermal Power
Short wavelength ion temperature gradient turbulence
Chowdhury, J.; Ganesh, R. [Institute for Plasma Research, Bhat, Gandhinagar (India); Brunner, S.; Lapillonne, X.; Villard, L. [CRPP, Association EURATOM-Confederation Suisse, EPFL, 1015 Lausanne (Switzerland); Jenko, F. [Max-Planck-Institut fuer Plasmaphysik Boltzmannstr. 2, D-85748 Garching (Germany)
2012-10-15T23:59:59.000Z
The ion temperature gradient (ITG) mode in the high wavenumber regime (k{sub y}{rho}{sub s}>1), referred to as short wavelength ion temperature gradient mode (SWITG) is studied using the nonlinear gyrokinetic electromagnetic code GENE. It is shown that, although the SWITG mode may be linearly more unstable than the standard long wavelength (k{sub y}{rho}{sub s}<1) ITG mode, nonlinearly its contribution to the total thermal ion heat transport is found to be low. We interpret this as resulting from an increased zonal flow shearing effect on the SWITG mode suppression.
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.
Feedback Control of Turbulent Shear Flows by Genetic Programming
Duriez, Thomas; von Krbek, Kai; Bonnet, Jean-Paul; Cordier, Laurent; Noack, Bernd R; Segond, Marc; Abel, Markus; Gautier, Nicolas; Aider, Jean-Luc; Raibaudo, Cedric; Cuvier, Christophe; Stanislas, Michel; Debien, Antoine; Mazellier, Nicolas; Kourta, Azeddine; Brunton, Steven L
2015-01-01T23:59:59.000Z
Turbulent shear flows have triggered fundamental research in nonlinear dynamics, like transition scenarios, pattern formation and dynamical modeling. In particular, the control of nonlinear dynamics is subject of research since decades. In this publication, actuated turbulent shear flows serve as test-bed for a nonlinear feedback control strategy which can optimize an arbitrary cost function in an automatic self-learning manner. This is facilitated by genetic programming providing an analytically treatable control law. Unlike control based on PID laws or neural networks, no structure of the control law needs to be specified in advance. The strategy is first applied to low-dimensional dynamical systems featuring aspects of turbulence and for which linear control methods fail. This includes stabilizing an unstable fixed point of a nonlinearly coupled oscillator model and maximizing mixing, i.e.\\ the Lyapunov exponent, for forced Lorenz equations. For the first time, we demonstrate the applicability of genetic p...
Masada, Youhei [Department of Computational Science, Kobe University, Kobe 657-8501 (Japan); Takiwaki, Tomoya [Division of Theoretical Astronomy, National Astronomical Observatory of Japan, Tokyo 181-8588 (Japan); Kotake, Kei, E-mail: ymasada@harbor.kobe-u.ac.jp [Faculty of Science, Department of Applied Physics, Fukuoka University, Fukuoka 814-0180 (Japan)
2015-01-01T23:59:59.000Z
Magnetorotational instability (MRI) in a convectively stable layer around the neutrinosphere is simulated by a three-dimensional model of a supernova core. To resolve MRI-unstable modes, a thin layer approximation considering only the radial global stratification is adopted. Our intriguing finding is that the convectively stable layer around the neutrinosphere becomes fully turbulent due to the MRI and its nonlinear penetration into the strongly stratified MRI-stable region. The intensity of the MRI-driven turbulence increases with magnetic flux threading the core, but is limited by the free energy stored in the differential rotation. The turbulent neutrinosphere is a natural consequence of rotating core-collapse and could exert a positive impact on the supernova mechanism.
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.
Turbulent Nonpremixed Flames (TNF): Experimental Data Archives and Computational Submodels
DOE Data Explorer [Office of Scientific and Technical Information (OSTI)]
In the 1990s an international collaboration formed around a series of workshops that became known collectively as the International Workshop on Measurement and Computation of Turbulent Non-Premixed Flames (TNF). An online library, hosted by Sandia National Laboratory (California) was established that provides data sets and submodels or "mechanisms" for the study of turbulence-chemistry interactions in turbulent nonpremixed and partially premixed combustion. Data are organized by flame types: simple jet flames, piloted jet flames, bluff body flames, and swirl flames. These data sets provide a means for collaborative comparisons of both measured and simulated/modeled research results and also assist scientists in determining priorities for further research. More than 20 data sets or databases are available from this website, along with various downloadable files of chemical mechanisms. The website also provides an extensive bibliography and the proceedings of the workshops themselves from 1996 through 2012. Information continues to be added to this collection.
The geometry and topology of turbulence in active nematics
Luca Giomi
2014-09-04T23:59:59.000Z
The problem of low Reynolds number turbulence in active nematic fluids is theoretically addressed. Using numerical simulations I demonstrate that an incompressible turbulent flow, in two-dimensional active nematics, consists of an ensemble of vortices whose areas are exponentially distributed within a range of scales. Building on this evidence, I construct a mean-field theory of active turbulence by which several measurable quantities, including the spectral densities and the correlation functions, can be analytically calculated. Due to the profound connection between the flow geometry and the topological properties of the nematic director, the theory sheds light on the mechanisms leading to the proliferation of topological defects in active nematics and provides a number of testable predictions. A hypothesis, inspired by Onsager's statistical hydrodynamics, is finally introduced to account for the equilibrium probability distribution of the vortex sizes.
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.
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.
Mesoscale Equipartition of kinetic energy in Quantum Turbulence
Salort, Julien; Lévêque, Emmanuel; 10.1209/0295-5075/94/24001
2012-01-01T23:59:59.000Z
The turbulence of superfluid helium is investigated numerically at finite temperature. Direct numerical simulations are performed with a "truncated HVBK" model, which combines the continuous description of the Hall-Vinen-Bekeravich-Khalatnikov equations with the additional constraint that this continuous description cannot extend beyond a quantum length scale associated with the mean spacing between individual superfluid vortices. A good agreement is found with experimental measurements of the vortex density. Besides, by varying the turbulence intensity only, it is observed that the inter-vortex spacing varies with the Reynolds number as $Re^{-3/4}$, like the viscous length scale in classical turbulence. In the high temperature limit, Kolmogorov's inertial cascade is recovered, as expected from previous numerical and experimental studies. As the temperature decreases, the inertial cascade remains present at large scales while, at small scales, the system evolves towards a statistical equipartition of kinetic ...
Temporal Intermittency of Energy Dissipation in Magnetohydrodynamic Turbulence
Zhdankin, Vladimir; Boldyrev, Stanislav
2015-01-01T23:59:59.000Z
Energy dissipation in magnetohydrodynamic (MHD) turbulence is known to be highly intermittent in space, being concentrated in sheet-like coherent structures. Much less is known about intermittency in time, another fundamental aspect of turbulence which has great importance for observations of solar flares and other space/astrophysical phenomena. In this Letter, we investigate the temporal intermittency of energy dissipation in numerical simulations of MHD turbulence. We consider four-dimensional spatiotemporal structures, "flare events", responsible for a large fraction of the energy dissipation. We find that although the flare events are often highly complex, they exhibit robust power-law distributions and scaling relations. We find that the probability distribution of dissipated energy has a power law index close to -1.75, similar to observations of solar flares, indicating that intense dissipative events dominate the heating of the system. We also discuss the temporal asymmetry of flare events as a signatu...
Model Reduction of Turbulent Fluid Flows Using the Supply Rate
Sharma, A S
2013-01-01T23:59:59.000Z
A method for finding reduced-order approximations of turbulent flow models is presented. The method preserves bounds on the production of turbulent energy in the sense of the $\\curly{L}_2$ norm of perturbations from a notional laminar profile. This is achieved by decomposing the Navier-Stokes system into a feedback arrangement between the linearised system and the remaining, normally neglected, nonlinear part. The linear system is reduced using a method similar to balanced truncation, but preserving bounds on the supply rate. The method involves balancing two algebraic Riccati equations. The bounds are then used to derive bounds on the turbulent energy production. An example of the application of the procedure to flow through a long straight pipe is presented. Comparison shows that the new method approximates the supply rate at least as well as, or better than, canonical balanced truncation.
A turbulent transport network model in MULTIFLUX coupled with TOUGH2
Danko, G.; Bahrami, D.; Birkholzer, J.T.
2011-02-15T23:59:59.000Z
A new numerical method is described for the fully iterated, conjugate solution of two discrete submodels, involving (a) a transport network model for heat, moisture, and airflows in a high-permeability, air-filled cavity; and (b) a variably saturated fractured porous medium. The transport network submodel is an integrated-parameter, computational fluid dynamics solver, describing the thermal-hydrologic transport processes in the flow channel system of the cavity with laminar or turbulent flow and convective heat and mass transport, using MULTIFLUX. The porous medium submodel, using TOUGH2, is a solver for the heat and mass transport in the fractured rock mass. The new model solution extends the application fields of TOUGH2 by integrating it with turbulent flow and transport in a discrete flow network system. We present demonstrational results for a nuclear waste repository application at Yucca Mountain with the most realistic model assumptions and input parameters including the geometrical layout of the nuclear spent fuel and waste with variable heat load for the individual containers. The MULTIFLUX and TOUGH2 model elements are fully iterated, applying a programmed reprocessing of the Numerical Transport Code Functionalization model-element in an automated Outside Balance Iteration loop. The natural, convective airflow field and the heat and mass transport in a representative emplacement drift during postclosure are explicitly solved in the new model. The results demonstrate that the direction and magnitude of the air circulation patterns and all transport modes are strongly affected by the heat and moisture transport processes in the surrounding rock, justifying the need for a coupled, fully iterated model solution such as the one presented in the paper.
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
Electron and proton heating by solar wind turbulence B. Breech,1
Oughton, Sean
magnetohydrodynamic (MHD) turbulence are generalized to incorporate separate internal energy equations for electronsElectron and proton heating by solar wind turbulence B. Breech,1 W. H. Matthaeus,2 S. R. Cranmer,3 and protons. Electron heat conduction is included. Energy is supplied by turbulent heating that affects both
Direct numerical simulation of turbulent heat transfer in annuli: effect of heat flux ratio.
Paris-Sud XI, Université de
Direct numerical simulation of turbulent heat transfer in annuli: effect of heat flux ratio. M-la-Vall´ee cedex 2, France (Dated: October 23, 2008) Abstract Fully developed turbulent flow and heat transfer square (rms) of temperature fluctuations, turbulent heat fluxes, heat transfer, ...). To validate
Friction factor for turbulent flow in rough pipes from Heisenberg's closure hypothesis
Esteban Calzetta
2009-04-17T23:59:59.000Z
We show that the main results of the analysis of the friction factor for turbulent pipe flow reported in G. Gioia and P. Chakraborty (GC), Phys. Rev. Lett. 96, 044502 (1996) can be recovered by assuming the Heisenberg closure hypothesis for the turbulent spectrum. This highlights the structural features of the turbulent spectrum underlying GC's analysis.
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
Turbulent transition in a truncated 1D model for shear flow
Dawes, Jon
to a `turbulent' state (i) takes place more abruptly, with a boundary between laminar and `turbulent' flow at fixed Reynolds number are found to be consistent with exponential distributions. Keywords: fluid flowTurbulent transition in a truncated 1D model for shear flow By J. H. P. Dawes and W. J. Giles
Computational Study of Turbulent Laminar Patterns in Couette Flow Dwight Barkley*
Barkley, Dwight
Computational Study of Turbulent Laminar Patterns in Couette Flow Dwight Barkley* Mathematics, 91403 Orsay, France (Received 29 March 2004; published 7 January 2005) Turbulent-laminar patterns near--undergoes a discontinuous transition from laminar flow to turbulence as the Reynolds number is increased. Because of its
Denny, Mark
coastal ocean because of the combination of smaller turbulent eddies and reduced currents. The decreaseCurrents and turbulence within a kelp forest (Macrocystis pyrifera): Insights from a dynamically pyrifera forest on currents and turbulence were investigated in a controlled laboratory setting using
NUMERICAL STUDY OF A TURBULENT HYDRAULIC JUMP Qun Zhao 1 Shubhra K. Misra1
Zhao, Qun
. Hydraulic jumps are commonly used as energy dissipators and they have been studied intensively by hydraulicNUMERICAL STUDY OF A TURBULENT HYDRAULIC JUMP Qun Zhao 1 Shubhra K. Misra1 Ib A. Svendsen 1 (Member of a turbulent hydraulic jump. The numerical model is based on RIPPLE (Kothe et al., 1994) with two turbulence
Varenna Proceedings, Sept. 1, 1998 The Dynamics of Small-Scale Turbulence-Driven Flows
Hammett, Greg
of a linearly undamped component of the flow which could build up in time and lower the final turbulence levelVarenna Proceedings, Sept. 1, 1998 The Dynamics of Small-Scale Turbulence-Driven Flows M. A. Beer investigate the dynamics of small-scale turbulence-driven sheared E B flows in nonlinear gyrofluid
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
Density Power Spectrum of Compressible Hydrodynamic Turbulent Flows
Jongsoo Kim; Dongsu Ryu
2005-07-26T23:59:59.000Z
Turbulent flows are ubiquitous in astrophysical environments, and understanding density structures and their statistics in turbulent media is of great importance in astrophysics. In this paper, we study the density power spectra, $P_{\\rho}$, of transonic and supersonic turbulent flows through one and three-dimensional simulations of driven, isothermal hydrodynamic turbulence with root-mean-square Mach number in the range of $1 \\la M_{\\rm rms} \\la 10$. From one-dimensional experiments we find that the slope of the density power spectra becomes gradually shallower as the rms Mach number increases. It is because the density distribution transforms from the profile with {\\it discontinuities} having $P_{\\rho} \\propto k^{-2}$ for $M_{\\rm rms} \\sim 1$ to the profile with {\\it peaks} having $P_{\\rho} \\propto k^0$ for $M_{\\rm rms} \\gg 1$. We also find that the same trend is carried to three-dimension; that is, the density power spectrum flattens as the Mach number increases. But the density power spectrum of the flow with $M_{\\rm rms} \\sim 1$ has the Kolmogorov slope. The flattening is the consequence of the dominant density structures of {\\it filaments} and {\\it sheets}. Observations have claimed different slopes of density power spectra for electron density and cold H I gas in the interstellar medium. We argue that while the Kolmogorov spectrum for electron density reflects the {\\it transonic} turbulence of $M_{\\rm rms} \\sim 1$ in the warm ionized medium, the shallower spectrum of cold H I gas reflects the {\\it supersonic} turbulence of $M_{\\rm rms} \\sim$ a few in the cold neutral medium.
Solar thermal financing guidebook
Williams, T.A.; Cole, R.J.; Brown, D.R.; Dirks, J.A.; Edelhertz, H.; Holmlund, I.; Malhotra, S.; Smith, S.A.; Sommers, P.; Willke, T.L.
1983-05-01T23:59:59.000Z
This guidebook contains information on alternative financing methods that could be used to develop solar thermal systems. The financing arrangements discussed include several lease alternatives, joint venture financing, R and D partnerships, industrial revenue bonds, and ordinary sales. In many situations, alternative financing arrangements can significantly enhance the economic attractiveness of solar thermal investments by providing a means to efficiently allocate elements of risk, return on investment, required capital investment, and tax benefits. A net present value approach is an appropriate method that can be used to investigate the economic attractiveness of alternative financing methods. Although other methods are applicable, the net present value approach has advantages of accounting for the time value of money, yielding a single valued solution to the financial analysis, focusing attention on the opportunity cost of capital, and being a commonly understood concept that is relatively simple to apply. A personal computer model for quickly assessing the present value of investments in solar thermal plants with alternative financing methods is presented in this guidebook. General types of financing arrangements that may be desirable for an individual can be chosen based on an assessment of his goals in investing in solar thermal systems and knowledge of the individual's tax situation. Once general financing arrangements have been selected, a screening analysis can quickly determine if the solar investment is worthy of detailed study.
Nonclassicality of Thermal Radiation
Lars M. Johansen
2004-02-16T23:59:59.000Z
It is demonstrated that thermal radiation of small occupation number is strongly nonclassical. This includes most forms of naturally occurring radiation. Nonclassicality can be observed as a negative weak value of a positive observable. It is related to negative values of the Margenau-Hill quasi-probability distribution.
Not Available
1980-06-01T23:59:59.000Z
Information is presented concerning fire risk and protection; transient thermal-hydraulic analysis and experiments; class 9 accidents and containment; diagnostics and in-service inspection; risk and cost comparison of alternative electric energy sources; fuel behavior and experiments on core cooling in LOCAs; reactor event reporting analysis; equipment qualification; post facts analysis of the TMI-2 accident; and computational methods.
Bowker, Jeffrey Charles (Gibsonia, PA); Sabol, Stephen M. (Orlando, FL); Goedjen, John G. (Oviedo, FL)
2001-01-01T23:59:59.000Z
A thermal barrier coating for hot gas path components of a combustion turbine based on a zirconia-scandia system. A layer of zirconium scandate having the hexagonal Zr.sub.3 Sc.sub.4 O.sub.12 structure is formed directly on a superalloy substrate or on a bond coat formed on the substrate.
Electron geodesic acoustic modes in electron temperature gradient mode turbulence
Anderson, Johan; Nordman, Hans [Department of Earth and Space Sciences, Chalmers University of Technology, SE-412 96 Goeteborg (Sweden); Singh, Raghvendra; Kaw, Predhiman [Institute for Plasma Research, Bhat, Gandhinagar, Gujarat 382428 (India)
2012-08-15T23:59:59.000Z
In this work, the first demonstration of an electron branch of the geodesic acoustic mode (el-GAM) driven by electron temperature gradient (ETG) modes is presented. The work is based on a fluid description of the ETG mode retaining non-adiabatic ions and the dispersion relation for el-GAMs driven nonlinearly by ETG modes is derived. A new saturation mechanism for ETG turbulence through the interaction with el-GAMs is found, resulting in a significantly enhanced ETG turbulence saturation level compared to the mixing length estimate.
Validating the BHR RANS model for variable density turbulence
Israel, Daniel M [Los Alamos National Laboratory; Gore, Robert A [Los Alamos National Laboratory; Stalsberg - Zarling, Krista L [Los Alamos National Laboratory
2009-01-01T23:59:59.000Z
The BHR RANS model is a turbulence model for multi-fluid flows in which density variation plays a strong role in the turbulence processes. In this paper they demonstrate the usefulness of BHR over a wide range of flows which include the effects of shear, buoyancy, and shocks. The results are in good agreement with experimental and DNS data across the entire set of validation cases, with no need to retune model coefficients between cases. The model has potential application to a number of aerospace related flow problems.
MEASUREMENTS AND COMPUTATIONS OF FUEL DROPLET TRANSPORT IN TURBULENT FLOWS
Joseph Katz and Omar Knio
2007-01-10T23:59:59.000Z
The objective of this project is to study the dynamics of fuel droplets in turbulent water flows. The results are essential for development of models capable of predicting the dispersion of slightly light/heavy droplets in isotropic turbulence. Since we presently do not have any experimental data on turbulent diffusion of droplets, existing mixing models have no physical foundations. Such fundamental knowledge is essential for understanding/modeling the environmental problems associated with water-fuel mixing, and/or industrial processes involving mixing of immiscible fluids. The project has had experimental and numerical components: 1. The experimental part of the project has had two components. The first involves measurements of the lift and drag forces acting on a droplet being entrained by a vortex. The experiments and data analysis associated with this phase are still in progress, and the facility, constructed specifically for this project is described in Section 3. In the second and main part, measurements of fuel droplet dispersion rates have been performed in a special facility with controlled isotropic turbulence. As discussed in detail in Section 2, quantifying and modeling the of droplet dispersion rate requires measurements of their three dimensional trajectories in turbulent flows. To obtain the required data, we have introduced a new technique - high-speed, digital Holographic Particle Image Velocimetry (HPIV). The technique, experimental setup and results are presented in Section 2. Further information is available in Gopalan et al. (2005, 2006). 2. The objectives of the numerical part are: (1) to develop a computational code that combines DNS of isotropic turbulence with Lagrangian tracking of particles based on integration of a dynamical equation of motion that accounts for pressure, added mass, lift and drag forces, (2) to perform extensive computations of both buoyant (bubbles) and slightly buoyant (droplets) particles in turbulence conditions relevant to the experiments, and (3) to explore whether the corresponding predictions can explain the experimentally-observed behavior of the rise and dispersion of oil droplets in isotropic turbulence. A brief summary of results is presented in Section 4.
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.
A Tree Swaying in a Turbulent Wind: A Scaling Analysis
Theo Odijk
2014-07-10T23:59:59.000Z
A tentative scaling theory is presented of a tree swaying in a turbulent wind. It is argued that the turbulence of the air within the crown is in the inertial regime. An eddy causes a dynamic bending response of the branches according to a time criterion. The resulting expression for the penetration depth of the wind yields an exponent which appears to be consistent with that pertaining to the morphology of the tree branches. An energy criterion shows that the dynamics of the branches is basically passive. The possibility of hydrodynamic screening by the leaves is discussed.
Plasticity and deformation of crystals: Analogies to turbulence
Choi, Woosong; Papanikolaou, Stefanos; Sethna, James P
2011-01-01T23:59:59.000Z
We describe intriguing analogies between our model of material deformation (how crystals deform under load) and fluid turbulence (how liquids flow under shear). Our model present mathematical, physical, and computational challenges, but offer intriguing new predictions of fractal, scale-invariant structure formation for experiments. We show here that these challenges are shared with classic models of turbulence. In particular, we find precisely analogous physical and mathematical challenges associated with the formation of singularities in the evolving flows, and associated computational challenges with even defining a solution in the continuum limit where the grid size and the viscosities go to zero.
Effective Thermal Conductivity of Graded Nanocomposites with Interfacial Thermal
Paulino, Glaucio H.
Effective Thermal Conductivity of Graded Nanocomposites with Interfacial Thermal Resistance H Engineering, Newmark Laboratory, 205 North Mathews Avenue, University of Illinois at Urbana-Champaign, Urbana, IL 61801 Department of Civil and Environmental Engineering, 4139 Engineering Gateway, University
Giant Thermal Rectification from Polyethylene Nanofiber Thermal Diodes
Zhang, Teng
2015-01-01T23:59:59.000Z
The realization of phononic computing is held hostage by the lack of high performance thermal devices. Here we show through theoretical analysis and molecular dynamics simulations that unprecedented thermal rectification factors (as large as 1.20) can be achieved utilizing the phase dependent thermal conductivity of polyethylene nanofibers. More importantly, such high thermal rectifications only need very small temperature differences (< 20 oC) across the device, which is a significant advantage over other thermal diodes which need temperature biases on the order of the operating temperature. Taking this into consideration, we show that the dimensionless temperature-scaled rectification factors of the polymer nanofiber diodes range from 12 to 25 - much larger than other thermal diodes (< 8). The polymer nanofiber thermal diode consists of a crystalline portion whose thermal conductivity is highly phase-sensitive and a cross-linked portion which has a stable phase. Nanoscale size effect can be utilized t...
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.
Fast Thermal Simulation for Architecture Level Dynamic Thermal Management
Tan, Sheldon X.-D.
Fast Thermal Simulation for Architecture Level Dynamic Thermal Management Pu Liu, Zhenyu Qi, Hang Li, Lingling Jin, Wei Wu, Sheldon X.-D. Tan, Jun Yang Department of Electrical Engineering temperature by dynamic thermal managements becomes necessary. This paper proposes a novel approach
A generic model for transport in turbulent shear flows
Newton, Andrew P. L.; Kim, Eun-Jin [Department of Applied Mathematics, University of Sheffield, Sheffield, S3 7RH (United Kingdom)
2011-05-15T23:59:59.000Z
Turbulence regulation by large-scale shear flows is crucial for a predictive modeling of transport in plasma. In this paper the suppression of turbulent transport by large-scale flows is studied numerically by measuring the turbulent diffusion D{sub t} and scalar amplitude
Jet Quenching and Holographic Thermalization
Elena Caceres; Arnab Kundu; Berndt Müller; Diana Vaman; Di-Lun Yang
2012-08-31T23:59:59.000Z
We employ the AdS/CFT correspondence to investigate the thermalization of the strongly-coupled plasma and the jet quenching of a hard probe traversing such a thermalizing medium.
Thermal Modeling of Lundell Alternators
Tang, Sai Chun
Thermal analysis of Lundell alternators used in automobiles is presented. An analytical thermal model for Lundell alternators is proposed, and procedures for acquiring the model parameters are elucidated. Based on the ...
Thermal Conductivity of Coated Paper
Kerr, Lei L [ORNL; Pan, Yun-Long [Smart Papers, Hamilton, OH 45013; Dinwiddie, Ralph Barton [ORNL; Wang, Hsin [ORNL; Peterson, Robert C. [Miami University, Oxford, OH
2009-01-01T23:59:59.000Z
In this paper, we introduce a method for measuring the thermal conductivity of paper using a hot disk system. To the best of our knowledge, few publications are found discussing the thermal conductivity of a coated paper although it is important to various forms of today s digital printing where heat is used for imaging as well as for toner fusing. This motivates us to investigate the thermal conductivity of paper coating. Our investigation demonstrates that thermal conductivity is affected by the coat weight and the changes in the thermal conductivity affect ink gloss and density. As the coat weight increases, the thermal conductivity increases. Both the ink gloss and density decrease as the thermal conductivity increases. The ink gloss appears to be more sensitive to the changes in the thermal conductivity.
Evolving opportunities for providing thermal comfort
Brager, Gail; Zhang, Hui; Arens, Edward
2015-01-01T23:59:59.000Z
field measurement of thermal environment and questionnaireand non-uniform thermal environments, PhD Thesis, Center forPerception of transient thermal environments: Pleasure and
Harvesting nanoscale thermal radiation using pyroelectric materials
Fang, Jin; Frederich, Hugo; Pilon, Laurent
2010-01-01T23:59:59.000Z
the other hand, energy transfer by thermal radiation betweenit was shown that energy transfer by thermal radi- ationpyroelectric energy conversion and nanoscale thermal
AQUIFER THERMAL ENERGY STORAGE-A SURVEY
Tsang, Chin Fu
2012-01-01T23:59:59.000Z
1978, High temperature underground thermal energy storage,in Proceedings, Thermal Energy Storage in Aquifers Workshop:High temperature underground thermal energy storage, in ATES
AQUIFER THERMAL ENERGY STORAGE-A SURVEY
Tsang, Chin Fu
2012-01-01T23:59:59.000Z
High temperature underground thermal energy storage, inProceedings, Thermal Energy Storage in Aquifers Workshop:underground thermal energy storage, in ATES newsletter:
Ocean Thermal Extractable Energy Visualization: Final Technical...
Ocean Thermal Extractable Energy Visualization: Final Technical Report Ocean Thermal Extractable Energy Visualization: Final Technical Report Report about the Ocean Thermal...
THERMAL ENERGY STORAGE IN AQUIFERS WORKSHOP
Authors, Various
2011-01-01T23:59:59.000Z
Survey of Thermal Energy Storage in Aquifers Coupled withAnnual Thermal Energy Storage Contractors' InformationLarge-Scale Thermal Energy Storage for Cogeneration and
AQUIFER THERMAL ENERGY STORAGE-A SURVEY
Tsang, Chin Fu
2012-01-01T23:59:59.000Z
the prob- lem of seasonal storage of thermal energy (Matheyto study seasonal storage of thermal energy: winter storagewithin the Seasonal Thermal Energy Storage Program managed
THERMAL ENERGY STORAGE IN AQUIFERS WORKSHOP
Authors, Various
2011-01-01T23:59:59.000Z
Survey of Thermal Energy Storage in Aquifers Coupled withLow Temperature Thermal Energy Storage Program of Oak Ridgefor Seasonal Thermal Energy Storage: An Overview of the DOE-
Modeling thermal comfort in stratified environments
Zhang, H.; Huizenga, C.; Arens, Edward A; Yu, T.
2005-01-01T23:59:59.000Z
non-uniform thermal environments", European Journal of7730, 1994, Moderate Thermal Environments – Determination offor assessing complex thermal environments,” Building and
Thermal Transport in Graphene Multilayers and Nanoribbons
Subrina, Samia
2011-01-01T23:59:59.000Z
1 CHAPTER 2 Thermal transport atvalues of graphene’s thermal conductivity and different1 Thermal conductivity : metals and non - metallic
Evolving opportunities for providing thermal comfort
Brager, Gail; Zhang, Hui; Arens, Edward
2015-01-01T23:59:59.000Z
control in offices for thermal comfort and energy savings.ANSI/ASHRAE 55-2013: Thermal environmental conditions forA global database of thermal comfort field experiments.
Thermal Conductivity of Polycrystalline Semiconductors and Ceramics
Wang, Zhaojie
2012-01-01T23:59:59.000Z
35, (3-6), Dames, C. ; Chen, G. , Thermal Conductivity ofProperties of Matter: Thermal conductivity: nonmetallicSociety), Dames, C. ; Chen, G. , Thermal Conductivity of
Thermal Conduction in Graphene and Graphene Multilayers
Ghosh, Suchismita
2009-01-01T23:59:59.000Z
1 1.2 Thermal transport atxv Introduction xii 1.1 Thermal conductivity and65 4.13 Thermal conductivity of graphene as a function of
THERMAL ENERGY STORAGE IN AQUIFERS WORKSHOP
Authors, Various
2011-01-01T23:59:59.000Z
Energy can be saved and thermal pollution reduced if a totalnatural flow, and thermal pollution caused by simultaneousStored Heat Energy and Thermal Pollution Daily stored heat
AQUIFER THERMAL ENERGY STORAGE-A SURVEY
Tsang, Chin Fu
2012-01-01T23:59:59.000Z
Reduction of air and thermal pollution are additionalsubsidence or upliftu thermal pollution, water chemistry,or ponds to avoid thermal pollution. Because periods of heat
Microviscometric studies on thermal diffusion
Reyna, Eddie
1959-01-01T23:59:59.000Z
for its improvement. This in~estigation was supported in part by the Convsir Division of General Dynamics Corporation. TABLE OF CONTENTS Chapter III INTRODUCTION EXPERINENTAL NETHODS AND PROCEDUPJIS Thermal Diffusion Column Viscosity Measurements.... The main interest of 6 tais work was the molecular weight dependence of the thermal diffusion coefficient and the suitability of thermal diffusion as a method of frac- tionation of polymers. Since the work of Debye and Bueche, applications of thermal...
Liquid metal thermal electric converter
Abbin, Joseph P. (Albuquerque, NM); Andraka, Charles E. (Albuquerque, NM); Lukens, Laurance L. (Albuquerque, NM); Moreno, James B. (Albuquerque, NM)
1989-01-01T23:59:59.000Z
A liquid metal thermal electric converter which converts heat energy to electrical energy. The design of the liquid metal thermal electric converter incorporates a unique configuration which directs the metal fluid pressure to the outside of the tube which results in the structural loads in the tube to be compressive. A liquid metal thermal electric converter refluxing boiler with series connection of tubes and a multiple cell liquid metal thermal electric converter are also provided.
Ocean Thermal Energy Conversion Basics
Broader source: Energy.gov [DOE]
A process called ocean thermal energy conversion (OTEC) uses the heat energy stored in the Earth's oceans to generate electricity.
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)
Supersonic turbulent boundary layers with periodic mechanical non-equilibrium
Ekoto, Isaac Wesley
2007-04-25T23:59:59.000Z
questions have been raised. The fundamental questions this dissertation addressed are: (1) What are the effects of wall topology with sharp versus blunt leading edges? and (2) Is it possible that a further reduction of turbulent scales can occur if surface...
Modeling Turbulent Hydraulic Fracture Near a Free Surface
Modeling Turbulent Hydraulic Fracture Near a Free Surface Victor C. Tsai Seismological Laboratory consider a hydraulic fracture problem in which the crack grows parallel to a free surface, subject to fully components. ^· Non-dimensionalized ·. 1 Introduction Hydraulic fracture has been studied for many years
Large-Scale Streamwise Turbulent Structures in Hypersonic Boundary Layers
English, Benjamin L.
2013-04-22T23:59:59.000Z
................................................................... 80 REFERENCES ......................................................................................................... 82 ix LIST OF FIGURES FIGURE Page 1 Typical laminar and turbulent boundary layer profiles. Figure taken from Ref. [1... configuration. Figure taken from Ref. [19] ............................................................................................ 12 5 WPG and SPG floor model profiles. Figure taken from Ref. [19] .... 14 6 Diamond roughness element topology...
Simulations of High Speed Turbulent Jets in Crossflow Xiaochuan Chai
Mahesh, Krishnan
Simulations of High Speed Turbulent Jets in Crossflow Xiaochuan Chai and Krishnan Mahesh-expanded sonic jet injected into a supersonic crossflow and an over-expanded supersonic jet injected into a subsonic crossflow. A finite volume compressible NavierStokes solver developed by Park & Mahesh (2007
Simulations of High Speed Turbulent Jets in Crossflows Xiaochuan Chai
Mahesh, Krishnan
Simulations of High Speed Turbulent Jets in Crossflows Xiaochuan Chai and Krishnan Mahesh-expanded sonic jet injected into a supersonic crossflow and an over-expanded supersonic jet injected into a subsonic crossflow, where the flow conditions are based on Santiago et al.'s (1997) and Beresh et al
Center for Turbulence Research Annual Research Briefs 2008
Prinz, Friedrich B.
breakup of turbulent liquid jets in crossflow By M. G. Pai, O. Desjardins AND H. Pitsch 1. Motivation and objectives The problem of breakup of a liquid fuel in a crossflow finds relevance in applications in a crossflow is a result of a complex process that includes development of instabilities along the liquid
The Solar Flare: A Strongly Turbulent Particle Accelerator
California at Berkeley, University of
Chapter 5 The Solar Flare: A Strongly Turbulent Particle Accelerator L. Vlahos, S. Krucker, and P) and particle acceleration during such an event are rarely discussed together in the same article. Many the topic of particle acceleration is often presented as an addi- tional complication to be addressed
On star formation rate and turbulent dissipation in galactic models
E. P. Kurbatov
2007-12-10T23:59:59.000Z
The models of star formation function and of dissipation of turbulent energy of interstellar medium are proposed. In star formation model the feedback of supernovae is taken into account. It is shown that hierarchical scenario of galaxy formation with proposed models is able to explain the observable star formation pause in the Galaxy.
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.
Center for Turbulence Research Annual Research Briefs 2008
Prinz, Friedrich B.
Turbulent multi-phase combustion is encountered in a number of engineering applica- tions, such as internal combustion engines and gas-turbine aircraft engines. Therefore, the ability to perform accurate numerical and combustion in a swirling combustor By K. Luo, O. Desjardins AND H. Pitsch 1. Motivation and objective
Kinetic dissipation and anisotropic heating in a turbulent collisionless plasma
Cassak, Paul
- lar wind find evidence that most of the turbulent energy at high wavenumber resides in highly oblique Laboratory, University of Delaware, Newark, Delaware 19716, USA Received 14 October 2008; accepted 12, differences from MHD arise, as energy dissipates into heat almost exclusively through the magnetic field
"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
Micro-jets in confined turbulent cross flow
Kelman, J.B.; Greenhalgh, D.A. [School of Engineering, Cranfield University, Cranfield, Bedfordshire MK43 0AL (United Kingdom); Whiteman, M. [Rolls-Royce plc, Combustion systems, Moor Lane, Derby DE24 8BJ (United Kingdom)
2006-03-01T23:59:59.000Z
The mixing of sub-millimetre diameter jets issuing into a turbulent cross flow is examined with a combination of laser diagnostic techniques. The cross flow stream is in a confined duct and the micro-jet issue from the sides of injector vanes. A range of cross jet momentum ratios, cross flow temperatures and turbulence intensities are investigated to examine the influence on the jet mixing. Methane, seeded with acetone, was used to measure the concentrations of the jets and the mixing of the jet fluid in the duct. Unlike previous jet in cross flow work, mixing appears to be dominated by the free stream turbulence, rather than the cross jet momentum ratios. Temperature increases in the free stream appear to increase the rate of mixing in the duct, despite the associated decrease in the Reynolds number. The dominance of the free stream turbulence in controlling the mixing is of particular interest in respect of gas turbine injection systems, as the cross jet momentum ratio is insufficient in defining the mixing process. (author)
Turbulence and Transport The Secrets of Magnetic Confinement
Greenwald, Martin
Turbulence and Transport The Secrets of Magnetic Confinement Martin Greenwald - MIT Plasma Science. · #12;CONFINEMENT REQUIREMENTS FOR FUSION THE LAWSON CRITERION In steady state, Fusion Power = Loss. Works for the H-bomb "Micro" explosions to be tested with NIF (Defense Program) 3 Magnetic Confinement
MULTISCALE NUMERICAL STUDY OF TURBULENT FLOW AND BUBBLE ENTRAINMENT
Kirby, James T.
MULTISCALE NUMERICAL STUDY OF TURBULENT FLOW AND BUBBLE ENTRAINMENT IN THE SURF ZONE BY GANGFENG MA . . . . . . . . . . . . . . . . . . . . . 3 1.1.2 Numerical Investigations . . . . . . . . . . . . . . . . . . . . . 5 1.2 Bubble Entrainment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2.4 Bubble Entrainment Model . . . . . . . . . . . . . . . . . . . . . . . 18 2.5 Bubble Breakup
Wind Energy Applications of Unified and Dynamic Turbulence Models
Heinz, Stefan
Wind Energy Applications of Unified and Dynamic Turbulence Models Stefan Heinz and Harish Gopalan applicable as a low cost alternative. 1 Introduction There is a growing interest in using wind energy suggests the possibility of providing 20% of the electricity in the U.S. by wind energy in 2030
Center for Turbulence Research Annual Research Briefs 2008
Prinz, Friedrich B.
Center for Turbulence Research Annual Research Briefs 2008 115 Spurious oscillations to the discontinuity in the ratio of specific heats in the energy equation and suggested a means to overcome, the findings are summarized and an outlook for future work is outlined. 2. Numerical methods For simplicity
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
AIAA980057 RELATING TURBULENCE TO WIND TURBINE BLADE LOADS
Sweetman, Bert
AIAA980057 RELATING TURBULENCE TO WIND TURBINE BLADE LOADS: PARAMETRIC STUDY WITH MULTIPLE that is most useful in estimating fatigue loads on wind turbine blades. The histograms of rainflow counted for flapwise loads on three horizontal axis wind tur bines(HAWTs). In the case of two of these turbines
Anisotropic constraints on energy distribution in rotating and stratified turbulence
Kurien, Susan
OFFPRINT Anisotropic constraints on energy distribution in rotating and stratified turbulence S) 24003 www.epljournal.org doi: 10.1209/0295-5075/84/24003 Anisotropic constraints on energy distribution enstrophy constrains the spectral distribution of horizontal kinetic energy and potential energy. Horizontal
Modeling Turbulent Hydraulic Fracture Near a Free Surface
Modeling Turbulent Hydraulic Fracture Near a Free Surface Victor C. Tsai Seismological Laboratory consider a hydraulic fracture problem in which the crack grows parallel to a free surface, subject to fully components. wall Wall shear stress. ^· Non-dimensionalized ·. 1 Introduction Hydraulic fracture has been
Lyapunov exponents of heavy particles in turbulence Jrmie Bec
Cencini, Massimo
Lyapunov exponents of heavy particles in turbulence Jérémie Bec CNRS UMR6202, Observatoire de la Ferrara, Italy Received 7 June 2006; accepted 7 August 2006; published online 7 September 2006 Lyapunov, a counterintuitive increase of the first Lyapunov exponent is observed. The flow intermittency is found to induce
Covariant Lyapunov Analysis of NavierStokes Turbulence
RIMSÂ1770 Covariant Lyapunov Analysis of NavierÂStokes Turbulence By Masanobu INUBUSHI January 2013 RESEARCH INSTITUTE FOR MATHEMATICAL SCIENCES KYOTO UNIVERSITY, Kyoto, Japan #12; Covariant Lyapunov of the important properties of chaos. Particularly, we employ covariant Lyapunov analysis recently developed
Covariant Lyapunov Analysis of Navier-Stokes Turbulence
RIMS-1770 Covariant Lyapunov Analysis of Navier-Stokes Turbulence By Masanobu INUBUSHI January 2013 RESEARCH INSTITUTE FOR MATHEMATICAL SCIENCES KYOTO UNIVERSITY, Kyoto, Japan #12;Covariant Lyapunov Analysis of chaos. Particularly, we employ covariant Lyapunov analysis recently developed by Ginelli et al. (2007
Ris-R-Report Investigation of turbulence measurements
many times that the mean horizontal wind speed measured by a lidar over flat terrain compares very well. We then evaluate this model by comparing the theoretical results to experimental data obtained.......................................................12 3.1 What can a cw conically scanning lidar tell us about turbulence?...12 3.2 Illustration
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.
Unstructured spectral element methods of simulation of turbulent flows
Henderson, R.D. [California Inst. of Technology, Pasadena, CA (United States)] [California Inst. of Technology, Pasadena, CA (United States); Karniadakis, G.E. [Brown Univ., Providence, RI (United States)] [Brown Univ., Providence, RI (United States)
1995-12-01T23:59:59.000Z
In this paper we present a spectral element-Fourier algorithm for simulating incompressible turbulent flows in complex geometries using unstructured quadrilateral meshes. To this end, we compare two different interface formulations for extending the conforming spectral element method in order to allow for surgical mesh refinement and still retain spectral accuracy: the Zanolli iterative procedure and variational patching based on auxiliary {open_quotes}mortar{close_quotes} functions. We present an interpretation of the original mortar element method as a patching scheme and develop direct and iterative solution techniques that make the method efficient for simulations of turbulent flows. The properties of the new method are analyzed in detail by studying the eigenspectra of the advection and diffusion operators. We then present numerical results that illustrate the flexibility as well as the exponential convergence of the new algorithm for nonconforming discretizations. We conclude with simulation studies of the turbulent cylinder wake at Re = 1000 (external flow) and turbulent flow over riblets at Re = 3280 (internal flow). 36 refs., 29 figs., 7 tabs.
LES of a Hydrogen-Enriched Lean Turbulent Premixed Flame
Groth, Clinton P. T.
LES of a Hydrogen-Enriched Lean Turbulent Premixed Flame Francisco E. Hern´andez-P´erez , Clinton the observed behaviour is examined. Hydrogen-hydrocarbon fuel blends appear to be a promising option to synergistically pave the way toward pure hydrogen-based combustion systems while alleviating green-house gas
MICROWAVE IMAGING REFLECTOMETRY FOR THE VISUALIZATION OF TURBULENCE IN TOKAMAKS
1 MICROWAVE IMAGING REFLECTOMETRY FOR THE VISUALIZATION OF TURBULENCE IN TOKAMAKS E. Mazzucato of density fluctuations in tokamaks. The proposed method is based on microwave reflectometry and consists, and forming an image of the reflecting plasma layer onto a 2D array of microwave receivers. Based on results
Microwave imaging reflectometry for the visualization of turbulence in tokamaks
Mazzucato, Ernesto
Microwave imaging reflectometry for the visualization of turbulence in tokamaks E. Mazzucato describes the results of an extensive numerical study of microwave reflectometry in tokamaks showing of the reflecting layer onto an array of microwave receivers, and the amplitude of fluctuations to be below
ECRH microwave beam broadening in the edge turbulent plasma
Sysoeva, E. V.; Gusakov, E. Z.; Popov, A. Yu. [Ioffe Institute, St. Petersburg, Russia and RL PAT SPbSPU, St. Petersburg (Russian Federation); Silva, F. da [Institute of Plasmas and Nuclear Fusion, IST, Lisbon (Portugal); Heuraux, S. [IJL UMR-7198 CNRS-Université de Lorraine, BP70239, 54506 Vandoeuvre Cedex (France)
2014-02-12T23:59:59.000Z
The influence of turbulent plasma density fluctuations on angular and spatial beam width is treated analytically in the framework of WKB based eikonal method. Reasonable agreement of analytical and numerical treatment results is demonstrated within the domain of quasi-optical approximation validity. Significant broadening of microwave beams is predicted for future ECRH experiments at ITER.
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...
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.
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
Turbulence: Modeling complex flow C.W. Oosterlee
Oosterlee, Cornelis W. "Kees"
grid should be such that they are captured. #15; Macro structure with length scale L, micro structure with the Kolmogorov length scale #17; #15; Number of grid points: #18; L #17; #19; 3 Turbulence/Folie--Nr. 7 #12; DNS storage: > 10 #2; 10 9 #15; number of computing operations: #24; 500 #15; number of time steps: #24; 10000