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
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.
Coshcous turbulence and its thermalization
Zhu, Jian-zhou [Los Alamos National Laboratory; Taylor, Mark [SNL
2008-01-01T23:59:59.000Z
Dissipation rate {mu}[cosh(k/k{sub c}) - 1] in Fourier space, which reduces to the Newtonian viscosity dissipation rate {nu}k{sup 2} for small k/k{sub c}, can be scaled to make a hydrodynamic system either actually or potentially converge to its Galerkin truncation. The former case acquires convergence to the truncation at a finite wavenumber k{sub G}; the latter realizes as the wavenumber grows to infinity. Intermittency reduction and vitiation of extended self-similarity (ESS) in the partially thermalized regime of turbulence are confirmed and clarified. Onsager's pictures of intermittent versus nonintermittent flows are visualized from thermalized numerical fields, showing cleanly spotty versus mistily uniform properties, the latter of which destroys self-organization and so the ESS property.
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...
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.
FLIHY EXPERIMENTAL FACILITIES FOR STUDYING OPEN CHANNEL TURBULENT FLOWS AND HEAT TRANSFER
California at Los Angeles, University of
1 FLIHY EXPERIMENTAL FACILITIES FOR STUDYING OPEN CHANNEL TURBULENT FLOWS AND HEAT TRANSFER B was constructed at UCLA to study open channel turbulent flow and heat transfer of low-thermal and low supercritical flow regimes (Fr>1), in which the surface waves are amplified and heat transfer is enhanced due
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.
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
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.
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.
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.
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.
Autoignition in turbulent two-phase flows
Borghesi, Giulio
2013-01-08T23:59:59.000Z
and spatial evolution of the macroscopic properties of the flow. These equations will be given in Chapter 2 and are known as the Navier-Stokes equa- tions. Depending on the application considered, different numerical techniques for solving the Navier... clusters worldwide will lead to a relaxation of these constraints in the future: simulations of flows with values of Re up to O(103) are starting to become common, and, in recent years, a turbulent lifted hydrogen jet flame with a jet Reynolds number of 11...
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.
Sandia Energy - Measuring Inflow and Wake Flow Turbulence Using...
Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)
that characterizes inflow and wake flow velocity and turbulence around a vertical axis turbine deployed at the Roza Canal, Yakima, Washington. The ADV was mounted on a...
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...
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.
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.
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.
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.
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.
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...
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
The Dynamics of SmallScale Turbulence Driven Flows
Hammett, Greg
the existence of a linearly undamped component of the flow which could build up in time and lower the finalThe Dynamics of SmallScale Turbulence Driven Flows M. A. Beer and G. W. Hammett PPPL APS DPP meeting, November 1997 The dynamics of smallscale fluctuation driven flows are of great in terest
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
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.
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.
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 patterns in wall-bounded flows: a Turing instability?
Manneville, Paul
2012-01-01T23:59:59.000Z
In their way to/from turbulence, plane wall-bounded flows display an interesting transitional regime where laminar and turbulent oblique bands alternate, the origin of which is still mysterious. In line with Barkley's recent work about the pipe flow transition involving reaction-diffusion concepts, we consider plane Couette flow in the same perspective and transform Waleffe's classical four-variable model of self-sustaining process into a reaction-diffusion model. We show that, upon fulfillment of a condition on the relative diffusivities of its variables, the featureless turbulent regime becomes unstable against patterning as the result of a Turing instability. A reduced two-variable model helps us to delineate the appropriate region of parameter space. An {\\it intrinsic} status is therefore given to the pattern's wavelength for the first time. Virtues and limitations of the model are discussed, calling for a microscopic support of the phenomenological approach.
Ignition of hydrogen/air mixing layer in turbulent flows
Im, H.G.; Chen, J.H. [Sandia National Labs., Livermore, CA (United States). Combustion Research Facility; Law, C.K. [Princeton Univ., NJ (United States). Dept. of Mechanical and Aerospace Engineering
1998-03-01T23:59:59.000Z
Autoignition of a scalar hydrogen/air mixing layer in homogeneous turbulence is studied using direct numerical simulation. An initial counterflow of unmixed nitrogen-diluted hydrogen and heated air is perturbed by two-dimensional homogeneous turbulence. The temperature of the heated air stream is chosen to be 1,100 K which is substantially higher than the crossover temperature at which the rates of the chain branching and termination reactions become equal. Three different turbulence intensities are tested in order to assess the effect of the characteristic flow time on the ignition delay. For each condition, a simulation without heat release is also performed. The ignition delay determined with and without heat release is shown to be almost identical up to the point of ignition for all of the turbulence intensities tested, and the predicted ignition delays agree well within a consistent error band. It is also observed that the ignition kernel always occurs where hydrogen is focused, and the peak concentration of HO{sub 2} is aligned well with the scalar dissipation rate. The dependence of the ignition delay on turbulence intensity is found to be nonmonotonic. For weak to moderate turbulence the ignition is facilitated by turbulence via enhanced mixing, while for stronger turbulence, whose timescale is substantially smaller than the ignition delay, the ignition is retarded due to excessive scalar dissipation, and hence diffusive loss, at the ignition location. However, for the wide range of initial turbulence fields studied, the variation in ignition delay due to the corresponding variation in turbulence intensity appears to be quite small.
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.
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.
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...
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
Notes 08. Turbulence flow in thin film bearings : Characteristics and Modeling
San Andres, Luis
2009-01-01T23:59:59.000Z
NOTES 8. TURBULENCE IN THIN FILM FLOWS. Dr. Luis San Andr?s ? 2009 1 Notes 8. Turbulence in Thin Film Flows Notes 8 detail the characteristics of turbulent flows and provide insight into the flow instabilities that precede transition from a... for averaging of turbulent flow velocities [s] NOTES 8. TURBULENCE IN THIN FILM FLOWS. Dr. Luis San Andr?s ? 2009 2 Ta 2 Re C R ?? ?? ?? . Taylor number ?? 1, 2, 3 i i u ? Components of velocity field [m/s] = ? ? ii uu?? ?? 1, 2, 3 , ii i uu...
Shock-induced turbulent flow in baffle systems
Kuhl, A.L. [Lawrence Livermore National Lab., CA (United States); Reichenbach, H. [Fraunhofer-Institut fuer Kurzzeitdynamik - Ernst-Mach-Institut (EMI), Freiburg im Breisgau (Germany)
1993-07-01T23:59:59.000Z
Experiments are described on shock propagation through 2-D aligned and staggered baffle systems. Flow visualization was provided by shadow and schlieren photography, recorded by the Cranz-Schardin camera. Also single-frame, infinite-fringe, color interferograms were used. Intuition suggests that this is a rather simple 2-D shock diffraction problem. However, flow visualization reveals that the flow rapidly evolved into a complex 3-D turbulent mixing problem. Mushroom-shaped mixing regions blocked the flow into the next baffle orifice. Thus energy was transferred from the directed kinetic energy (induced by the shock) to rotational energy of turbulent mixing, and then dissipated by molecular effects. These processes dramatically dissipate the strength of the shock wave. The experiments provide an excellent test case that could be used to assess the accuracy of computer code calculations of such problems.
Kosuga, Yusuke
2012-01-01T23:59:59.000Z
Turbulent plasma and flow generation . . . . . . . . . . .of Intrinsic Rotation Generation in Tokamaks . . 2.12.2.2 Flow generation and stationary state . . . . . 2.3
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.
Radiative Transfer of Sound Waves in a Random Flow: Turbulent Scattering and ModeCoupling
Ryzhik, Lenya
Radiative Transfer of Sound Waves in a Random Flow: Turbulent Scattering and ModeÂCoupling Albert the sound wave propagation in a random flow, whose mean flow is large compared with its fluctuation and the turbulent scattering and modeÂcoupling of sound waves. We show that, because of the flowÂstraining term
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.
Gyrotactic trapping in laminar and turbulent Kolmogorov flow
Francesco Santamaria; Filippo De Lillo; Massimo Cencini; Guido Boffetta
2014-10-07T23:59:59.000Z
Phytoplankton patchiness, namely the heterogeneous distribution of microalgae over multiple spatial scales, dramatically impacts marine ecology. A spectacular example of such heterogeneity occurs in thin phytoplankton layers (TPLs), where large numbers of photosynthetic microorganisms are found within a small depth interval. Some species of motile phytoplankton can form TPLs by gyrotactic trapping due to the interplay of their particular swimming style (directed motion biased against gravity) and the transport by a flow with shear along the direction of gravity. Here we consider gyrotactic swimmers in numerical simulations of the Kolmogorov shear flow, both in laminar and turbulent regimes. In the laminar case, we show that the swimmer motion is integrable and the formation of TPLs can be fully characterized by means of dynamical systems tools. We then study the effects of rotational Brownian motion or turbulent fluctuations (appearing when the Reynolds number is large enough) on TPLs. In both cases we show that TPLs become transient, and we characterize their persistence.
On integrating LES and laboratory turbulent flow experiments
Grinstein, Fernando Franklin [Los Alamos National Laboratory
2008-01-01T23:59:59.000Z
Critical issues involved in large eddy simulation (LES) experiments relate to the treatment of unresolved subgrid scale flow features and required initial and boundary condition supergrid scale modelling. The inherently intrusive nature of both LES and laboratory experiments is noted in this context. Flow characterization issues becomes very challenging ones in validation and computational laboratory studies, where potential sources of discrepancies between predictions and measurements need to be clearly evaluated and controlled. A special focus of the discussion is devoted to turbulent initial condition issues.
Turbulent flow of gas in fractures
Koh, Wong In
1974-01-01T23:59:59.000Z
sises of 40 - 60, 20 - 40 and 10 - 20 mesh and with varying concentration of proppants . The confining pressure was varied for each core up to $, 000 psi step by step. The proppant concentration in each fracture was varied up to a complete monolayer... an ovex'bux'den pressure of 4, 000 psi, the reduction in flow capaoity would vary from 86 $ to 76 4 with corresponding change of pressure dxop from 2, 000 psi to 7, 000 psi across a 320 ft long fractuxe. ACKHOWLEDGENEN% The author wishes to extend...
A New Aerosol Flow System for Photochemical and Thermal Studies...
Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)
Aerosol Flow System for Photochemical and Thermal Studies of Tropospheric Aerosols. A New Aerosol Flow System for Photochemical and Thermal Studies of Tropospheric Aerosols....
Rothstein, Jonathan
Drag reduction in turbulent flows over superhydrophobic surfaces Robert J. Daniello, Nicholas E, micropatterned superhydrophobic surfaces, previously noted for their ability to provide laminar flow drag reduction, are capable of reducing drag in the turbulent flow regime. Superhydrophobic surfaces contain
Adiabatic thermal Child-Langmuir flow
Mok, Rachel V. (Rachel Verla)
2013-01-01T23:59:59.000Z
A simulation model is presented for the verification of the recently developed steady-state one-dimensional adiabatic thermal Child-Langmuir flow theory. In this theory, a self-consistent Poisson equation is developed ...
Laminar-turbulent separatrix in a boundary layer flow
Biau, Damien
2013-01-01T23:59:59.000Z
The transitional boundary layer flow over a flat plate is investigated. The boundary layer flow is known to develop unstable Tollmien-Schlichting waves above a critical value of the Reynolds number. However, it is also known that this transition can be observed for sub-critical Reynolds numbers. In that case, the basin of attraction of the laminar state coexists with the sustained turbulence. In this article, the trajectory on the separatrix between these two states is simulated. The state on the separatrix is independent from the initial condition and is dynamically connected to both the laminar flow and the turbulence. Such an edge state provides information regarding the basic features of the transitional flow. The solution takes the form of a low speed streak, flanked by two quasi-streamwise sinuous vortices. The shape of the streaks is close to that simulated with the linear optimal perturbation method. This solution is compared to existing results concerning streak breakdown. The simulations are realize...
Coherent structures in ion temperature gradient turbulence-zonal flow
Singh, Rameswar, E-mail: rameswar.singh@lpp.polytechnique.fr [Laboratoire de Physique des Plasmas, Ecole Polytechnique, Route de Saclay, 91128 Palaiseau Cedex (France); Institute for Plasma Research, Bhat, Gandhinagar 382 428 (India); Singh, R. [Institute for Plasma Research, Bhat, Gandhinagar 382 428 (India); WCI Center for Fusion Theory, National Fusion Research Institute, Daejeon 305-333 (Korea, Republic of); Kaw, P. [Institute for Plasma Research, Bhat, Gandhinagar 382 428 (India); Gürcan, Ö. D. [Laboratoire de Physique des Plasmas, Ecole Polytechnique, Route de Saclay, 91128 Palaiseau Cedex (France); Diamond, P. H. [WCI Center for Fusion Theory, National Fusion Research Institute, Daejeon 305-333 (Korea, Republic of); CMTFO and CASS, University of California, San Diego, California 92093 (United States)
2014-10-15T23:59:59.000Z
Nonlinear stationary structure formation in the coupled ion temperature gradient (ITG)-zonal flow system is investigated. The ITG turbulence is described by a wave-kinetic equation for the action density of the ITG mode, and the longer scale zonal mode is described by a dynamic equation for the m?=?n?=?0 component of the potential. Two populations of trapped and untrapped drift wave trajectories are shown to exist in a moving frame of reference. This novel effect leads to the formation of nonlinear stationary structures. It is shown that the ITG turbulence can self-consistently sustain coherent, radially propagating modulation envelope structures such as solitons, shocks, and nonlinear wave trains.
On the Peterlin approximation for turbulent flows of polymer solutions
Dario Vincenzi; Prasad Perlekar; Luca Biferale; Federico Toschi
2015-05-26T23:59:59.000Z
We study the impact of the Peterlin approximation on the statistics of the end-to-end separation of poly- mers in a turbulent flow. The FENE and FENE-P models are numerically integrated along a large number of Lagrangian trajectories resulting from a direct numerical simulation of three-dimensional homogeneous isotropic turbulence. Although the FENE-P model yields results in qualitative agreement with those of the FENE model, quantitative differences emerge. The steady-state probability of large extensions is overesti- mated by the FENE-P model. The alignment of polymers with the eigenvectors of the rate-of-strain tensor and with the direction of vorticity is weaker when the Peterlin approximation is used. At large Weissenberg numbers, both the correlation times of the extension and of the orientation of polymers are underestimated by the FENE-P model.
On the Peterlin approximation for turbulent flows of polymer solutions
Vincenzi, Dario; Biferale, Luca; Toschi, Federico
2015-01-01T23:59:59.000Z
We study the impact of the Peterlin approximation on the statistics of the end-to-end separation of poly- mers in a turbulent flow. The FENE and FENE-P models are numerically integrated along a large number of Lagrangian trajectories resulting from a direct numerical simulation of three-dimensional homogeneous isotropic turbulence. Although the FENE-P model yields results in qualitative agreement with those of the FENE model, quantitative differences emerge. The steady-state probability of large extensions is overesti- mated by the FENE-P model. The alignment of polymers with the eigenvectors of the rate-of-strain tensor and with the direction of vorticity is weaker when the Peterlin approximation is used. At large Weissenberg numbers, both the correlation times of the extension and of the orientation of polymers are underestimated by the FENE-P model.
Fine-Scale Zonal Flow Suppression of Electron Temperature Gradient Turbulence
Lin, Zhihong
as an explanation for the long time build up of the zonal flow in ETG turbulence and it is shown that the generationFine-Scale Zonal Flow Suppression of Electron Temperature Gradient Turbulence S.E. Parker , J continue to grow algebraically (proportional to time). These fine-scale zonal flows have a radial wave
DRAFT August 29, 1998 The Dynamics of Small-Scale Turbulence-Driven Flows
Hammett, Greg
the existence of a linearly undamped component of the flow which could build up in time and lower the finalDRAFT August 29, 1998 The Dynamics of Small-Scale Turbulence-Driven Flows M. A. Beer and G. W the dynamics of small-scale turbulence-driven sheared ¢¡¤£ flows in nonlinear gyrofluid simulations
FliHy experimental facilities for studying open channel turbulent flows and heat transfer
Abdou, Mohamed
FliHy experimental facilities for studying open channel turbulent flows and heat transfer B. Freeze) facility was constructed at UCLA to study open channel turbulent flow and heat transfer of low supercritical flow regimes (Fr /1), in which the surface waves are amplified and heat transfer is enhanced due
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.
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.
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.
Organized Oscillations of Initially-Turbulent Flow Past a Cavity
J.C. Lin; D. Rockwell
2002-09-17T23:59:59.000Z
Flow past an open cavity is known to give rise to self-sustained oscillations in a wide variety of configurations, including slotted-wall, wind and water tunnels, slotted flumes, bellows-type pipe geometries, high-head gates and gate slots, aircraft components and internal piping systems. These cavity-type oscillations are the origin of coherent and broadband sources of noise and, if the structure is sufficiently flexible, flow-induced vibration as well. Moreover, depending upon the state of the cavity oscillation, substantial alterations of the mean drag may be induced. In the following, the state of knowledge of flow past cavities, based primarily on laminar inflow conditions, is described within a framework based on the flow physics. Then, the major unresolved issues for this class of flows will be delineated. Self-excited cavity oscillations have generic features, which are assessed in detail in the reviews of Rockwell and Naudascher, Rockwell, Howe and Rockwell. These features, which are illustrated in the schematic of Figure 1, are: (i) interaction of a vorticity concentration(s) with the downstream corner, (ii) upstream influence from this corner interaction to the sensitive region of the shear layer formed from the upstream corner of the cavity; (iii) conversion of the upstream influence arriving at this location to a fluctuation in the separating shear layer; and (iv) amplification of this fluctuation in the shear layer as it develops in the streamwise direction. In view of the fact that inflow shear-layer in the present investigation is fully turbulent, item (iv) is of particular interest. It is generally recognized, at least for laminar conditions at separation from the leading-corner of the cavity, that the disturbance growth in the shear layer can be described using concepts of linearized, inviscid stability theory, as shown by Rockwell, Sarohia, and Knisely and Rockwell. As demonstrated by Knisely and Rockwell, on the basis of experiments interpreted with the aid of linearized theory, not only the fundamental component of the shear layer instability may be present, but a number of additional, primarily lower frequency components can exist as well. In fact, the magnitude of these components can be of the same order as the fundamental component. These issues have not been addressed for the case of a fully-turbulent in-flow and its separation from the leading corner of the cavity.
The propagation of kinetic energy across scales in turbulent flows
Cardesa, José I; Dong, Siwei; Jiménez, Javier
2015-01-01T23:59:59.000Z
A temporal study of energy transfer across length scales is performed in 3D numerical simulations of homogeneous shear flow and isotropic turbulence, at Reynolds numbers in the range $Re_{\\lambda}=107-384$. The average time taken by perturbations in the energy flux to travel between scales is measured and shown to be additive, as inferred from the agreement between the total travel time from a given scale to the smallest dissipative motions, and the time estimated from successive jumps through intermediate scales. Our data suggests that the propagation of disturbances in the energy flux is independent of the forcing and that it defines a `velocity' that determines the energy flux itself. These results support that the cascade is, on average, a scale-local process where energy is continuously transmitted from one scale to the next in order of decreasing size.
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...
Fannjiang, Albert
Radiative Transfer of Sound Waves in a Random Flow: Turbulent Scattering, Straining, and Mode and Applied Mathematics Vol. 61, No. 5, pp. 1545-1577 RADIATIVE TRANSFER OF SOUND WAVES IN A RANDOM FLOW the sound wave propagation in a random flow, whose mean flow is large compared with its fluctuation
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. ...
Laminar and turbulent nozzle-jet flows and their acoustic near-field
Bühler, Stefan; Obrist, Dominik; Kleiser, Leonhard [Institute of Fluid Dynamics, ETH Zurich, 8092 Zurich (Switzerland)
2014-08-15T23:59:59.000Z
We investigate numerically the effects of nozzle-exit flow conditions on the jet-flow development and the near-field sound at a diameter-based Reynolds number of Re{sub D} = 18?100 and Mach number Ma = 0.9. Our computational setup features the inclusion of a cylindrical nozzle which allows to establish a physical nozzle-exit flow and therefore well-defined initial jet-flow conditions. Within the nozzle, the flow is modeled by a potential flow core and a laminar, transitional, or developing turbulent boundary layer. The goal is to document and to compare the effects of the different jet inflows on the jet flow development and the sound radiation. For laminar and transitional boundary layers, transition to turbulence in the jet shear layer is governed by the development of Kelvin-Helmholtz instabilities. With the turbulent nozzle boundary layer, the jet flow development is characterized by a rapid changeover to a turbulent free shear layer within about one nozzle diameter. Sound pressure levels are strongly enhanced for laminar and transitional exit conditions compared to the turbulent case. However, a frequency and frequency-wavenumber analysis of the near-field pressure indicates that the dominant sound radiation characteristics remain largely unaffected. By applying a recently developed scaling procedure, we obtain a close match of the scaled near-field sound spectra for all nozzle-exit turbulence levels and also a reasonable agreement with experimental far-field data.
Boyer, Edmond
) suggesting that when particle inertia increases, particle acceler- ation variance decreases due to bothAcceleration statistics of solid particles in turbulent channel flow R. Zamansky, I. Vinkovic in near-wall turbulence Phys. Fluids 24, 035110 (2012) Smoothed particle hydrodynamics simulations
Slinn, Donald
an improved understanding of oscillatory flow over sand ripples. [3] The wave bottom boundary layer (WBBL the ripple crest produce a continuously turbulent boundary layer, differing from results obtained processes; KEYWORDS: turbulent boundary layer, drag coefficient, dissipation rate Citation: Barr, B. C., D
Evaluating Subgrid-Scale Models for Large-Eddy Simulation of Turbulent Katabatic Flow
Fedorovich, Evgeni
of LES for reproducing stably-stratified turbulent boundary layers [2]. Under stably-stratified conditions, the characteristic length scale of the small-scale turbulent motions decrease, placing a larger analytically for a laminar slope flow in a stably- stratified environment. The Prandtl solution
Shear flow effects on ion thermal transport in tokamaks
Tajima, T.; Horton, W.; Dong, J.Q. [Univ. of Texas, Austin, TX (United States). Institute for Fusion Studies; Kishimoto, Y. [JAERI (Japan). Naka Fusion Research
1995-03-01T23:59:59.000Z
From various laboratory and numerical experiments, there is clear evidence that under certain conditions the presence of sheared flows in a tokamak plasma can significantly reduce the ion thermal transport. In the presence of plasma fluctuations driven by the ion temperature gradient, the flows of energy and momentum parallel and perpendicular to the magnetic field are coupled with each other. This coupling manifests itself as significant off-diagonal coupling coefficients that give rise to new terms for anomalous transport. The authors derive from the gyrokinetic equation a set of velocity moment equations that describe the interaction among plasma turbulent fluctuations, the temperature gradient, the toroidal velocity shear, and the poloidal flow in a tokamak plasma. Four coupled equations for the amplitudes of the state variables radially extended over the transport region by toroidicity induced coupling are derived. The equations show bifurcations from the low confinement mode without sheared flows to high confinement mode with substantially reduced transport due to strong shear flows. Also discussed is the reduced version with three state variables. In the presence of sheared flows, the radially extended coupled toroidal modes driven by the ion temperature gradient disintegrate into smaller, less elongated vortices. Such a transition to smaller spatial correlation lengths changes the transport from Bohm-like to gyrobohm-like. The properties of these equations are analyzed. The conditions for the improved confined regime are obtained as a function of the momentum-energy deposition rates and profiles. The appearance of a transport barrier is a consequence of the present theory.
Preliminary Study of Turbulent Flow in the Lower Plenum of a Gas-Cooled Reactor
T. Gallaway; D.P. Guillen; H.M. McIlroy, Jr.; S.P. Antal
2007-09-01T23:59:59.000Z
A preliminary study of the turbulent flow in a scaled model of a portion of the lower plenum of a gas-cooled advanced reactor concept has been conducted. The reactor is configured such that hot gases at various temperatures exit the coolant channels in the reactor core, where they empty into a lower plenum and mix together with a crossflow past vertical cylindrical support columns, then exit through an outlet duct. An accurate assessment of the flow behavior will be necessary prior to final design to ensure that material structural limits are not exceeded. In this work, an idealized model was created to mimic a region of the lower plenum for a simplified set of conditions that enabled the flow to be treated as an isothermal, incompressible fluid with constant properties. This is a first step towards assessing complex thermal fluid phenomena in advanced reactor designs. Once such flows can be computed with confidence, heated flows will be examined. Experimental data was obtained using three-dimensional Particle Image Velocimetry (PIV) to obtain non-intrusive flow measurements for an unheated geometry. Computational fluid dynamic (CFD) predictions of the flow were made using a commercial CFD code and compared to the experimental data. The work presented here is intended to be scoping in nature, since the purpose of this work is to identify improvements that can be made to subsequent computations and experiments. Rigorous validation of computational predictions will eventually be necessary for design and analysis of new reactor concepts, as well as for safety analysis and licensing calculations.
Dispersed Phase of Non-Isothermal Particles in Rotating Turbulent Flows
Pandya, R V R
2015-01-01T23:59:59.000Z
We suggest certain effects, caused by interaction between rotation and gravitation with turbulence structure, for the cooling/heating of dispersed phase of non-isothermal particles in rotating turbulent fluid flows. These effects are obtained through the derivation of kinetic or probability density function based macroscopic equations for the particles. In doing so, for one-way temperature coupling, we also show that homogeneous, isotropic non-isothermal fluid turbulence does not influence the mean temperature (though it influences mean velocity) of the dispersed phase of particles settling due to gravitational force in the isotropic turbulence.
Srinivasan, Siddarth
We demonstrate a reduction in the measured inner wall shear stress in moderately turbulent Taylor-Couette flows by depositing sprayable superhydrophobic microstructures on the inner rotor surface. The magnitude of reduction ...
Meyers, Johan
2012-01-01T23:59:59.000Z
As a generalization of the mass-flux based classical stream-tube, the concept of momentum and energy transport tubes is discussed as a flow visualization tool. These transport tubes have the property, respectively, that no fluxes of momentum or energy exist over their respective tube mantles. As an example application using data from large-eddy simulation, such tubes are visualized for the mean-flow structure of turbulent flow in large wind farms, in fully developed wind-turbine-array boundary layers. The three-dimensional organization of energy transport tubes changes considerably when turbine spacings are varied, enabling the visualization of the path taken by the kinetic energy flux that is ultimately available at any given turbine within the array.
Fluctuations around Bjorken Flow and the onset of turbulent phenomena
Stefan Floerchinger; Urs Achim Wiedemann
2012-08-17T23:59:59.000Z
We study how fluctuations in fluid dynamic fields can be dissipated or amplified within the characteristic spatio-temporal structure of a heavy ion collision. The initial conditions for a fluid dynamic evolution of heavy ion collisions may contain significant fluctuations in all fluid dynamical fields, including the velocity field and its vorticity components. We formulate and analyze the theory of local fluctuations around average fluid fields described by Bjorken's model. For conditions of laminar flow, when a linearized treatment of the dynamic evolution applies, we discuss explicitly how fluctuations of large wave number get dissipated while modes of sufficiently long wave-length pass almost unattenuated or can even be amplified. In the opposite case of large Reynold's numbers (which is inverse to viscosity), we establish that (after suitable coordinate transformations) the dynamics is governed by an evolution equation of non-relativistic Navier-Stokes type that becomes essentially two-dimensional at late times. One can then use the theory of Kolmogorov and Kraichnan for an explicit characterization of turbulent phenomena in terms of the wave-mode dependence of correlations of fluid dynamic fields. We note in particular that fluid dynamic correlations introduce characteristic power-law dependences in two-particle correlation functions.
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
Hydrodynamical adaptive mesh refinement simulations of turbulent flows - I. Substructure in a wind
Iapichino, L; Schmidt, W; Niemeyer, J C
2008-01-01T23:59:59.000Z
The problem of the resolution of turbulent flows in adaptive mesh refinement (AMR) simulations is investigated by means of 3D hydrodynamical simulations in an idealised setup, representing a moving subcluster during a merger event. AMR simulations performed with the usual refinement criteria based on local gradients of selected variables do not properly resolve the production of turbulence downstream of the cluster. Therefore we apply novel AMR criteria which are optimised to follow the evolution of a turbulent flow. We demonstrate that these criteria provide a better resolution of the flow past the subcluster, allowing us to follow the onset of the shear instability, the evolution of the turbulent wake and the subsequent back-reaction on the subcluster core morphology. We discuss some implications for the modelling of cluster cold fronts.
Hydrodynamical adaptive mesh refinement simulations of turbulent flows - I. Substructure in a wind
L. Iapichino; J. Adamek; W. Schmidt; J. C. Niemeyer
2008-07-01T23:59:59.000Z
The problem of the resolution of turbulent flows in adaptive mesh refinement (AMR) simulations is investigated by means of 3D hydrodynamical simulations in an idealised setup, representing a moving subcluster during a merger event. AMR simulations performed with the usual refinement criteria based on local gradients of selected variables do not properly resolve the production of turbulence downstream of the cluster. Therefore we apply novel AMR criteria which are optimised to follow the evolution of a turbulent flow. We demonstrate that these criteria provide a better resolution of the flow past the subcluster, allowing us to follow the onset of the shear instability, the evolution of the turbulent wake and the subsequent back-reaction on the subcluster core morphology. We discuss some implications for the modelling of cluster cold fronts.
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.
GPU accelerated flow solver for direct numerical simulation of turbulent flows
Salvadore, Francesco [CASPUR – via dei Tizii 6/b, 00185 Rome (Italy)] [CASPUR – via dei Tizii 6/b, 00185 Rome (Italy); Bernardini, Matteo, E-mail: matteo.bernardini@uniroma1.it [Department of Mechanical and Aerospace Engineering, University of Rome ‘La Sapienza’ – via Eudossiana 18, 00184 Rome (Italy)] [Department of Mechanical and Aerospace Engineering, University of Rome ‘La Sapienza’ – via Eudossiana 18, 00184 Rome (Italy); Botti, Michela [CASPUR – via dei Tizii 6/b, 00185 Rome (Italy)] [CASPUR – via dei Tizii 6/b, 00185 Rome (Italy)
2013-02-15T23:59:59.000Z
Graphical processing units (GPUs), characterized by significant computing performance, are nowadays very appealing for the solution of computationally demanding tasks in a wide variety of scientific applications. However, to run on GPUs, existing codes need to be ported and optimized, a procedure which is not yet standardized and may require non trivial efforts, even to high-performance computing specialists. In the present paper we accurately describe the porting to CUDA (Compute Unified Device Architecture) of a finite-difference compressible Navier–Stokes solver, suitable for direct numerical simulation (DNS) of turbulent flows. Porting and validation processes are illustrated in detail, with emphasis on computational strategies and techniques that can be applied to overcome typical bottlenecks arising from the porting of common computational fluid dynamics solvers. We demonstrate that a careful optimization work is crucial to get the highest performance from GPU accelerators. The results show that the overall speedup of one NVIDIA Tesla S2070 GPU is approximately 22 compared with one AMD Opteron 2352 Barcelona chip and 11 compared with one Intel Xeon X5650 Westmere core. The potential of GPU devices in the simulation of unsteady three-dimensional turbulent flows is proved by performing a DNS of a spatially evolving compressible mixing layer.
Turbulent flow and drag over fixed two-and three-dimensional dunes Jeremy G. Venditti1,2
Venditti, Jeremy G.
measurements of turbulent flow were obtained over a fixed flat bed, two- dimensional (2-D) dunes and four types over 2-D dunes conforms with previous observations of flow over mobile and fixed bed forms. Bed formTurbulent flow and drag over fixed two- and three-dimensional dunes Jeremy G. Venditti1,2 Received
L. Iapichino; J. C. Niemeyer
2008-07-01T23:59:59.000Z
The development of turbulent gas flows in the intra-cluster medium and in the core of a galaxy cluster is studied by means of adaptive mesh refinement (AMR) cosmological simulations. A series of six runs was performed, employing identical simulation parameters but different criteria for triggering the mesh refinement. In particular, two different AMR strategies were followed, based on the regional variability of control variables of the flow and on the overdensity of subclumps, respectively. We show that both approaches, albeit with different results, are useful to get an improved resolution of the turbulent flow in the ICM. The vorticity is used as a diagnostic for turbulence, showing that the turbulent flow is not highly volume-filling but has a large area-covering factor, in agreement with previous theoretical expectations. The measured turbulent velocity in the cluster core is larger than 200 km/s, and the level of turbulent pressure contribution to the cluster hydrostatic equilibrium is increased by using the improved AMR criteria.
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
Magnetohydrodynamic lattice Boltzmann simulations of turbulence and rectangular jet flow
Riley, Benjamin Matthew
2009-05-15T23:59:59.000Z
relaxation time (SRT) parameter for the Maxwell’s stress tensor is developed for this study. In the MHD homogeneous turbulence studies, the kinetic/magnetic energy and enstrophy decays, kinetic enstrophy evolution, and vorticity alignment with the strain...
Interpolation between DarcyWeisbach and Darcy for laminar and turbulent flows
Walter, M.Todd
submerged the result yields the DarcyWeisbach equation for turbulent flow in pipes and open channels. When is in agreement with DarcyÕs law in porous media. Thus our equation interpolates between and reduces to, the two of the appropriate DarcyWeisbach equation, e.g. see [24], which states that the flow velocity, V, is proportional
Interpolation between DarcyWeisbach and Darcy for laminar and turbulent flows
Walter, M.Todd
the DarcyWeisbach equation for turbulent flow in pipes and open channels. When the obstacles are only with DarcyÕs law in porous media. Thus our equation interpolates between and reduces to, the two fundamental DarcyWeisbach equation, e.g. see [24], which states that the flow velocity, V, is proportional
An energy preserving formulation for the simulation of multiphase turbulent flows.
Fuster, Daniel
An energy preserving formulation for the simulation of multiphase turbulent flows. Abstract In this manuscript we propose an energy preserving formulation for the simulation of multiphase flows. The new jumps across the interface including surface tension effects. 1 Introduction Nowadays the simulation
Rolland, Joran
2011-01-01T23:59:59.000Z
Plane Couette flow, the flow between two parallel planes moving in opposite directions, is an example of wall-bounded flow experiencing a transition to turbulence with an ordered coexistence of turbulent and laminar domains in some range of Reynolds numbers [R_g,R_t]. When the aspect-ratio is sufficiently large, this coexistence occurs in the form of alternately turbulent and laminar oblique bands. As R goes up trough the upper threshold R_t, the bands disappear progressively to leave room to a uniform regime of featureless turbulence. This continuous transition is studied here by means of under-resolved numerical simulations understood as a modelling approach adapted to the long time, large aspect-ratio limit. The state of the system is quantitatively characterised using standard observables (turbulent fraction and turbulence intensity inside the bands). A pair of complex order parameters is defined for the pattern which is further analysed within a standard Ginzburg--Landau formalism. Coefficients of the mo...
Numerical simulations of aggregate breakup in bounded and unbounded turbulent flows
Matthaus U. Babler; Luca Biferale; Luca Brandt; Ulrike Feudel; Ksenia Guseva; Alessandra S. Lanotte; Cristian Marchioli; Francesco Picano; Gaetano Sardina; Alfredo Soldati; Federico Toschi
2015-02-17T23:59:59.000Z
Breakup of small aggregates in fully developed turbulence is studied by means of direct numerical simulations in a series of typical bounded and unbounded flow configurations, such as a turbulent channel flow, a developing boundary layer and homogeneous isotropic turbulence. The simplest criterion for breakup is adopted, whereas aggregate breakup occurs when the local hydrodynamic stress $\\sigma\\sim \\varepsilon^{1/2}$, with $\\varepsilon$ being the energy dissipation at the position of the aggregate, overcomes a given threshold $\\sigma_\\mathrm{cr}$, which is characteristic for a given type of aggregates. Results show that the breakup rate decreases with increasing threshold. For small thresholds, it develops a universal scaling among the different flows. For high thresholds, the breakup rates show strong differences between the different flow configurations, highlighting the importance of non-universal mean-flow properties. To further assess the effects of flow inhomogeneity and turbulent fluctuations, theresults are compared with those obtained in a smooth stochastic flow. Furthermore, we discuss the limitations and applicability of a set of independent proxies.
Self-sustaining turbulence in a restricted nonlinear model of plane Couette flow
Thomas, Vaughan L.; Gayme, Dennice F. [Department of Mechanical Engineering, Johns Hopkins University, Baltimore, Maryland, 21218 (United States); Lieu, Binh K.; Jovanovi?, Mihailo R. [Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota, 55455 (United States); Farrell, Brian F. [School of Engineering and Applied Science, Harvard University, Cambridge, Massachusetts, 02138 (United States); Ioannou, Petros J. [Department of Physics, National and Kapodistrian University of Athens, Panepistimiopolis, Zografos, Athens, 15784 (Greece)
2014-10-15T23:59:59.000Z
This paper demonstrates the maintenance of self-sustaining turbulence in a restricted nonlinear (RNL) model of plane Couette flow. The RNL system is derived directly from the Navier-Stokes equations and permits higher resolution studies of the dynamical system associated with the stochastic structural stability theory (S3T) model, which is a second order approximation of the statistical state dynamics of the flow. The RNL model shares the dynamical restrictions of the S3T model but can be easily implemented by reducing a DNS code so that it retains only the RNL dynamics. Comparisons of turbulence arising from DNS and RNL simulations demonstrate that the RNL system supports self-sustaining turbulence with a mean flow as well as structural and dynamical features that are consistent with DNS. These results demonstrate that the simplified RNL system captures fundamental aspects of fully developed turbulence in wall-bounded shear flows and motivate use of the RNL/S3T framework for further study of wall-turbulence.
Investigation of Turbulent transition in plane Couette flows Using Energy Gradient Method
Hua-Shu Dou; Boo Cheong Khoo
2010-06-07T23:59:59.000Z
The energy gradient method has been proposed with the aim of better understanding the mechanism of flow transition from laminar flow to turbulent flow. In this method, it is demonstrated that the transition to turbulence depends on the relative magnitudes of the transverse gradient of the total mechanical energy which amplifies the disturbance and the energy loss from viscous friction which damps the disturbance, for given imposed disturbance. For a given flow geometry and fluid properties, when the maximum of the function K (a function standing for the ratio of the gradient of total mechanical energy in the transverse direction to the rate of energy loss due to viscous friction in the streamwise direction) in the flow field is larger than a certain critical value, it is expected that instability would occur for some initial disturbances. In this paper, using the energy gradient analysis, the equation for calculating the energy gradient function K for plane Couette flow is derived. The result indicates that K reaches the maximum at the moving walls. Thus, the fluid layer near the moving wall is the most dangerous position to generate initial oscillation at sufficient high Re for given same level of normalized perturbation in the domain. The critical value of K at turbulent transition, which is observed from experiments, is about 370 for plane Couette flow when two walls move in opposite directions (anti-symmetry). This value is about the same as that for plane Poiseuille flow and pipe Poiseuille flow (385-389). Therefore, it is concluded that the critical value of K at turbulent transition is about 370-389 for wall-bounded parallel shear flows which include both pressure (symmetrical case) and shear driven flows (anti-symmetrical case).
Mesoscale flows in large aspect ratio simulations of turbulent compressible convection
F. Rincon; F. Lignieres; M. Rieutord
2006-11-28T23:59:59.000Z
We present the results of a very large aspect ratio (42.6) numerical simulation of fully compressible turbulent convection in a polytropic atmosphere, and focus on the properties of large-scale flows. Mesoscale patterns dominate the turbulent energy spectrum. We show that these structures, which had already been observed in Boussinesq simulations by Cattaneo et al. (2001), have a genuine convective origin and do not result directly from collective interactions of the smaller scales of the flow, even though their growth is strongly affected by nonlinear transfers. If this result is relevant to the solar photosphere, it suggests that the dominant convective mode below the Sun's surface may be at mesoscales.
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
Model for the spatio-temporal intermittency of the energy dissipation in turbulent flows
Fabio Lepreti; Vincenzo Carbone; Pierluigi Veltri
2007-02-08T23:59:59.000Z
Modeling the intermittent behavior of turbulent energy dissipation processes both in space and time is often a relevant problem when dealing with phenomena occurring in high Reynolds number flows, especially in astrophysical and space fluids. In this paper, a dynamical model is proposed to describe the spatio-temporal intermittency of energy dissipation rate in a turbulent system. This is done by using a shell model to simulate the turbulent cascade and introducing some heuristic rules, partly inspired by the well known $p$-model, to construct a spatial structure of the energy dissipation rate. In order to validate the model and to study its spatially intermittency properties, a series of numerical simulations have been performed. These show that the level of spatial intermittency of the system can be simply tuned by varying a single parameter of the model and that scaling laws in agreement with those obtained from experiments on fully turbulent hydrodynamic flows can be recovered. It is finally suggested that the model could represent a useful tool to simulate the spatio-temporal intermittency of turbulent energy dissipation in those high Reynolds number astrophysical fluids where impulsive energy release processes can be associated to the dynamics of the turbulent cascade.
Victoria, University of
A Detailed Analysis of Guard-Heated Wall Shear Stress Sensors for Turbulent Flows by Seyed Ali Ale A Detailed Analysis of Guard-Heated Wall Shear Stress Sensors for Turbulent Flows by Seyed Ali Ale Etrati-dimensional analysis of the performance of multi-element guard-heated hot-film wall shear stress microsensors
Stretching of polymers around the Kolmogorov scale in a turbulent shear flow
Jahanshah Davoudi; Joerg Schumacher
2006-01-03T23:59:59.000Z
We present numerical studies of stretching of Hookean dumbbells in a turbulent Navier-Stokes flow with a linear mean profile, =Sy. In addition to the turbulence features beyond the viscous Kolmogorov scale \\eta, the dynamics at the equilibrium extension of the dumbbells significantly below eta is well resolved. The variation of the constant shear rate S causes a change of the turbulent velocity fluctuations on all scales and thus of the intensity of local stretching rate of the advecting flow. The latter is measured by the maximum Lyapunov exponent lambda_1 which is found to increase as \\lambda_1 ~ S^{3/2}, in agreement with a dimensional argument. The ensemble of up to 2 times 10^6 passively advected dumbbells is advanced by Brownian dynamics simulations in combination with a pseudospectral integration for the turbulent shear flow. Anisotropy of stretching is quantified by the statistics of the azimuthal angle $\\phi$ which measures the alignment with the mean flow axis in the x-y shear plane, and the polar angle theta which determines the orientation with respect to the shear plane. The asymmetry of the probability density function (PDF) of phi increases with growing shear rate S. Furthermore, the PDF becomes increasingly peaked around mean flow direction (phi= 0). In contrast, the PDF of the polar angle theta is symmetric and less sensitive to changes of S.
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...
Turbulent Von Karman Swirling Flows , R. Schiestel2
Paris-Sud XI, Université de
is often used for studying fundamental aspects of developed turbulence and especially of magneto-hydrodynamic-rotating disks (R = 92.5 mm) enclosed by a stationary cylinder (Rc = 100 mm) (Fig.1). The in- terdisk spacing H a volumic drag force in the equation of V the tangential velocity compo- nent: f = nCD(1,2r - V)|1,2r - V
Turbulent Flow Effects on the Biological Performance of Hydro-Turbines
Richmond, Marshall C.; Romero Gomez, Pedro DJ
2014-08-25T23:59:59.000Z
The hydro-turbine industry uses Computational Fluid Dynamics (CFD) tools to predict the flow conditions as part of the design process for new and rehabilitated turbine units. Typically the hydraulic design process uses steady-state simulations based on Reynolds-Averaged Navier-Stokes (RANS) formulations for turbulence modeling because these methods are computationally efficient and work well to predict averaged hydraulic performance, e.g. power output, efficiency, etc. However, in view of the increasing emphasis on environmental concerns, such as fish passage, the consideration of the biological performance of hydro-turbines is also required in addition to hydraulic performance. This leads to the need to assess whether more realistic simulations of the turbine hydraulic environment ?those that resolve unsteady turbulent eddies not captured in steady-state RANS computations? are needed to better predict the occurrence and extent of extreme flow conditions that could be important in the evaluation of fish injury and mortality risks. In the present work, we conduct unsteady, eddy-resolving CFD simulations on a Kaplan hydro-turbine at a normal operational discharge. The goal is to quantify the impact of turbulence conditions on both the hydraulic and biological performance of the unit. In order to achieve a high resolution of the incoming turbulent flow, Detached Eddy Simulation (DES) turbulence model is used. These transient simulations are compared to RANS simulations to evaluate whether extreme hydraulic conditions are better captured with advanced eddy-resolving turbulence modeling techniques. The transient simulations of key quantities such as pressure and hydraulic shear flow that arise near the various components (e.g. wicket gates, stay vanes, runner blades) are then further analyzed to evaluate their impact on the statistics for the lowest absolute pressure (nadir pressures) and for the frequency of collisions that are known to cause mortal injury in fish passing through hydro-turbines.
An Analytical Study of Thermophoretic Particulate Deposition in Turbulent Pipe Flows
Abarham, Mehdi [University of Michigan; Hoard, John W. [University of Michigan; Assanis, Dennis [University of Michigan; Styles, Dan [Ford Motor Company; Sluder, Scott [ORNL; Storey, John Morse [ORNL
2010-01-01T23:59:59.000Z
The presence of a cold surface in non-isothermal pipe flows conveying submicron particles causes thermophoretic particulate deposition. In this study, an analytical method is developed to estimate thermophoretic particulate deposition efficiency and its effect on overall heat transfer coefficient of pipe flows in transition and turbulent flow regimes. The proposed analytical solution has been validated against experiments conducted at Oak Ridge National Laboratory. Exhaust gas carrying submicron soot particles was passed through pipes with a constant wall temperature and various designed boundary conditions to correlate transition and turbulent flow regimes. Prediction of the reduction in heat transfer coefficient and particulate mass deposited has been compared with experiments. The results of the analytical method are in a reasonably good agreement with experiments.
Amini, Noushin
2012-02-14T23:59:59.000Z
through the core of an annular pebble bed VHTR. The complex geometry of the core and the highly turbulent nature of the coolant flow passing through the gaps of fuel pebbles make this case quite challenging. In this experiment, a high frequency Hot Wire...
Numerical Study of Steady Turbulent Flow through Bifurcated Nozzles in Continuous Casting
Thomas, Brian G.
. The effects of nozzle design and casting process operating variables on the jet characteristics exitingNumerical Study of Steady Turbulent Flow through Bifurcated Nozzles in Continuous Casting FADY M. NAJJAR, BRIAN G. THOMAS, and DONALD E. HERSHEY Bifurcated nozzles are used in continuous casting
RESEARCH ARTICLE Developing and fully developed turbulent flow in ribbed channels
Thole, Karen A.
RESEARCH ARTICLE Developing and fully developed turbulent flow in ribbed channels Nicholas D features, such as ribs, are often placed along the walls of a channel to increase the convective surface- dence on the Reynolds number. A staggered rib-roughened channel study was performed using time
Temperature fluctuations and anomalous scaling in low-Mach-number compressible turbulent flow
Elperin, Tov
Temperature fluctuations and anomalous scaling in low-Mach-number compressible turbulent flow Tov 25 October 1996; revised manuscript received 20 February 1997 Temperature fluctuations in a low pressure fluctuations, the anomalous scaling may occur in the second moment of the temperature field
Measurement and simulation of a droplet population in a turbulent flow field Rbert Bords a,1
John, Volker
online 30 May 2012 Keywords: Two-phase turbulent flow Disperse droplet population Non-intrusive are determined by non-intrusive measurements. A direct discretization of the 4D equation for the droplet size deter- mined by means of non-intrusive measurement techniques. In this way, suitable time
Large-eddy simulation of turbulent cavitating flow in a micro channel
Egerer, Christian P., E-mail: christian.egerer@aer.mw.tum.de; Hickel, Stefan; Schmidt, Steffen J.; Adams, Nikolaus A. [Institute of Aerodynamics and Fluid Mechanics, Technische Universität München, Boltzmannstr. 15, 85748 Garching bei München (Germany)
2014-08-15T23:59:59.000Z
Large-eddy simulations (LES) of cavitating flow of a Diesel-fuel-like fluid in a generic throttle geometry are presented. Two-phase regions are modeled by a parameter-free thermodynamic equilibrium mixture model, and compressibility of the liquid and the liquid-vapor mixture is taken into account. The Adaptive Local Deconvolution Method (ALDM), adapted for cavitating flows, is employed for discretizing the convective terms of the Navier-Stokes equations for the homogeneous mixture. ALDM is a finite-volume-based implicit LES approach that merges physically motivated turbulence modeling and numerical discretization. Validation of the numerical method is performed for a cavitating turbulent mixing layer. Comparisons with experimental data of the throttle flow at two different operating conditions are presented. The LES with the employed cavitation modeling predicts relevant flow and cavitation features accurately within the uncertainty range of the experiment. The turbulence structure of the flow is further analyzed with an emphasis on the interaction between cavitation and coherent motion, and on the statistically averaged-flow evolution.
Energy flux fluctuations in a finite volume of turbulent flow
Mahesh Bandi; Walter Goldburg; John Cressman Jr.; Alain Pumir
2006-07-19T23:59:59.000Z
The flux of turbulent kinetic energy from large to small spatial scales is measured in a small domain B of varying size R. The probability distribution function of the flux is obtained using a time-local version of Kolmogorov's four-fifths law. The measurements, made at a moderate Reynolds number, show frequent events where the flux is backscattered from small to large scales, their frequency increasing as R is decreased. The observations are corroborated by a numerical simulation based on the motion of many particles and on an explicit form of the eddy damping.
Some questions regarding the understanding and prediction of turbulent flow
Heinz, Stefan
more com- petitive industrial processes involving fluid flows. Internal combustion engine, energy predictions: the computational costs of such direct numerical simulation (DNS) do not allow applications
Structure of Turbulence in Katabatic Flows below and above the Wind-Speed Maximum
Grachev, Andrey A; Di Sabatino, Silvana; Fernando, Harindra J S; Pardyjak, Eric R; Fairall, Christopher W
2015-01-01T23:59:59.000Z
Measurements of small-scale turbulence made over the complex-terrain atmospheric boundary layer during the MATERHORN Program are used to describe the structure of turbulence in katabatic flows. Turbulent and mean meteorological data were continuously measured at multiple levels at four towers deployed along the East lower slope (2-4 deg) of Granite Mountain. The multi-level observations made during a 30-day long MATERHORN-Fall field campaign in September-October 2012 allowed studying of temporal and spatial structure of katabatic flows in detail, and herein we report turbulence and their variations in katabatic winds. Observed vertical profiles show steep gradients near the surface, but in the layer above the slope jet the vertical variability is smaller. It is found that the vertical (normal to the slope) momentum flux and horizontal (along the slope) heat flux in a slope-following coordinate system change their sign below and above the wind maximum of a katabatic flow. The vertical momentum flux is directed...
THE TRANSPORT OF LOW-FREQUENCY TURBULENCE IN ASTROPHYSICAL FLOWS. I. GOVERNING EQUATIONS
Zank, G. P.; Dosch, A.; Florinski, V.; Webb, G. M. [Center for Space Plasma and Aeronomic Research (CSPAR), University of Alabama in Huntsville, Huntsville, AL 35805 (United States); Hunana, P. [Universite de Nice Sophia Antipolis, CNRS, Observatoire de la Cote dAzur, BP 4229 06304, Nice Cedex 4 (France); Matthaeus, W. H. [Bartol Research Institute, University of Delaware, Newark, DE 19711 (United States)
2012-01-20T23:59:59.000Z
Numerous problems in space physics and astrophysics require a detailed understanding of the transport and dissipation of low-frequency turbulence in an expanding magnetized flow. We employ a scale-separated decomposition of the incompressible MHD equations (based on an Elssaesser description) and develop a moment hierarchy to describe the transport of the total energy density in fluctuations, the cross-helicity, the energy difference, and correlation lengths corresponding to forward- and backward-propagating modes and to the energy difference. The dissipation terms for the various transport equations are derived. One-point closure schemes are utilized. The technical elements of this work that distinguish it from previous studies are (1) the inclusion of the large-scale background inhomogeneous Alfvenic velocity V{sub A} at a level of detail greater than before, (2) the introduction of a tractable slow timescale closure to eliminate high-frequency interference terms that is likely to prove a useful approximation for practical problems related to the transport of turbulence in an inhomogeneous flow such as the solar wind or solar corona, and finally, (3) we develop a simplified phenomenology for the energy difference or equivalently residual energy that may be useful for practical applications. This yields a coupled system of six equations that describes the transport of turbulence in inhomogeneous sub-Alfvenic and super-Alfvenic flows. The turbulence transport equations are quasi-linear in their spatial evolution operators and nonlinear in the dissipation terms, making the model equations relatively tractable to analysis.
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Schilling, Oleg; Mueschke, Nicholas J.
2010-01-01T23:59:59.000Z
Data from a 1152X760X1280 direct numerical simulation (DNS) of a transitional Rayleigh-Taylor mixing layer modeled after a small Atwood number water channel experiment is used to comprehensively investigate the structure of mean and turbulent transport and mixing. The simulation had physical parameters and initial conditions approximating those in the experiment. The budgets of the mean vertical momentum, heavy-fluid mass fraction, turbulent kinetic energy, turbulent kinetic energy dissipation rate, heavy-fluid mass fraction variance, and heavy-fluid mass fraction variance dissipation rate equations are constructed using Reynolds averaging applied to the DNS data. The relative importance of mean and turbulent production, turbulent dissipationmore »and destruction, and turbulent transport are investigated as a function of Reynolds number and across the mixing layer to provide insight into the flow dynamics not presently available from experiments. The analysis of the budgets supports the assumption for small Atwood number, Rayleigh/Taylor driven flows that the principal transport mechanisms are buoyancy production, turbulent production, turbulent dissipation, and turbulent diffusion (shear and mean field production are negligible). As the Reynolds number increases, the turbulent production in the turbulent kinetic energy dissipation rate equation becomes the dominant production term, while the buoyancy production plateaus. Distinctions between momentum and scalar transport are also noted, where the turbulent kinetic energy and its dissipation rate both grow in time and are peaked near the center plane of the mixing layer, while the heavy-fluid mass fraction variance and its dissipation rate initially grow and then begin to decrease as mixing progresses and reduces density fluctuations. All terms in the transport equations generally grow or decay, with no qualitative change in their profile, except for the pressure flux contribution to the total turbulent kinetic energy flux, which changes sign early in time (a countergradient effect). The production-to-dissipation ratios corresponding to the turbulent kinetic energy and heavy-fluid mass fraction variance are large and vary strongly at small evolution times, decrease with time, and nearly asymptote as the flow enters a self-similar regime. The late-time turbulent kinetic energy production-to-dissipation ratio is larger than observed in shear-driven turbulent flows. The order of magnitude estimates of the terms in the transport equations are shown to be consistent with the DNS at late-time, and also confirms both the dominant terms and their evolutionary behavior. These results are useful for identifying the dynamically important terms requiring closure, and assessing the accuracy of the predictions of Reynolds-averaged Navier-Stokes and large-eddy simulation models of turbulent transport and mixing in transitional Rayleigh-Taylor instability-generated flow.« less
DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)
Schilling, Oleg [Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); Mueschke, Nicholas J. [Texas A and M Univ., College Station, TX (United States)
2010-01-01T23:59:59.000Z
Data from a 1152X760X1280 direct numerical simulation (DNS) of a transitional Rayleigh-Taylor mixing layer modeled after a small Atwood number water channel experiment is used to comprehensively investigate the structure of mean and turbulent transport and mixing. The simulation had physical parameters and initial conditions approximating those in the experiment. The budgets of the mean vertical momentum, heavy-fluid mass fraction, turbulent kinetic energy, turbulent kinetic energy dissipation rate, heavy-fluid mass fraction variance, and heavy-fluid mass fraction variance dissipation rate equations are constructed using Reynolds averaging applied to the DNS data. The relative importance of mean and turbulent production, turbulent dissipation and destruction, and turbulent transport are investigated as a function of Reynolds number and across the mixing layer to provide insight into the flow dynamics not presently available from experiments. The analysis of the budgets supports the assumption for small Atwood number, Rayleigh/Taylor driven flows that the principal transport mechanisms are buoyancy production, turbulent production, turbulent dissipation, and turbulent diffusion (shear and mean field production are negligible). As the Reynolds number increases, the turbulent production in the turbulent kinetic energy dissipation rate equation becomes the dominant production term, while the buoyancy production plateaus. Distinctions between momentum and scalar transport are also noted, where the turbulent kinetic energy and its dissipation rate both grow in time and are peaked near the center plane of the mixing layer, while the heavy-fluid mass fraction variance and its dissipation rate initially grow and then begin to decrease as mixing progresses and reduces density fluctuations. All terms in the transport equations generally grow or decay, with no qualitative change in their profile, except for the pressure flux contribution to the total turbulent kinetic energy flux, which changes sign early in time (a countergradient effect). The production-to-dissipation ratios corresponding to the turbulent kinetic energy and heavy-fluid mass fraction variance are large and vary strongly at small evolution times, decrease with time, and nearly asymptote as the flow enters a self-similar regime. The late-time turbulent kinetic energy production-to-dissipation ratio is larger than observed in shear-driven turbulent flows. The order of magnitude estimates of the terms in the transport equations are shown to be consistent with the DNS at late-time, and also confirms both the dominant terms and their evolutionary behavior. These results are useful for identifying the dynamically important terms requiring closure, and assessing the accuracy of the predictions of Reynolds-averaged Navier-Stokes and large-eddy simulation models of turbulent transport and mixing in transitional Rayleigh-Taylor instability-generated flow.
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.
Vrme-och strmningsteknik / Thermal and flow engineering Massverfring & separationsteknik /
Zevenhoven, Ron
VÃ¤rme- och strÃ¶mningsteknik / Thermal and flow engineering MassÃ¶verfÃ¶ring & separationsteknik to control the humidity. This will absorb some naphthalene from the air, which then in turn gives increased
Simulation of Combustion and Thermal Flow in an Industrial Boiler
Saripalli, R.; Wang, T.; Day, B.
2005-01-01T23:59:59.000Z
insight into the detailed thermal-flow and combustion in the boiler and showing possible reasons for superheater tube rupture. The exhaust gas temperature is consistent with the actual results from the infrared thermograph inspection....
Modification of turbulent structure in channel flows by microbubble injection close to the wall
Gutierrez Torres, Claudia del Carmen
2005-11-01T23:59:59.000Z
. There is a decrease in the activity of the wall in creating turbulence at high drag reduction cases manifested by a decrease of ejections (bursts) from the wall. A double pulse PIV system was used by Kawaguchi and Feng (2001) to clarify the spatial... additives is different from the drag-reducing flows, showing a reduction in the random vortex motion for the drag-reducing flow. It was also observed that for the water flow there is penetration from low speed fluid into high-speed region (ejection...
Vrme-och strmningsteknik / Thermal and flow engineering Massverfring & separationsteknik /
Zevenhoven, Ron
VÃ¤rme- och strÃ¶mningsteknik / Thermal and flow engineering MassÃ¶verfÃ¶ring & separationsteknik Ã¥tminstone 95%. #12;VÃ¤rme- och strÃ¶mningsteknik / Thermal and flow engineering MassÃ¶verfÃ¶ring in the vessel is 1 liter while for the gas the volume is 0.1 liter. The mass transfer is controlled by a mass
Dispersion of swimming algae in laminar and turbulent channel flows: theory and simulations
Croze, O A; Ahmed, M; Bees, M A; Brandt, L
2012-01-01T23:59:59.000Z
Algal swimming is often biased by environmental cues, e.g. gravitational and viscous torques drive cells towards downwelling fluid (gyrotaxis). In view of biotechnological applications, it is important to understand how such biased swimming affects cell dispersion in a flow. Here, we study the dispersion of gyrotactic swimming algae in laminar and turbulent channel flows. By direct numerical simulation (DNS) of cell motion within upwelling and downwelling channel flows, we evaluate time-dependent measures of dispersion for increasing values of the flow Peclet (Reynolds) numbers, Pe (Re). Furthermore, we derive an analytical `swimming Taylor-Aris dispersion' theory, using flow-dependent transport parameters given by existing microscopic models. In the laminar regime, DNS results and analytical predictions compare very well, providing the first confirmation that cells' response to flow is best described by the generalized-Taylor-dispersion microscopic model. We predict that cells drift along a channel faster th...
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.
Creating Small Gas Bubbles in Flowing Mercury Using Turbulence at an Orifice
Wendel, Mark W [ORNL; Abdou, Ashraf A [ORNL; Paquit, Vincent C [ORNL; Felde, David K [ORNL; Riemer, Bernie [ORNL
2010-01-01T23:59:59.000Z
Pressure waves created in liquid mercury pulsed spallation targets have been shown to create cavitation damage to the target container. One way to mitigate such damage would be to absorb the pressure pulse energy into a dispersed population of small bubbles, however, creating such a population in mercury is difficult due to the high surface tension and particularly the non-wetting behavior of mercury on gas-injection hardware. If the larger injected gas bubbles can be broken down into small bubbles after they are introduced to the flow, then the material interface problem is avoided. Research at the Oak Ridge National Labarotory is underway to develop a technique that has shown potential to provide an adequate population of small-enough bubbles to a flowing spallation target. This technique involves gas injection at an orifice of a geometry that is optimized to the turbulence intensity and pressure distribution of the flow, while avoiding coalescence of gas at injection sites. The most successful geometry thus far can be described as a square-toothed orifice having a 2.5 bar pressure drop in the nominal flow of 12 L/s for one of the target inlet legs. High-speed video and high-resolution photography have been used to quantify the bubble population on the surface of the mercury downstream of the gas injection sight. Also, computational fluid dynamics has been used to optimize the dimensions of the toothed orifice based on a RANS computed mean flow including turbulent energies such that the turbulent dissipation and pressure field are best suited for turbulent break-up of the gas bubbles.
Rossby and Drift Wave Turbulence and Zonal Flows: the Charney-Hasegawa-Mima model and its extensions
Colm Connaughton; Sergey Nazarenko; Brenda Quinn
2014-07-07T23:59:59.000Z
A detailed study of the Charney-Hasegawa-Mima model and its extensions is presented. These simple nonlinear partial differential equations suggested for both Rossby waves in the atmosphere and also drift waves in a magnetically-confined plasma exhibit some remarkable and nontrivial properties, which in their qualitative form survive in more realistic and complicated models, and as such form a conceptual basis for understanding the turbulence and zonal flow dynamics in real plasma and geophysical systems. Two idealised scenarios of generation of zonal flows by small-scale turbulence are explored: a modulational instability and turbulent cascades. A detailed study of the generation of zonal flows by the modulational instability reveals that the dynamics of this zonal flow generation mechanism differ widely depending on the initial degree of nonlinearity. A numerical proof is provided for the extra invariant in Rossby and drift wave turbulence -zonostrophy and the invariant cascades are shown to be characterised by the zonostrophy pushing the energy to the zonal scales. A small scale instability forcing applied to the model demonstrates the well-known drift wave - zonal flow feedback loop in which the turbulence which initially leads to the zonal flow creation, is completely suppressed and the zonal flows saturate. The turbulence spectrum is shown to diffuse in a manner which has been mathematically predicted. The insights gained from this simple model could provide a basis for equivalent studies in more sophisticated plasma and geophysical fluid dynamics models in an effort to fully understand the zonal flow generation, the turbulent transport suppression and the zonal flow saturation processes in both the plasma and geophysical contexts as well as other wave and turbulence systems where order evolves from chaos.
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: Alternative1 First Use of Energy for All Purposes (Fuel and Nonfuel), 2002; Level:Energy: Grid Integration Redefining What'sis Taking Over OurThe Iron Spin Transition in2,EHSS A-Zand Analysis Utilities (TAU)TuningTurbulence
Gravity Surface Wave Bifurcation in a Highly Turbulent Swirling Flow
Witten, Thomas A.
: The `base state' of Taylor-Couette flow. The slight asymmetry seen in this photo appears to undergo-Couette gravity wave, we used a capacitive height sensor that consists of a copper wire covered with a thin layer a Q/h 2 · 1 r · dr (2) C = 2 ln (b/a) · h (3) Therefore, our sensor turns the varying height
Rudy, Alexander; Srinath, Srikar; Ammons, S Mark; Gavel, Donald
2015-01-01T23:59:59.000Z
We present the laboratory verification of a method for re- moving the effects of frozen-flow atmospheric turbulence using a Linear Quadratic Gaussian (LQG) controller, also known as a Kalman Filter. This method, which we term "Predictive Fourier Control," can identify correlated atmospheric motions due to layers of frozen flow turbulence, and can predictively remove the effects of these correlated motions in real-time. Our laboratory verification suggests a factor of 3 improvement in the RMS residual wavefront error and a 10% improvement in measured Strehl of the system. We found that the RMS residual wavefront error was suppressed from 35.0 nm to 11.2 nm due to the use of Predictive Fourier Control, and that the far field Strehl improved from 0.479 to 0.520.
The effect of diamagnetic flows on turbulent driven ion toroidal rotation
Lee, J. P. [Courant Institute of Mathematical Sciences, New York University, New York, New York 10003 (United States)] [Courant Institute of Mathematical Sciences, New York University, New York, New York 10003 (United States); Barnes, M. [Institute for Fusion Studies, The 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); Parra, F. I. [Rudolf Peierls Centre for Theoretical Physics, Oxford University, Oxford OX1 3NP (United Kingdom)] [Rudolf Peierls Centre for Theoretical Physics, Oxford University, Oxford OX1 3NP (United Kingdom); Belli, E. A.; Candy, J. [General Atomics, San Diego, California 92121 (United States)] [General Atomics, San Diego, California 92121 (United States)
2014-05-15T23:59:59.000Z
Turbulent momentum redistribution determines the radial profile of rotation in a tokamak. The momentum transport driven by diamagnetic flow effects is an important piece of the radial momentum transport for sub-sonic rotation, which is often observed in experiments. In a non-rotating state, the diamagnetic flow and the E × B flow must cancel. The diamagnetic flow and the E × B flow have different effects on the turbulent momentum flux, and this difference in behavior induces intrinsic rotation. The momentum flux is evaluated using gyrokinetic equations that are corrected to higher order in the ratio of the poloidal Larmor radius to the minor radius, which requires evaluation of the diamagnetic corrections to Maxwellian equilibria. To study the momentum transport due to diamagnetic flow effects, three experimental observations of ion rotation are examined. First, a strong pressure gradient at the plasma edge is shown to result in a significant inward momentum transport due to the diamagnetic effect, which may explain the observed peaking of rotation in a high confinement mode. Second, the direction of momentum transport is shown to change as collisionality increases, which is qualitatively consistent with the observed reversal of intrinsic rotation by varying plasma density and current. Last, the dependence of the intrinsic momentum flux on the magnetic shear is found, and it may explain the observed rotation changes in the presence of lower hybrid current drive.
Xu, Ying
2005-05-01T23:59:59.000Z
Many particle-laden flows in engineering applications involve turbulent gas flows. Modeling multiphase turbulent flows is an important research topic with applications in fluidized beds and particle conveying. A predictive multiphase turbulence model can help CFD codes to be more useful for engineering applications, such as the scale-up in the design of circulating fluidized combustor and coal gasifications. In engineering applications, the particle volume fraction can vary from dilute (<10{sup -4}) to dense ({approx} 50%). It is reasonable to expect that multiphase turbulence models should at least satisfy some basic modeling and performance criteria and give reasonable predictions for the canonical problems in dilute particle-laden turbulent flows. In this research, a comparative assessment of predictions from Simonin and Ahmadi's turbulence models is performed with direct numerical simulation (DNS) for two canonical problems in particle-laden turbulent flows. Based on the comparative assessment, some criteria and the areas for model improvement are identified: (1) model for interphase TKE transfer, especially the time scale of interphase TKE transfer, and (2) correct prediction of TKE evolution with variation of particle Stokes number. Some deficiencies that are identified in the Simonin and Ahmadi models, limit the applicability. A new multiphase turbulence model, the Equilibration of Energy Model (EEM), is proposed in this work. In EEM, a multiscale interaction time scale is proposed to account for the interaction of a particle with a range of eddy sizes. EEM shows good agreement with the DNS results for particle-laden isotropic turbulence. For particle-laden homogeneous shear flows, model predictions from EEM can be further improved if the dissipation rate in fluid phase is modeled with more accuracy.
Drag Reduction Study by Wavelet Analysis of Differential Pressure Signals in Turbulent Flow
Ling Zhen; Yassin, A. Hassan; Dominguez-Ontiveros, Elvis [Nuclear Engineering Department, Texas A and M University, College Station, Texas 77843 (United States)
2004-07-01T23:59:59.000Z
Drag reduction was studied when micro-bubbles with low void fractions were injected in the boundary layer of a turbulent channel flow. The particle tracking velocimetry (PIV) flow measurement technique was used to measure two-dimensional full velocity fields. Since pressure field distribution is associated with turbulence behavior and dissipation, it is important to study the changes of the pressure field. However, the differential pressure signals are difficult to analyze due to irregularity. The characteristics of these signals have been studied by traditional statistical methods. In this study, the multi-resolution technique of wavelet transform based on localized wavelet functions is utilized to nonlinear pressure signals. By using continuous wavelet transform method, the pressure signals in the turbulent flow can be decomposed into its approximations and details at different resolutions. The magnitudes of the coefficients represent the energy distribution at different scales and this also can facilitate the visual observation of the energy transition process. The wavelet decomposition coefficients at different scales plot would provide a tool to further our understanding of drag reduction mechanism via micro-bubbles injection. (authors)
Decay of swirl in turbulent two phase flow
Neeley, Patrick Foster
1971-01-01T23:59:59.000Z
loop required a straight circular pipe, a con- stant head tank, a flow control device, a mixing tank, a swirl producing mechanism, a dye injection system, and a drainage system. Polyoxides are thoroughly mixed with tap water in the mixing tank... concentrations of the Polyox were put into the water in a uniform procedure in order to obtain consist. ent results. A venturi mixer was designed and used to di perse the polymer particles into the water in the mixing tank. The vigorous stir- ring bv the jet...
Simulations of Turbulent Flows with Strong Shocks and Density Variations: Final Report
Sanjiva Lele
2012-10-01T23:59:59.000Z
The target of this SciDAC Science Application was to develop a new capability based on high-order and high-resolution schemes to simulate shock-turbulence interactions and multi-material mixing in planar and spherical geometries, and to study Rayleigh-Taylor and Richtmyer-Meshkov turbulent mixing. These fundamental problems have direct application in high-speed engineering flows, such as inertial confinement fusion (ICF) capsule implosions and scramjet combustion, and also in the natural occurrence of supernovae explosions. Another component of this project was the development of subgrid-scale (SGS) models for large-eddy simulations of flows involving shock-turbulence interaction and multi-material mixing, that were to be validated with the DNS databases generated during the program. The numerical codes developed are designed for massively-parallel computer architectures, ensuring good scaling performance. Their algorithms were validated by means of a sequence of benchmark problems. The original multi-stage plan for this five-year project included the following milestones: 1) refinement of numerical algorithms for application to the shock-turbulence interaction problem and multi-material mixing (years 1-2); 2) direct numerical simulations (DNS) of canonical shock-turbulence interaction (years 2-3), targeted at improving our understanding of the physics behind the combined two phenomena and also at guiding the development of SGS models; 3) large-eddy simulations (LES) of shock-turbulence interaction (years 3-5), improving SGS models based on the DNS obtained in the previous phase; 4) DNS of planar/spherical RM multi-material mixing (years 3-5), also with the two-fold objective of gaining insight into the relevant physics of this instability and aiding in devising new modeling strategies for multi-material mixing; 5) LES of planar/spherical RM mixing (years 4-5), integrating the improved SGS and multi-material models developed in stages 3 and 5. This final report is outlined as follows. Section 2 shows an assessment of numerical algorithms that are best suited for the numerical simulation of compressible flows involving turbulence and shock phenomena. Sections 3 and 4 deal with the canonical shock-turbulence interaction problem, from the DNS and LES perspectives, respectively. Section 5 considers the shock-turbulence inter-action in spherical geometry, in particular, the interaction of a converging shock with isotropic turbulence as well as the problem of the blast wave. Section 6 describes the study of shock-accelerated mixing through planar and spherical Richtmyer-Meshkov mixing as well as the shock-curtain interaction problem In section 7 we acknowledge the different interactions between Stanford and other institutions participating in this SciDAC project, as well as several external collaborations made possible through it. Section 8 presents a list of publications and presentations that have been generated during the course of this SciDAC project. Finally, section 9 concludes this report with the list of personnel at Stanford University funded by this SciDAC project.
Bauer, Georg; Gamnitzer, Peter [Institute for Computational Mechanics, Technische Universität München, Boltzmannstr. 15, 85747 Garching (Germany)] [Institute for Computational Mechanics, Technische Universität München, Boltzmannstr. 15, 85747 Garching (Germany); Gravemeier, Volker, E-mail: vgravem@lnm.mw.tum.de [Institute for Computational Mechanics, Technische Universität München, Boltzmannstr. 15, 85747 Garching (Germany) [Institute for Computational Mechanics, Technische Universität München, Boltzmannstr. 15, 85747 Garching (Germany); Emmy Noether Research Group “Computational Multiscale Methods for Turbulent Combustion”, Technische Universität München, Boltzmannstr. 15, 85747 Garching (Germany); Wall, Wolfgang A. [Institute for Computational Mechanics, Technische Universität München, Boltzmannstr. 15, 85747 Garching (Germany)] [Institute for Computational Mechanics, Technische Universität München, Boltzmannstr. 15, 85747 Garching (Germany)
2013-10-15T23:59:59.000Z
Highlights: •We present a computational method for coupled multi-ion transport in turbulent flow. •The underlying formulation is a variational multiscale finite element method. •It is combined with the isogeometric concept for electrochemical systems. •Coupled multi-ion transport in fully turbulent Taylor–Couette flow is simulated. •This example is an important model problem for rotating cylinder electrodes. -- Abstract: Electrochemical processes, such as electroplating of large items in galvanic baths, are often coupled to turbulent flow. In this study, we propose an isogeometric residual-based variational multiscale finite element method for multi-ion transport in dilute electrolyte solutions under turbulent flow conditions. In other words, this means that the concepts of isogeometric discretization and variational multiscale methods are successfully combined for developing a method capable of simulating the challenging problem of coupled multi-ion transport in turbulent flow. We present a comprehensive three-dimensional computational method taking into account, among others, coupled convection–diffusion-migration equations subject to an electroneutrality constraint in combination with phenomenological electrode-kinetics modeling. The electrochemical subproblem is one-way coupled to turbulent incompressible flow via convection. Ionic mass transfer in turbulent Taylor–Couette flow is investigated, representing an important model problem for rotating-cylinder-electrode configurations. Multi-ion transport as considered here is an example for mass transport at high Schmidt number (Sc=1389). An isogeometric discretization is especially advantageous for the present problem, since (i) curved boundaries can be represented exactly, and (ii) it has been proven to provide very accurate solutions for flow quantities when being applied in combination with residual-based variational multiscale modeling. We demonstrate that the method is robust and provides results which are in good agreement with direct numerical simulation results as well as empirical mass-transfer correlations reported in literature.
Thermally-driven flows between a Leidenfrost solid and a ratchet surface
Hardt, Steffen; Baier, Tobias
2012-01-01T23:59:59.000Z
The significance of thermally-driven flows for the propulsion of Leidenfrost solids on a ratchet surface is studied based on a numerical solution of the Boltzmann equation. In contrast to a previous analysis, it is found that no significant thermal creep flow is established. Instead, the flow pattern is dominated by thermal edge and thermal-stress slip flow, the latter being directed opposite to thermal creep flow. However, in total thermally-induced flows only make a minor contribution to the propulsion of Leidenfrost solids on ratchet surfaces which is dominated by the pressure-driven flow due to the sublimating solid.
Evolution and lifetimes of flow topology in a turbulent boundary layer G. E. Elsinga and I. Marusic
Marusic, Ivan
-similar forms of fluid flow and heat-mass transfer in turbulent boundary layer flow of a nanofluid Phys. Fluids that are coherent in time and space, commonly referred to as eddies or coherent structures.1 They are fundamental remain regarding the dynamics and time scales of these coherent motions. In this study we provide a first
The friction factor of two-dimensional rough-boundary turbulent soap film flows
Nicholas Guttenberg; Nigel Goldenfeld
2009-03-25T23:59:59.000Z
We use momentum transfer arguments to predict the friction factor $f$ in two-dimensional turbulent soap-film flows with rough boundaries (an analogue of three-dimensional pipe flow) as a function of Reynolds number Re and roughness $r$, considering separately the inverse energy cascade and the forward enstrophy cascade. At intermediate Re, we predict a Blasius-like friction factor scaling of $f\\propto\\textrm{Re}^{-1/2}$ in flows dominated by the enstrophy cascade, distinct from the energy cascade scaling of $\\textrm{Re}^{-1/4}$. For large Re, $f \\sim r$ in the enstrophy-dominated case. We use conformal map techniques to perform direct numerical simulations that are in satisfactory agreement with theory, and exhibit data collapse scaling of roughness-induced criticality, previously shown to arise in the 3D pipe data of Nikuradse.
Electromagnetically and Thermally Driven Flow Phenomena in Electroslag Welding
Eagar, Thomas W.
) Electromagnetically and Thermally Driven Flow Phenomena in Electroslag Welding A. H. DILAWARI, J for the Electroslag Welding Process. In the formulation, allowance has been made {or both etee- tromagnetic and b in the use of electroslag welding (ESW), particularly for the construction of thick walled pressure vessels
Department of Chemical Engineering Thermal and Flow Engineering Laboratory
Zevenhoven, Ron
Department of Chemical Engineering Thermal and Flow Engineering Laboratory Ron Zevenhoven Course of Physics that (chemical) engineers have to work with haven't changed since then, an update was called for for quite a few of ÅA's chemical engineering students. This text is produced in two languages for several
Simultaneous fog formation and thermophoretic droplet deposition in a turbulent pipe flow
Epstein, M.; Hauser, G.M. (Fauske and Associates, Inc., Burr Ridge, IL (USA))
1991-02-01T23:59:59.000Z
Simultaneous aerosol formation by equilibrium condensation and the migration of the resulting droplets to the cold surface by thermophoresis is studied theoretically for a turbulent pipe flow. The problem is one in which a mixture of a vapor and noncondensable gas flows into a section of pipe where the pipe wall is cooled to below the dew point of the vapor. Because the temperature gradient at the pipe wall decays to zero once the gas travels far enough into the pipe, only some fraction of the droplets formed will deposit on the pipe wall. The equations of energy and diffusion suggest that turbulence leads to a discontinuity in the aerosol (fog) concentration at the boundary between the fog and clear regions. Numerical solutions are obtained for CsOH fog formation and deposition in steam flow, a particular case of current practical interest in water reactor safety. The axial and radial variations of the aerosol and vapor concentrations are displayed graphically, as are the location of the fog boundary as a function of axial distance and the efficiency of deposition as a function of the pipe wall temperature.
Gas flow driven by thermal creep in dusty plasma
Flanagan, T. M.; Goree, J. [Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242 (United States)
2009-10-15T23:59:59.000Z
Thermal creep flow (TCF) is a flow of gas driven by a temperature gradient along a solid boundary. Here, TCF is demonstrated experimentally in a dusty plasma. Stripes on a glass box are heated by laser beam absorption, leading to both TCF and a thermophoretic force. The design of the experiment allows isolating the effect of TCF. A stirring motion of the dust particle suspension is observed. By eliminating all other explanations for this motion, we conclude that TCF at the boundary couples by drag to the bulk gas, causing the bulk gas to flow, thereby stirring the suspension of dust particles. This result provides an experimental verification, for the field of fluid mechanics, that TCF in the slip-flow regime causes steady-state gas flow in a confined volume.
Inviscid Limits for a Stochastically Forced Shell Model of Turbulent Flow
Susan Friedlander; Nathan Glatt-Holtz; Vlad Vicol
2014-04-03T23:59:59.000Z
We establish the anomalous mean dissipation rate of energy in the inviscid limit for a stochastic shell model of turbulent fluid flow. The proof relies on viscosity independent bounds for stationary solutions and on establishing ergodic and mixing properties for the viscous model. The shell model is subject to a degenerate stochastic forcing in the sense that noise acts directly only through one wavenumber. We show that it is hypo-elliptic (in the sense of Hormander) and use this property to prove a gradient bound on the Markov semigroup.
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...
Sippola, Mark R.; Nazaroff, William W.
2002-06-01T23:59:59.000Z
This report reviews published experimental and theoretical investigations of particle deposition from turbulent flows and considers the applicability of this body of work to the specific case of particle deposition from flows in the ducts of heating, ventilating and air conditioning (HVAC) systems. Particle deposition can detrimentally affect the performance of HVAC systems and it influences the exposure of building occupants to a variety of air pollutants. The first section of this report describes the types of HVAC systems under consideration and discusses the components, materials and operating parameters commonly found in these systems. The second section reviews published experimental investigations of particle deposition rates from turbulent flows and considers the ramifications of the experimental evidence with respect to HVAC ducts. The third section considers the structure of turbulent airflows in ventilation ducts with a particular emphasis on turbulence investigations that have been used as a basis for particle deposition models. The final section reviews published literature on predicting particle deposition rates from turbulent flows.
Chaotic mean wind in turbulent thermal convection and long-term correlations in solar activity
A. Bershadskii
2009-12-25T23:59:59.000Z
It is shown that correlation function of the mean wind velocity in a turbulent thermal convection (Rayleigh number $Ra \\sim 10^{11}$) exhibits exponential decay with a very long correlation time, while corresponding largest Lyapunov exponent is certainly positive. These results together with the reconstructed phase portrait indicate presence of a chaotic component in the examined mean wind. Telegraph approximation is also used to study relative contribution of the chaotic and stochastic components to the mean wind fluctuations and an equilibrium between these components has been studied. Since solar activity is based on the thermal convection processes, it is reasoned that the observed solar activity long-term correlations can be an imprint of the mean wind chaotic properties. In particular, correlation function of the daily sunspots number exhibits exponential decay with a very long correlation time and corresponding largest Lyapunov exponent is certainly positive, also relative contribution of the chaotic and stochastic components follows the same pattern as for the convection mean wind.
Enhanced thermal and gas flow performance in a three-way catalytic...
Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site
thermal and gas flow performance in a three-way catalytic converter through use of insulation within the ceramic monolith Enhanced thermal and gas flow performance in a three-way...
Paik, Joongcheol [University of Minnesota; Sotiropoulos, Fotis [University of Minnesota; Sale, Michael J [ORNL
2005-06-01T23:59:59.000Z
A numerical method is developed for carrying out unsteady Reynolds-averaged Navier-Stokes (URANS) simulations and detached-eddy simulations (DESs) in complex 3D geometries. The method is applied to simulate incompressible swirling flow in a typical hydroturbine draft tube, which consists of a strongly curved 90 degree elbow and two piers. The governing equations are solved with a second-order-accurate, finite-volume, dual-time-stepping artificial compressibility approach for a Reynolds number of 1.1 million on a mesh with 1.8 million nodes. The geometrical complexities of the draft tube are handled using domain decomposition with overset (chimera) grids. Numerical simulations show that unsteady statistical turbulence models can capture very complex 3D flow phenomena dominated by geometry-induced, large-scale instabilities and unsteady coherent structures such as the onset of vortex breakdown and the formation of the unsteady rope vortex downstream of the turbine runner. Both URANS and DES appear to yield the general shape and magnitude of mean velocity profiles in reasonable agreement with measurements. Significant discrepancies among the DES and URANS predictions of the turbulence statistics are also observed in the straight downstream diffuser.
Flow field studies of a new series of turbulent premixed stratified flames
Seffrin, F.; Fuest, F.; Dreizler, A. [Technische Universitaet Darmstadt, Center of Smart Interfaces, Reaktive Stroemungen und Messtechnik, Petersenstr. 32, 64287 Darmstadt (Germany); Geyer, D. [Hochschule Darmstadt, Thermodynamik und Alternative Antriebe, Haardtring 100, 64295 Darmstadt (Germany)
2010-02-15T23:59:59.000Z
This paper presents a new burner design for lean premixed stratified combustion for experiments to validate models for numerical simulations. The burner demonstrates combustion phenomena relevant to technological applications, where flames are often turbulent, lean premixed, and stratified. The generic burner was designed for high Reynolds number flows and can stabilize a variety of different lean premixed flames. The burner's design and its versatile operational conditions are introduced. Shear, stratification, and fuel type are parametrically varied to provide a sound database of related flow configurations. Reacting and corresponding non-reacting configurations are examined. Experimental setups and the results of laser Doppler velocimetry (LDV) and particle image velocimetry (PIV) are presented and discussed. LDV measurements provide radial profiles of mean axial velocity, mean radial velocity, and turbulent kinetic energy as well as integral time scales. High-speed PIV is introduced as a novel technique to determine integral time and length scales and provide 2D 2-component velocity fields and related quantities, such as vorticity. (author)
Notes 10. A thermohydrodynamic bulk-flow model for fluid film bearings
San Andres, Luis
2009-01-01T23:59:59.000Z
The complete set of bulk-flow equations for the analysis of turbulent flow fluid film bearings. Importance of thermal effects in process fluid applications. A CFD method for solution of the bulk-flow equations....
Momentum and heat fluxes in a turbulent air flow over a wet, smooth boundary
Rice, Warren
1958-01-01T23:59:59.000Z
Idealized sketch, of boundary layer flow regions................ .............45 Figure 2 Schematic diagram of wind tunnel. . . . 46 Figure 3 Photograph of wind tunnel............ .. 47 Figure 4 Photograph of wind tunnel............ .. 47 Figure 5... mechanism and probe.................. .. 49 Figure 9 Distances of interest in the momentum and thermal boundary layers ............ 50 Figure 10 A typical velocity and temperature profile comparison .................. .. 51 Figure 1 1 Variation...
Prakash, C.; Zerkle, R. [General Electric Co., Cincinnati, OH (United States)
1995-04-01T23:59:59.000Z
The present study deals with the numerical prediction of turbulent flow and heat transfer in a 2:1 aspect ratio rectangular duct with ribs don the two shorter sides. The ribs are of square cross section, staggered and aligned normal (90 deg) to the main flow direction. The ratio of rib height to duct hydraulic diameter equals 0.063, and the ratio of rib spacing to rib height equals 10. The duct may be stationary or rotating. The axis of rotation is normal to the axis of the duct and parallel to the ribbed walls (i.e., the ribbed walls form the leading and the trailing faces). The problem is three dimensional and fully elliptic; hence, for computational economy, the present analysis deals only with a periodically fully developed situation where the calculation domain is limited to the region between two adjacent ribs. Turbulence is modeled with the {kappa}-{epsilon} model in conjunction with wall functions. However, since the rib height is small, use of wall functions necessitates that the Reynolds number be kept high. (Attempts to use a two-layer model that permits integration to the wall did not yield satisfactory results and such modeling issues are discussed at length.) Computations are made here for Reynolds number in the range 30,000--100,000 and for Rotation number = 0 (stationary), 0.06, and 0.12. For the stationary case, the predicted heat transfer agrees well with the experimental correlations. Due to the Coriolis-induced secondary flow, rotation is found to enhance heat transfer from the trailing and the side walls, while decreasing heat transfer from the leading face. Relative to the corresponding stationary case, the effect of rotation is found to be less for a ribbed channel as compared to a smooth channel.
Brandenburg, Axel
of applications (environmental sciences, physics of the atmosphere and meteorology, industrial turbulent flows://pof.aip.org/resource/1/PHFLE6/v24/i7 Published by the American Institute of Physics. Related Articles Light attenuation scale is large in comparison with the integral scale of the turbulence. The strength of this effect
Flow Turbulence Combust (2009) 82:437453 DOI 10.1007/s10494-008-9145-3
2009-01-01T23:59:59.000Z
an important role in the design and analysis of practical combustion devices such as internal combustion engines, industrial burners and furnaces, and gas turbine combustors. Combustion of hydrocarbon fuelsFlow Turbulence Combust (2009) 82:437453 DOI 10.1007/s10494-008-9145-3 Efficient Implementation
Pontaza, Juan Pablo
2013-02-22T23:59:59.000Z
-Stokes equations and the energy equation in conjunction with a two-layer K-Epsilon isotropic eddy viscosity model and a near-wall Reynolds-Stress closure model. The fundamental cases of fully developed turbulent pipe flow and an axisymmetric jet impinging on a...
Gong, Munan
2015-01-01T23:59:59.000Z
We investigate prestellar core formation and accretion based on three-dimensional hydrodynamic simulations. Our simulations represent local $\\sim 1$pc regions within giant molecular clouds where a supersonic turbulent flow converges, triggering star formation in the post-shock layer. We include turbulence and self-gravity, applying sink particle techniques, and explore a range of inflow Mach number ${\\cal M}=2-16$. Two sets of cores are identified and compared: $t_1$-cores are identified of a time snapshot in each simulation, representing dense structures in a single cloud map; $t_\\mathrm{coll}$-cores are identified at their individual time of collapse, representing the initial mass reservoir for accretion. We find that cores and filaments form and evolve at the same time. At the stage of core collapse, there is a well-defined, converged characteristic mass for isothermal fragmentation that is comparable to the critical Bonner-Ebert mass at the post-shock pressure. The core mass functions (CMFs) of $t_\\mathrm...
S. S. Zilitinkevich; T. Elperin; N. Kleeorin; V. L'vov; I. Rogachevskii
2009-08-18T23:59:59.000Z
We advance our prior energy- and flux-budget turbulence closure model (Zilitinkevich et al., 2007, 2008) for the stably stratified atmospheric flows and extend it accounting for additional vertical flux of momentum and additional productions of turbulent kinetic energy, turbulent potential energy (TPE) and turbulent flux of potential temperature due to large-scale internal gravity waves (IGW). Main effects of IGW are following: the maximal value of the flux Richardson number (universal constant 0.2-0.25 in the no-IGW regime) becomes strongly variable. In the vertically homogeneous stratification, it increases with increasing wave energy and can even exceed 1. In the heterogeneous stratification, when IGW propagate towards stronger stratification, the maximal flux Richardson number decreases with increasing wave energy, reaches zero and then becomes negative. In other words, the vertical flux of potential temperature becomes counter-gradient. IGW also reduce anisotropy of turbulence and increase the share of TPE in the turbulent total energy. Depending on the direction (downward or upward), IGW either strengthen or weaken the total vertical flux of momentum. Predictions from the proposed model are consistent with available data from atmospheric and laboratory experiments, direct numerical simulations and large-eddy simulations.
Turbulent flow over a house in a simulated hurricane boundary layer
Taylor, Zachary; Gurka, Roi; Kopp, Gregory
2009-01-01T23:59:59.000Z
Every year hurricanes and other extreme wind storms cause billions of dollars in damage worldwide. For residential construction, such failures are usually associated with roofs, which see the largest aerodynamic loading. However, determining aerodynamic loads on different portions of North American houses is complicated by the lack of clear load paths and non-linear load sharing in wood frame roofs. This problem of fluid-structure interaction requires both wind tunnel testing and full-scale structural testing. A series of wind tunnel tests have been performed on a house in a simulated atmospheric boundary layer (ABL), with the resulting wind-induced pressures applied to the full-scale structure. The ABL was simulated for flow over open country terrain where both velocity and turbulence intensity profiles, as well as spectra, were matched with available full scale measurements for this type of terrain. The first set of measurements was 600 simultaneous surface pressure measurements over the entire house. A key...
Universal Model of Finite-Reynolds Number Turbulent Flow in Channels and Pipes
L'vov, Victor S; Rudenko, Oleksii; 10.1103/PhysRevLett.100.054504
2009-01-01T23:59:59.000Z
In this Letter we suggest a simple and physically transparent analytical model of the pressure driven turbulent wall-bounded flows at high but finite Reynolds numbers Re. The model gives accurate qualitative description of the profiles of the mean-velocity and Reynolds-stresses (second order correlations of velocity fluctuations) throughout the entire channel or pipe in the wide range of Re, using only three Re-independent parameters. The model sheds light on the long-standing controversy between supporters of the century-old log-law theory of von-K\\`arm\\`an and Prandtl and proposers of a newer theory promoting power laws to describe the intermediate region of the mean velocity profile.
Universal Model of Finite-Reynolds Number Turbulent Flow in Channels and Pipes
Victor S. L'vov; Itamar Procaccia; Oleksii Rudenko
2007-12-07T23:59:59.000Z
In this Letter we suggest a simple and physically transparent analytical model of the pressure driven turbulent wall-bounded flows at high but finite Reynolds numbers Re. The model gives accurate qualitative description of the profiles of the mean-velocity and Reynolds-stresses (second order correlations of velocity fluctuations) throughout the entire channel or pipe in the wide range of Re, using only three Re-independent parameters. The model sheds light on the long-standing controversy between supporters of the century-old log-law theory of von-K\\`arm\\`an and Prandtl and proposers of a newer theory promoting power laws to describe the intermediate region of the mean velocity profile.
Experiments measuring particle deposition from fully developed turbulent flow in ventilation ducts
Sippola, Mark R.; Nazaroff, William W.
2003-08-01T23:59:59.000Z
Particle deposition in ventilation ducts influences particle exposures of building occupants and may lead to a variety of indoor air quality concerns. Experiments have been performed in a laboratory to study the effects of particle size and air speed on deposition rates of particles from turbulent air flows in galvanized steel and internally insulated ducts with hydraulic diameters of 15.2 cm. The duct systems were constructed of materials typically found in commercial heating, ventilating and air conditioning (HVAC) systems. In the steel duct system, experiments with nominal particle sizes of 1, 3, 5, 9 and 16 {micro}m were conducted at each of three nominal air speeds: 2.2, 5.3 and 9.0 m/s. In the insulated duct system, deposition rates of particles with nominal sizes of 1, 3, 5, 8 and 13 {micro}m were measured at nominal air speeds of 2.2, 5.3 and 8.8 m/s. Fluorescent techniques were used to directly measure the deposition velocities of monodisperse fluorescent particles to duct surfaces (floor, wall and ceiling) at two straight duct sections where the turbulent flow profile was fully developed. In steel ducts, deposition rates were higher to the duct floor than to the wall, which were, in turn, greater than to the ceiling. In insulated ducts, deposition was nearly the same to the duct floor, wall and ceiling for a given particle size and air speed. Deposition to duct walls and ceilings was greatly enhanced in insulated ducts compared to steel ducts. Deposition velocities to each of the three duct surface orientations in both systems were found to increase with increasing particle size or air velocity over the ranges studied. Deposition rates measured in the current experiments were in general agreement with the limited observations of similar systems by previous researchers.
Basic research model of gas combustion in turbulent flow. Annual report, 1 June 1988-30 June 1989
Dahm, W.J.A.; Tryggvason, G.; Krasny, R.
1989-01-01T23:59:59.000Z
The report describes the development currently underway of a basic research model for gas combustion in turbulent flow. The model being developed is fundamentally different from the conventional types of turbulence models currently in use for flame calculations, both in terms of the underlying physical approximations made and in the numerical techniques used to implement them. The present approach is based on the idea that many of the precise and detailed fine scale processes at work in turbulent combustion have a simple self-similar structure, and as a result do not need to be continually recomputed in full detail. These can be modeled using results from recent experimental research into the fine scales of turbulent flows. Results obtained to date from this model have been carefully compared with finite difference simulations of the full governing equations for several simple test cases, and show that even complex and highly nonlinear phenomena such as local extinction of reactions in the flow field are correctly reproduced by the model. The model directly incorporates the strong coupling between the fluid dynamics and combustion chemistry in the flame. Work presently underway is incorporating volume source effects into the model.
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...
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 . . . . . . . . . . . .
The absence of inactive regions in turbulent flow: Evidence from light scattering experiments
Pak, Hyuk Kyu
prediction3) for large q,4 hasled to modelswhich imply that the turbulence consists of "active" regions
Hydro-thermal flow in a rough fracture EC Contract SES6-CT-2003-502706
Schmittbuhl, Jean
Hydro-thermal flow in a rough fracture EC Contract SES6-CT-2003-502706 PARTICIPANT ORGANIZATION NAME: CNRS Synthetic 2nd year report Related with Work Package............ HYDRO-THERMAL FLOW in the influence of a realistic geometry of the fracture on its hydro-thermal response. Several studies have
MULTIPLE SOLUTIONS FOR COMPRESSIBLE TURBULENT FLOW CHRISTOPHE BERTHON AND FREDERIC COQUEL
Coquel, FrÃ©dÃ©ric
continuous in the natural neighborhood of a null turbulent energy. For such models, we prove the existence of infinitely many distinct traveling wave solutions which exhibit positive turbulent energy but connect connecting end states with null turbulent energy. Due to the interplay between the relaxation term
Schuster, Eugenio
2014-05-02T23:59:59.000Z
The strong coupling between the different physical variables involved in the plasma transport phenomenon and the high complexity of its dynamics call for a model-based, multivariable approach to profile control where those predictive models could be exploited. The overall objective of this project has been to extend the existing body of work by investigating numerically and experimentally active control of unstable fluctuations, including fully developed turbulence and the associated cross-field particle transport, via manipulation of flow profiles in a magnetized laboratory plasma device. Fluctuations and particle transport can be monitored by an array of electrostatic probes, and Ex#2;B flow profiles can be controlled via a set of biased concentric ring electrodes that terminate the plasma column. The goals of the proposed research have been threefold: i- to develop a predictive code to simulate plasma transport in the linear HELCAT (HELicon-CAThode) plasma device at the University of New Mexico (UNM), where the experimental component of the proposed research has been carried out; ii- to establish the feasibility of using advanced model-based control algorithms to control cross-field turbulence-driven particle transport through appropriate manipulation of radial plasma flow profiles, iii- to investigate the fundamental nonlinear dynamics of turbulence and transport physics. Lehigh University (LU), including Prof. Eugenio Schuster and one full-time graduate student, has been primarily responsible for control-oriented modeling and model-based control design. Undergraduate students have also participated in this project through the National Science Foundation Research Experience for Undergraduate (REU) program. The main goal of the LU Plasma Control Group has been to study the feasibility of controlling turbulence-driven transport by shaping the radial poloidal flow profile (i.e., by controlling flow shear) via biased concentric ring electrodes.
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.
Dahm, W.J.A.; Tryggvason, G.; Krasny, R.
1992-02-17T23:59:59.000Z
The report describes progress made in extending a local integral method (LIM) model for approximately simulating vorticity transport and mixing, as well as molecular diffusion and reaction of chemical species, in natural gas combustion. The LIM model is fundamentally different from conventional approaches for numerically simulating combustion in turbulent flames, and is based on the experimental observation that the strain-diffusion balance which establishes the mixing and reaction scales in turbulent flames leads to a self-similar internal structure which does not need to be continually re-computed. Instead, these scales are represented by a family of self-similar profile shapes, whose moments are allowed to evolve freely to satisfy the governing equations. The resulting LIM computations thus need only to track the evolution of a material surface in the flow, and solve ODE's (ordinary differential equations) on the surface, rather than PDE's (partial differential equations) throughout the whole flame. The present report describes the application of the LIM model for computing the evolution of conserved scalar fields and the resulting equilibrium reaction processes, and presents results from sample calculations. It also describes the extension of the model to relatively detailed four-step methane-air kinetics together with the thermal nitric oxide mechanism, incorporating asymmetric profiles, and presents results from validation calculations. The application of the LIM approach to the vorticity field is also described.
Turbulence modeling of the Von Karman flow: viscous and inertial stirrings
Paris-Sud XI, Université de
and significant novelty of this paper is the use of a drag force in the momentum equations to reproduce by a cylinder, known as the Von K´arm´an [3] geometry, is of practical importance in many industrial devices turbulence and especially of magneto-hydrodynamic turbulence. From an academic point of view, the laminar
transfer of Momentum Turbulent (Reynolds) stresses Heat Turbulent heat flux Mass Turbulent: Fundamental equations · Averaging · Flow equations · Turbulence equations Part II: Characteristics, RWTH Aachen, 08.03.2010 Reynolds' experiment: Inject dye into pipe flow Observe filament at different
Balasubramanian, Sridhar [Los Alamos National Laboratory; Prestridge, Katherine P [Los Alamos National Laboratory; Orlicz, Gregory C [Los Alamos National Laboratory; Balasubramaniam, Balakumar J [Los Alamos National Laboratory
2010-11-15T23:59:59.000Z
The study of influence of initial conditions [amplitude ({delta}) and wavelength ({lambda}) of perturbations] on variable-density flows stems from the the recent work done by Dimonte et at. 2004, Miles et al. 2005 and Balakumar et al. 2008a, where it was shown that both Richtmyer-Meshkov (R-M) and Rayleigh-Taylor (R-T) turbulent flows are not truly self similar and have a strong initial conditions dependence on turbulence transport and mixing. However, so far most of the work on this topic has been numerical studies which suggest that for multi-mode systems, the emergence of a regime of self-similar instability growth independent of the initial conditions does not occur. Experimental evidence is needed to verify this theory. Thus, the present work focuses on conducting an experimental study at moderate Mach number (Ma = 1.2) to understand the effects of multi-mode perturbations of the shocked interface on instability growth rate and mixing for R-M flows, which are important mechanisms in inertial confinement fusion reactions, supernovae, combustion and general fluid mixing processes. The ongoing 3-D numerical simulations using ILES will be used for validation of our experimental results. The experiments to study R-M turbulence and mixing are carreid out at the Los Alamos Gas Shock Tube facility shown in Figure I and described in detail in Balakumar et al. 2008b. A heavy gas curtain of SF{sub 6}, surrounded on both sides by ambient air, representing a light/heavy/light interface is flowed through a varicose nozzle (shown in Figure 1c). This initial interface is then accelerated by a Mach 1.2 shock, generated in the driver section. Simultaneous Particle Image Velocimetry (PIV) and Planar Laser Induced Fluorescence (PLIF) diagnostics are used to characterize the initial conditions and also image the evolving flow to measure instantaneous velocity and density fields. The evolving structures are re-shocked at various times using a moveable reflecting wall to study the initial condition effects on turbulence and mixing. Mean flow fields are averaged from an ensemble of experiments whose initial density fields correlate to within 97% of each other. From the mean field, the fluctuating quantities are determined, and the density self-correlations and density-velocity correlations are calculated.
TURBULENT HEATING OF THE DISTANT SOLAR WIND BY INTERSTELLAR PICKUP PROTONS IN A DECELERATING FLOW
Isenberg, Philip A.
Previous models of solar wind heating by interstellar pickup proton-driven turbulence have assumed that the wind speed is a constant in heliocentric radial position. However, the same pickup process, which is taken to ...
Shear flow generation and energetics in electromagnetic turbulence V. Naulin, A. Kendl, O. E generation mechanisms via the Reynolds stress, Maxwell stress, and geodesic acoustic mode (GAM) transfer of mechanisms for the generation of shear flows connected to the low- to high confinement (LH-) transition have
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...
Zevenhoven, Ron
7 feb 13Åbo Akademi Univ - Thermal and Flow Engineering Piispankatu 8, 20500 Turku 1/82 Thermodynamics of separation processes Ron Zevenhoven Åbo Akademi University Thermal and Flow EngineeringThermodynamics course # 424304.0 v. 2013 ÅA 424304 7 feb 13Åbo Akademi Univ - Thermal and Flow Engineering Piispankatu 8
Coarse-grained transport of a turbulent flow via moments of the Reynolds-averaged Boltzmann equation
Abramov, Rafail V
2015-01-01T23:59:59.000Z
Here we introduce new coarse-grained variables for a turbulent flow in the form of moments of its Reynolds-averaged Boltzmann equation. With the exception of the collision moments, the transport equations for the new variables are identical to the usual moment equations, and thus naturally lend themselves to the variety of already existing closure methods. Under the anelastic turbulence approximation, we derive equations for the Reynolds-averaged turbulent fluctuations around the coarse-grained state. We show that the global relative entropy of the coarse-grained state is bounded from above by the Reynolds average of the fine-grained global relative entropy, and thus obeys the time decay bound of Desvillettes and Villani. This is similar to what is observed in the rarefied gas dynamics, which makes the Grad moment closure a good candidate for truncating the hierarchy of the coarse-grained moment equations. We also show that, under additional assumptions on the form of the coarse-grained collision terms, one a...
Wake Turbulence of Two NREL 5-MW Wind Turbines Immersed in a Neutral Atmospheric Boundary-Layer Flow
Bashioum, Jessica L; Schmitz, Sven; Duque, Earl P N
2013-01-01T23:59:59.000Z
The fluid dynamics video considers an array of two NREL 5-MW turbines separated by seven rotor diameters in a neutral atmospheric boundary layer (ABL). The neutral atmospheric boundary-layer flow data were obtained from a precursor ABL simulation using a Large-Eddy Simulation (LES) framework within OpenFOAM. The mean wind speed at hub height is 8m/s, and the surface roughness is 0.2m. The actuator line method (ALM) is used to model the wind turbine blades by means of body forces added to the momentum equation. The fluid dynamics video shows the root and tip vortices emanating from the blades from various viewpoints. The vortices become unstable and break down into large-scale turbulent structures. As the wakes of the wind turbines advect further downstream, smaller-scale turbulence is generated. It is apparent that vortices generated by the blades of the downstream wind turbine break down faster due to increased turbulence levels generated by the wake of the upstream wind turbine.
Effect of migrating bed topography on flow turbulence: implications for modeling sediment transport
Foufoula-Georgiou, Efi
recent results related to the space-time characterization of gravel bed elevation, near-bed 3D turbulence may not be published in the printed book but will be used in review and editing and may be used in web of these PDFs from Gaussian form calls for looking beyond the distribution of the energy across scales (spectrum
IMECE2009-13258 SIMULATION OF OPEN CHANNEL TURBULENT FLOW OVER BRIDGE
Kostic, Milivoje M.
computational fluid dynamics (CFD) software. An iterative computational methodology is developed for predicting surface above channel bed * h - Inundation ratio k m2 /s2 Turbulence kinetic energy bridgeL m Length, USA #12;2. INTRODUCTION The design of new bridges and scour risk evaluation of existing bridges can
MAGNETOHYDRODYNAMIC AND THERMAL ISSUES OF THE SiCf0SiC FLOW CHANNEL INSERT
Abdou, Mohamed
) made of a silicon carbide composite (SiCf /SiC), which serves as electric and thermal insulator considered. The computa- tions were performed in a parametric form, using the electric and thermal. INTRODUCTION Flow channel inserts ~FCIs! made of a silicon car- bide composite ~SiCf 0SiC! were first proposed
A finite element model of the turbulent flow field in a centrifugal impeller
Hlavaty, Steven Todd
1993-01-01T23:59:59.000Z
, or for applications such as pumps utilizing a liquid as the working medium. Full ellipticity of the flow- governing equations throughout the computational domain is rigorously retained. As a result, the model is conceptually capable of predicting real-flow effects... such as flow separation and recirculation, regardless of whether such complex flow behavior is local or massive. Applicability of the model is illustrated using a typical pump impeller of the purely centrifugal type. In presenting the computed flow field...
Modelling the convective flow in solar thermal receivers K.C. Yeh; G. Hughes & K. Lovegrove
value energy conversions such as heat engine cycles or chemical process to be carried outModelling the convective flow in solar thermal receivers K.C. Yeh; G. Hughes & K. Lovegrove, Canberra AUSTRALIA E-mail: u3370739@anu.edu.au The natural convective flow inside a concentrating solar
The mathematical structure of multiphase thermal models of flow in porous media
- tions, Darcy's law for volumetric flow rates and an energy equation in terms of enthalpy. The model with the formulation and numerical solution of equations for modelling multicomponent, two-phase, thermal fluid flow is closed with an equation of state and phase equilibrium con- ditions that determine the distribution
A thermodynamical formulation for chemically active multi-phase turbulent flows
Ahmadi, G.; Cao, J.
1995-03-01T23:59:59.000Z
A generalized thermodynamics for chemically active multiphase solid-fluid mixtures in turbulent state of motion is formulated. The global equations of balance for each phase are ensemble averaged and the local conservation laws for the mean motions are derived. The averaged and the local conservation laws for the mean motions are derived. The averaged form of the Clausius-Duhem inequality is used and the thermodynamics of the chemically active mixtures in turbulent motion is studied. Particular attention is given to the species concentration and chemical reaction effects, in addition to transport and interaction of the phasic fluctuation energies. Based on the averaged entropy inequality, constitutive equations for the stresses, energy, heat and mass fluxes of various species are developed. The explicit governing equations of motion are derived and discussed.
Convex-Based Thermal Management for 3D MPSoCs Using DVFS and Variable-Flow Liquid Cooling
De Micheli, Giovanni
management using variable-flow liquid cooling. 1 Introduction Power and thermal management are important] is a thermal model tool that calculates transient temperature response given the physical and power consumptionConvex-Based Thermal Management for 3D MPSoCs Using DVFS and Variable-Flow Liquid Cooling Francesco
Paris-Sud XI, Université de
of diffusive fluxes. Numerical results on an example of real-life thermal oil-recovery in a reservoir refinement, compositional Darcy flow, thermal flow, finite volume method 1 Introduction The thermal under a non-isothermal condition. The governing equations are the conservation of the amount of each
Zevenhoven, Ron
10.2.2013Åbo Akademi Univ - Thermal and Flow Engineering Piispankatu 8, 20500 Turku 1 University Thermal and Flow Engineering Laboratory / Värme- och strömningsteknik tel. 3223 ; ron.zevenhoven@abo.fi Process EngineeringThermodynamics course # 424304.0 v. 2013 ÅA 424304 10.2.2013Åbo Akademi Univ - Thermal
Thermal boundary layer development in dispersed flow film boiling
Hull, Lawrence M.
1982-01-01T23:59:59.000Z
Dispersed flow film boiling consists of a dispersion of droplets which are carried over a very hot surface by their vapor. This process occurs in cryogenic equipment and wet steam turbines. It is also of interest in the ...
Imaging Fluid Flow in Geothermal Wells Using Distributed Thermal Perturbation Sensing
Freifeld, B.; Finsterle, S.
2010-12-10T23:59:59.000Z
The objective of Task 2 is to develop a numerical method for the efficient and accurate analysis of distributed thermal perturbation sensing (DTPS) data for (1) imaging flow profiles and (2) in situ determination of thermal conductivities and heat fluxes. Numerical forward and inverse modeling is employed to: (1) Examine heat and fluid flow processes near a geothermal well under heating and cooling conditions; (2) Demonstrate ability to interpret DTPS thermal profiles with acceptable estimation uncertainty using inverse modeling of synthetic temperature data; and (3) Develop template model and analysis procedure for the inversion of temperature data collected during a thermal perturbation test using fiber-optic distributed temperature sensors. This status report summarizes initial model developments and analyses.
Elperin, Tov
, cyclone dust separation, abrasive water-jet cutting and in turbulent com- bustion see, e.g., Refs. 1
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.
Department of Chemical Engineering Thermal and Flow Engineering Laboratory
Zevenhoven, Ron
: continuous distillation, packed tower columns 7.5 Particle technology, multi-phase flows 8. Short introductions to process equipment and design; biotechnology; process dynamics and control 8.1 Process equipment and design 8.2 Biotechnology 8.3 Process dynamics and control Note: Chapter 7 and 8 are not part of the exam
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
Luo, Xian
We have developed fast numerical algorithms [1] for flows with complex moving domains, e.g. propellers in free-space and impellers in waterjets, by combining the smoothed profile method (SPM, [2, 3, 4]) with the spectral ...
Turbulence suppression in channel flows by small amplitude transverse wall oscillations
Jovanovic, Mihailo
and experimental investigations in channel,24 pipe,57 and boundary layer811 flows. In this paper, we model oscillatory wall motion or an oscillatory spanwise body force showed that a substantial drag reduction up
Kosuga, Yusuke
2012-01-01T23:59:59.000Z
entropy production via heat input. Comparison of the resultsis ultimately set by heat input, it seems that we can viewconverted flow. In Venus, heat input from the Sun drives
Yu, W.; France, D. M.; Timofeeva, E. V.; Singh, D.; Routbort, J. L. (Energy Systems); ( NE)
2010-01-01T23:59:59.000Z
Heat transfer enhancement criteria for nanofluids over their base fluids are presented based on three separate considerations: Reynolds number, flow velocity, and pumping power. Analyses presented show that, among the three comparisons, the constant pumping power comparison is the most unambiguous; the constant flow velocity comparison can be quite reasonable under certain conditions but the constant Reynolds number comparison (the most commonly used in the engineering literature for nanofluids) distorts the physical situation, and therefore, should not be used
Flow distribution analysis on the cooling tube network of ITER thermal shield
Nam, Kwanwoo; Chung, Wooho; Noh, Chang Hyun; Kang, Dong Kwon; Kang, Kyoung-O; Ahn, Hee Jae; Lee, Hyeon Gon [ITER Korea, National Fusion Research Institute, Daejeon 305-333 (Korea, Republic of)
2014-01-29T23:59:59.000Z
Thermal shield (TS) is to be installed between the vacuum vessel or the cryostat and the magnets in ITER tokamak to reduce the thermal radiation load to the magnets operating at 4.2K. The TS is cooled by pressurized helium gas at the inlet temperature of 80K. The cooling tube is welded on the TS panel surface and the composed flow network of the TS cooling tubes is complex. The flow rate in each panel should be matched to the thermal design value for effective radiation shielding. This paper presents one dimensional analysis on the flow distribution of cooling tube network for the ITER TS. The hydraulic cooling tube network is modeled by an electrical analogy. Only the cooling tube on the TS surface and its connecting pipe from the manifold are considered in the analysis model. Considering the frictional factor and the local loss in the cooling tube, the hydraulic resistance is expressed as a linear function with respect to mass flow rate. Sub-circuits in the TS are analyzed separately because each circuit is controlled by its own control valve independently. It is found that flow rates in some panels are insufficient compared with the design values. In order to improve the flow distribution, two kinds of design modifications are proposed. The first one is to connect the tubes of the adjacent panels. This will increase the resistance of the tube on the panel where the flow rate is excessive. The other design suggestion is that an orifice is installed at the exit of tube routing where the flow rate is to be reduced. The analysis for the design suggestions shows that the flow mal-distribution is improved significantly.
Turbulent models of ice giant internal dynamics: Dynamos, heat transfer, and zonal flows
, atmospheric circulation patterns, and thermal emissions that are distinct from other planets in our Solar additional constraints and suggest that these plan- ets may be modeled as three nested regions: (i) an outermost molecular envelope largely composed of hydrogen and helium; (ii) a weakly conducting ionic ocean
High Accuracy Numerical Methods for Thermally Perfect Gas Flows with Chemistry
Soatto, Stefano
High Accuracy Numerical Methods for Thermally Perfect Gas Flows with Chemistry Ronald P. Fedkiw with calculations of a 1-D reacting shock tube and a 2-D combustor. 2 #12; 1 Introduction Chemically reacting, high or the incineration of waste in a dump combustor. The combination of energetic chemical reactions and compressible gas
Probabilistic Velocity Estimation for Autonomous Miniature Airships using Thermal Air Flow Sensors
Teschner, Matthias
Probabilistic Velocity Estimation for Autonomous Miniature Airships using Thermal Air Flow Sensors J¨org M¨uller Oliver Paul Wolfram Burgard Abstract-- Recently, autonomous miniature airships have be- come a growing research field. Whereas airships are attractive as they can move freely in the three
Three-dimensional turbulent swirling flow in a cylinder: Experiments and computations
Gupta, Amit
is cycloning, where particles are separated from a fluid owing to centrifugal forces imparted by a swirling axial. But a few cylin- drical cyclones of the type described here have been used to separate liquid Abstract Dynamics of the three-dimensional flow in a cyclone with tangential inlet and tangential exit were
Direct numerical simulation of a reacting turbulent channel flow with thermo-chemical ablation
Nicoud, Franck
species; 2) pyrolysis of the composite material resin (series of chemical reactions arising and multicompo- nent physics, multi-phase flow dynamics, thermo-structural mechanics of composite materials attack. Graphite and carbon-carbon composites are widely used because they offer excellent thermo
A phenomenological model to describe turbulent friction in permeable-wall flows
Katul, Gabriel
the description of bulk flow over rough surfaces employ the so- called Darcy-Weisbach equation, a phenomenological-Re relation in the mid 1940s that enabled wide-usage of the Darcy-Weisbach equation first in hydraulic- and area-averaged velocity V via a so-called friction factor f. The Darcy-Weisbach equa- tion, named after
European Research Community On Flow Turbulence And Combustion ERCOFTAC Bulletin 30 45
Gui, Lichuan
systems. Reported examples of applications include the measurements of droplets in a spray jet [1], bubbles in water flow [2], cavitation bubbles [3], solid particles in a mixing tank [4]. Such experiments require a sufficiently high degree of transparency of the multiphase system in order to allow illumination
Falkovich, Gregory
. Punzmann Plasma Research Laboratory, Research School of Physical Sciences and Engineering, Australian in magnetized plasma research, since it offers a very effective method of turbulence control [13
Thermal/chemical degradation of ceramic cross-flow filter materials
Alvin, M.A.; Lane, J.E.; Lippert, T.E.
1989-11-01T23:59:59.000Z
This report summarizes the 14-month, Phase 1 effort conducted by Westinghouse on the Thermal/Chemical Degradation of Ceramic Cross-Flow Filter Materials program. In Phase 1 expected filter process conditions were identified for a fixed-bed, fluid-bed, and entrained-bed gasification, direct coal fired turbine, and pressurized fluidized-bed combustion system. Ceramic cross-flow filter materials were also selected, procured, and subjected to chemical and physical characterization. The stability of each of the ceramic cross-flow materials was assessed in terms of potential reactions or phase change as a result of process temperature, and effluent gas compositions containing alkali and fines. In addition chemical and physical characterization was conducted on cross-flow filters that were exposed to the METC fluid-bed gasifier and the New York University pressurized fluidized-bed combustor. Long-term high temperature degradation mechanisms were proposed for each ceramic cross-flow material at process operating conditions. An experimental bench-scale test program is recommended to be conducted in Phase 2, generating data that support the proposed cross-flow filter material thermal/chemical degradation mechanisms. Papers on the individual subtasks have been processed separately for inclusion on the data base.
Popov, Pavel P., E-mail: ppopov@uci.edu; Pope, Stephen B.
2014-01-15T23:59:59.000Z
This work addresses the issue of particle mass consistency in Large Eddy Simulation/Probability Density Function (LES/PDF) methods for turbulent reactive flows. Numerical schemes for the implicit and explicit enforcement of particle mass consistency (PMC) are introduced, and their performance is examined in a representative LES/PDF application, namely the Sandia–Sydney Bluff-Body flame HM1. A new combination of interpolation schemes for velocity and scalar fields is found to better satisfy PMC than multilinear and fourth-order Lagrangian interpolation. A second-order accurate time-stepping scheme for stochastic differential equations (SDE) is found to improve PMC relative to Euler time stepping, which is the first time that a second-order scheme is found to be beneficial, when compared to a first-order scheme, in an LES/PDF application. An explicit corrective velocity scheme for PMC enforcement is introduced, and its parameters optimized to enforce a specified PMC criterion with minimal corrective velocity magnitudes.
Kinetic Theory of Turbulent Multiphase Phase | The Ames Laboratory
Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)
solids particles interacting with a turbulent gas phase such as those in gasification rectors. Understanding the transport of heat and mass in turbulent flows, and...
Zevenhoven, Ron
23.11.2014Åbo Akademi Univ - Thermal and Flow Engineering Piispankatu 8, 20500 Turku 1/36 7. Air conditioning, cooling towers Ron Zevenhoven Åbo Akademi University Thermal and Flow Engineering Laboratory Engineering Piispankatu 8, 20500 Turku 2/36 7.1 Humid air #12;23.11.2014 Åbo Akademi Univ - Thermal and Flow
Elliptic flow of thermal dileptons as a probe of QCD matter
Payal Mohanty; Victor Roy; Sabyasachi Ghosh; Santosh K. Das; Bedangadas Mohanty; Sourav Sarkar; Jane Alam; Asis K. Chaudhuri
2012-03-13T23:59:59.000Z
We study the variation of elliptic flow of thermal dileptons with transverse momentum and invariant mass of the pairs for Pb+Pb collisions at $\\sqrt{s_{NN}}$ = 2.76 TeV. The dilepton productions from quark gluon plasma (QGP) and hot hadrons have been considered including the spectral change of light vector mesons in the thermal bath. The space time evolution has been carried out within the frame work of 2+1 dimensional ideal hydrodynamics with lattice+hadron resonance gas equation of state. We find that a judicious selection of invariant mass(M) and transverse momentum (p_T) windows can be used to extract the collective properties of quark matter, hadronic matter and also get a distinct signature of medium effects on vector mesons. Our results indicate a reduction of elliptic flow (v_2) for M beyond phi mass, which if observed experimentally would give the measure of v_2 of the partonic phase.
Thermal and Flow Engineering Laboratory course 424512 E Ron Zevenhoven c.s.
Zevenhoven, Ron
of as it is transported across the cell boundaries "e" and "w", using xxdx d axax )()( The grid to be used. For the heat conductivity, use k = 2 W/(m.K). Questions 5 and 6 after J. Brännbacka (2005, 2006). In exam 2008CFD2013 P 32 1 x 15°C 0°C 47°C x WW W P E EE w e x x #12;Thermal and Flow Engineering Laboratory course
A Generic Model for the Resuspension of Multilayer Aerosol Deposits by Turbulent Flow
Friess, H.; Yadigaroglu, G. [Swiss Federal Institute of Technology (Switzerland)
2001-06-15T23:59:59.000Z
An idealized lattice structure is considered of multilayer aerosol deposits, where every particle at the deposit surface is associated with a resuspension rate constant depending on a statistically distributed particle parameter and on flow conditions. The response of this generic model is represented by a set of integrodifferential equations. As a first application of the general formalism, the behavior of Fromentin's multilayer model is analyzed, and the model parameters are adapted to experimental data. In addition, improved relations between model parameters and physical input parameters are proposed. As a second application, a method is proposed for building multilayer models by using resuspension rate constants of existing monolayer models. The method is illustrated by a sample of monolayer data resulting from the model of Reeks, Reed, and Hall. Also discussed is the error to be expected if a monolayer resuspension model, which works well for thin aerosol deposits, is applied to thick deposits under the classical monolayer assumption that all deposited particles interact with the fluid at all times.
Estrada Perez, Carlos Eduardo
2014-12-12T23:59:59.000Z
In this work, visualization experimental techniques that provide whole-field and multi-scale measurements of the liquid turbulence parameters, liquid and heater wall temperatures, and gas phase local parameters, were used to study subcooled boiling...
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)
Marco Ruggieri; Francesco Scardina; Salvatore Plumari; Vincenzo Greco
2014-07-09T23:59:59.000Z
In this article we report on our results about the computation of the elliptic flow of the quark-gluon-plasma produced in relativistic heavy ion collisions, simulating the expansion of the fireball by solving the relativistic Boltzmann equation for the parton distribution function tuned at a fixed shear viscosity to entropy density ratio $\\eta/s$. Our main goal is to put emphasis on the role of a saturation scale in the initial gluon spectrum, which makes the initial distribution far from a thermalized one. We find that the presence of the saturation scale reduces the efficiency in building-up the elliptic flow, even if the thermalization process is quite fast $\\tau_{therm} \\approx 0.8 \\,\\rm fm/c$ and the pressure isotropization even faster $\\tau_{isotr} \\approx 0.3 \\,\\rm fm/c$. The impact of the non-equilibrium implied by the saturation scale manifests for non-central collisions and can modify the estimate of the viscosity respect to the assumption of full thermalization in $p_T$-space. We find that the estimate of $\\eta/s$ is modified from $\\eta/s \\approx 2/4\\pi$ to $\\eta/s \\approx 1/4\\pi$ at RHIC and from $\\eta/s \\approx 3/4\\pi$ to $\\eta/s \\approx 2/4\\pi$ at LHC. We complete our investigation by a study of the thermalization and isotropization times of the fireball for different initial conditions and values of $\\eta/s$ showing how the latter affects both isotropization and thermalization. Lastly, we have seen that the range of values explored by the phase-space distribution function $f$ is such that at $p_T<0.5\\, \\rm GeV$ the inner part of the fireball stays with occupation number significantly larger than unity despite the fast longitudinal expansion, which might suggest the possibility of the formation of a transient Bose-Einstein Condensate.
Islam, Obaidul
1963-01-01T23:59:59.000Z
THE DETERMINATION OF THE TURBULENT INTENSITIES IN A TRANSITIONAL FLOW FROM A SMOOTH TO A ROUGH WALL WITH ZERO PRESSURE GRADIENT IN A TWO-DIMENSIONAL CHANNEL A Thesis By Ol3AIDU I. ISLAM Submitted to the Graduate School of. tire Agricultural... WALL WITH ZERO PRESSURE GRADIENT IN A TWO DIMENSIONAL. GHANNEL A Thesis By OBAIDUL ISLAM Approved as to style and content by: F / F Ghairma p'f mm tg Head of Department May 1963 ACKNOWLEDGMENTS Grateful acknowledgment is made to the Texas...
Thermal characteristics of air flow cooling in the lithium ion batteries experimental chamber
Lukhanin A.; Rohatgi U.; Belyaev, A.; Fedorchenko, D.; Khazhmuradov, M.; Lukhanin, O; Rudychev, I.
2012-07-08T23:59:59.000Z
A battery pack prototype has been designed and built to evaluate various air cooling concepts for the thermal management of Li-ion batteries. The heat generation from the Li-Ion batteries was simulated with electrical heat generation devices with the same dimensions as the Li-Ion battery (200 mm x 150 mm x 12 mm). Each battery simulator generates up to 15W of heat. There are 20 temperature probes placed uniformly on the surface of the battery simulator, which can measure temperatures in the range from -40 C to +120 C. The prototype for the pack has up to 100 battery simulators and temperature probes are recorder using a PC based DAQ system. We can measure the average surface temperature of the simulator, temperature distribution on each surface and temperature distributions in the pack. The pack which holds the battery simulators is built as a crate, with adjustable gap (varies from 2mm to 5mm) between the simulators for air flow channel studies. The total system flow rate and the inlet flow temperature are controlled during the test. The cooling channel with various heat transfer enhancing devices can be installed between the simulators to investigate the cooling performance. The prototype was designed to configure the number of cooling channels from one to hundred Li-ion battery simulators. The pack is thermally isolated which prevents heat transfer from the pack to the surroundings. The flow device can provide the air flow rate in the gap of up to 5m/s velocity and air temperature in the range from -30 C to +50 C. Test results are compared with computational modeling of the test configurations. The present test set up will be used for future tests for developing and validating new cooling concepts such as surface conditions or heat pipes.
Dahm, W.J.A.; Tryggvason, G.; Krasny, R.
1992-09-30T23:59:59.000Z
The report describes progress made in the past twelve months in developing a local integral method (LIM) model for numerically simulating natural gas mixing and combustion in complex flames. The LIM model is fundamentally different from conventional approaches for numerically simulating combustion in turbulent flames. It is based on the experimental observation that the strain-diffusion balance which establishes the mixing and reaction scales in turbulent flames leads to a self-similar internal structure in the diffusion-reaction layers which does not need to be continually re-computed. Instead, these diffusion and reaction scales are represented by a set of self-similar profile shapes whose moments are allowed to evolve freely to satisfy the governing equations. The resulting LIM computations thus need only follow the evolution of material surface in the flow, and then solve ODE's (ordinary differential equations) on the surface, rather than PDE's (partial differential equations) throughout the whole flame. Results obtained to date show that the model is capable of correctly predicting even highly sensitive non-linear characteristics associated with the combustion processes in turbulent natural gas flames, including the local flame extinction phenomenon in large Zeldovich number Arrhenius kinetics. The simplicity of the LIM technique allows large reductions in computational time in comparison with traditional computational approaches, thus allowing far more complex reaction chemistry to be addressed, as well as ranges of Reynolds, Schmidt and Damkohler numbers which are otherwise completely inaccessible to simulation.
Evidence for radial flow of thermal dileptons in high-energy nuclear collisions
NA60 Collaboration; R. Arnaldi
2007-11-12T23:59:59.000Z
The NA60 experiment at the CERN SPS has studied low-mass dimuon production in 158 AGeV In-In collisions. An excess of pairs above the known meson decays has been reported before. We now present precision results on the associated transverse momentum spectra. The slope parameter Teff extracted from the spectra rises with dimuon mass up to the rho, followed by a sudden decline above. While the initial rise is consistent with the expectations for radial flow of a hadronic decay source, the decline signals a transition to an emission source with much smaller flow. This may well represent the first direct evidence for thermal radiation of partonic origin in nuclear collisions.
Fully coupled thermal-mechanical-fluid flow model for nonliner geologic systems
Hart, R.D.
1981-01-01T23:59:59.000Z
A single model is presented which describes fully coupled thermal-mechanical-fluid flow behavior of highly nonlinear, dynamic or quasistatic, porous geologic systems. The mathematical formulation for the model utilizes the continuum theory of mixtures to describe the multiphase nature of the system, and incremental linear constitutive theory to describe the path dependency of nonlinear material behavior. The model, incorporated in an explicit finite difference numerical procedure, was implemented in two different computer codes. A special-purpose one-dimensional code, SNEAKY, was written for initial validation of the coupling mechanisms and testing of the coupled model logic. A general purpose commercially available code, STEALTH, developed for modeling dynamic nonlinear thermomechanical processes, was modified to include fluid flow behavior and the coupling constitutive model. The fully explicit approach in the coupled calculation facilitated the inclusion of the coupling mechanisms and complex constitutive behavior. Analytical solutions pertaining to consolidation theory for soils, thermoelasticity for solids, and hydrothermal convection theory provided verification of stress and fluid flow, stress and conductive heat transfer, and heat transfer and fluid flow couplings, respectively, in the coupled model. A limited validation of the adequacy of the coupling constitutive assumptions was also performed by comparison with the physical response from two laboratory tests. Finally, the full potential of the coupled model is illustrated for geotechnical applications in energy-resource related areas. Examples in the areas of nuclear waste isolation and cut-and-fill mining are cited.
Chakraborty Thakur, S.; Fedorczak, N.; Manz, P.; Tynan, G. R.; Xu, M. [Center for Momentum Transport and Flow Organization, University of California at San Diego, San Diego, California 92093 (United States); Center for Energy Research, University of California at San Diego, San Diego, California 92093 (United States); McCarren, D.; Scime, E. E. [Department of Physics, West Virginia University, Morgantown, West Virginia 26506 (United States); Lee, T. [Center for Energy Research, University of California at San Diego, San Diego, California 92093 (United States)
2012-08-15T23:59:59.000Z
Using laser induced fluorescence (LIF), radial profiles of azimuthal ion fluid velocity and ion temperature are measured in the controlled shear de-correlation experiment (CSDX) linear helicon plasma device. Ion velocities and temperatures are derived from the measured Doppler broadened velocity distribution functions of argon ions. The LIF system employs a portable, high power (>300 mW), narrowband ({approx}1 MHz) tunable diode laser-based system operating at 668.614 nm. Previous studies in CSDX have shown the existence of a radially sheared azimuthal flow as measured with time delay estimation methods and Mach probes. Here, we report the first LIF measurements of sheared plasma fluid flow in CSDX. Above a critical magnetic field, the ion fluid flow profile evolves from radially uniform to peaked on axis with a distinct reversed flow region at the boundary, indicating the development of a sheared azimuthal flow. Simultaneously, the ion temperature also evolves from a radially uniform profile to a profile with a gradient. Measurements in turbulent and coherent drift wave mode dominated plasmas are compared.
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.
Forcing-type-dependent stability of steady states in a turbulent swirling flow B. Saint-Michel,1,
Brest, Université de
states and reveal dynamical regimes that bear similarities with low-dimensional systems. We suggest statistical systems, and that it may be applicable to other turbulent systems. PACS numbers: 47.20.Ky, 05 of systems such as 2D Euler equations [3, 4], Blume-Emery-Griffiths model [5], and random graphs [6]. More
Lin, Zhihong
coupling, the same back-action process can deform the spectral distribution in inertia range from the powerTH/2-31 Simulations on the Nonlinear Mode Coupling in Multiple-scale Drift-type Turbulence@energy.kyoto-u.ac.jp Abstract: The dynamics of secondary, anisotropic coherent structures behaving as a stationary wave
Kim, John
A numerical study of the effects of superhydrophobic surface on skin- friction drag in turbulent;PHYSICS OF FLUIDS 25, 110815 (2013) A numerical study of the effects of superhydrophobic surface on skin; accepted 21 May 2013; published online 11 September 2013) Superhydrophobic surfaces have attracted much
Abdou, Mohamed
sufficiently large heat transfer using high Prandtl number fluid coolant, high turbulence is required, and the heat transfer characteristics of low Prandtl number fluids are con heat transfer (low film temperature drop) to cool first wall structures. In order to obtain
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
Zevenhoven, Ron
.iea.org/publications/freepublications/publication/Solar_Heating_Cooling_Road map_2012_WEB.pdf 3.12.2014 Åbo Akademi Univ - Thermal and Flow Engineering - Piispankatu 8, 20500.iea.org/publications/freepublications/publication/Solar_Heating_Cooling_Road map_2012_WEB.pdf #12;3.12.2014Åbo Akademi Univ - Thermal and Flow Engineering - Piispankatu 8, 20500.12.2014Åbo Akademi Univ - Thermal and Flow Engineering - Piispankatu 8, 20500 Turku 8/56 http://www.brighton-webs
Turbulent Transition in an Electromagnetically Levitated Droplet
Mountziaris, T. J.
Turbulent Transition in an Electromagnetically Levitated Droplet Christina R. Rizer, Robert W a marked transition from laminar to turbulent flow, which can be observed by following the movement, will oscillate and break apart, marking the transition to turbulence. Using videos taken of these metal samples
Watt, J. B.; Haberl, J. S.
the premature drop-out of magnetic-type tangential paddlewheel sensors, as well as several in-situ diagnostic measures for ascertaining whether or not a flow meter is experiencing turbulent conditions or if a flow sensor's output signal is suffering a degraded... per second for magnetic-type, and 0.5 to 2 feet per second for non-magnetic-type flow sensors deviated from the actual flow by 20% or more which makes the measurement of flow and thermal energy use in this regime highly suspect. Figure 4 also indicates...
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.
A STUDY OF ATES THERMAL BEHAVIOR USING A STEADY FLOW MODEL
Doughty, Christine
2013-01-01T23:59:59.000Z
and Warman, J.c. , "Thermal energy storage in a confinedProceedings of Thermal Energy Storage in Aquifers Workshop,c.F. , ~Aquifer thermal energy storage- parameter study,~
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.
A one-way coupled, EulerLagrangian simulation of bubble coalescence in a turbulent pipe flow
Mahesh, Krishnan
modifies the speed of sound in the bubbly mixture, which has implications for marine acoustic signatures. GasÂliquid flow at microgravity conditions Â I. Dispersed bubble and slug flow. Int. J. Multiphase- ical in many heat transfer problems where liquid water contacting a hot surface boils and the resulting
Cumulant expansions for atmospheric flows
Ait-Chaalal, Farid; Meyer, Bettina; Marston, J B
2015-01-01T23:59:59.000Z
The equations governing atmospheric flows are nonlinear, and consequently the hierarchy of cumulant equations is not closed. But because atmospheric flows are inhomogeneous and anisotropic, the nonlinearity may manifests itself only weakly through interactions of mean fields with disturbances such as thermals or eddies. In such situations, truncations of the hierarchy of cumulant equations hold promise as a closure strategy. We review how truncations at second order can be used to model and elucidate the dynamics of turbulent atmospheric flows. Two examples are considered. First, we study the growth of a dry convective boundary layer, which is heated from below, leading to turbulent upward energy transport and growth of the boundary layer. We demonstrate that a quasilinear truncation of the equations of motion, in which interactions of disturbances among each other are neglected but interactions with mean fields are taken into account, can successfully capture the growth of the convective boundary layer. Seco...
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 fluid dynamics can...
Abdou, Mohamed
magnetohydrodynamic flows in a vertical rectangular duct N. Vetcha, S. Smolentsev, M. Abdou, and R. Moreau Citation in a vertical rectangular duct N. Vetcha,1 S. Smolentsev,1,a) M. Abdou,1 and R. Moreau2 1 Mechanical
Zonal flow excitation by drift waves in toroidal plasmas
L Chen; Z. Lin; R. White
2000-06-13T23:59:59.000Z
Recent 3D gyrokinetic and gyrofluid simulations in toroidal plasmas have demonstrated that zonal flows play a crucial role in regulating the nonlinear evolution of electrostatic drift-wave instabilities such as the ion temperature gradient (ITG) modes and, as a consequence, the level of the anomalous ion thermal transport, and that zonal flows could be spontaneously excited by ITG turbulence, suggesting parametric instability processes as the generation mechanism. Diamond et. al. have proposed the modulational instability of drift-wave turbulence ( plasmons ) in a slab-geometry treatment.
Ko, Hanseo
1994-01-01T23:59:59.000Z
diameter for Re = 5, 000, 10, 000, and 20, 000. 15 Figure 3 Figure 4. Comparison of different roughness factors (e, = 0, 0. 1, 1. 0, and 10 mm) for dimensionless deposition velocity. Correlation of dimensionless deposition velocity and dimensionless... time for flow rate = 57 I/min, Re = 5, 000, and tube diameter = 15. 8 mm. 17 19 Figure 5. Correlation of dimensionless deposition velocity including electric migration velocity ( Vz = 0. 01, 0. 05, and 0. 1 mm/s) and dimensionless time for flow...
Lakshmipathy, Sunil
2010-07-14T23:59:59.000Z
in various wall bounded flows. The road map towards our goal includes: (i) Comparing a-priori and a-posteriori eddy viscosity values to establish whether PANS is capable of producing the pre-specified level of reduction. (ii) Investigating the scaling of PANS...
Anh Bui; Nam Dinh; Brian Williams
2013-09-01T23:59:59.000Z
In addition to validation data plan, development of advanced techniques for calibration and validation of complex multiscale, multiphysics nuclear reactor simulation codes are a main objective of the CASL VUQ plan. Advanced modeling of LWR systems normally involves a range of physico-chemical models describing multiple interacting phenomena, such as thermal hydraulics, reactor physics, coolant chemistry, etc., which occur over a wide range of spatial and temporal scales. To a large extent, the accuracy of (and uncertainty in) overall model predictions is determined by the correctness of various sub-models, which are not conservation-laws based, but empirically derived from measurement data. Such sub-models normally require extensive calibration before the models can be applied to analysis of real reactor problems. This work demonstrates a case study of calibration of a common model of subcooled flow boiling, which is an important multiscale, multiphysics phenomenon in LWR thermal hydraulics. The calibration process is based on a new strategy of model-data integration, in which, all sub-models are simultaneously analyzed and calibrated using multiple sets of data of different types. Specifically, both data on large-scale distributions of void fraction and fluid temperature and data on small-scale physics of wall evaporation were simultaneously used in this work’s calibration. In a departure from traditional (or common-sense) practice of tuning/calibrating complex models, a modern calibration technique based on statistical modeling and Bayesian inference was employed, which allowed simultaneous calibration of multiple sub-models (and related parameters) using different datasets. Quality of data (relevancy, scalability, and uncertainty) could be taken into consideration in the calibration process. This work presents a step forward in the development and realization of the “CIPS Validation Data Plan” at the Consortium for Advanced Simulation of LWRs to enable quantitative assessment of the CASL modeling of Crud-Induced Power Shift (CIPS) phenomenon, in particular, and the CASL advanced predictive capabilities, in general. This report is prepared for the Department of Energy’s Consortium for Advanced Simulation of LWRs program’s VUQ Focus Area.
S. S. Zilitinkevich; T. Elperin; N. Kleeorin; I. Rogachevskii
2007-02-19T23:59:59.000Z
We propose a new turbulence closure model based on the budget equations for the key second moments: turbulent kinetic and potential energies: TKE and TPE (comprising the turbulent total energy: TTE = TKE + TPE) and vertical turbulent fluxes of momentum and buoyancy (proportional to potential temperature). Besides the concept of TTE, we take into account the non-gradient correction to the traditional buoyancy flux formulation. The proposed model grants the existence of turbulence at any gradient Richardson number, Ri. Instead of its critical value separating - as usually assumed - the turbulent and the laminar regimes, it reveals a transition interval, 0.11. Predictions from this model are consistent with available data from atmospheric and lab experiments, direct numerical simulation (DNS) and large-eddy simulation (LES).
Marcos, Ph.D. Massachusetts Institute of Technology
2011-01-01T23:59:59.000Z
Bacteria are ubiquitous and play a critical role in many contexts. Their environment is nearly always dynamic due to the prevalence of fluid flow: creeping flow in soil, highly sheared flow in bodily conduits, and turbulent ...
Sahoo, Dipankar
2008-10-10T23:59:59.000Z
staff members, Karen Knabe, Andrea Loggins, and Colleen Leatherman for their help with official paper work which saved me a lot of time. I extend my gratitude to all employees at the Oran W Nicks Low Speed Wind Tunnel for their valuable assistance... ..................................................... 31 4.1 Oran Nicks Low-Speed Wind Tunnel .................................................. 31 4.1.1 The DSF Inserts ..................................................................... 32 4.1.2 Tunnel Flow...
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.
Carper, Herbert Jackson
1962-01-01T23:59:59.000Z
A STUDY OF THE TURBULENT INTENSITIES AND CORRELATION COEFFICIENTS IN THE INCOMPRESSIBLE FLOW OF AIR IN TRANSITION FROM A SMOOTH TO A ROUGH WALL IN A TWO-DIMENSIONAL CHANNEL A Thesis By HERBERT JACKSON CARPER JR. Submitted to the Graduate... COEFFICIENTS IN THE INCOMPRESSIBLE FLOW OF AIR IN TRANSITION FROM A SMOOTH TO A ROUGH WALL IN A TWO-DIMENSIONAL CHANNEL A Thesis By HERBERT JACKSON CARPER JR. Approved as to style and content by: (Chairm of o e) (Head of Department) August 1962 853958...
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...
Zevenhoven, Ron
. Vapour-compression refrigeration processes Ron Zevenhoven Åbo Akademi University Thermal and Flow") Refrigeration course # 424503.0 v. 2014 ÅA 424503 Refrigeration / Kylteknik 9.11.2014Åbo Akademi Univ - Thermal of a refrigerant fluid Picture: ÇB98 liquid-vapour saturation dome 1-2 and 3-4: reversible and isothermal 2-3 and 4
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.
Zevenhoven, Ron
. Refrigeration process comparison; process equipment Ron Zevenhoven Åbo Akademi University Themal and Flow") Refrigeration course # 424503.0 v. 2014 ÅA 424503 Refrigeration / Kylteknik 12.11.2014Åbo Akademi Univ - Thermal and Flow Engineering Piispankatu 8, 20500 Turku 2/32 4.1 Refrigeration process comparison #12;12.11.2014Åbo
Boo, Jin-Hyo
Characteristics of Thermal-Flow Fields in a PECVD Reactor with Various Operating Conditions Jae-Sang Baek and Youn be influenced by the reactor geometry, the thermo-flow conditions, and the operation procedure. In this study, the effects of various operating conditions and the shapes of the PECVD reactor are considered to elucidate
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
Cyclone separator having boundary layer turbulence control
Krishna, Coimbatore R. (Mt. Sinai, NY); Milau, Julius S. (Port Jefferson, NY)
1985-01-01T23:59:59.000Z
A cyclone separator including boundary layer turbulence control that is operable to prevent undue build-up of particulate material at selected critical areas on the separator walls, by selectively varying the fluid pressure at those areas to maintain the momentum of the vortex, thereby preventing particulate material from inducing turbulence in the boundary layer of the vortical fluid flow through the separator.
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
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
Turbulence and turbulent mixing in natural fluids
Gibson, Carl H
2010-01-01T23:59:59.000Z
Turbulence and turbulent mixing in natural fluids begins with big bang turbulence powered by spinning combustible combinations of Planck particles and Planck antiparticles. Particle prograde accretion on a spinning pair releases 42% of the particle rest mass energy to produce more fuel for turbulent combustion. Negative viscosity and negative turbulence stresses work against gravity, creating mass-energy and space-time from the vacuum. Turbulence mixes cooling temperatures until a quark-gluon strong-force SF freeze-out. Gluon-viscosity anti-gravity ({\\Lambda}SF) exponentially inflates the fireball to preserve big bang turbulence information at scales larger than ct as the first fossil turbulence. Cosmic microwave background CMB temperature anisotropies show big bang turbulence fossils along with fossils of weak plasma turbulence triggered (10^12 s) as plasma viscous forces permit gravitational fragmentation on supercluster to galaxy mass scales (10^13 s). Turbulent morphologies and viscous-turbulent lengths a...
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.
Thermal non-equilibrium in dispersed flow film boiling in a vertical tube
Forslund, Robert Paul
1966-01-01T23:59:59.000Z
The departure from thermal equilibrium between a dispersed liquid phase and its vapor at high quality during film boiling is investigated, The departure from equilibruim is manifested by the high resistance to heat transfer ...
Lattice ellipsoidal statistical BGK model for thermal non-equilibrium flows
Meng, Jianping
A thermal lattice Boltzmann model is constructed on the basis of the ellipsoidal statistical Bhatnagar–Gross–Krook (ES-BGK) collision operator via the Hermite moment representation. The resulting lattice ES-BGK model uses ...
An analog analysis of transient heat flow in solids with temperature-dependent thermal properties
Lee, Dwain Edward
1964-01-01T23:59:59.000Z
they both are based on the same approximation of the thermal properties. Since these two methods of solution of the same problem produce almost the same results, the usefulness of the constant property analog method of solution must be found elsewhere... calculations. Therefore, it is concluded that the better the approximation of the variation of the thermal properties allowed by a method of solution, the more closely that method of solution will agree with the actual physical problem. In particular...
TURBULENT FRBRNNING MVK130 Turbulent Combustion
TURBULENT FÖRBRÄNNING MVK130 Turbulent Combustion Poäng: 3.0 Betygskala: TH Valfri för: M4 to combustion, McGraw-Hill 1996. #12;
Overview of the TurbSim Stochastic Inflow Turbulence Simulator
Kelley, N. D.; Jonkman, B. J.
2005-09-01T23:59:59.000Z
The TurbSim stochastic inflow turbulence code was developed to provide a numerical simulation of a full-field flow that contains coherent turbulence structures that reflect the proper spatiotemporal turbulent velocity field relationships seen in instabilities associated with nocturnal boundary layer flows that are not represented well by the IEC Normal Turbulence Models (NTM). Its purpose is to provide the wind turbine designer with the ability to drive design code (FAST or MSC.ADAMS) simulations of advanced turbine designs with simulated inflow turbulence environments that incorporate many of the important fluid dynamic features known to adversely affect turbine aeroelastic response and loading.
A STUDY OF ATES THERMAL BEHAVIOR USING A STEADY FLOW MODEL
Doughty, Christine
2013-01-01T23:59:59.000Z
Fluid Heat Storage Systems in the Ground. Extraction ofof the storage aquifer lies 40 m below the ground surface,water storage. The influence of regional ground water flow
Calculation of heat flow and temperature fields for building envelopes containing thermal bridges
Childs, K.W.
1988-01-01T23:59:59.000Z
In a preliminary meeting held at the Princeton University Center for Energy and Environmental Studies on March 14-15, 1988, Soviet and American representatives discussed these problems in some detail. After minor modifications, final problem definitions for six of the thermal bridges were generated. The seventh thermal bridge, originally submitted by the USSR, was withdrawn temporarily to add some further clarification. A common format for presenting the results was agreed upon, and both American and Soviet specialists subsequently solved the six problems. This paper presents the US solutions prepared at ORNL. 52 figs., 6 tabs.
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.
FLOW CONDITIONING DESIGN IN TURBULENT
/L) Â· Free surface = interface between fluorescing (bright) water and (dark) air Â· Image obliquely with B-Injection Fusion Energy) #12;3 Motivation Â· Effective protection Minimize clearance between edge of liquid sheet) at FWHM Â· Positioning controlled by two linear stages Â· Water seeded with TiO2 particles (typical dia. 0
Momentum and thermal boundary-layer thickness in a stagnation flow chemical vapor deposition reactor
Dandy, David
reactor David S. Dandy and Jungheum Yun Department of Chemical Engineering, Colorado State University stagnation flows characteristic of highly convective chemical vapor deposition pedestal reactors. Expressions of diamond via low- pressure chemical vapor deposition, direct current (dc) arcjet reactor systems38 have
Imaging Fluid Flow in Geothermal Wells Using Distributed Thermal Perturbation Sensing
Broader source: Energy.gov [DOE]
Project objective: A New Geothermal Well Imaging Tool. 1.To develop a robust and easily deployable DTPS for monitoring in geothermal wells; and 2. Develop the associated analysis methodology for flow imaging; and?when possible by wellbore conditions?to determine in situthermal conductivity and basal heat flux.
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.
A study of flow in stratified reservoirs by use of the thermal analogy
Pickering, Charles William
1960-01-01T23:59:59.000Z
. Uren discussed the possible significance of this nonuniformity in his f927 paper on the theoretical aspects of waterflooding, Since this time the problem of vertical permeability variations has been the subject of much discussion and numerous papers... calculations are steady-state flow conditions, unit znobility ratio, linear geometry, average or homogeneous porosity and negligible capillary pressure and gravity effects. 3 Stiles uses these assumptions to derive his waterflood equa- tions and keep...
Flow and Temperature Fields Generated by a Thermally Activated Interventional Vascular Device
McCurrin, Casey
2012-10-19T23:59:59.000Z
........................ 51 24 Zoom of Previous Image to Show Heating Effects ................................... 52 25 Comparisons between Analytical and CFD Annulus Profiles .................. 53 26 Temperature Field for Low Flow... by Sakakibara et al. [22] and Coolen et al. [23] in which the investigated temperature ranges were 40 K and 0.7 K, respectively. Two different CFD codes [24] for analyzing the case of a heated cylinder show qualitative agreement with experimental results from...
Dept. of Chemical Engineering Thermal and Flow Engineering Lab course 424508 E Ron Zevenhoven
Zevenhoven, Ron
temperature of 25 °C and that they have the same thermo-physical properties of = 0.15 W/m·K for heat a width W = 0.5 m (in the third, z direction), calculate the heat loss Q (in W) from this plate, if it has a length L = 1 m (in the x-direction) and assuming that the fluid is flowing around the plate
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
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.
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...
Two-dimensional AMR simulations of colliding flows
Niklaus, Markus; Niemeyer, Jens C
2009-01-01T23:59:59.000Z
Colliding flows are a commonly used scenario for the formation of molecular clouds in numerical simulations. Due to the thermal instability of the warm neutral medium, turbulence is produced by cooling. We carry out a two-dimensional numerical study of such colliding flows in order to test whether statistical properties inferred from adaptive mesh refinement (AMR) simulations are robust with respect to the applied refinement criteria. We compare probability density functions of various quantities as well as the clump statistics and fractal dimension of the density fields in AMR simulations to a static-grid simulation. The static grid with 2048^2 cells matches the resolution of the most refined subgrids in the AMR simulations. The density statistics is reproduced fairly well by AMR. Refinement criteria based on the cooling time or the turbulence intensity appear to be superior to the standard technique of refinement by overdensity. Nevertheless, substantial differences in the flow structure become apparent. In...
Zevenhoven, Ron
of low-temperature (waste) heat, replacing sources of (unnecessarily) high temperature heat (and, 3) outside water heat and 4) heat from another indoor space, or 5) waste heat from a process1.12.2014Åbo Akademi Univ - Thermal and Flow Engineering Piispankatu 8, 20500 Turku 1/24 8. Heat
Polymer dynamics in random flow with mean shear K. Turitsyn
Fominov, Yakov
Polymer dynamics in random flow with mean shear K. Turitsyn Landau Institute for theoretical;Outline · Motivation: Elastic turbulence · Experimental setup · Flow and polymer models · Results: 1. Angular statistics 2. Polymer elongation distribution · Conclusion #12;Elastic Turbulence Elastic
Flow and Transport in Regions with Aquatic Vegetation
Nepf, Heidi
This review describes mean and turbulent flow and mass transport in the presence of aquatic vegetation. Within emergent canopies, the turbulent length scales are set by the stem diameter and spacing, and the mean flow is ...
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
Propagating and stationary superfluid turbulent fronts
Castiglione, J.; Murphy, P.J.; Tough, J.T.; Hayot, F. [Ohio State Univ., Columbus, OH (United States)] [and others
1995-09-01T23:59:59.000Z
The authors have observed that the critical heat current for the transition to superfluid turbulence in weakly nonuniform circular channels depends strongly on the flow direction. This observation is particularly surprising since no other property of the turbulence appears to have such a dependence. In a nonuniform channel the critical heat current is associated with a stationary front between the laminar and turbulent flow. The authors propose a new model for super-fluid turbulent fronts which explains the asymmetry of the critical heat currents in a simple way. The model is based on the subcritical nature of the transition, and the generic description of such a bifurcation by the Ginzburg-Landau equation. As a bonus, the model also explains a long-standing problem in superfluid physics-the nature of propagating fronts in uniform channels. The results of this analysis of both the uniform and nonuniform channel data also provide new information about the vortex line drift velocity.
Turbulent Transport in Tokamak Plasmas with Rotational Shear
Barnes, M.; Highcock, E. G. [Rudolf Peierls Centre for Theoretical Physics, University of Oxford, Oxford OX1 3NP (United Kingdom); Euratom/CCFE Fusion Association, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); Parra, F. I.; Schekochihin, A. A. [Rudolf Peierls Centre for Theoretical Physics, University of Oxford, Oxford OX1 3NP (United Kingdom); Cowley, S. C.; Roach, C. M. [Euratom/CCFE Fusion Association, Culham Science Centre, Abingdon OX14 3DB (United Kingdom)
2011-04-29T23:59:59.000Z
Nonlinear gyrokinetic simulations are conducted to investigate turbulent transport in tokamak plasmas with rotational shear. At sufficiently large flow shears, linear instabilities are suppressed, but transiently growing modes drive subcritical turbulence whose amplitude increases with flow shear. This leads to a local minimum in the heat flux, indicating an optimal ExB shear value for plasma confinement. Local maxima in the momentum fluxes are observed, implying the possibility of bifurcations in the ExB shear. The critical temperature gradient for the onset of turbulence increases with flow shear at low flow shears; at higher flow shears, the dependence of heat flux on temperature gradient becomes less stiff. The turbulent Prandtl number is found to be largely independent of temperature and flow gradients, with a value close to unity.
Development of slotted orifice flow conditioner
Ihfe, Larry Michael
1994-01-01T23:59:59.000Z
for the two flow conditioners. A baseline Co was also plotted for comparative purposes. 24 RESULTS LDA Veloci Profile and Turbulence Intensi Anal sis The velocity profile and turbulence intensity measurements obtained using the LDA are shown in figures...
Thermal impact of an eccentric annular flow around a mixed-oxide pin - An in-pile observation
Lee, M.J.; Strain, R.V.; Lambert, J.D.B.; Feldman, E.E. (Argonne National Laboratory, IL (USA)); Nomura, S. (Power Reactor and Nuclear Fuels Development Corporation, Tokyo (Japan))
1989-11-01T23:59:59.000Z
In a typical subassembly of a liquid-metal reactor, slightly unsymmetric coolant flow and temperature distribution around fuel pins is common and inevitable. The geometric location away from the subassembly center and the irradiation-induced rod bowing are among the primary reasons for such occurrences. Studies of the hydrodynamics of the skewed coolant distribution and the associated fuel pin heat transfer are extensive in both computer modeling and laboratory experimental work. In-pile verification of the phenomenon, however, has been rare. High temperature in fuel pins and the perturbation from temperature-monitoring devices discourage such an endeavor. Recent evidence of the sensitive response of the fuel-sodium reaction product (FSRP) to its decomposition temperature, however, might make in-pile verification possible. The clearly demarcated interface of the FSRP would serve as an excellent thermal monitor that reveals the temperature contour within the fuel. This finding from the postirradiation examination (PIE) of mixed-oxide (MOX) pins, is one of the spin-offs of the run-beyond-cladding-breach (RBCB) program jointly sponsored by the U.S. Department of Energy and the Power Reactor and Nuclear Fuel Development Corporation of Japan. The FSRP fuel interface is thus a good benchmark for verifying fuel and coolant temperature distributions. The RBCB experiment and the associated analysis are discussed and conclusions are presented.
Ecological collapse and the emergence of traveling waves at the onset of shear turbulence
Shih, Hong-Yan; Goldenfeld, Nigel
2015-01-01T23:59:59.000Z
The transition to turbulence exhibits remarkable spatio-temporal behavior that continues to defy detailed understanding. Near the onset to turbulence in pipes, transient turbulent regions decay either directly or, at higher Reynolds numbers through splitting, with characteristic time-scales that exhibit a super-exponential dependence on Reynolds number. Here we report numerical simulations of transitional pipe flow, showing that a zonal flow emerges at large scales, activated by anisotropic turbulent fluctuations; in turn, the zonal flow suppresses the small-scale turbulence leading to stochastic predator-prey dynamics. We show that this "ecological" model of transitional turbulence reproduces the super-exponential lifetime statistics and phenomenology of pipe flow experiments. Our work demonstrates that a fluid on the edge of turbulence is mathematically analogous to an ecosystem on the edge of extinction, and provides an unbroken link between the equations of fluid dynamics and the directed percolation univ...
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.
Abdou, Mohamed
turbulent open channel water flows B. Freeze, S. Smolentsev *, N. Morley, M. Abdou UCLA, Department Abstract Interfacial heat transport in open channel turbulent flows is strongly dependent on surface waves and mass transport across a flowing liquid interface has become an increasingly important topic during
Turbulent Compressibilty of Protogalactic Gas
John Scalo; Anirban Biswas
2001-11-09T23:59:59.000Z
The star formation rate in galaxies should be related to the fraction of gas that can attain densities large enough for gravitational collapse. In galaxies with a turbulent interstellar medium, this fraction is controlled by the effective barotropic index $gamma = dlog P/dlog (rho)$ which measures the turbulent compressibility. When the cooling timescale is smaller than the dynamical timescale, gamma can be evaluated from the derivatives of cooling and heating functions, using the condition of thermal equilibrium. We present calculations of gamma for protogalaxies in which the metal abundance is so small that H_2 and HD cooling dominates. For a heating rate independent of temperature and proportional to the first power of density, the turbulent gas is relatively "hard", with $gamma >= 1$, at large densities, but moderately "soft", $gamma <= 0.8$, at densities below around $10^4 cm^(-3)$. At low temperatures the density probability distribution should fall ra pidly for densities larger than this value, which corresponds physically to the critical density at which collisional and radiative deexcitation rate s of HD are equal. The densities attained in turbulent protogalaxies thus depend on the relatively large deuterium abundance in our universe. We expect the same physical effect to occur in higher metallicity gas with different coolants. The case in which adiabatic (compressional) heating due to cloud collapse dominates is also discussed, and suggests a criterion for the maximum mass of Population III stars.
Aspects of Wave Turbulence in Preheating
José A. Crespo; H. P. de Oliveira
2014-06-04T23:59:59.000Z
In this work we have studied the nonlinear preheating dynamics of the $\\frac{1}{4} \\lambda \\phi^4$ inflationary model. 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 matter distributions are fields instead of usual fluids. Therefore, turbulence develops due to the nonlinear interations of waves, here represented by the small inhomogeneities of the inflaton field. We present relevant aspects of wave turbulence such as the Kolmogorov-Zakharov spectrum in frequency and wave number domains that indicates that there are a transfer of energy 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...
Abbett, Bill
THE DYNAMIC EVOLUTION OF TWISTED MAGNETIC FLUX TUBES IN A THREE-DIMENSIONAL CONVECTING FLOW. II of strong downdrafts, convective flows dominate the evolution, flux tubes of any shape rapidly lose cohesion for a horizontal magnetic flux tube or layer to be preferentially transported in one vertical direction over
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
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
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
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.
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.
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
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.
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
Östh, Jan; Krajnovi?, Siniša
2013-01-01T23:59:59.000Z
We investigate a hierarchy of eddy-viscosity terms in POD Galerkin models to account for a large fraction of unresolved fluctuation energy. These Galerkin methods are applied to Large Eddy Simulation data for a flow around the vehicle-like bluff body call Ahmed body. This flow has three challenges for any reduced-order model: a high Reynolds number, coherent structures with broadband frequency dynamics, and meta-stable asymmetric base flow states. The Galerkin models are found to be most accurate with modal eddy viscosities as proposed by Rempfer & Fasel (1994). Robustness of the model solution with respect to initial conditions, eddy viscosity values and model order is only achieved for state-dependent eddy viscosities as proposed by Noack, Morzynski & Tadmor (2011). Only the POD system with state-dependent modal eddy viscosities can address all challenges of the flow characteristics. All parameters are analytically derived from the Navier-Stokes based balance equations with the available data. We ar...
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.
AIAA-92-5101 Hypersonic Turbulent
Texas at Arlington, University of
were ob- tained in a Mach 8, turbulent, cold flow p a d a11cxpan- sion corner subjected to shock of reduced fluctuation levels. Thcsc fea- tures may be exploited in inlet design by impinging thc cowl shock = undisturbed boundary layer pit = Pitot sh = shock U = upstream influcnce W = mean wall value 1, 2, 2', 3, 4 00
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.
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
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}})\
Scaled Experimental Modeling of VHTR Plenum Flows
ICONE 15
2007-04-01T23:59:59.000Z
Abstract The Very High Temperature Reactor (VHTR) is the leading candidate for the Next Generation Nuclear Power (NGNP) Project in the U.S. which has the goal of demonstrating the production of emissions free electricity and hydrogen by 2015. Various scaled heated gas and water flow facilities were investigated for modeling VHTR upper and lower plenum flows during the decay heat portion of a pressurized conduction-cooldown scenario and for modeling thermal mixing and stratification (“thermal striping”) in the lower plenum during normal operation. It was concluded, based on phenomena scaling and instrumentation and other practical considerations, that a heated water flow scale model facility is preferable to a heated gas flow facility and to unheated facilities which use fluids with ranges of density to simulate the density effect of heating. For a heated water flow lower plenum model, both the Richardson numbers and Reynolds numbers may be approximately matched for conduction-cooldown natural circulation conditions. Thermal mixing during normal operation may be simulated but at lower, but still fully turbulent, Reynolds numbers than in the prototype. Natural circulation flows in the upper plenum may also be simulated in a separate heated water flow facility that uses the same plumbing as the lower plenum model. However, Reynolds number scaling distortions will occur at matching Richardson numbers due primarily to the necessity of using a reduced number of channels connected to the plenum than in the prototype (which has approximately 11,000 core channels connected to the upper plenum) in an otherwise geometrically scaled model. Experiments conducted in either or both facilities will meet the objectives of providing benchmark data for the validation of codes proposed for NGNP designs and safety studies, as well as providing a better understanding of the complex flow phenomena in the plenums.
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
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.
Overview of the TurbSim Stochastic Inflow Turbulence Simulator: Version 1.10
Kelley, N. D.; Jonkman, B. J.
2006-09-01T23:59:59.000Z
The Turbsim stochastic inflow turbulence code was developed to provide a numerical simulation of a full-field flow that contains coherent turbulence structures that reflect the proper spatiotemporal turbulent velocity field relationships seen in instabilities associated with nocturnal boundary layer flows. This report provides the user with an overview of how the TurbSim code has been developed and some of the theory behind that development.
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.
Large-eddy simulation of a wind turbine wake in turbulent
Firestone, Jeremy
Large-eddy simulation of a wind turbine wake in turbulent neutral shear flow Shengbai Xie, Cristina-similar velocity profile existing in the wake after a wind turbine? How does the wake influence the vertical? Motivation #12; Large-eddy simulation for turbulent flow field Actuator-line model for wind turbine ui
Sridharan, Kumar; Anderson, Mark; Allen, Todd; Corradini, Michael
2012-01-30T23:59:59.000Z
The goal of this NERI project was to perform research on high temperature fluoride and chloride molten salts towards the long-term goal of using these salts for transferring process heat from high temperature nuclear reactor to operation of hydrogen production and chemical plants. Specifically, the research focuses on corrosion of materials in molten salts, which continues to be one of the most significant challenges in molten salts systems. Based on the earlier work performed at ORNL on salt properties for heat transfer applications, a eutectic fluoride salt FLiNaK (46.5% LiF-11.5%NaF-42.0%KF, mol.%) and a eutectic chloride salt (32%MgCl2-68%KCl, mole %) were selected for this study. Several high temperature candidate Fe-Ni-Cr and Ni-Cr alloys: Hastelloy-N, Hastelloy-X, Haynes-230, Inconel-617, and Incoloy-800H, were exposed to molten FLiNaK with the goal of understanding corrosion mechanisms and ranking these alloys for their suitability for molten fluoride salt heat exchanger and thermal storage applications. The tests were performed at 850Ã?Â?Ã?Â?Ã?Â?Ã?Â?C for 500 h in sealed graphite crucibles under an argon cover gas. Corrosion was noted to occur predominantly from dealloying of Cr from the alloys, an effect that was particularly pronounced at the grain boundaries Alloy weight-loss due to molten fluoride salt exposure correlated with the initial Cr-content of the alloys, and was consistent with the Cr-content measured in the salts after corrosion tests. The alloysÃ?Â?Ã?Â¢Ã?Â?Ã?Â?Ã?Â?Ã?Â? weight-loss was also found to correlate to the concentration of carbon present for the nominally 20% Cr containing alloys, due to the formation of chromium carbide phases at the grain boundaries. Experiments involving molten salt exposures of Incoloy-800H in Incoloy-800H crucibles under an argon cover gas showed a significantly lower corrosion for this alloy than when tested in a graphite crucible. Graphite significantly accelerated alloy corrosion due to the reduction of Cr from solution by graphite and formation on Cr-carbide on the graphite surface. Ni-electroplating dramatically reduced corrosion of alloys, although some diffusion of Fe and Cr were observed occur through the Ni plating. A pyrolytic carbon and SiC (PyC/SiC) CVD coating was also investigated and found to be effective in mitigating corrosion. The KCl-MgCl2 molten salt was less corrosive than FLiNaK fluoride salts for corrosion tests performed at 850oC. Cr dissolution in the molten chloride salt was still observed and consequently Ni-201 and Hastelloy N exhibited the least depth of attack. Grain-boundary engineering (GBE) of Incoloy 800H improved the corrosion resistance (as measured by weight loss and maximum depth of attack) by nearly 50% as compared to the as-received Incoloy 800H sample. Because Cr dissolution is an important mechanism of corrosion, molten salt electrochemistry experiments were initiated. These experiments were performed using anodic stripping voltammetry (ASV). Using this technique, the reduction potential of Cr was determined against a Pt quasi-reference electrode as well as against a Ni(II)-Ni reference electrode in molten FLiNaK at 650 oC. The integrated current increased linearly with Cr-content in the salt, providing for a direct assessment of the Cr concentration in a given salt of unknown Cr concentration. To study heat transfer mechanisms in these molten salts over the forced and mixed convection regimes, a forced convective loop was constructed to measure heat transfer coefficients, friction factors and corrosion rates in different diameter tubes in a vertical up flow configuration in the laminar flow regime. Equipment and instrumentation for the forced convective loop was designed, constructed, and tested. These include a high temperature centrifugal pump, mass flow meter, and differential pressure sensing capabilities to an uncertainty of < 2 Pa. The heat transfer coefficient for the KCl-MgCl2 salt was measured in t
Magnusson, Sigurður Pétur
2014-01-01T23:59:59.000Z
Human exposure to air pollutants and thermal stress in urban areas are public health concerns. The year 2008 was the first year when more than half of the human population lived in urban areas. Studies of the urban air ...
Ozturk, Burak
2009-05-15T23:59:59.000Z
.18 (S R =80 mm)........................................103 Figure 11.1. Static pressure distributions at Re=110,000 and reduced frequencies S=0, 1.59, 3.18 (no rod, 160 mm, 80 mm), SS=Separation start, SE= Separation end...................................................110 Figure 11.2. Time-averaged hot-film distributions at Re=110,000 and reduced frequencies S=0, 1.59, 3.18 (no rod, 160 mm, 80 mm)...........................112 Figure 11.3. Ensemble averaged velocity as a function for (a) steady flow case S=0 (S R...
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.
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.
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...
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.
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...
James E. O'Brien; Piyush Sabharwall; SuJong Yoon
2001-09-01T23:59:59.000Z
A new high-temperature multi-fluid, multi-loop test facility for advanced nuclear applications is under development at the Idaho National Laboratory. The facility will include three flow loops: high-temperature helium, molten salt, and steam/water. Molten salts have been identified as excellent candidate heat transport fluids for primary or secondary coolant loops, supporting advanced high temperature and small modular reactors (SMRs). Details of some of the design aspects and challenges of this facility, which is currently in the conceptual design phase, are discussed. A preliminary design configuration will be presented, with the required characteristics of the various components. The loop will utilize advanced high-temperature compact printed-circuit heat exchangers (PCHEs) operating at prototypic intermediate heat exchanger (IHX) conditions. The initial configuration will include a high-temperature (750°C), high-pressure (7 MPa) helium loop thermally integrated with a molten fluoride salt (KF-ZrF4) flow loop operating at low pressure (0.2 MPa) at a temperature of ~450°C. Experiment design challenges include identification of suitable materials and components that will withstand the required loop operating conditions. Corrosion and high temperature creep behavior are major considerations. The facility will include a thermal energy storage capability designed to support scaled process heat delivery for a variety of hybrid energy systems and grid stabilization strategies. Experimental results obtained from this research will also provide important data for code ve
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.
K. V. Ramesh; R. Thaokar; J. Ravi Prakash; R. Prabhakar
2015-01-29T23:59:59.000Z
The dynamics of adhesion of a spherical micro-particle to a ligand-coated wall, in shear flow, is studied using a Langevin equation that accounts for thermal fluctuations, hydrodynamic interactions and adhesive interactions. Contrary to the conventional assumption that thermal fluctuations play a negligible role at high P$\\acute{e}$clet numbers, we find that for particles with low surface densities of receptors, rotational diffusion caused by fluctuations about the flow and gradient directions aids in bond formation, leading to significantly greater adhesion on average, compared to simulations where thermal fluctuations are completely ignored. The role of wall hydrodynamic interactions on the steady state motion of a particle, when the particle is close to the wall, has also been explored. At high P$\\acute{e}$clet numbers, the shear induced force that arises due to the stresslet part of the Stokes dipole, plays a dominant role, reducing the particle velocity significantly, and affecting the states of motion of the particle. The coupling between the translational and rotational degrees of freedom of the particle, brought about by the presence of hydrodynamic interactions, is found to have no influence on the binding dynamics. On the other hand, the drag coefficient, which depends on the distance of the particle from the wall, plays a crucial role at low rates of bond formation. A significant difference in the effect of both the shear force and the position dependent drag force, on the states of motion of the particle, is observed when the P$\\acute{e}$let number is small.
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.
Karniadakis, G.E.; Orszag, S.A. (Princeton Univ., NJ (United States))
1993-03-01T23:59:59.000Z
Computational fluid dynamics and the numerical prediction of fluid flow in the understanding and modeling of turbulence is discussed with emphasis on the development of direct numerical simulation (DNS) of high-Reynolds number turbulent flows. Recent advances in computer systems and their use in turbulence simulation are reviewed and the need for parallel processing to achieve teraflop speeds necessary for DNS is discussed. Computer system architectures, nodes, and parallel computers currently in use are reviewed. Spectral, spectral-element, particle, and hybrid difference methods of solving incompressible- and compressible-flow problems are examined. Four applications of parallel computers to turbulent flow problems are presented and future developments in computer systems are discussed. 24 refs.
Longitudinal dispersion in vegetated flow
Murphy, Enda
2006-01-01T23:59:59.000Z
Vegetation is ubiquitous in rivers, estuaries and wetlands, strongly influencing both water conveyance and mass transport. The plant canopy affects both mean and turbulent flow structure, and thus both advection and ...
Chen, Xingyuan; Miller, Gretchen R.; Rubin, Yoram; Baldocchi, Dennis
2012-09-13T23:59:59.000Z
The heat pulse method is widely used to measure water flux through plants; it works by inferring the velocity of water through a porous medium from the speed at which a heat pulse is propagated through the system. No systematic, non-destructive calibration procedure exists to determine the site-specific parameters necessary for calculating sap velocity, e.g., wood thermal diffusivity and probe spacing. Such parameter calibration is crucial to obtain the correct transpiration flux density from the sap flow measurements at the plant scale; and consequently, to up-scale tree-level water fluxes to canopy and landscape scales. The purpose of this study is to present a statistical framework for estimating the wood thermal diffusivity and probe spacing simutaneously from in-situ heat response curves collected by the implanted probes of a heat ratio apparatus. Conditioned on the time traces of wood temperature following a heat pulse, the parameters are inferred using a Bayesian inversion technique, based on the Markov chain Monte Carlo sampling method. The primary advantage of the proposed methodology is that it does not require known probe spacing or any further intrusive sampling of sapwood. The Bayesian framework also enables direct quantification of uncertainty in estimated sap flow velocity. Experiments using synthetic data show that repeated tests using the same apparatus are essential to obtain reliable and accurate solutions. When applied to field conditions, these tests are conducted during different seasons and automated using the existing data logging system. The seasonality of wood thermal diffusivity is obtained as a by-product of the parameter estimation process, and it is shown to be affected by both moisture content and temperature. Empirical factors are often introduced to account for the influence of non-ideal probe geometry on the estimation of heat pulse velocity, and they are estimated in this study as well. The proposed methodology can be applied for the calibration of existing heat ratio sap flow systems at other sites. It is especially useful when an alternative transpiration calibration device, such as a lysimeter, is not available.
Non-thermal Plasma Chemistry Non-thermal Thermal
Greifswald, Ernst-Moritz-Arndt-UniversitÃ¤t
-thermal Plasma Chemical Flow Reactor #12;Werner von Siemens ,, ... construction of an apparatus generation (1857) pollution control volatile organic components, NOx reforming, ... radiation sources excimer;LeuchtstoffrÃ¶hre Plasma-Bildschirm Energiesparlampe #12;electrical engineering light sources textile industry
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
Small-scale magnetic buoyancy and magnetic pumping effects in a turbulent convection
I. Rogachevskii; N. Kleeorin
2006-05-18T23:59:59.000Z
We determine the nonlinear drift velocities of the mean magnetic field and nonlinear turbulent magnetic diffusion in a turbulent convection. We show that the nonlinear drift velocities are caused by the three kinds of the inhomogeneities, i.e., inhomogeneous turbulence; the nonuniform fluid density and the nonuniform turbulent heat flux. The inhomogeneous turbulence results in the well-known turbulent diamagnetic and paramagnetic velocities. The nonlinear drift velocities of the mean magnetic field cause the small-scale magnetic buoyancy and magnetic pumping effects in the turbulent convection. These phenomena are different from the large-scale magnetic buoyancy and magnetic pumping effects which are due to the effect of the mean magnetic field on the large-scale density stratified fluid flow. The small-scale magnetic buoyancy and magnetic pumping can be stronger than these large-scale effects when the mean magnetic field is smaller than the equipartition field. We discuss the small-scale magnetic buoyancy and magnetic pumping effects in the context of the solar and stellar turbulent convection. We demonstrate also that the nonlinear turbulent magnetic diffusion in the turbulent convection is anisotropic even for a weak mean magnetic field. In particular, it is enhanced in the radial direction. The magnetic fluctuations due to the small-scale dynamo increase the turbulent magnetic diffusion of the toroidal component of the mean magnetic field, while they do not affect the turbulent magnetic diffusion of the poloidal field.
Rutland, Christopher J.
2009-04-26T23:59:59.000Z
The Terascale High-Fidelity Simulations of Turbulent Combustion (TSTC) project is a multi-university collaborative effort to develop a high-fidelity turbulent reacting flow simulation capability utilizing terascale, massively parallel computer technology. The main paradigm of the approach is direct numerical simulation (DNS) featuring the highest temporal and spatial accuracy, allowing quantitative observations of the fine-scale physics found in turbulent reacting flows as well as providing a useful tool for development of sub-models needed in device-level simulations. Under this component of the TSTC program the simulation code named S3D, developed and shared with coworkers at Sandia National Laboratories, has been enhanced with new numerical algorithms and physical models to provide predictive capabilities for turbulent liquid fuel spray dynamics. Major accomplishments include improved fundamental understanding of mixing and auto-ignition in multi-phase turbulent reactant mixtures and turbulent fuel injection spray jets.
A New Proof on Net Upscale Energy Cascade in 2D and QG Turbulence
Eleftherios Gkioulekas; Ka Kit Tung
2006-09-30T23:59:59.000Z
A general proof that more energy flows upscale than downscale in two-dimensional (2D) turbulence and barotropic quasi-geostrophic (QG) turbulence is given. A proof is also given that in Surface QG turbulence, the reverse is true. Though some of these results are known in restricted cases, the proofs given here are pedagogically simpler, require fewer assumptions and apply to both forced and unforced cases.
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.
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.
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.
Stretching of polymers in a turbulent environment
Bruno Eckhardt; Jochen Kronjaeger; Joerg Schumacher
2002-01-20T23:59:59.000Z
The interaction of polymers with small-scale velocity gradients can trigger a coil-stretch transition in the polymers. We analyze this transition within a direct numerical simulation of shear turbulence with an Oldroyd-B model for the polymer. In the coiled state the lengths of polymers are distributed algebraically with an exponent alpha=2 gamma-1/De, where gamma is a characteristic stretching rate of the flow and De the Deborah number. In the stretched state we demonstrate that the length distribution of the polymers is limited by the feedback to the flow.
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.
Direct Numerical Simulations of Interfacial Turbulence at Low Froude and Weber Numbers
Zhang, Qi
2014-05-22T23:59:59.000Z
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2.1 Thermal signature of ocean surface and related subsurface dynamics 3 1.2.2 Surfactant effects on ocean surface . . . . . . . . . . . . . . . . . 5 1.2.3 Gas transfer and active thermography on turbulent buoyant con- vection... and investigation of passive scalar beneath the surfactant contaminated free surface. 6 1.2.3 Gas transfer and active thermography on turbulent buoyant convection One of the objectives of the IR thermal signature and subsurface dynamics study is to unveil...
Multiphase Turbulent Flow Ken Kiger -UMCP
Gruner, Daniel S.
emulsions Multi-phase Steam bubble in H20 Ice slurry Coal particles in air Sand particle in H20 #12://www.physics.utoronto.ca/~nonlin/turbidity/turbidity.html #12;Material processing generation of particles & composite materials Energy production coal
Power spectra of outflow-driven turbulence
Moraghan, Anthony; Yoon, Suk-Jin
2015-01-01T23:59:59.000Z
We investigate the power spectra of outflow-driven turbulence through high-resolution three-dimensional isothermal numerical simulations where the turbulence is driven locally in real-space by a simple spherical outflow model. The resulting turbulent flow saturates at an average Mach number of ~2.5 and is analysed through density and velocity power spectra, including an investigation of the evolution of the solenoidal and compressional components. We obtain a shallow density power spectrum with a slope of ~-1.2 attributed to the presence of a network of localised dense filamentary structures formed by strong shock interactions. The total velocity power spectrum slope is found to be ~-2.0, representative of Burgers shock dominated turbulence model. The density weighted velocity power spectrum slope is measured as ~-1.6, slightly less than the expected Kolmogorov scaling value (slope of -5/3) found in previous works. The discrepancy may be caused by the nature of our real space driving model and we suggest ther...
Effect of turbulent heat transfer on continuous ingot solidification
Shyy, W.; Chen, M.H. (Univ. of Florida, Gainesville, FL (United States). Dept. of Aerospace Engineering); Pang, Y.; Wei, D.Y. (GE Aircraft Engines, Engineering Materials Technology Labs., Lynn, MA (United States)); Hunter, G.B. (GE Aircraft Engines, Engineering Materials Technology Labs., Cincinnati, OH (United States))
1993-01-01T23:59:59.000Z
For many continuous ingot casting processes, turbulent heat transfer in the molten pool plays a critical role which, along with buoyancy and surface tension, is responsible for the quality of the end products. Based on a modified low Reynolds number K-[epsilon] two-equation closure, accounting for the phase change and mushy zone formation, the effect of turbulent heat transfer on the solidification characteristics during titanium alloy ingot casting in an electron beam melting process is investigated. The overall heat transfer rate is enhanced by turbulent transport via two sources, one through the correlated velocity and temperature fluctuations present for both single- and multi-phase flows, and the other through the correlated velocity and release of latent heat fluctuations which are unique to the flows with phase change. The roles played by both mechanisms are identified and assessed. The present turbulence model predicts that although the mushy zone defined by the mean temperature field is generally of substantial thickness as a result of the convection effect, the actual instantaneous zone thickness varies substantially due to turbulence effect. This finding is in contrast to the traditionally held viewpoint, based on the conduction analysis, of a generally thin mushy zone. The impact of turbulent heat transfer on local dendrite formation and remelting is illustrated and the issues involved in model development highlighted.
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
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
Srivastava, A K; Murawski, K; Dwivedi, B N; Mohan, A
2014-01-01T23:59:59.000Z
Using one-arcsecond-slit scan observations from the Hinode/EUV Imaging Spectrometer (EIS) on 05 February 2007, we find the plasma outflows in the open and expanding coronal funnels at the eastern boundary of AR 10940. The Doppler velocity map of Fe XII 195.120 A shows that the diffuse close-loop system to be mostly red-shifted. The open arches (funnels) at the eastern boundary of AR exhibit blue-shifts with a maximum speed of about 10-15 km/s. This implies outflowing plasma through these magnetic structures. In support of these observations, we perform a 2D numerical simulation of the expanding coronal funnels by solving the set of ideal MHD equations in appropriate VAL-III C initial temperature conditions using the FLASH code. We implement a rarefied and hotter region at the footpoint of the model funnel, which results in the evolution of slow plasma perturbations propagating outward in the form of plasma flows. We conclude that the heating, which may result from magnetic reconnection, can trigger the observ...
Brown, Michael R.
material must be decoupled from the magnetic fields by turbulent diffusivity. Second, competition between a competition between the con- vective and diffusive terms of Eq. (1). The Riga group recently reported in the skin depth of an oscillating magnetic field with a magnetic probe array also indicating a reduction
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 ...
Formation of large-scale structures by turbulence in rotating planets
Constantinou, Navid C
2015-01-01T23:59:59.000Z
This thesis presents a newly developed theory for the formation and maintenance of eddy-driven jets in planetary turbulence. The novelty is that jet formation and maintenance is studied as a dynamics of the statistics of the flow rather than a dynamics of individual realizations. This is pursued using Stochastic Structural Stability Theory (S3T) which studies the closed dynamics of the first two cumulants of the full statistical state dynamics of the flow after neglecting or parameterizing third and higher-order cumulants. With this statistical closure large-scale structure formation is studied in barotropic turbulence on a $\\beta$-plane. It is demonstrated that at analytically predicted critical parameter values the homogeneous turbulent state undergoes a bifurcation becoming inhomogeneous with the emergence of large-scale zonal and/or non-zonal flows. The mechanisms by which the turbulent Reynolds stresses organize to reinforce infinitesimal mean flow inhomogeneities, thus leading to this statistical state ...
Sóbester, András
(wind or marine) can generate, estimating carbon dioxide exchange between forests and the atmosphere-Dimensional (2-D) flow, where mean turbulent properties are uniform (or almost uniform) along one direction
Benno Rumpf Laura Biven
2005-03-04T23:59:59.000Z
The turbulent energy flow of the onedimensional Majda-McLaughlin-Tabak equation is studied numerically. The system exhibits weak turbulence for weak driving forces, while weak turbulence coexists with strongly nonlinear intermittent collapses when the system is strongly driven. These two types of dynamics can be distinguished by their energy and particle fluxes. The weakly turbulent process can be characterized by fluxes in wavenumber space, while additional fluxes in amplitude space emerge in the intermittent process. The particle flux is directed from low amplitudes towards high amplitudes, and the energy flows in the opposite direction.
arm blood flow: Topics by E-print Network
Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)
We present an experimental study of a turbulent von K'arm'an flow produced in a cylindrical container using two propellers. The mean flow can be considered stationary up...
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.
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 ...
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.
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.
Notes 09. Fluid inertia and turbulence in fluid film bearings
San Andres, Luis
2009-01-01T23:59:59.000Z
. Luis San Andr?s ? 2009 14 References: Constantinescu, V.N., 1962, ?Analysis of Bearings Operating in the Turbulent Flow Regime,? ASME Journal of Lubrication Technology, Vol. 82, pp. 139-151. Hashimoto, H., S. Wada, M. Sumitomo, 1989, ?The Effects...
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
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
Turbulent Combustion Luc Vervisch
Kern, Michel
;19 "Perfect" combustion modes: Fuel + Oxidizer () Products Engines, gas turbines... Laboratory experiment1 Turbulent Combustion Modeling Luc Vervisch INSA de Rouen, IUF, CORIA-CNRS Quelques problÃ¨mes rencontrÃ©s en chimie numÃ©rique : Hydrologie - Combustion - AtmosphÃ¨re 16 dÃ©cembre, INRIA Rocquencourt #12
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.
Beyond the Betz Theory - Blockage, Wake Mixing and Turbulence
Nishino, Takafumi
2013-01-01T23:59:59.000Z
Recent analytical models concerning the limiting efficiency of marine hydrokinetic (MHK) devices are reviewed with an emphasis on the significance of blockages (of local as well as global flow passages) and wake mixing. Also discussed is the efficiency of power generation from fully developed turbulent open channel flows. These issues are primarily concerned with the design/optimization of tidal turbine arrays; however, some of them are relevant to wind turbines as well.
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.
California at Berkeley, University of
to kinetic and thermal particle energies. In this Letter we use space plasma as a turbulence laboratory the strongly turbulent solar wind down- stream of Earth's bow shock, the so-called magnetosheath (magnetic field), and CIS (ions) experiments [17]. At 09:35 UT the spacecraft crossed the bow shock
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.
The life-cycle of drift-wave turbulence driven by small scale instability
Colm Connaughton; Sergey Nazarenko; Brenda Quinn
2010-12-16T23:59:59.000Z
We demonstrate theoretically and numerically the zonal-flow/drift-wave feedback mechanism for the LH transition in an idealised model of plasma turbulence driven by a small scale instability. Zonal flows are generated by a secondary modulational instability of the modes which are directly driven by the primary instability. The zonal flows then suppress the small scales thereby arresting the energy injection into the system, a process which can be described using nonlocal wave turbulence theory. Finally, the arrest of the energy input results in saturation of the zonal flows at a level which can be estimated from the theory and the system reaches stationarity without damping of the large scales.
Study of natural circulation in a VHTR after a LOFA using different turbulence models
Yu-Hsin Tung; Yuh-Ming Ferng; Richard W. Johnson; Ching-Chang Chieng
2013-10-01T23:59:59.000Z
Natural convection currents in the core are anticipated in the event of the failure of the gas circulator in a prismatic gas-cooled very high temperature reactor (VHTR). The paths that the helium coolant takes in forming natural circulation loops and the effective heat transport are of interest. The heated flow in the reactor core is turbulent during normal operating conditions and at the beginning of the LOFA with forced convection, but the flow may significantly be slowed down after the event and laminarized with mixed convection. In the present study, the potential occurrence and effective heat transport of natural circulation are demonstrated using computational fluid dynamic (CFD) calculations with different turbulence models as well as laminar flow. Validations and recommendation on turbulence model selection are conducted. The study concludes that large loop natural convection is formed due to the enhanced turbulence levels by the buoyancy effect and the turbulent regime near the interface of upper plenum and flow channels increases the flow resistance for channel flows entering upper plenum and thus less heat can be removed from the core than the prediction by laminar flow assumption.
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.
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.
Anderson, Michael E
2015-01-01T23:59:59.000Z
We detect emission from [Fe XXI] $\\lambda$1354.1, which is a tracer of $10^7$ K gas, in archival HST-COS spectra from the centers of the well-known elliptical galaxies M87 and NGC 4696. The detections are at moderate significance, with S/N of 4.9 and 4.1 respectively. Using this line, we measure the kinematics of the hot gaseous halos in these galaxies, which are stirred by turbulence and bulk flows. The hot gas has a mean velocity which is consistent with zero relative to each galaxy, although in the case of M87 spatial broadening by the off-axis nucleus may be introducing a slight artificial blueshift. In both systems we measure velocity dispersions for this line, which are likely contaminated by spatial broadening. We estimate the effect of spatial broadening and infer turbulent line-of sight velocities of $105^{+28}_{-22}$ km/s and $85^{+22}_{-18}$ km/s, corresponding to turbulent pressures of $7^{+4}_{-3}$% and $5\\pm2$% of the total thermal pressure in these respective galaxies. These uncertainties inclu...
The Hydrodynamics of Flow Stimuli Matthew J. McHenry and James C. Liao
McHenry, Matt
· Rheotaxis · Swimming · Turbulence · Vortex street · Unsteady flow 1 Introduction The lateral line system · Hair cell · Ka´rma´n gait · Lateral line · Localization · Neuromast · Predation · Reynolds number
A. Y. Poludnenko; E. G. Blackman; A. Frank
2002-01-24T23:59:59.000Z
We consider the stability of an accretion disk wind to cloud formation when subject to a central radiation force. For a vertical launch velocity profile that is Keplerian or flatter and the presence of a significant radiation pressure, the wind flow streamlines cross in a conical layer. We argue that such regions are highly unstable, and are natural sites for supersonic turbulence and, consequently, density compressions. We suggest that combined with thermal instability these will all conspire to produce clouds. Such clouds can exist in dynamical equilibrium, constantly dissipating and reforming. As long as there is an inner truncation radius to the wind, our model emerges with a biconical structure similar to that inferred by Elvis (2000) for the broad line region (BLR) of active galactic nuclei (AGN). Our results may also apply to other disk-wind systems.
Towards Understanding the Poor Thermal Stability of V5+ Electrolyte...
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the Poor Thermal Stability of V5+ Electrolyte Solution in Vanadium Redox Flow Batteries. Towards Understanding the Poor Thermal Stability of V5+ Electrolyte Solution in...
King, Bradley Donald
2013-12-31T23:59:59.000Z
controlled during calcite precipitation. Ouachita tectonism caused tectonically valved and gravity-driven fluid flow sourced from the Anadarko basin and possibly involved sandstone aquifers or basement. Mechanisms of ancient fluid flow appear to contrast...
Turbulent Reconnection and Its Implications
Lazarian, Alex; Vishniac, Ethan T; Kowal, Grzegorz
2015-01-01T23:59:59.000Z
Magnetic reconnection is a process of magnetic field topology change, which is one of the most fundamental processes in magnetized plasmas. In most astrophysical environments the Reynolds numbers are large and therefore the transition to turbulence is inevitable. This turbulence must be taken into account for any theory of magnetic reconnection, since the initially laminar configurations can transit to the turbulence state, what is demonstrated by 3D high resolution numerical simulations. We discuss ideas of how turbulence can modify reconnection with the focus on the Lazarian & Vishniac (1999) reconnection model and present numerical evidence supporting the model and demonstrate that it is closely connected to the concept of Richardson diffusion and compatible with the Lagrangian dynamics of magnetized fluids. We point out that the Generalized Ohm's Law, that accounts for turbulent motion, predicts the subdominance of the microphysical plasma effects for a realistically turbulent media. We show that on o...
Nonclassical Velocity Statistics in a Turbulent Atomic Bose-Einstein Condensate
White, A. C.; Barenghi, C. F.; Proukakis, N. P.; Youd, A. J.; Wacks, D. H. [School of Mathematics and Statistics, Newcastle University, Newcastle upon Tyne, NE1 7RU (United Kingdom)
2010-02-19T23:59:59.000Z
In a recent experiment Paoletti et al. [Phys. Rev. Lett. 101, 154501 (2008)] monitored the motion of tracer particles in turbulent superfluid helium and inferred that the velocity components do not obey the Gaussian statistics observed in ordinary turbulence. Motivated by their experiment, we create a small 3D turbulent state in an atomic Bose-Einstein condensate, compute directly the velocity field, and find similar nonclassical power-law tails. We obtain similar results in 2D trapped and 3D homogeneous condensates, and in classical 2D vortex points systems. This suggests that non-Gaussian turbulent velocity statistics describe a fundamental property of quantum turbulence. We also track the decay of the vortex tangle in the presence of the thermal cloud.
Linden, Paul F.
International Journal of Ventilation ISSN 1473-3315 Volume 4 No 4 ________________________________________________________________________________________________________________________ ________________________________________________________________________________________________________________________ 301 Interacting Turbulent Plumes in a Naturally Ventilated Enclosure P. F. Linden1 and N. B. Kaye2 1 of turbulent plumes is examined in the context of building ventilation flows. Recent models for natural
Protostellar outflow-driven turbulence
Christopher D. Matzner
2007-01-01T23:59:59.000Z
Protostellar outflows crisscross the regions of star cluster formation, stirring turbulence and altering the evolution of the forming cluster. We model the stirring of turbulent motions by protostellar outflows, building on an observation that the scaling law of supersonic turbulence implies a momentum cascade analogous to the energy cascade in Kolmogorov turbulence. We then generalize this model to account for a diversity of outflow strengths, and for outflow collimation, both of which enhance turbulence. For a single value of its coupling coefficient the model is consistent with turbulence simulations by Li & Nakamura and, plausibly, with observations of the NGC 1333 cluster-forming region. Outflow-driven turbulence is strong enough to stall collapse in cluster-forming regions for several crossing times, relieving the mismatch between star formation and turbulent decay rates. The predicted line-width-size scaling implies radial density indices between -1 and -2 for regions supported by outflow-driven turbulence, with a tendency for steeper profiles in regions that are more massive or have higher column densities.
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.
Osinski, Charles Anthony
1963-01-01T23:59:59.000Z
zero and unity. The Ostwald- de Waele Equation (4), commonly known as the power law, is sometimes used to describe fluid behavior of this type. The rheological equation is (4) where the parameters "k" and "n" are constant for a particular fluid... be extended to include Reynolds numbers and the type of flow determined to be laminar and/or turbulent. It is assumed that the transition from laminar to turbulent flow occurs at a Reynolds number of 2100, the numeric distribution of Reynolds numbers...
Section 10: Turbulence and reactive flows 1 Section 10: Turbulence and reactive flows
Kohlenbach, Ulrich
premixed combustion is recently a theme of interest in gas turbines and other industrial applications combustion LES in- cluding thickened flame model A. Hosseinzadeh, A. Sadiki, J. Janicka (TU Darmstadt) Lean-premixed flames. However, instabilities occurring in a combustion chamber under lean premixed combustion, may lead
Reconnection outflow generated turbulence in the solar wind
Vörös, Z; Semenov, V S; Zaqarashvili, T V; Bruno, R; Khodachenko, M
2014-01-01T23:59:59.000Z
Petschek-type time-dependent reconnection (TDR) and quasi-stationary reconnection (QSR) models are considered to understand reconnection outflow structures and the features of the associated locally generated turbulence in the solar wind. We show that the outflow structures, such as discontinuites, Kelvin-Helmholtz (KH) unstable flux tubes or continuous space filling flows cannot be distinguished from one-point WIND measurements. In both models the reconnection outflows can generate more or less spatially extended turbulent boundary layers (TBDs). The structure of an unique extended reconnection outflow is investigated in detail. The analysis of spectral scalings and break locations show that reconnection outflows can control the local field and plasma conditions which may play in favor of one or another turbulent dissipation mechanisms with their characteristic scales and wavenumbers.
Simulation of lean premixed turbulent combustion
2008-01-01T23:59:59.000Z
turbulent methane combustion. Proc. Combust. Inst. , 29:in premixed turbulent combustion. Proc. Combust. Inst. ,for zero Mach number combustion. Combust. Sci. Technol. ,
Advanced Computational Methods for Turbulence and Combustion...
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Advanced Computational Methods for Turbulence and Combustion Advanced Computational Methods for Turbulence and Combustion Bell.png Key Challenges: Development and application of...
Ortiz, Alejandra C
2012-01-01T23:59:59.000Z
This study describes the spatial distribution of sediment deposition in the wake of a circular patch of model vegetation and the effect of the patch on turbulence and mean flow. Two difference types pf vegetation were used ...
Distribution of particles and bubbles in turbulence at small Stokes number
Itzhak Fouxon
2011-10-11T23:59:59.000Z
The inertia of particles driven by the turbulent flow of the surrounding fluid makes them prefer certain regions of the flow. The heavy particles lag behind the flow and tend to accumulate in the regions with less vorticity, while the light particles do the opposite. As a result of the long-time evolution, the particles distribute over a multi-fractal attractor in space. We consider this distribution using our recent results on the steady states of chaotic dynamics. We describe the preferential concentration analytically and derive the correlation functions of density and the fractal dimensions of the attractor. The results are obtained for real turbulence and are testable experimentally.
Title of dissertation: Dispersion of ion gyrocenters in models of anisotropic plasma turbulence
Anlage, Steven
ABSTRACT Title of dissertation: Dispersion of ion gyrocenters in models of anisotropic plasma Department of Physics Turbulent dispersion of ion gyrocenters in a magnetized plasma is studied gradient, the focus is on transport parallel to the shear flow. The prescribed flow produces strongly
LES of the adverse-pressure gradient turbulent boundary layer M. Inoue a,
Marusic, Ivan
at the University of Melbourne wind tunnel where a plate section with zero pressure gradient is followed by section accurate simulations, for example, of separated flow on the wings of airplanes or for flow through turbine such as the amplified wake of the mean velocity profile and the increasing turbulence intensity in the outer region
WaveTurbulence Interactions in a Breaking Mountain Wave CRAIG C. EPIFANIO AND TINGTING QIAN
energy budget for the wave shows that the turbulence production is almost entirely due to the mean shear Department of Atmospheric Sciences, Texas A&M University, College Station, Texas (Manuscript received 15 May. Most of the production is at the top of the leeside shooting flow, where the mean-flow Richardson
Thermal Storage and Advanced Heat Transfer Fluids (Fact Sheet)
Not Available
2010-08-01T23:59:59.000Z
Fact sheet describing NREL CSP Program capabilities in the area of thermal storage and advanced heat transfer fluids: measuring thermophysical properties, measuring fluid flow and heat transfer, and simulating flow of thermal energy and fluid.
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.
ENHANCED DISSIPATION RATE OF MAGNETIC FIELD IN STRIPED PULSAR WINDS BY THE EFFECT OF TURBULENCE
Takamoto, Makoto [Department of Physics, Kyoto University, Oiwake-cho, Kitashirakawa, Sakyo-ku, Kyoto 606-8502 (Japan); Inoue, Tsuyoshi [Department of Physics and Mathematics, Aoyama Gakuin University, Fuchinobe, Chuou-ku, Sagamihara 252-5258 (Japan); Inutsuka, Shu-ichiro, E-mail: takamoto@tap.scphys.kyoto-u.ac.jp, E-mail: inouety@phys.aoyama.ac.jp, E-mail: inutsuka@nagoya-u.jp [Department of Physics, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602 (Japan)
2012-08-10T23:59:59.000Z
In this paper, we report on turbulent acceleration of the dissipation of the magnetic field in the post-shock region of a Poynting flux-dominated flow, such as the Crab pulsar wind nebula. We have performed two-dimensional resistive relativistic magnetohydrodynamics simulations of subsonic turbulence driven by the Richtmyer-Meshkov instability at the shock fronts of the Poynting flux-dominated flows in pulsar winds. We find that turbulence stretches current sheets which substantially enhances the dissipation of the magnetic field, and that most of the initial magnetic field energy is dissipated within a few eddy-turnover times. We also develop a simple analytical model for turbulent dissipation of the magnetic field that agrees well with our simulations. The analytical model indicates that the dissipation rate does not depend on resistivity even in the small resistivity limit. Our findings can possibly alleviate the {sigma}-problem in the Crab pulsar wind nebulae.
Turbulence modeling and the physics of the intra-cluster medium
Iapichino, L; Schmidt, W; Niemeyer, J C
2009-01-01T23:59:59.000Z
FEARLESS (Fluid mEchanics with Adaptively Refined Large Eddy SimulationS) is a new numerical scheme arising from the combined use of subgrid scale (SGS) model for turbulence at the unresolved length scales and adaptive mesh refinement (AMR) for resolving the large scales. This tool is especially suitable for the study of turbulent flows in strongly clumped media. In this contribution, the main features of FEARLESS are briefly outlined. We then summarize the main results of FEARLESS cosmological simulations of galaxy cluster evolution. In clusters, the production of turbulence is closely correlated with merger events; for minor mergers, we find that turbulent dissipation affects the cluster energy budget only locally. The level of entropy in the cluster core is enhanced in FEARLESS simulations, in accord with a better modeling of the unresolved flow, and with its feedback on the resolved mixing in the ICM.
Numerical dissipation and the bottleneck effect in simulations of compressible isotropic turbulence
Schmidt, W; Niemeyer, J C
2004-01-01T23:59:59.000Z
Energy spectrum functions computed from data of various three-dimensional simulations of forced isotropic turbulence are investigated. The piece-wise parabolic method (PPM) was used to treat flows with Mach number of the order unity. The dissipation is of purely numerical origin. For the dimensionless mean rate of dissipation, we find values in agreement with results from other, mostly incompressible turbulence simulations. The so-called bottleneck phenomenon is also present in the turbulence energy spectra. Although the bottleneck reduces the range of nearly inertial scales considerably, we were able to estimate the value of the Kolmogorov constant. In the statistically stationary regime, $C\\approx 1.7$ for strictly subsonic turbulence, but also in the presence of shocklets in moderately transonic flows. As compressive components become more significant, however, the value of $C$ appears to decrease. Moreover, we discuss length scales related to numerical dissipation, in particular, an effective numerical le...
New near-wall two-equation model for turbulent heat transport
Torii, Shuichi [Kagoshima Univ. (Japan). Dept. of Mechanical Engineering; Yang, W.J. [Univ. of Michigan, Ann Arbor, MI (United States). Dept. of Mechanical Engineering and Applied Mechanics
1996-03-01T23:59:59.000Z
An anisotropic two-equation model is proposed to determine turbulent heat flux in a channel flow up to the wall. The turbulent heat fluxes are given in the form of an anisotropic eddy diffusivity representation in which both the isotropic and anisotropic eddy diffusivities of heat are expressed using the temperature variance {ovr t{sup 2}}, the dissipation rate of temperature fluctuations {var_epsilon}{sub t}, and the velocity gradient. The proposed model is tested through application to an incompressible, two-dimensional, turbulent channel flow with the neglect of buoyant heat transfer. Calculated results are compared with the direct numerical simulation data. It is disclosed from the study that the proposed anisotropic {ovr t{sup 2}}-{var_epsilon}{sub t} heat transfer model predicts reasonably well the distributions of the time-averaged temperature, normal and streamwise turbulent heat fluxes, temperature variance, dissipation rates, and these near-wall budgets.
Terascale High-Fidelity Simulations of Turbulent Combustion with Detailed Chemistry
Im, Hong G [University of Michigan] [University of Michigan; Trouve, Arnaud [University of Maryland] [University of Maryland; Rutland, Christopher J [University of Wisconsin] [University of Wisconsin; Chen, Jacqueline H [Sandia National Laboratories] [Sandia National Laboratories
2012-08-13T23:59:59.000Z
The TSTC project is a multi-university collaborative effort to develop a high-fidelity turbulent reacting flow simulation capability utilizing terascale, massively parallel computer technology. The main paradigm of our approach is direct numerical simulation (DNS) featuring highest temporal and spatial accuracy, allowing quantitative observations of the fine-scale physics found in turbulent reacting flows as well as providing a useful tool for development of sub-models needed in device-level simulations. The code named S3D, developed and shared with Chen and coworkers at Sandia National Laboratories, has been enhanced with new numerical algorithms and physical models to provide predictive capabilities for spray dynamics, combustion, and pollutant formation processes in turbulent combustion. Major accomplishments include improved characteristic boundary conditions, fundamental studies of auto-ignition in turbulent stratified reactant mixtures, flame-wall interaction, and turbulent flame extinction by water spray. The overarching scientific issue in our recent investigations is to characterize criticality phenomena (ignition/extinction) in turbulent combustion, thereby developing unified criteria to identify ignition and extinction conditions. The computational development under TSTC has enabled the recent large-scale 3D turbulent combustion simulations conducted at Sandia National Laboratories.
Zonal Flow as Pattern Formation
Parker, Jeffrey B
2015-01-01T23:59:59.000Z
In this section, we examine the transition from statistically homogeneous turbulence to inhomogeneous turbulence with zonal flows. Statistical equations of motion can be derived from the quasilinear approximation to the Hasegawa-Mima equation. We review recent work that finds a bifurcation of these equations and shows that the emergence of zonal flows mathematically follows a standard type of pattern formation. We also show that the dispersion relation of modulational instability can be extracted from the statistical equations of motion in a certain limit. The statistical formulation can thus be thought to offer a more general perspective on growth of coherent structures, namely through instability of a full turbulent spectrum. Finally, we offer a physical perspective on the growth of large-scale structures.
Power-law wrinkling turbulence-flame interaction model for astrophysical flames
Jackson, Aaron P. [Laboratories for Computational Physics and Fluid Dynamics, Naval Research Laboratory, Washington, DC (United States); Townsley, Dean M. [Department of Physics and Astronomy, The University of Alabama, Tuscaloosa, AL (United States); Calder, Alan C. [Department of Physics and Astronomy, The State University of New York - Stony Brook, Stony Brook, NY (United States)
2014-04-01T23:59:59.000Z
We extend a model for turbulence-flame interactions (TFI) to consider astrophysical flames with a particular focus on combustion in Type Ia supernovae. The inertial range of the turbulent cascade is nearly always under-resolved in simulations of astrophysical flows, requiring the use of a model in order to quantify the effects of subgrid-scale wrinkling of the flame surface. We provide implementation details to extend a well-tested TFI model to low-Prandtl number flames for use in the compressible hydrodynamics code FLASH. A local, instantaneous measure of the turbulent velocity is calibrated for FLASH and verification tests are performed. Particular care is taken to consider the relation between the subgrid rms turbulent velocity and the turbulent flame speed, especially for high-intensity turbulence where the turbulent flame speed is not expected to scale with the turbulent velocity. Finally, we explore the impact of different TFI models in full-star, three-dimensional simulations of Type Ia supernovae.
Rotation Rate of Particle Pairs in Homogeneous Isotropic Turbulence
Daddi-Moussa-Ider, Abdallah
2015-01-01T23:59:59.000Z
Understanding the dynamics of particles in turbulent flow is important in many environmental and industrial applications. In this paper, the statistics of particle pair orientation is numerically studied in homogeneous isotropic turbulent flow, with Taylor microscale Rynolds number of 300. It is shown that the Kolmogorov scaling fails to predict the observed probability density functions (PDFs) of the pair rotation rate and the higher order moments accurately. Therefore, a multifractal formalism is derived in order to include the intermittent behavior that is neglected in the Kolmogorov picture. The PDFs of finding the pairs at a given angular velocity for small relative separations, reveals extreme events with stretched tails and high kurtosis values. Additionally, The PDFs are found to be less intermittent and follow a complementary error function distribution for larger separations.
Wang, T.-S.; Foote, John; Litchford, Ron [NASA Marshall Space Flight Center, Huntsville, Alabama, 35812 (United States)
2006-01-20T23:59:59.000Z
The objective of this effort is to perform design analyses for a non-nuclear hot-hydrogen materials tester, as a first step towards developing efficient and accurate multiphysics, thermo-fluid computational methodology to predict environments for hypothetical solid-core, nuclear thermal engine thrust chamber design and analysis. The computational methodology is based on a multidimensional, finite-volume, turbulent, chemically reacting, thermally radiating, unstructured-grid, and pressure-based formulation. The multiphysics invoked in this study include hydrogen dissociation kinetics and thermodynamics, turbulent flow, convective, and thermal radiative heat transfers. The goals of the design analyses are to maintain maximum hot-hydrogen jet impingement energy and to minimize chamber wall heating. The results of analyses on three test fixture configurations and the rationale for final selection are presented. The interrogation of physics revealed that reactions of hydrogen dissociation and recombination are highly correlated with local temperature and are necessary for accurate prediction of the hot-hydrogen jet temperature.
Andrey Beresnyak; Alex Lazarian
2008-05-06T23:59:59.000Z
We present a model for nonlinear decay of the weak wave in three-dimensional incompressible magnetohydrodynamic (MHD) turbulence. We show that the decay rate is different for parallel and perpendicular waves. We provide a general formula for arbitrarily directed waves and discuss particular limiting cases known in the literature. We test our predictions with direct numerical simulations of wave decay in three-dimensional MHD turbulence, and discuss the influence of turbulent damping on the development of linear instabilities in the interstellar medium and on other important astrophysical processes.
Glenn E McCreery; Keith G Condie
2006-09-01T23:59:59.000Z
The Very High Temperature Reactor (VHTR) is the leading candidate for the Next Generation Nuclear Power (NGNP) Project in the U.S. which has the goal of demonstrating the production of emissions free electricity and hydrogen by 2015. The present document addresses experimental modeling of flow and thermal mixing phenomena of importance during normal or reduced power operation and during a loss of forced reactor cooling (pressurized conduction cooldown) scenario. The objectives of the experiments are, 1), provide benchmark data for assessment and improvement of codes proposed for NGNP designs and safety studies, and, 2), obtain a better understanding of related phenomena, behavior and needs. Physical models of VHTR vessel upper and lower plenums which use various working fluids to scale phenomena of interest are described. The models may be used to both simulate natural convection conditions during pressurized conduction cooldown and turbulent lower plenum flow during normal or reduced power operation.
Persson, Ola
shown that the ABL has a complicated structure involving generally quasi-persistent, thermal. These sensors were chosen to obtain observations of the thermal, kinematic and turbulent structure in the lowest beams. The wind profiler was deployed on the bow of the Oden during the entire cruise. It provided
Ezer,Tal
mixing. Surface waves can enhance turbulence kinetic energy and mixing of the upper ocean via wave interaction on the MellorYamada scheme and upper ocean thermal structure are examined and compared with each scheme. The behaviors of the MellorYamada scheme, as well as the simulated upper ocean thermal structure
Magnetohydrodynamic turbulent cascade of coronal loop magnetic fields
Rappazzo, A. F. [Instituto de Astrofisica de Canarias, E-38200 La Laguna, Tenerife (Spain); Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109 (United States); Bartol Research Institute, Department of Physics and Astronomy, University of Delaware, Delaware 19716 (United States); Velli, M. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109 (United States)
2011-06-15T23:59:59.000Z
The Parker model for coronal heating is investigated through a high resolution simulation. An inertial range is resolved where fluctuating magnetic energy E{sub M}(k{sub perpendicular}){proportional_to}k{sub perpendicular}{sup -2.7} exceeds kinetic energy E{sub K}(k{sub perpendicular}){proportional_to}k{sub perpendicular}{sup -0.6}. Increments scale as {delta}b{sub l}{approx_equal}l{sup -0.85}and {delta}u{sub l}{approx_equal}l{sup +0.2} with velocity increasing at small scales, indicating that magnetic reconnection plays a prime role in this turbulent system. We show that spectral energy transport is akin to standard magnetohydrodynamic (MHD) turbulence even for a system of reconnecting current sheets sustained by the boundary. In this new MHD turbulent cascade, kinetic energy flows are negligible while cross-field flows are enhanced, and through a series of ''reflections'' between the two fields, cascade more than half of the total spectral energy flow.
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.
Hakima Bessaih; Benedetta Ferrario
2011-03-10T23:59:59.000Z
Gaussian measures of Gibbsian type are associated with some shell models of 3D turbulence; they are constructed by means of the energy, a conserved quantity for the 3D inviscid and unforced shell model. We prove the existence of a unique global flow for a stochastic viscous shell model and a global flow for the deterministic inviscid shell model, with the property that these Gibbs measures are invariant for these flows.
Turbulence at Hydroelectric Power Plants and its Potential Effects on Fish.
Cada, Glenn F.; Odeh, Mufeed
2001-01-01T23:59:59.000Z
The fundamental influence of fluid dynamics on aquatic organisms is receiving increasing attention among aquatic ecologists. For example, the importance of turbulence to ocean plankton has long been a subject of investigation (Peters and Redondo 1997). More recently, studies have begun to emerge that explicitly consider the effects of shear and turbulence on freshwater invertebrates (Statzner et al. 1988; Hart et al. 1996) and fishes (Pavlov et al. 1994, 1995). Hydraulic shear stress and turbulence are interdependent natural fluid phenomena that are important to fish, and consequently it is important to develop an understanding of how fish sense, react to, and perhaps utilize these phenomena under normal river flows. The appropriate reaction to turbulence may promote movement of migratory fish or prevent displacement of resident fish. It has been suggested that one of the adverse effects of flow regulation by hydroelectric projects is the reduction of normal turbulence, particularly in the headwaters of reservoirs, which can lead to disorientation and slowing of migration (Williams et al. 1996; Coutant et al. 1997; Coutant 1998). On the other hand, greatly elevated levels of shear and turbulence may be injurious to fish; injuries can range from removal of the mucous layer on the body surface to descaling to torn opercula, popped eyes, and decapitation (Neitzel et al. 2000a,b). Damaging levels of fluid stress can occur in a variety of circumstances in both natural and man-made environments. This paper discusses the effects of shear stress and turbulence on fish, with an emphasis on potentially damaging levels in man-made environments. It defines these phenomena, describes studies that have been conducted to understand their effects, and identifies gaps in our knowledge. In particular, this report reviews the available information on the levels of turbulence that can occur within hydroelectric power plants, and the associated biological effects. The final section provides the preliminary design of an experimental apparatus that will be used to expose fish to representative levels of turbulence in the laboratory.
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.
Flame Interactions in Turbulent Premixed Twin V-flames
Dunstan, T. D.; Swaminathan, N.; Bray, K. N. C.; Kingsbury, N. G.
2013-01-16T23:59:59.000Z
diminish with increasing turbulence intensity, and so it is unlikely that any significant influence remains within the regions of interest for the flames presented here. It should also be noted that no energy is added to the flow in the current implemen... . A flow-chart summary is given in Fig. 2, and an example of the procedure applied to two-dimensional test data is shown in Fig. 3. The AFE procedure used here comprises three principal stages: (1) the binarised c field data from two successive time...
Zevenhoven, Ron
, food, pollution, health and quality of life, population growth, consumption Cooling and freezing air affects moisture loss from products, etc. Picture: ÇB98 23.11.2014 Åbo Akademi Univ - Thermal, and avoiding high air velocities Picture:http://www.sun-dried-tomatoes.com/information.html Picture:http://res2
UNH Thermal WorkshopUNH Thermal Workshop or how important isor how important is
) EPA grants to UNH for thermal regimes of Northeast g g Streams and Thermal Impacts of Stormwater BMPs response curves Ecological targets Enviro. flow targets Implement program River types alteration Statewide
The influence of a magnetic field on turbulent heat transfer of a high Prandtl number fluid
Nakaharai, H. [Department of Advanced Energy Engineering Science, Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga-kouen 6-1, Kasuga, Fukuoka 816-8580 (Japan); Takeuchi, J.; Morley, N.B.; Abdou, M.A. [Mechanical and Aerospace Engineering Department, University of California, Los Angeles, CA 90095-1597 (United States); Yokomine, T. [Faculty of Energy Engineering Science, Kyushu University, Kasuga-kouen 6-1, Kasuga, Fukuoka 816-8580 (Japan); Kunugi, T. [Department of Nuclear Engineering, Kyoto University, Yoshida, Sakyo, Kyoto 606-8501 (Japan); Satake, S. [Department of Applied Electronics, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510 (Japan)
2007-10-15T23:59:59.000Z
The influence of a transverse magnetic field on the local and average heat transfer of an electrically conducting, turbulent fluid flow with high Prandtl number was studied experimentally. The mechanism of heat transfer modification due to magnetic field is considered with aid of available numerical simulation data for turbulent flow field. The influence of the transverse magnetic field on the heat transfer was to suppress the temperature fluctuation and to steepen the mean temperature gradient in near-wall region in the direction parallel to the magnetic field. The mean temperature gradient is not influenced compared to the temperature fluctuation in the direction vertical to the magnetic field. (author)
Turbulent Friction in Rough Pipes and the Energy Spectrum of the Phenomenological Theory
G. Gioia; Pinaki Chakraborty
2005-12-20T23:59:59.000Z
The classical experiments on turbulent friction in rough pipes were performed by J. Nikuradse in the 1930's. Seventy years later, they continue to defy theory. Here we model Nikuradse's experiments using the phenomenological theory of Kolmog\\'orov, a theory that is widely thought to be applicable only to highly idealized flows. Our results include both the empirical scalings of Blasius and Strickler, and are otherwise in minute qualitative agreement with the experiments; they suggest that the phenomenological theory may be relevant to other flows of practical interest; and they unveil the existence of close ties between two milestones of experimental and theoretical turbulence.
A model for gyrotactic pattern formation of motile micro-organisms in turbulence
Gustavsson, K; Jonsson, P R; Mehlig, B
2015-01-01T23:59:59.000Z
Recent studies show that the dynamics of motile organisms subject to gravitational torques in turbulence gives rise to patchiness. Spherical motile organisms gather in down-welling regions of the turbulent flow. We determine how shape affects preferential sampling and small-scale spatial clustering (determining local encounter rates) by analysing a statistical model in two and three spatial dimensions. By recursively refining approximations for the paths the organisms take through the flow we determine analytically how preferential sampling and small-scale clustering in the model depend upon the dimensionless parameters of the problem. We show that singularities ("caustics") occur in the dynamics and discuss how these singularities affect spatial patterns.
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.
Large-eddy simulation of multiphase flows in complex combustors
Mahesh, Krishnan
Large-eddy simulation of multiphase flows in complex combustors S. V. Apte1 , K. Mahesh2 , F. Ham1 to accurately predict reacting multi-phase flows in practical combustors involving complex physical phenomena-turbine combustor geometries to evaluate the predictions made for multiphase, turbulent flow. 1 Introduction
F h iForschungsseminar Strmungskontrolle -Flow Control
Haller-Dintelmann, Robert
over cavities - Control of the wake behind a cylinder - Modelling of laminar to turbulent transition - Control of atomization - Drops on smart interfaces: flow manipulation and control Field effect flowF h iForschungsseminar StrÃ¶mungskontrolle - Flow Control In diesem Forschungsseminar, welches von
Noise correction of turbulent spectra obtained from Acoustic Doppler Velocimeters
Durgesh, Vibhav; Thomson, Jim; Richmond, Marshall C.; Polagye, Brian
2014-03-02T23:59:59.000Z
Accurately estimated auto-spectral density functions are essential for characterization of turbulent flows, and they also have applications in computational fluid dynamics modeling, site and inflow characterization for hydrokinetic turbines, and inflow turbulence generation. The Acoustic Doppler Velocimeter (ADV) provides single-point temporally resolved data, that are used to characterize turbulent flows in rivers, seas, and oceans. However, ADV data are susceptible to contamination from various sources, including instrument noise, which is the intrinsic limit to the accuracy of acoustic velocity measurements. Due to the presence of instrument noise, the spectra obtained are altered at high frequencies. The focus of this study is to develop a robust and effective method for accurately estimating auto-spectral density functions from ADV data by reducing or removing the spectral contribution derived from instrument noise. For this purpose, the “Noise Auto-Correlation” (NAC) approach was developed, which exploits the correlation properties of instrument noise to identify and remove its contribution from spectra. The spectra estimated using the NAC approach exhibit increased fidelity and a slope of -5/3 in the inertial range, which is typically observed for turbulent flows. Finally, this study also compares the effectiveness of low-pass Gaussian filters in removing instrument noise with that of the NAC approach. For the data used in this study, both the NAC and Gaussian filter approaches are observed to be capable of removing instrument noise at higher frequencies from the spectra. However, the NAC results are closer to the expected frequency power of -5/3 in the inertial sub-range.
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.
D. M. McEligot; K.G. Condie; G. E. Mc Creery; H. M. Mc Ilroy
2005-09-01T23:59:59.000Z
The objective of the present report is to document the design of our first experiment to measure generic flow phenomena expected to occur in the lower plenum of a typical prismatic VHTR (Very High Temperature Reactor) concept. In the process, fabrication sketches are provided for the use of CFD (computational fluid dynamics) analysts wishing to employ the data for assessment of their proposed codes. The general approach of the project is to develop new benchmark experiments for assessment in parallel with CFD and coupled CFD/systems code calculations for the same geometry. One aspect of the complex flow in a prismatic VHTR is being addressed: flow and thermal mixing in the lower plenum ("hot streaking" issue). Current prismatic VHTR concepts were examined to identify their proposed flow conditions and geometries over the range from normal operation to decay heat removal in a pressurized cooldown. Approximate analyses were applied to determine key non-dimensional parameters and their magnitudes over this operating range. The flow in the lower plenum can locally be considered to be a situation of multiple jets into a confined crossflow -- with obstructions. Flow is expected to be turbulent with momentum-dominated turbulent jets entering; buoyancy influences are estimated to be negligible in normal full power operation. Experiments are needed for the combined features of the lower plenum flows. Missing from the typical jet experiments available are interactions with nearby circular posts and with vertical posts in the vicinity of vertical walls - with near stagnant surroundings at one extreme and significant crossflow at the other.
Rényi entropy flows from quantum heat engines
Mohammad H. Ansari; Yuli V. Nazarov
2015-03-20T23:59:59.000Z
We evaluate Renyi entropy flows from generic quantum heat engines (QHE) to a weakly-coupled probe environment kept in thermal equilibrium. We show that the flows are determined not only by heat flow but also by a quantum coherent flow that can be separately measured in experiment apart from the heat flow measurement. The same pertains to Shanon entropy flow. This appeals for a revision of the concept of entropy flows in quantum nonequlibrium thermodynamics.
Atmospheric and Wake Turbulence Impacts on Wind Turbine Fatigue Loading: Preprint
Lee, S.; Churchfield, M.; Moriarty, P.; Jonkman, J.; Michalakes, J.
2011-12-01T23:59:59.000Z
Large-eddy simulations of atmospheric boundary layers under various stability and surface roughness conditions are performed to investigate the turbulence impact on wind turbines. In particular, the aeroelastic responses of the turbines are studied to characterize the fatigue loading of the turbulence present in the boundary layer and in the wake of the turbines. Two utility-scale 5 MW turbines that are separated by seven rotor diameters are placed in a 3 km by 3 km by 1 km domain. They are subjected to atmospheric turbulent boundary layer flow and data is collected on the structural response of the turbine components. The surface roughness was found to increase the fatigue loads while the atmospheric instability had a small influence. Furthermore, the downstream turbines yielded higher fatigue loads indicating that the turbulent wakes generated from the upstream turbines have significant impact.
Turbulent magnetic pumping in a Babcock-Leighton solar dynamo model
G. Guerrero; E. M. de Gouveia Dal Pino
2008-03-24T23:59:59.000Z
The turbulent pumping effect corresponds to the transport of magnetic flux due to the presence of density and turbulence gradients in convectively unstable layers. In the induction equation it appears as an advective term and for this reason it is expected to be important in the solar and stellar dynamo processes. In this work, we have explored the effects of the turbulent pumping in a flux-dominated Babcock-Leighton solar dynamo model with a solar-like rotation law. The results reveal the importance of the pumping mechanism for solving current limitations in mean field dynamo modeling such as the storage of the magnetic flux and the latitudinal distribution of the sunspots. In the case that a meridional flow is assumed to be present only in the upper part of the convective zone, it is the full turbulent pumping that regulates both the period of the solar cycle and the latitudinal distribution of the sunspots activity.
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 ...
Thermal/MechanicalThermal/Mechanical Properties of WoodProperties of Wood--PVCPVC
.composites. Heat flow, heat capacity, andHeat flow, heat capacity, and enthalpyenthalpy Glass transition/Mechanical Analysis TechniquesThermal/Mechanical Analysis Techniques #12;Rubbery Leathery Viscous liquid Rigid (Semi
Effects of turbulent diffusion on the chemistry of diffuse clouds
P. Lesaffre; M. Gerin; P. Hennebelle
2007-04-24T23:59:59.000Z
Aims. We probe the effect of turbulent diffusion on the chemistry at the interface between a cold neutral medium (CNM) cloudlet and the warm neutral medium (WNM). Methods. We perform moving grid, multifluid, 1D, hydrodynamical simulations with chemistry including thermal and chemical diffusion. The diffusion coefficients are enhanced to account for turbulent diffusion. We post-process the steady-states of our simulations with a crude model of radiative transfer to compute line profiles. Results. Turbulent diffusion spreads out the transition region between the CNM and the WNM. We find that the CNM slightly expands and heats up: its CH and H$_2$ content decreases due to the lower density. The change of physical conditions and diffusive transport increase the H$^+$ content in the CNM which results in increased OH and H$_2$O. Diffusion transports some CO out of the CNM. It also brings H$_2$ into contact with the warm gas with enhanced production of CH$^+$, H$_3^+$, OH and H$_2$O at the interface. O lines are sensitive to the spread of the thermal profile in the intermediate region between the CNM and the WNM. Enhanced molecular content at the interface of the cloud broadens the molecular line profiles and helps exciting transitions of intermediate energy. The relative molecular yield are found higher for bigger clouds. Conclusions. Turbulent diffusion can be the source of additional molecular production and should be included in chemical models of the interstellar medium (ISM). It also is a good candidate for the interpretation of observational problems such as warm H$_2$, CH$^+$ formation and presence of H$_3^+$.
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.
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
Francis, Simone
2006-04-12T23:59:59.000Z
influenced flow at the Flower Garden Banks, two small but thriving coral reef ecosystems in the northwest Gulf of Mexico. Flow past the modeled banks is characterized by vortex shedding, turbulent wake formation and strong return velocities in the near...
Turbulence and Magnetic Fields in Clouds
Shantanu Basu
2004-11-15T23:59:59.000Z
We discuss several categories of models which may explain the IMF, including the possible role of turbulence and magnetic fields.
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
Stability, Energetics, and Turbulent Transport in
Torquato, Salvatore
fields" Department of Astrophysical Sciences Spring Colloquium Steve Cowley (UK Atomic Energy Authority of solar-wind turbulence" Chris Chen (UC Berkeley) 2:40pm "Energy spectra in MHD turbulenceStability, Energetics, and Turbulent Transport in Astrophysical, Fusion, and Solar Plasmas 8
Energy spectra of finite temperature superfluid helium-4 turbulence
Kivotides, Demosthenes [Department of Aeronautics, Imperial College London, London SW7 2AZ (United Kingdom)
2014-10-15T23:59:59.000Z
A mesoscopic model of finite temperature superfluid helium-4 based on coupled Langevin-Navier-Stokes dynamics is proposed. Drawing upon scaling arguments and available numerical results, a numerical method for designing well resolved, mesoscopic calculations of finite temperature superfluid turbulence is developed. The application of model and numerical method to the problem of fully developed turbulence decay in helium II, indicates that the spectral structure of normal-fluid and superfluid turbulence is significantly more complex than that of turbulence in simple-fluids. Analysis based on a forced flow of helium-4 at 1.3 K, where viscous dissipation in the normal-fluid is compensated by the Lundgren force, indicate three scaling regimes in the normal-fluid, that include the inertial, low wavenumber, Kolmogorov k{sup ?5/3} regime, a sub-turbulence, low Reynolds number, fluctuating k{sup ?2.2} regime, and an intermediate, viscous k{sup ?6} range that connects the two. The k{sup ?2.2} regime is due to normal-fluid forcing by superfluid vortices at high wavenumbers. There are also three scaling regimes in the superfluid, that include a k{sup ?3} range that corresponds to the growth of superfluid vortex instabilities due to mutual-friction action, and an adjacent, low wavenumber, k{sup ?5/3} regime that emerges during the termination of this growth, as superfluid vortices agglomerate between intense normal-fluid vorticity regions, and weakly polarized bundles are formed. There is also evidence of a high wavenumber k{sup ?1} range that corresponds to the probing of individual-vortex velocity fields. The Kelvin waves cascade (the main dynamical effect in zero temperature superfluids) appears to be damped at the intervortex space scale.
Proton Kinetic Effects in Vlasov and Solar Wind Turbulence
Servidio, S; Valentini, F; Perrone, D; Califano, F; Chapman, S; Matthaeus, W H; Veltri, P
2013-01-01T23:59:59.000Z
Kinetic plasma processes have been investigated in the framework of solar wind turbulence, employing Hybrid Vlasov-Maxwell (HVM) simulations. The dependency of proton temperature anisotropy T_{\\perp}/T_{\\parallel} on the parallel plasma beta \\beta_{\\parallel}, commonly observed in spacecraft data, has been recovered using an ensemble of HVM simulations. By varying plasma parameters, such as plasma beta and fluctuation level, the simulations explore distinct regions of the parameter space given by T_{\\perp}/T_{\\parallel} and \\beta_{\\parallel}, similar to solar wind sub-datasets. Moreover, both simulation and solar wind data suggest that temperature anisotropy is not only associated with magnetic intermittent events, but also with gradient-type structures in the flow and in the density. This connection between non-Maxwellian kinetic effects and various types of intermittency may be a key point for understanding the complex nature of plasma turbulence.
Turbulent heat transfer performance of single stage turbine
Amano, R.S.; Song, B.
1999-07-01T23:59:59.000Z
To increase the efficiency and the power of modern power plant gas turbines, designers are continually trying to raise the maximum turbine inlet temperature. Here, a numerical study based on the Navier-Stokes equations on a three-dimensional turbulent flow in a single stage turbine stator/rotor passage has been conducted and reported in this paper. The full Reynolds-stress closure model (RSM) was used for the computations and the results were also compared with the computations made by using the Launder-Sharma low-Reynolds-number {kappa}-{epsilon} model. The computational results obtained using these models were compared in order to investigate the turbulence effect in the near-wall region. The set of the governing equations in a generalized curvilinear coordinate system was discretized by using the finite volume method with non-staggered grids. The numerical modeling was performed to interact between the stator and rotor blades.
Analogy between turbulence and quantum gravity: beyond Kolmogorov's 1941 theory
S. Succi
2011-11-14T23:59:59.000Z
Simple arguments based on the general properties of quantum fluctuations have been recently shown to imply that quantum fluctuations of spacetime obey the same scaling laws of the velocity fluctuations in a homogeneous incompressible turbulent flow, as described by Kolmogorov 1941 (K41) scaling theory. Less noted, however, is the fact that this analogy rules out the possibility of a fractal quantum spacetime, in contradiction with growing evidence in quantum gravity research. In this Note, we show that the notion of a fractal quantum spacetime can be restored by extending the analogy between turbulence and quantum gravity beyond the realm of K41 theory. In particular, it is shown that compatibility of a fractal quantum-space time with the recent Horava-Lifshitz scenario for quantum gravity, implies singular quantum wavefunctions. Finally, we propose an operational procedure, based on Extended Self-Similarity techniques, to inspect the (multi)-scaling properties of quantum gravitational fluctuations.
Turbulence transport with nonlocal interactions
Linn, R.R.; Clark, T.T.; Harlow, F.H.; Turner, L.
1998-03-01T23:59:59.000Z
This preliminary report describes a variety of issues in turbulence transport analysis with particular emphasis on closure procedures that are nonlocal in wave-number and/or physical space. Anomalous behavior of the transport equations for large scale parts of the turbulence spectrum are resolved by including the physical space nonlocal interactions. Direct and reverse cascade processes in wave-number space are given a much richer potential for realistic description by the nonlocal formulations. The discussion also describes issues, many still not resolved, regarding new classes of self-similar form functions.
Secret Hidden in Navier-Stokes Equations: Singularity and Criterion of Turbulent Transition
Hua-Shu Dou
2014-12-28T23:59:59.000Z
A new formulation of the Navier-Stokes equation, in terms of the gradient of the total mechanical energy, is derived for the time-averaged flows, and the singular point possibly existing in the Navier-Stokes equation is exactly found. Transition of a laminar flow to turbulence must be implemented via this singular point. For pressure driven flows, this singular point corresponds to the inflection point on the velocity profile. It is found that the stability of a flow depends on the direction of the gradient of the total mechanical energy for incompressible pressure-driven flow. When this direction is nearer the normal direction of the streamline, the flow is more unstable. It is further demonstrated that the existence of the singularity in the time-averaged Navier-Stokes equation is the necessary and sufficient condition for the turbulent transition. In turbulent transition, it is observed that the role of disturbance is to promote the flow approaching to produce this singular point. These results are the most important part of the energy gradient theory.
Excitation of flow instabilities due to nonlinear scale invariance
Prasad Datta, Dhurjati, E-mail: dp-datta@yahoo.com [Department of Mathematics, University of North Bengal, Siliguri, West Bengal 734013 (India); Sen, Sudip [National Institute of Aerospace (NASA-LaRC), 100 Exploration Way, Hampton, Virginia 23666 (United States); College of William and Mary, Williamsburg, Virginia 23187 (United States)
2014-05-15T23:59:59.000Z
A novel route to instabilities and turbulence in fluid and plasma flows is presented in kinetic Vlasov-Maxwell model. New kind of flow instabilities is shown to arise due to the availability of new kinetic energy sources which are absent in conventional treatments. The present approach is based on a scale invariant nonlinear analytic formalism developed to address irregular motions on a chaotic attractor or in turbulence in a more coherent manner. We have studied two specific applications of this turbulence generating mechanism. The warm plasma Langmuir wave dispersion relation is shown to become unstable in the presence of these multifractal measures. In the second application, these multifractal measures are shown to induce naturally non-Gaussian, i.e., a stretched, Gaussian distribution and anomalous transport for tracer particles from the turbulent advection-diffusion transport equation in a Vlasov plasma flow.
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.
Primordial magnetic field amplification from turbulent reheating
Calzetta, Esteban [Departamento de Física, FCEyN-UBA and IFIBA-CONICET, Cdad. Universitaria, Buenos Aires (Argentina); Kandus, Alejandra, E-mail: calzetta@df.uba.ar, E-mail: kandus@uesc.br [LATO - DCET - UESC. Rodovia Ilhéus-Itabuna, km 16 s/n, CEP: 45662-900, Salobrinho, Ilhéus-BA (Brazil)
2010-08-01T23:59:59.000Z
We analyze the possibility of primordial magnetic field amplification by a stochastic large scale kinematic dynamo during reheating. We consider a charged scalar field minimally coupled to gravity. During inflation this field is assumed to be in its vacuum state. At the transition to reheating the state of the field changes to a many particle/anti-particle state. We characterize that state as a fluid flow of zero mean velocity but with a stochastic velocity field. We compute the scale-dependent Reynolds number Re(k), and the characteristic times for decay of turbulence, t{sub d} and pair annihilation t{sub a}, finding t{sub a} << t{sub d}. We calculate the rms value of the kinetic helicity of the flow over a scale L and show that it does not vanish. We use this result to estimate the amplification factor of a seed field from the stochastic kinematic dynamo equations. Although this effect is weak, it shows that the evolution of the cosmic magnetic field from reheating to galaxy formation may well be more complex than as dictated by simple flux freezing.
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.
Evaluation of the Effects of Turbulence on the Behavior of Migratory Fish, 2002 Final Report.
Odeh, Mufeed.
2002-03-01T23:59:59.000Z
The fundamental influence of fluid dynamics on aquatic organisms is receiving increasing attention among aquatic ecologists. For example, the importance of turbulence to ocean plankton has long been a subject of investigation (Peters and Redondo 1997). More recently, studies have begun to emerge that explicitly consider the effects of shear and turbulence on freshwater invertebrates (Statzner et al. 1988; Hart et al. 1996) and fishes (Pavlov et al. 1994, 1995). Hydraulic shear stress and turbulence are interdependent natural hydraulic phenomena that are important to fish, and consequently it is important to develop an understanding of how fish sense, react to, and perhaps utilize these phenomena under normal river flows. The appropriate reaction to turbulence may promote movement of migratory fish (Coutant 1998) or prevent displacement of resident fish. It has been suggested that one of the adverse effects of flow regulation by hydroelectric projects is the reduction of normal turbulence, particularly in the headwaters of reservoirs, which can lead to disorientation and slowing of migration (Williams et al. 1996; Coutant et al. 1997; Coutant 1998). On the other hand, greatly elevated levels of shear and turbulence may be injurious to fish; injuries can range from removal of the mucous layer on the body surface to descaling to torn opercula, popped eyes, and decapitation (Neitzel et al. 2000a,b). Damaging levels of fluid stress, such turbulence, can occur in a variety of circumstances in both natural and man-made environments. This report discusses the effects of shear stress and turbulence on fish, with an emphasis on potentially damaging levels in man-made environments. It defines these phenomena, describes studies that have been conducted to understand their effects, and identifies gaps in our knowledge. In particular, this report reviews the available information on the levels of turbulence that can occur within hydroelectric power plants, and the associated biological effects. Furthermore, this report describes an experimental apparatus designed to test the effect of turbulence on fish, and defines its hydraulics. It gives the results of experiments in which three different fish species were exposed to representative levels of turbulence in the laboratory.
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.
Caustics in turbulent aerosols
M. Wilkinson; B. Mehlig
2004-11-03T23:59:59.000Z
Networks of caustics can occur in the distribution of particles suspended in a randomly moving gas. These can facilitate coagulation of particles by bringing them into close proximity, even in cases where the trajectories do not coalesce. We show that the long-time morphology of these caustic patterns is determined by the Lyapunov exponents lambda_1, lambda_2 of the suspended particles, as well as the rate J at which particles encounter caustics. We develop a theory determining the quantities J, lambda_1, lambda_2 from the statistical properties of the gas flow, in the limit of short correlation times.
Integrated Study of the Nonlinear Dynamics of Collisional Drift Wave Turbulence
George R. Tynan
2012-04-24T23:59:59.000Z
An existing linear magnetized plasma device, the Controlled Shear Decorrelation experiment (CSDX) was used to study the transition from a state of coherent wave like activity to a state of turbulent activity using the magnetic field and thus magnetization of the plasma as the control parameter. The results show the onset of coherent drift waves consistent with linear stability analysis. As the magnetization is raised, at first multiple harmonics appear, consistent with wave steepening. This period is then followed by the beginning of nonlinear interactions between different wave modes, which then results in the formation of narrow frequency but distributed azimuthal wave number fluctuations that are consistent with the formation of long-lived coherent nonlinear structures within the plasmas. These structures, termed quasicoherent modes, persist as the magnetic field is raised. Measurements of turbulent momentum flux indicate that the plasma is also forming an azimuthally symmetric radially sheared fluid flow that is nonlinearly driven by smaller scaled turbulent fluctuations. Further increases in the magnetic field result in the breakup of the quasicoherent mode, and the clear formation of the sheared flow. Numerical simulations of the experiment reproduce the formation of the sheared flow via a vortex merging process, and confirm that the experiment is providing the first clear experimental evidence of the formation of sheared zonal flows from drift turbulent fluctuations in a magnetized plasma.
A Scalable Turbulent Mixing Aerosol Reactor for Oxide-Coated Silicon Nanoparticles
Atwater, Harry
energy supplied to the reactor by high velocity gas jets. The apparatus described here increased the throughput by a factor of 100 above previous laminar flow reactors, and the induced fast mixing enables scaleA Scalable Turbulent Mixing Aerosol Reactor for Oxide-Coated Silicon Nanoparticles Dean M. Holunga
Overview of a Methodology for Scaling the Indeterminate Equations of Wall Turbulence
Fife, Paul
by the present authors have focused on the fundamental multiscaling be- haviors of the time averaged dynamical Couette-Poiseuille flow, and fully developed turbulent heat transfer in a channel. Nomenclature T Reynolds shear stress Kinematic viscosity Mass density Superscript m Denotes maximum value Superscript
Cascading process in the flute-mode turbulence of a plasma
Gonzalez, R.; Gomez, D.; Ferro Fontan, C. (Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, (1428) Buenos Aires (Argentina) Instituto de Astronomia y Fisica del Espacio, C C No. 67, Sucursal 28, (1428) Buenos Aires (Argentina)); Sicardi Schifino, A.C.; Montagne, R. (Instituto de Fisica, Facultad de Ciencias, Universidad de la Republica, CC 10773, CP 11200, Montevideo (Uruguay) Instituto de Fisica, Facultad de Ingenieria, Universidad de la Republica, CC No. 30, CP 11000, Montevideo (Uruguay))
1993-06-01T23:59:59.000Z
The cascades of ideal invariants in the flute-mode turbulence are analyzed by considering a statistics based on an elementary three-mode coupling process. The statistical dynamics of the system is investigated on the basis of the existence of the physically most important (PMI) triad. When finite ion Larmor radius effects are considered, the PMI triad describes the formation of zonal flows.
Energy and enstrophy transfer in numerical simulations of two-dimensional' turbulence
Vallis, Geoff
Energy and enstrophy transfer in numerical simulations of two-dimensional' turbulence Mathew E a significant fraction of the flow field,w and energy spectra from these simulations have slopes significantly October 1992; accepted 25 March 1993) Numerical simulations of statistically steady two-dimensional (2-D
Using cavitation to measure statistics of low-pressure events in large-Reynolds-number turbulence
La Porta, Arthur
Using cavitation to measure statistics of low-pressure events in large-Reynolds-number turbulence A is studied using cavitation. The flow is seeded with microscopic gas bubbles and the hydrostatic pressure is reduced until large negative pressure fluctuations trigger cavitation. Cavitation is detected via light
Near-wall modeling of an isothermal vertical wall using one-dimensional turbulence
DesJardin, Paul E.
[5]. The challenge in modeling this class of flows is the coupling between the heat transfer approaches are considered for describing the heat transfer from a vertical isothermal wall. In this approach at the wall surface and the generation of turbulence from buoyancy forces, which in turn, affect
J.T. Birkholzer; N. Halecky; S.W> Webb; P.F. Peterson; G.S. Bodvarsson
2006-10-11T23:59:59.000Z
In heated tunnels such as those designated for emplacement of radioactive waste at the proposed geologic repository at Yucca Mountain, temperature gradients cause natural convection processes that may significantly influence the moisture conditions in the tunnels and in the surrounding fractured rock. Large-scale convection cells in the heated tunnels would provide an effective mechanism for turbulent mixing and axial transport of vapor generated from evaporation of pore water in the nearby formation. As a result, vapor would be transported from the elevated-temperature sections of the tunnels into cool end sections (where no waste is emplaced), would condense there, and subsequently drain into underlying rock units. To study these processes, we have developed a new simulation method that couples existing tools for simulating thermal-hydrological (TH) conditions in the fractured formation with a module that approximates turbulent natural convection in heated emplacement drifts. The new method simultaneously handles (1) the flow and energy transport processes in the fractured rock, (2) the flow and energy transport processes in the cavity, and (3) the heat and mass exchange at the rock-cavity interface. An application is presented studying the future TH conditions within and near a representative waste emplacement tunnel at Yucca Mountain. Particular focus is on the potential for condensation along the emplacement section, a possible result of heat output differences between individual waste packages.
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.
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
Surface Stresses and Turbulent Fluxes: Problems in Mesoscale Modeling over Terrain
: Turbulent mixing in breaking waves (Epifanio and Qian, 2008) LES for breaking mountain wave Flow past a hill) = Dx Ly (u, v, w) = Dy One kinematic condition (no flow through the boundary): w = u h x + v h y at the boundary and combine with the kinematic condition Lx ui,j,0 vi,j,0 wi,j,0 = f (Dx i,j , interior) , Ly
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.
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.
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 ...
Numerical dissipation and the bottleneck effect in simulations of compressible isotropic turbulence
W. Schmidt; W. Hillebrandt; J. C. Niemeyer
2005-03-15T23:59:59.000Z
The piece-wise parabolic method (PPM) is applied to simulations of forced isotropic turbulence with Mach numbers $\\sim 0.1... 1$. The equation of state is dominated by the Fermi pressure of an electron-degenerate fluid. The dissipation in these simulations is of purely numerical origin. For the dimensionless mean rate of dissipation, we find values in agreement with known results from mostly incompressible turbulence simulations. The calculation of a Smagorinsky length corresponding to the rate of numerical dissipation supports the notion of the PPM supplying an implicit subgrid scale model. In the turbulence energy spectra of various flow realisations, we find the so-called bottleneck phenomenon, i.e., a flattening of the spectrum function near the wavenumber of maximal dissipation. The shape of the bottleneck peak in the compensated spectrum functions is comparable to what is found in turbulence simulations with hyperviscosity. Although the bottleneck effect reduces the range of nearly inertial length scales considerably, we are able to estimate the value of the Kolmogorov constant. For steady turbulence with a balance between energy injection and dissipation, it appears that $C\\approx 1.7$. However, a smaller value is found in the case of transonic turbulence with a large fraction of compressive components in the driving force. Moreover, we discuss length scales related to the dissipation, in particular, an effective numerical length scale $\\Delta_{\\mathrm{eff}}$, which can be regarded as the characteristic smoothing length of the implicit filter associated with the PPM.
Hornsby, W. A.; Peeters, A. G.; Snodin, A. P.; Casson, F. J.; Camenen, Y.; Szepesi, G. [Department of Physics, Centre for Fusion, Space, and Astrophysics, University of Warwick, Coventry (United Kingdom); Siccinio, M.; Poli, E. [Max-Planck-Institut fuer Plasmaphysik, Boltzmannstrasse 2, D-85748 Garching bei Muenchen (Germany)
2010-09-15T23:59:59.000Z
The interaction between small scale turbulence (of the order of the ion Larmor radius) and mesoscale magnetic islands is investigated within the gyrokinetic framework. Turbulence, driven by background temperature and density gradients, over nonlinear mode coupling, pumps energy into long wavelength modes, and can result in an electrostatic vortex mode that coincides with the magnetic island. The strength of the vortex is strongly enhanced by the modified plasma flow response connected with the change in topology, and the transport it generates can compete with the parallel motion along the perturbed magnetic field. Despite the stabilizing effect of sheared plasma flows in and around the island, the net effect of the island is a degradation of the confinement. When density and temperature gradients inside the island are below the threshold for turbulence generation, turbulent fluctuations still persist through turbulence convection and spreading. The latter mechanisms then generate a finite transport flux and, consequently, a finite pressure gradient in the island. A finite radial temperature gradient inside the island is also shown to persist due to the trapped particles, which do not move along the field around the island. In the low collisionality regime, the finite gradient in the trapped population leads to the generation of a bootstrap current, which reduces the neoclassical drive.
Xiao Yong; Holod, Ihor; Zhang Wenlu; Lin Zhihong [Department of Physics and Astronomy, University of California, Irvine, California 92697 (United States); Klasky, Scott [Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)
2010-02-15T23:59:59.000Z
The collisionless trapped electron mode turbulence is investigated by global gyrokinetic particle simulation. The zonal flow dominated by low frequency and short wavelength acts as a very important saturation mechanism. The turbulent eddies are mostly microscopic, but with a significant portion in the mesoscale. The ion heat transport is found to be diffusive and follows the local radial profile of the turbulence intensity. However, the electron heat transport demonstrates some nondiffusive features and only follows the global profile of the turbulence intensity. The nondiffusive features of the electron heat transport is further confirmed by nonlognormal statistics of the flux-surface-averaged electron heat flux. The radial and time correlation functions are calculated to obtain the radial correlation length and autocorrelation time. Characteristic time scale analysis shows that the zonal flow shearing time and eddy turnover time are very close to the effective decorrelation time, which suggests that the trapped electrons move with the fluid eddies. The fluidlike behaviors of the trapped electrons and the persistence of the mesoscale eddies contribute to the transition of the electron turbulent transport from gyro-Bohm scaling to Bohm scaling when the device size decreases.
Zonal Flow as Pattern Formation: Merging Jets and the Ultimate Jet Length Scale
Jeffrey B. Parker and John A. Krommes
2013-01-30T23:59:59.000Z
Zonal flows are well known to arise spontaneously out of turbulence. It is shown that for statisti- cally averaged equations of quasigeostrophic turbulence on a beta plane, zonal flows and inhomoge- neous turbulence fit into the framework of pattern formation. There are many implications. First, the zonal flow wavelength is not unique. Indeed, in an idealized, infinite system, any wavelength within a certain continuous band corresponds to a solution. Second, of these wavelengths, only those within a smaller subband are linearly stable. Unstable wavelengths must evolve to reach a stable wavelength; this process manifests as merging jets.
Inclusion of turbulence in solar modeling
L. H. Li; F. J. Robinson; P. Demarque; S. Sofia; D. B. Guenther
2001-11-07T23:59:59.000Z
The general consensus is that in order to reproduce the observed solar p-mode oscillation frequencies, turbulence should be included in solar models. However, until now there has not been any well-tested efficient method to incorporate turbulence into solar modeling. We present here two methods to include turbulence in solar modeling within the framework of the mixing length theory, using the turbulent velocity obtained from numerical simulations of the highly superadiabatic layer of the sun at three stages of its evolution. The first approach is to include the turbulent pressure alone, and the second is to include both the turbulent pressure and the turbulent kinetic energy. The latter is achieved by introducing two variables: the turbulent kinetic energy per unit mass, and the effective ratio of specific heats due to the turbulent perturbation. These are treated as additions to the standard thermodynamic coordinates (e.g. pressure and temperature). We investigate the effects of both treatments of turbulence on the structure variables, the adiabatic sound speed, the structure of the highly superadiabatic layer, and the p-mode frequencies. We find that the second method reproduces the SAL structure obtained in 3D simulations, and produces a p-mode frequency correction an order of magnitude better than the first method.
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 / (\
New Hampshire, University of
Thermal Sciences The thermal sciences area involves the study of energy conversion and transmission, power generation, the flow of liquids and gases, and the transfer of thermal energy (heat) by means in virtually all energy conversion devices and systems. One may think of the jet engine as a mechanical device
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.
Mandelis, Andreas
, transient, and novel hybrid heat-flow methods. In the periodic thermal-wave method, a sample of known
Mixing at the external boundary of a submerged turbulent jet
A. Eidelman; T. Elperin; N. Kleeorin; G. Hazak; I. Rogachevskii; O. Sadot; I. Sapir-Katiraie
2009-05-11T23:59:59.000Z
We study experimentally and theoretically mixing at the external boundary of a submerged turbulent jet. In the experimental study we use Particle Image Velocimetry and an Image Processing Technique based on the analysis of the intensity of the Mie scattering to determine the spatial distribution of tracer particles. An air jet is seeded with the incense smoke particles which are characterized by large Schmidt number and small Stokes number. We determine the spatial distributions of the jet fluid characterized by a high concentration of the particles and of the ambient fluid characterized by a low concentration of the tracer particles. In the data analysis we use two approaches, whereby one approach is based on the measured phase function for the study of the mixed state of two fluids. The other approach is based on the analysis of the two-point second-order correlation function of the particle number density fluctuations generated by tangling of the gradient of the mean particle number density by the turbulent velocity field. This gradient is formed at the external boundary of a submerged turbulent jet. We demonstrate that PDF of the phase function of a jet fluid penetrating into an external flow and the two-point second-order correlation function of the particle number density do not have universal scaling and cannot be described by a power-law function. The theoretical predictions made in this study are in a qualitative agreement with the obtained experimental results.
Profiles of heating in turbulent coronal magnetic loops
E. Buchlin; P. J. Cargill; S. J. Bradshaw; M. Velli
2007-02-28T23:59:59.000Z
Context: The location of coronal heating in magnetic loops has been the subject of a long-lasting controversy: does it occur mostly at the loop footpoints, at the top, is it random, or is the average profile uniform? Aims: We try to address this question in model loops with MHD turbulence and a profile of density and/or magnetic field along the loop. Methods: We use the ShellAtm MHD turbulent heating model described in Buchlin & Velli (2006), with a static mass density stratification obtained by the HydRad model (Bradshaw & Mason 2003). This assumes the absence of any flow or heat conduction subsequent to the dynamic heating. Results: The average profile of heating is quasi-uniform, unless there is an expansion of the flux tube (non-uniform axial magnetic field) or the variation of the kinetic and magnetic diffusion coefficients with temperature is taken into account: in the first case the heating is enhanced at footpoints, whereas in the second case it is enhanced where the dominant diffusion coefficient is enhanced. Conclusions: These simulations shed light on the consequences on heating profiles of the complex interactions between physical effects involved in a non-uniform turbulent coronal loop.
Numerical simulations of compressively driven interstellar turbulence: I. Isothermal gas
Schmidt, Wolfram; Hupp, Markus; Kern, Sebastian; Niemeyer, Jens C
2008-01-01T23:59:59.000Z
We performed numerical simulations of supersonic isothermal turbulence driven by mostly compressive large-scale forcing, using both a static grid and adaptive mesh refinement with an effective resolution N=768^3. After a transient phase dominated by shocks, turbulence evolves into a steady state with an RMS Mach number about 2.5, in which cloud-like structures of over-dense gas are surrounded by highly rarefied gas. The index of the turbulence energy spectrum function beta = 2.0 in the shock-dominated phase. As the flow approaches statistical equilibrium, the spectrum flattens, with beta = 1.9. For the scaling exponent of the root mean square velocity fluctuation, we obtain gamma = 0.43 from the velocity structure functions of second order. These results are well within the range of observed scaling properties for the velocity dispersion in molecular clouds. Calculating structure functions of order p=1,...,5, we find for all scaling exponents significant deviations from the Kolmogorov-Burgers model proposed b...
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
McKee, G; Gohil, P; Schlossberg, D; Boedo, J; Burrell, K; deGrassie, J; Groebner, R; Makowski, M; Moyer, R; Petty, C; Rhodes, T; Schmitz, L; Shafer, M; Solomon, W; Umansky, M; Wang, G; White, A; Xu, X
2008-10-13T23:59:59.000Z
The injected power required to induce a transition from L-mode to H-mode plasmas is found to depend strongly on the injected neutral beam torque and consequent plasma toroidal rotation. Edge turbulence and flows, measured near the outboard midplane of the plasma (0.85 < r/a < 1.0) on DIII-D with the high-sensitivity 2D beam emission spectroscopy (BES) system, likewise vary with rotation and suggest a causative connection. The L-H power threshold in plasmas with the ion {del}B drift away from the X-point decreases from 4-6 MW with co-current beam injection, to 2-3 MW with near zero net injected torque, and to <2 MW with counter injection. Plasmas with the ion {del}B drift towards the X-point exhibit a qualitatively similar though less pronounced power threshold dependence on rotation. 2D edge turbulence measurements with BES show an increasing poloidal flow shear as the L-H transition is approached in all conditions. At low rotation, the poloidal flow of turbulent eddies near the edge reverses prior to the L-H transition, generating a significant poloidal flow shear that exceeds the measured turbulence decorrelation rate. This increased poloidal turbulence velocity shear may facilitate the L-H transition. No such reversal is observed in high rotation plasmas. The poloidal turbulence velocity spectrum exhibits a transition from a Geodesic Acoustic Mode zonal flow to a higher-power, lower frequency, zero-mean-frequency zonal flow as rotation varies from co-current to balanced during a torque scan at constant injected neutral beam power, perhaps also facilitating the L-H transition. This reduced power threshold at lower toroidal rotation may benefit inherently low-rotation plasmas such as ITER.
MATCHED-INDEX-OF-REFRACTION FLOW FACILITY FOR FUNDAMENTAL AND APPLIED RESEARCH
Piyush Sabharwall; Carl Stoots; Donald M. McEligot; Richard Skifton; Hugh McIlroy
2014-11-01T23:59:59.000Z
Significant challenges face reactor designers with regard to thermal hydraulic design and associated modeling for advanced reactor concepts. Computational thermal hydraulic codes solve only a piece of the core. There is a need for a whole core dynamics system code with local resolution to investigate and understand flow behavior with all the relevant physics and thermo-mechanics. The matched index of refraction (MIR) flow facility at Idaho National Laboratory (INL) has a unique capability to contribute to the development of validated computational fluid dynamics (CFD) codes through the use of state-of-the-art optical measurement techniques, such as Laser Doppler Velocimetry (LDV) and Particle Image Velocimetry (PIV). PIV is a non-intrusive velocity measurement technique that tracks flow by imaging the movement of small tracer particles within a fluid. At the heart of a PIV calculation is the cross correlation algorithm, which is used to estimate the displacement of particles in some small part of the image over the time span between two images. Generally, the displacement is indicated by the location of the largest peak. To quantify these measurements accurately, sophisticated processing algorithms correlate the locations of particles within the image to estimate the velocity (Ref. 1). Prior to use with reactor deign, the CFD codes have to be experimentally validated, which requires rigorous experimental measurements to produce high quality, multi-dimensional flow field data with error quantification methodologies. Computational thermal hydraulic codes solve only a piece of the core. There is a need for a whole core dynamics system code with local resolution to investigate and understand flow behavior with all the relevant physics and thermo-mechanics. Computational techniques with supporting test data may be needed to address the heat transfer from the fuel to the coolant during the transition from turbulent to laminar flow, including the possibility of an early laminarization of the flow (Refs. 2 and 3) (laminarization is caused when the coolant velocity is theoretically in the turbulent regime, but the heat transfer properties are indicative of the coolant velocity being in the laminar regime). Such studies are complicated enough that computational fluid dynamics (CFD) models may not converge to the same conclusion. Thus, experimentally scaled thermal hydraulic data with uncertainties should be developed to support modeling and simulation for verification and validation activities. The fluid/solid index of refraction matching technique allows optical access in and around geometries that would otherwise be impossible while the large test section of the INL system provides better spatial and temporal resolution than comparable facilities. Benchmark data for assessing computational fluid dynamics can be acquired for external flows, internal flows, and coupled internal/external flows for better understanding of physical phenomena of interest. The core objective of this study is to describe MIR and its capabilities, and mention current development areas for uncertainty quantification, mainly the uncertainty surface method and cross-correlation method. Using these methods, it is anticipated to establish a suitable approach to quantify PIV uncertainty for experiments performed in the MIR.
Increasing the chemical content of turbulent flame models through the use of parallel computing
Yam, C.G.; Armstrong, R.; Koszykowski, M.L. [Sandia National Labs., Livermore, CA (United States); Chen, J.Y. [California Univ., Berkeley, CA (United States); Bui-Pham, M.N. [Lawrence Berkeley National Lab., CA (United States)
1996-10-01T23:59:59.000Z
This report outlines the effort to model a time-dependent, 2- dimensional, turbulent, nonpremixed flame with full chemistry with the aid of parallel computing tools. In this study, the mixing process and the chemical reactions occurring in the flow field are described in terms of the single-point probability density function (PDF), while the turbulent viscosity is determined by the standard kappa-epsilon model. The initial problem solved is a H[sub 2]/Air flame whose chemistry is described by 28 elementary reactions involving 9 chemical species.
Yokoi, N. [Institute of Industrial Science, University of Tokyo, Tokyo (Japan)] [Institute of Industrial Science, University of Tokyo, Tokyo (Japan); Higashimori, K.; Hoshino, M. [Department of Earth and Planetary Science, University of Tokyo, Tokyo (Japan)] [Department of Earth and Planetary Science, University of Tokyo, Tokyo (Japan)
2013-12-15T23:59:59.000Z
Through the enhancement of transport, turbulence is expected to contribute to the fast reconnection. However, the effects of turbulence are not so straightforward. In addition to the enhancement of transport, turbulence under some environment shows effects that suppress the transport. In the presence of turbulent cross helicity, such dynamic balance between the transport enhancement and suppression occurs. As this result of dynamic balance, the region of effective enhanced magnetic diffusivity is confined to a narrow region, leading to the fast reconnection. In order to confirm this idea, a self-consistent turbulence model for the magnetic reconnection is proposed. With the aid of numerical simulations where turbulence effects are incorporated in a consistent manner through the turbulence model, the dynamic balance in the turbulence magnetic reconnection is confirmed.
Sedimentation of finite-size spheres in quiescent and turbulent environments
Fornari, Walter; Brandt, Luca
2015-01-01T23:59:59.000Z
Sedimentation of a solid phase is widely encountered in applications and environmental flows, yet little is known about the behavior of finite-size particles in homogeneous isotropic turbulence. To fill this gap, we perform Direct Numerical Simulations of sedimentation in quiescent and turbulent environments using an Immersed Boundary Method to account for the dispersed rigid spherical particles. The solid volume fractions considered are 0.5-1%, while the solid to fluid density ratio is 1.02. The particle radius is chosen to be approximately 6 Komlogorov lengthscales. The results show that the mean settling velocity is lower in an already turbulent flow than in a still fluid. The reduction with respect to a single particle in quiescent fluid is about 12% and 14% for the two volume fractions investigated. The probability density function of the particle velocity is almost Gaussian in a turbulent flow, whereas it displays large positive tails in still fluid. These tails are associated to the rare fast sedimenta...
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.
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.
Numerical Modeling of Thermal EOR: Comprehensive Coupling of an AMR-Based Model
Paris-Sud XI, Université de
Flow and Geomechanics N. Guy*, G. Enchéry and G. Renard IFP Energies nouvelles, 1-4 avenue de Bois of Thermal EOR: Comprehensive Coupling of an AMR-Based Model of Thermal Fluid Flow and Geomechanics when both thermal fluid flow and geomechanics are coupled in order to take into account variations
Thermophoretic transport of particles that act as volumetric heat sources in natural convection flow
Conklin, J.C.; Krane, R.J. (Oak Ridge National Lab., TN (USA); Tennessee Univ., Knoxville, TN (USA). Dept. of Mechanical and Aerospace Engineering)
1989-01-01T23:59:59.000Z
The natural convection boundary layer with suspended heat generating aerosol particles adjacent to a cooled, isothermal, vertical wall was investigated for the following circumstances: laminar and turbulent flow, large temperature differences between the wall and the fluid, stable thermal stratification far from the wall, and fluid participation in thermal radiation heat transfer. The deposition of aerosol particles by thermophoresis was investigated. A scaling analysis showed the negligible effect inside the boundary layer of the particulate heat source strengths of practical interest. Only the temperature of the fluid far from the wall is affected appreciably by the heat sources. The scaled boundary layer differential equations are transformed to a nonsimilarity form for numerical solution using two different methods. An expression for the ratio of mass transfer to heat transfer coefficients was developed to simplify the computation of thermophoretic particle deposition at the wall for the case of constant temperature conditions far from the wall. Variable thermophysical property effect for the three gases of steam, air, and hydrogen were investigated. A dimensionless ratio of transfer coefficients for large temperature differences and turbulent flow was computed as a product of the laminar constant property results and a ratio of the known thermophysical properties at the wall and far from the wall. An approximation of the laminar constant property results for all three gases is developed in terms of the known wall and fluid temperatures, Prandtl number, and a thermophoretic constant. This allows particle deposition to be computed from a known heat transfer coefficient without explicitly solving the particle conservation equation. 120 refs., 29 figs., 21 tabs.
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...
Turbulence in Global Simulations of Magnetized Thin Accretion Disks
Kris Beckwith; Philip J. Armitage; Jacob B. Simon
2011-05-09T23:59:59.000Z
We use a global magnetohydrodynamic simulation of a geometrically thin accretion disk to investigate the locality and detailed structure of turbulence driven by the magnetorotational instability (MRI). The model disk has an aspect ratio $H / R \\simeq 0.07$, and is computed using a higher-order Godunov MHD scheme with accurate fluxes. We focus the analysis on late times after the system has lost direct memory of its initial magnetic flux state. The disk enters a saturated turbulent state in which the fastest growing modes of the MRI are well-resolved, with a relatively high efficiency of angular momentum transport $ > \\approx 2.5 \\times 10^{-2}$. The accretion stress peaks at the disk midplane, above and below which exists a moderately magnetized corona with patches of superthermal field. By analyzing the spatial and temporal correlations of the turbulent fields, we find that the spatial structure of the magnetic and kinetic energy is moderately well-localized (with correlation lengths along the major axis of $2.5H$ and $1.5H$ respectively), and generally consistent with that expected from homogenous incompressible turbulence. The density field, conversely, exhibits both a longer correlation length and a long correlation time, results which we ascribe to the importance of spiral density waves within the flow. Consistent with prior results, we show that the mean local stress displays a well-defined correlation with the local vertical flux, and that this relation is apparently causal (in the sense of the flux stimulating the stress) during portions of a global dynamo cycle. We argue that the observed flux-stress relation supports dynamo models in which the structure of coronal magnetic fields plays a central role in determining the dynamics of thin-disk accretion.
Power Electronics Thermal Control (Presentation)
Narumanchi, S.
2010-05-05T23:59:59.000Z
Thermal management plays an important part in the cost of electric drives in terms of power electronics packaging. Very promising results have been obtained by using microporous coatings and skived surfaces in conjunction with single-phase and two-phase flows. Sintered materials and thermoplastics with embedded fibers show significant promise as thermal interface materials, or TIMs. Appropriate cooling technologies depend on the power electronics package application and reliability.
Thermal desorption for passive dosimeter
Liu, Wen-Chen
1981-01-01T23:59:59.000Z
instrument in the field, such as portable gas chromatography or photoionization. However, these instruments usually are expensive and inap- (2) propriate for a personal monitoring program. Indirect methods involve collecting the toxicants in certain media..., the thermal desorber contained four ma)or parts: a purging gas purifi- cation chamber, a desorption oven, a syringe type collection chamber and a gas chromatographic sample infection loop. A diagram of sample flow from purge gas source through the thermal...
Mimicking a turbulent signal: sequential multiaffine processes
L. Biferale; G. Boffetta; A. Celani; A. Crisanti; A. Vulpiani
1997-11-03T23:59:59.000Z
An efficient method for the construction of a multiaffine process, with prescribed scaling exponents, is presented. At variance with the previous proposals, this method is sequential and therefore it is the natural candidate in numerical computations involving synthetic turbulence. The application to the realization of a realistic turbulent-like signal is discussed in detail. The method represents a first step towards the realization of a realistic spatio-temporal turbulent field.
Meziane, M.; Eichwald, O.; Ducasse, O.; Marchal, F. [Universite de Toulouse, UPS, INPT, LAPLACE (Laboratoire Plasma et Conversion d'Energie), Toulouse Cedex 9 F-31062 (France); Sarrette, J. P.; Yousfi, M. [Universite de Toulouse, UPS, INPT, LAPLACE (Laboratoire Plasma et Conversion d'Energie), Toulouse Cedex 9 F-31062 (France); CNRS, LAPLACE, Toulouse F-31062 (France)
2013-04-21T23:59:59.000Z
The present paper is devoted to the 2D simulation of an Atmospheric Corona Discharge Reactor (ACDR) involving 10 pins powered by a DC high voltage and positioned 7 mm above a grounded metallic plane. The corona reactor is periodically crossed by thin mono filamentary streamers with a natural repetition frequency of some tens of kHz. The simulation involves the electro-dynamic, chemical kinetic, and neutral gas hydrodynamic phenomena that influence the kinetics of the chemical species transformation. Each discharge stage (including the primary and the secondary streamers development and the resulting thermal shock) lasts about one hundred nanoseconds while the post-discharge stages occurring between two successive discharge phases last one hundred microseconds. The ACDR is crossed by a lateral air flow including 400 ppm of NO. During the considered time scale of 10 ms, one hundred discharge/post-discharge cycles are simulated. The simulation involves the radical formation and thermal exchange between the discharges and the background gas. The results show how the successive discharges activate the flow gas and how the induced turbulence phenomena affect the redistribution of the thermal energy and the chemical kinetics inside the ACDR.
Thermal Gradient Holes At Breitenbush Hot Springs Area (Ingebritsen...
(1993) Heat Flow From Four New Research Drill Holes In The Western Cascades, Oregon, Usa Additional References Retrieved from "http:en.openei.orgwindex.php?titleThermalGr...
McEligot, D.M.; Condie, K.G.; Foust, T.D.; McCreery, G.E.; Pink, R.J.; Stacey, D.E. (INEEL); Shenoy, A.; Baccaglini, G. (General Atomics); Pletcher, R.H. (Iowa State U.); Wallace, J.M.; Vukoslavcevic, P. (U. Maryland); Jackson, J.D. (U. Manchester, UK); Kunugi, T. (Kyoto U., Japan); Satake, S.-i. (Tokyo U. Science, Japan)
2002-12-31T23:59:59.000Z
The ultimate goal of the study is the improvement of predictive methods for safety analyses and design of advanced reactors for higher efficiency and enhanced safety and for deployable reactors for electrical power generation, process heat utilization and hydrogen generation. While key applications would be advanced gas-cooled reactors (AGCRs) using the closed Brayton cycle (CBC) for higher efficiency (such as the proposed Gas Turbine - Modular Helium Reactor (GT-MHR) of General Atomics [Neylan and Simon, 1996]), results of the proposed research should also be valuable in reactor systems with supercritical flow or superheated vapors, e.g., steam. Higher efficiency leads to lower cost/kwh and reduces life-cycle impacts of radioactive waste (by reducing waters/kwh). The outcome will also be useful for some space power and propulsion concepts and for some fusion reactor concepts as side benefits, but they are not the thrusts of the investigation. The objective of the project is to provide fundamental thermal fluid physics knowledge and measurements necessary for the development of the improved methods for the applications.
Investigation on the Core Bypass Flow in a Very High Temperature Reactor
Hassan, Yassin
2013-10-22T23:59:59.000Z
Uncertainties associated with the core bypass flow are some of the key issues that directly influence the coolant mass flow distribution and magnitude, and thus the operational core temperature profiles, in the very high-temperature reactor (VHTR). Designers will attempt to configure the core geometry so the core cooling flow rate magnitude and distribution conform to the design values. The objective of this project is to study the bypass flow both experimentally and computationally. Researchers will develop experimental data using state-of-the-art particle image velocimetry in a small test facility. The team will attempt to obtain full field temperature distribution using racks of thermocouples. The experimental data are intended to benchmark computational fluid dynamics (CFD) codes by providing detailed information. These experimental data are urgently needed for validation of the CFD codes. The following are the project tasks: • Construct a small-scale bench-top experiment to resemble the bypass flow between the graphite blocks, varying parameters to address their impact on bypass flow. Wall roughness of the graphite block walls, spacing between the blocks, and temperature of the blocks are some of the parameters to be tested. • Perform CFD to evaluate pre- and post-test calculations and turbulence models, including sensitivity studies to achieve high accuracy. • Develop the state-of-the art large eddy simulation (LES) using appropriate subgrid modeling. • Develop models to be used in systems thermal hydraulics codes to account and estimate the bypass flows. These computer programs include, among others, RELAP3D, MELCOR, GAMMA, and GAS-NET. Actual core bypass flow rate may vary considerably from the design value. Although the uncertainty of the bypass flow rate is not known, some sources have stated that the bypass flow rates in the Fort St. Vrain reactor were between 8 and 25 percent of the total reactor mass flow rate. If bypass flow rates are on the high side, the quantity of cooling flow through the core may be considerably less than the nominal design value, causing some regions of the core to operate at temperatures in excess of the design values. These effects are postulated to lead to localized hot regions in the core that must be considered when evaluating the VHTR operational and accident scenarios.
Kolesnikov, R.A.; Krommes, J.A.
2005-09-22T23:59:59.000Z
The collisionless limit of the transition to ion-temperature-gradient-driven plasma turbulence is considered with a dynamical-systems approach. The importance of systematic analysis for understanding the differences in the bifurcations and dynamics of linearly damped and undamped systems is emphasized. A model with ten degrees of freedom is studied as a concrete example. A four-dimensional center manifold (CM) is analyzed, and fixed points of its dynamics are identified and used to predict a ''Dimits shift'' of the threshold for turbulence due to the excitation of zonal flows. The exact value of that shift in terms of physical parameters is established for the model; the effects of higher-order truncations on the dynamics are noted. Multiple-scale analysis of the CM equations is used to discuss possible effects of modulational instability on scenarios for the transition to turbulence in both collisional and collisionless cases.
Scale-selective turbulence reduction in H-mode plasmas in the TJ-II stellarator
Happel, T.; Conway, G. D.; Stroth, U. [Max-Planck-Institut fuer Plasmaphysik, Association Euratom-IPP, 85748 Garching (Germany); Estrada, T.; Blanco, E.; Hidalgo, C.; Collaboration: TJ-II Team
2011-10-15T23:59:59.000Z
Wavenumber spectra of density turbulence in L- and H-mode plasmas have been measured in the TJ-II stellarator by means of Doppler reflectometry. A pronounced suppression of the density fluctuation level is observed in H-mode close to the radial position of maximum radial electric field (E{sub r}) shear. Furthermore, intermediate scale density turbulence is reduced preferentially. This effect can be interpreted within the framework of vortex stretching feeding energy through Reynolds stress into zonal flows, while shear decorrelation of turbulent structures might not play a central role in TJ-II. Moreover, it is shown that in both L- and H-mode, the phase velocity of density fluctuations does not depend on the structure scale.
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...
atmospheric optical turbulence: Topics by E-print Network
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Next Page Last Page Topic Index 1 Atmospheric Turbulence and its Influence on Adaptive Optics Physics Websites Summary: Atmospheric Turbulence and its Influence on Adaptive Optics...
Wavelet analysis study of microbubble drag reduction in a boundary channel flow
Zhen, Ling
2006-04-12T23:59:59.000Z
Particle Image Velocimetry (PIV) and pressure measurement techniques were performed to investigate the drag reduction due to microbubble injection in the boundary layer of a fully developed turbulent channel flow. ...
LES of an Inclined Jet into a Supersonic Turbulent Crossflow
Ferrante, Antonino; Dimotakis, Paul E; Stephens, Mike; Adams, Paul; Walters, Richard
2009-01-01T23:59:59.000Z
This short article describes flow parameters, numerical method, and animations of the fluid dynamics video "LES of an Inclined Jet into a Supersonic Turbulent Crossflow" (http://ecommons.library.cornell.edu/bitstream/1813/14073/3/GFM-2009.mpg [high-resolution] and http://ecommons.library.cornell.edu/bitstream/1813/14073/2/GFM-2009-web.m1v [low-resolution] video). We performed large-eddy simulation with the sub-grid scale (LES-SGS) stretched-vortex model of momentum and scalar transport to study the gas-dynamics interactions of a helium inclined round jet into a supersonic ($M=3.6$) turbulent (\\Reth$ =13\\times10^3$) air flow over a flat surface. The video shows the temporal development of Mach-number and magnitude of density-gradient in the mid-span plane, and isosurface of helium mass-fraction and $\\lam_2$ (vortical structures). The identified vortical structures are sheets, tilted tubes, and discontinuous rings. The vortical structures are shown to be well correlated in space and time with helium mass-fracti...
Forrest E. Ames
2002-10-01T23:59:59.000Z
Endwall heat transfer distributions taken in a large-scale low speed linear cascade facility are documented for mock catalytic and dry low NOx (DLN) combustion systems. Inlet turbulence levels range from about 1.0 percent for the mock Catalytic combustor condition to 14 percent for the mock dry low NOx combustor system. Stanton number contours are presented at both turbulence conditions for Reynolds numbers based on true chord length and exit conditions ranging from 500,000 to 2,000,000. Catalytic combustor endwall heat transfer shows the influence of the complex three-dimensional flow field, while the effects of individual vortex systems are less evident for the mock dry low NOx cases. Turbulence scales have been documented for both cases. Inlet boundary layers are relatively thin for the mock catalytic combustor case while inlet flow approximates a channel flow with high turbulence for the mock DLN combustor case. Inlet boundary layer parameters are presented across the inlet passage for the three Reynolds numbers and both the mock catalytic and DLN combustor inlet cases. Both midspan and 95 percent span pressure contours are included. This research provides a well-documented database taken across a range of Reynolds numbers and turbulence conditions for assessment of endwall heat transfer predictive capabilities.
Thermal Monitoring Approaches for Energy Savings Verification
McBride, J. R.; Bohmer, C. J.; Lippman, R. H.; Zern, M. J.
This paper reviews and summarizes techniques for monitoring thermal energy flows for the purpose of verifying energy savings in industrial and large institutional energy conservation projects. Approaches for monitoring hot and chilled water, steam...
Kelley, N.D.
1992-11-01T23:59:59.000Z
We have recently expanded the numerical turbulence simulation (SNLWIND) developed by Veers [1] to include all three components of the turbulent wind vector. We have also configured the code to simulate the characteristics of turbulent wind fields upwind and downwind of a large wind farm, as well as over uniform, flat terrain. Veers`s original method only simulates the longitudinal component of the wind in neutral flow. This paper overviews the development of spectral distribution, spatial coherence, and cross correlation models used to expired the SNLWIND code to include the three components of the turbulent wind over a range of atmospheric stabilities. These models are based on extensive measurements of the turbulence characteristics immediately upwind and downwind of a large wind farm in San Gorgonio Pass, California.
Kelley, N.D.
1992-11-01T23:59:59.000Z
We have recently expanded the numerical turbulence simulation (SNLWIND) developed by Veers [1] to include all three components of the turbulent wind vector. We have also configured the code to simulate the characteristics of turbulent wind fields upwind and downwind of a large wind farm, as well as over uniform, flat terrain. Veers's original method only simulates the longitudinal component of the wind in neutral flow. This paper overviews the development of spectral distribution, spatial coherence, and cross correlation models used to expired the SNLWIND code to include the three components of the turbulent wind over a range of atmospheric stabilities. These models are based on extensive measurements of the turbulence characteristics immediately upwind and downwind of a large wind farm in San Gorgonio Pass, California.
Mean flow and turbulence characteristics in whirling annular seals
Thames, Howard Davis
1992-01-01T23:59:59.000Z
of the test rig with the annular seal installed 15: Dimensions of the Annular Rotor . 16: Components of the 3D Laser Doppler Velocimetry System 15 17 . . 19 Figure 17: Raw Doppler signal with high frequency noise and pedestal Figure 18: Doppler signal... 64: Figure 65: Figure 66: Figure 67: Figure 68: Figure 69: Figure 70: Figure 71: Figure 72: Figure 73: Figure 74: Figure 75: Figure 76: Figure 77: Case 2 Vector Plots at Constant Axial Positions 13-17 99 Case 2 Mean Velocity Contours...
Investigation of Flow, Turbulence, and Dispersion within Built Environments
Pan, Hansheng
2011-01-01T23:59:59.000Z
ratio. With these properties, hydrogen is an ideal fuel toproperties ………………………………………………………….185 Table A6.2 Test modes and weighting factors for marine applications (ISO-8178 E3).187 xix Table A6.3 Hydrogen
Investigation of Flow, Turbulence, and Dispersion within Built Environments
Pan, Hansheng
2011-01-01T23:59:59.000Z
For example, at 75% engine load, hydrogen production of 22there are numerous hydrogen engine-powered vehicles rangingT. Hydrogen-fueled internal combustion engines. Progress in
Direct numerical simulation of turbulent Taylor–Couette flow
2007-08-23T23:59:59.000Z
The hot-wire anemometry measurements by Smith &. Townsend (1982) and Townsend (1984) for a radius ratio 0.667 suggested that for. Taylor numbers below ...
NUMERICAL MODELING OF TURBULENT FLOW IN A COMBUSTION TUNNEL
Ghoniem, A.F.
2013-01-01T23:59:59.000Z
corresponding to a propane-air mixture at (a) 0.02 and v Kbehind a step in a propane~air mixture at an ""0.57 enteringphotographically propane~air this Fig. The mixture, with
Simulation Analysis of Zero Mean Flow Edge Turbulence in LAPD
Friedman, Brett
2013-01-01T23:59:59.000Z
transiently in- jected energy, mix it around, and sustainnonlinearities are available to mix energy among eigenmodes.con- serve the total energy, can mix the energy between