scholarly journals Turbulent transport and mixing in transitional Rayleigh-Taylor unstable flow: A priori assessment of gradient-diffusion and similarity modeling

2017 ◽  
Vol 96 (6) ◽  
Author(s):  
Oleg Schilling ◽  
Nicholas J. Mueschke
Keyword(s):  
Turbulent Transport ◽  
A Priori ◽  
Unstable Flow ◽  
Gradient Diffusion ◽  
Transport And Mixing

scholarly journals Analytic slowing-down distributions as modified by turbulent transport

2018 ◽  
Vol 84 (6) ◽  
Author(s):  
G. J. Wilkie
Keyword(s):  
Particle Density ◽  
Plasma Heating ◽  
Turbulent Transport ◽  
A Priori ◽  
High Energy ◽  
Relative Strength ◽  
Distribution Functions ◽  
Toroidal Plasmas ◽  
Model Distribution ◽  
Phase Space Transport

The effect of electrostatic microturbulence on fast particles rapidly decreases at high energy, but can be significant at moderate energy. Previous studies found that, in addition to changes in the energetic particle density, this results in non-trivial changes to the equilibrium velocity distribution. These effects have implications for plasma heating and the stability of Alfvén eigenmodes, but make multiscale simulations much more difficult without further approximations. Here, several related analytic model distribution functions are derived from first principles. A single dimensionless parameter characterizes the relative strength of turbulence relative to collisions, and this parameter appears as an exponent in the model distribution functions. Even the most simple of these models reproduces key features of the numerical phase-space transport solution and provides a useful a priori heuristic for determining how strong the effect of turbulence is on the redistribution of energetic particles in toroidal plasmas.

Euler-Euler Large-Eddy Simulation Approach for Non Isothermal Particle-Laden Turbulent Jet

2008 ◽  
Author(s):  
Enrica Masi ◽  
Benoiˆt Be´dat ◽  
Mathieu Moreau ◽  
Olivier Simonin
Keyword(s):  
Large Eddy Simulation ◽  
Particle Temperature ◽  
Turbulent Transport ◽  
A Priori ◽  
Particle Simulation ◽  
Dispersed Phase ◽  
Two Phase Flows ◽  
Two Phase ◽  
Eddy Simulation ◽  
Large Eddy

This paper presents an Euler-Euler Large-Eddy Simulation (LES) approach for the numerical modeling of non isothermal dispersed turbulent two-phase flows. The proposed approach is presented and validated by a priori tests from an Euler-Lagrange database, provided using discrete particle simulation (DPS) of the particle phase coupled with direct numerical simulation (DNS) of the turbulent carrier flow, in a non isothermal particle-laden temporal jet configuration. A statistical approach, the Mesoscopic Eulerian Formalism (MEF) [Fe´vrier et al., J. Fluid Mech., 2005, vol. 533, pp. 1–46], is used to write local and instantaneous Eulerian equations for the dispersed phase and then, by spatial averaging, to derive the LES equations governing the filtered variables. In this work, the MEF approach is extended to scalar variables transported by the particles in order to develop LES for reactive turbulent dispersed two-phase flows with mass and heat turbulent transport. This approach leads to separate the instantaneous particle temperature distribution in a Mesoscopic Eulerian field, shared by all the particles, and a Random Uncorrelated distribution which may be characterized in terms of Eulerian fields of particle moments such as the uncorrelated temperature variance. In this paper, the DPS-DNS numerical database is presented, LES Eulerian equations for the dispersed phase are derived in the frame of the Mesoscopic approach and models for the unresolved subgrid and random uncorrelated terms are proposed and a priori tested using the DPS-DNS database.

On the Role of Correlation Between Instantaneous Velocity and Pressure-Gradient in Large-Scale Turbulence

2003 ◽  
Author(s):  
Shinnosuke Obi
Keyword(s):  
Pressure Gradient ◽  
Reynolds Stress ◽  
Large Scale ◽  
Stress Component ◽  
Turbulent Transport ◽  
Velocity Correlation ◽  
Gradient Diffusion ◽  
Scale Turbulence ◽  
The Individual

Turbulent transport of Reynolds stress by triple moment of fluctuating velocity and pressure-velocity correlation are evaluated from a DNS for wake of a rectangular cylinder located in a uniform flow. The turbulent diffusion transport of turbulent kinetic energy hardly correlates with its gradient vector, indicating that the generally accepted gradient diffusion model is inadequate. It is inferred that the separate modeling of the individual Reynolds stress component provides a better possibility for modeling the turbulent transport in this flow, because of the strong departure from the equilibrium state of turbulence. The possibility of the direct modeling of the pressure gradient-velocity correlation is discussed.

scholarly journals Shear-driven transport and mixing in the interiors of massive stars

2016 ◽  
Vol 12 (S329) ◽  
pp. 434-434
Author(s):  
Vincent Prat ◽  
Stéphane Mathis
Keyword(s):  
Numerical Simulations ◽  
Massive Stars ◽  
Turbulent Transport ◽  
Hydrodynamic Instabilities ◽  
Transport And Mixing

AbstractTurbulent transport and mixing generated by hydrodynamic instabilities triggered by rotation gradients are key mechanisms in the evolution of massive stars. We present here a summary of the progresses on shear-induced mixing obtained with numerical simulations, along with a new prescription for horizontal turbulence.

scholarly journals Turbulent transport and mixing in the multimode narrowband Richtmyer-Meshkov instability

2019 ◽  
Vol 31 (9) ◽  
pp. 096105 ◽  
Author(s):  
B. Thornber ◽  
J. Griffond ◽  
P. Bigdelou ◽  
I. Boureima ◽  
P. Ramaprabhu ◽  
...  
Keyword(s):  
Turbulent Transport ◽  
Transport And Mixing

scholarly journals Turbulent transport of momentum and heat in a swirling flame. Retardation of mixing and counter-gradient diffusion.

1987 ◽  
Vol 53 (488) ◽  
pp. 1418-1426
Author(s):  
Toshimi TAKAGI ◽  
Tatsuyuki OKAMOTO ◽  
Masanori TAJI ◽  
Yoshizumi NAKASUJI ◽  
Takefumi KONDOH
Keyword(s):  
Turbulent Transport ◽  
Gradient Diffusion ◽  
Swirling Flame ◽  
Flame Retardation

scholarly journals First principles-based multiscale atomistic methods for input into first principles nonequilibrium transport across interfaces

2018 ◽  
Vol 116 (37) ◽  
pp. 18193-18201 ◽  
Author(s):  
Tao Cheng ◽  
Andres Jaramillo-Botero ◽  
Qi An ◽  
Daniil V. Ilyin ◽  
Saber Naserifar ◽  
...  
Keyword(s):  
First Principles ◽  
Equations Of State ◽  
Turbulent Transport ◽  
Computational Effort ◽  
Atomistic Simulations ◽  
Nonequilibrium Transport ◽  
Atomic Structures ◽  
Starting Point ◽  
Transport And Mixing ◽  
The Continuum

This issue of PNAS features “nonequilibrium transport and mixing across interfaces,” with several papers describing the nonequilibrium coupling of transport at interfaces, including mesoscopic and macroscopic dynamics in fluids, plasma, and other materials over scales from microscale to celestial. Most such descriptions describe the materials in terms of the density and equations of state rather than specific atomic structures and chemical processes. It is at interfacial boundaries where such atomistic information is most relevant. However, there is not yet a practical way to couple these phenomena with the atomistic description of chemistry. The starting point for including such information is the quantum mechanics (QM). However, practical QM calculations are limited to a hundred atoms for dozens of picoseconds, far from the scales required to inform the continuum level with the proper atomistic description. To bridge this enormous gap, we need to develop practical methods to extend the scale of the atomistic simulation by several orders of magnitude while retaining the level of QM accuracy in describing the chemical process. These developments would enable continuum modeling of turbulent transport at interfaces to incorporate the relevant chemistry. In this perspective, we will focus on recent progress in accomplishing these extensions in first principles-based atomistic simulations and the strategies being pursued to increase the accuracy of very large scales while dramatically decreasing the computational effort.

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