TY - JOUR

T1 - Turbulent thermal diffusion in strongly stratified turbulence

T2 - Theory and experiments

AU - Amir, G.

AU - Bar, N.

AU - Eidelman, A.

AU - Elperin, T.

AU - Kleeorin, N.

AU - Rogachevskii, I.

N1 - Funding Information:
This work has been supported by the Israel Science Foundation governed by the Israeli Academy of Sciences (Grant No. 1210/15).
Publisher Copyright:
© 2017 American Physical Society.

PY - 2017/6/1

Y1 - 2017/6/1

N2 - Turbulent thermal diffusion is a combined effect of the temperature stratified turbulence and inertia of small particles. It causes the appearance of a nondiffusive turbulent flux of particles in the direction of the turbulent heat flux. This nondiffusive turbulent flux of particles is proportional to the product of the mean particle number density and the effective velocity of inertial particles. The theory of this effect has been previously developed only for small temperature gradients and small Stokes numbers [Phys. Rev. Lett. 76, 224 (1996)PRLTAO0031-900710.1103/PhysRevLett.76.224]. In this study, a generalized theory of turbulent thermal diffusion for arbitrary temperature gradients and Stokes numbers has been developed. The laboratory experiments in the oscillating grid turbulence and in the multifan produced turbulence have been performed to validate the theory of turbulent thermal diffusion in strongly stratified turbulent flows. It has been shown that the ratio of the effective velocity of inertial particles to the characteristic vertical turbulent velocity for large Reynolds numbers is less than 1. The effective velocity of inertial particles as well as the effective coefficient of turbulent thermal diffusion increase with Stokes numbers reaching the maximum at small Stokes numbers and decreases for larger Stokes numbers. The effective coefficient of turbulent thermal diffusion also decreases with the mean temperature gradient. It has been demonstrated that the developed theory is in a good agreement with the results of the laboratory experiments.

AB - Turbulent thermal diffusion is a combined effect of the temperature stratified turbulence and inertia of small particles. It causes the appearance of a nondiffusive turbulent flux of particles in the direction of the turbulent heat flux. This nondiffusive turbulent flux of particles is proportional to the product of the mean particle number density and the effective velocity of inertial particles. The theory of this effect has been previously developed only for small temperature gradients and small Stokes numbers [Phys. Rev. Lett. 76, 224 (1996)PRLTAO0031-900710.1103/PhysRevLett.76.224]. In this study, a generalized theory of turbulent thermal diffusion for arbitrary temperature gradients and Stokes numbers has been developed. The laboratory experiments in the oscillating grid turbulence and in the multifan produced turbulence have been performed to validate the theory of turbulent thermal diffusion in strongly stratified turbulent flows. It has been shown that the ratio of the effective velocity of inertial particles to the characteristic vertical turbulent velocity for large Reynolds numbers is less than 1. The effective velocity of inertial particles as well as the effective coefficient of turbulent thermal diffusion increase with Stokes numbers reaching the maximum at small Stokes numbers and decreases for larger Stokes numbers. The effective coefficient of turbulent thermal diffusion also decreases with the mean temperature gradient. It has been demonstrated that the developed theory is in a good agreement with the results of the laboratory experiments.

UR - http://www.scopus.com/inward/record.url?scp=85025610353&partnerID=8YFLogxK

U2 - 10.1103/PhysRevFluids.2.064605

DO - 10.1103/PhysRevFluids.2.064605

M3 - Article

AN - SCOPUS:85025610353

SN - 2469-990X

VL - 2

JO - Physical Review Fluids

JF - Physical Review Fluids

IS - 6

M1 - 064605

ER -