Detection of turbulent thermal diffusion of particles in numerical simulations

TL;DR

This paper uses direct numerical simulations to demonstrate turbulent thermal diffusion causes particle accumulation in temperature minima, forming large-scale inhomogeneities, especially for particles with Stokes numbers near one.

Contribution

It provides the first detailed numerical evidence of turbulent thermal diffusion affecting inertial particles in temperature-stratified turbulence.

Findings

Peak particle density occurs at temperature minima for Stokes numbers < 1

Maximum effect at Stokes number around unity

Inertial particles form large-scale inhomogeneities due to turbulent thermal diffusion

Abstract

The phenomenon of turbulent thermal diffusion in temperature-stratified turbulence causing a non-diffusive turbulent flux of inertial and non-inertial particles in the direction of the turbulent heat flux is found using direct numerical simulations (DNS). In simulations with and without gravity, this phenomenon is found to cause a peak in the particle number density around the minimum of the mean fluid temperature for Stokes numbers less than 1, where the Stokes number is the ratio of particle Stokes time to turbulent Kolmogorov time at the viscous scale. Turbulent thermal diffusion causes the formation of large-scale inhomogeneities in the spatial distribution of inertial particles. The strength of this effect is maximum for Stokes numbers around unity, and decreases again for larger values. The dynamics of inertial particles is studied using Lagrangian modelling in forced temperature-stratified turbulence, whereas non-inertial particles and the fluid are described using DNS in an Eulerian framework.