  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.
