Multiscale clustering of heavy and light small particles in turbulent channel flow at high Reynolds numbers

Abstract

To understand the fundamental mechanism of the clustering of heavy and light small particles in high-Reynolds-number wall turbulence, we conduct direct numerical simulations of particle dispersions in turbulent channel flow at the friction Reynolds number Reτ=2000. Heavy and light particles form clusters with different shapes, and the cluster size is larger for particles with longer relaxation time. To reveal the origin of these multiscale clusters of particles, we investigate particle distributions around multiscale vortices. Vortices tend to sweep out heavy particles and tend to attract light ones with a relaxation time comparable with their turnover time. These clustering phenomena due to coherent vortices can occur irrespective of their size, existing height and the friction Reynolds number. We can therefore explain the multiscale nature of particle clustering in terms of the time scale matching between particles and vortices.