DNS experiments on the settling of heavy particles in homogeneous turbulence: Two-way coupling and Reynolds number effects

Abstract

The present study addresses the effects of two-way fluid-particle interaction ("two-way coupling") on the settling of heavy particles in homogeneous turbulence. The modification of turbulence by the particles and the resulting effects on the settling velocity are analyzed by taking into account Reynolds number effects. The turbulent carrier fluid phase is resolved by direct numerical simulation (DNS) and the particle phase by the Lagrangian point-particle approximation. Results are presented for two Taylor microscale Reynolds numbers Rλ = 40 and 130. While for R λ = 40 the Kolmogorov time scale, tη, is found almost unaltered by the two-way coupling, it is found significantly decreased for Rλ = 130. The consequent modification of the particle Stokes number St = τp/tη, τp being the particle response time, shows that comparisons between one-way coupling numerical data and two-way coupling numerical or experimental data may be inconsistent. This is particularly relevant for the particle settling in turbulence which has been previously shown to be strongly influenced by the dynamical interaction of the small flow scales with the particles.