Particle velocity distributions and velocity fluctuations of non-Brownian settling particles by particle-resolved direct numerical simulation

Abstract

Settling dynamics of non-Brownian particles is investigated using particle-resolved direct numerical simulations. There are two aims of this paper: first is to study the variation of particle velocity fluctuations with solid volume for a wide range of settling Reynolds number; second is to investigate the effects of solid volume fraction and settling Reynolds number on the distribution of particle velocity fluctuations after reaching the steady state. Simulations are performed in the periodic domain and the settling Reynolds number and solid volume fraction are varied from 0.5 to 400 and 0.01 to 0.2, respectively. It is observed that particle velocity fluctuations increase with increase in solid volume fraction for settling Reynolds number less than 100. Further increase in the settling Reynolds number alters the behavior of settling particles, making the particle velocity fluctuations either remain nearly constant or even decrease with the increase in solid volume fraction. For dense suspensions, it is observed by simulations that the distribution of particle velocities has Gaussian form during settling. However, for dilute and moderately dense suspensions, particle velocity distribution becomes non-Gaussian for the studied range of settling Reynolds number. At the end of paper, the physics behind the scaling of particle velocity fluctuations with solid volume fraction and the distribution of particle velocity fluctuations during settling is explained.