Effect of bi-dispersity on particle microstructures in settling of particles at high Reynolds number

Abstract

During settling of particles, at high Reynolds number (Re ≳ 250) dilute suspension of particles form clusters. It is primarily due to entrapment of downstream particles in the wakes of upstream particles. In literature, it is still unknown about the effect of bi-dispersity on particle clustering and is investigated in this paper using particle resolved direct numerical simulations. Particle-fluid and particle-particle interactions are modeled using immersed boundary method and discrete element method respectively. In simulations, total solid volume fraction is about 1% and based on Sauter mean diameter the settling Reynolds number is about 400. For studying the effects of bi-dispersity, two particle diameter ratios are studied i.e. 2:1 and 3:1. Solid volume fraction for each particle diameter is varied from 1:1, 1:2 and 2:1. Simulations are also done for monodisperse particles for benchmarking and studying whether the range of Reynolds number is suitable for particle clustering. After reaching steady state, instantaneous location of particles and nearest neighbor distance perpendicular to settling direction is studied for quantifying particle clusters. Simulations showed that vertical column like clusters for small sized particles decrease by increasing solid volume fraction of large sized particles.