On the dynamics and collisions of settling spheroidal particles

In this study, we perform particle-resolved simulations of settling spheroidal particles, considering oblate and prolate spheroids and spheres, and investigate the shape effect on the particle dynamics in suspensions with volume fraction 1% and 5%. We first examine the single-point statistics of the translational and rotational motion of the settling particles. The horizontal velocity has a symmetrical distribution with standard deviation dependent on the particle shape. The greater horizontal velocity fluctuations of the non-spherical particles, compared to that of spheres, are attributed to the horizontal drift of settling spheroids with oblique orientations induced by the fluid-particle and particle-particle interactions. The fluctuation of particle vertical velocity, instead, is skewed under the effect of wake-induced hydrodynamic interactions. Further, we explore the particle pair statistics, which demonstrate the formation of column-like particle micro-structures for the lowest volume fraction considered. This clustering is more pronounced for spheroidal particles than spheres, due to the stronger attractions among vertically-aligned settling spheroids. Moreover, the particle pair statistics are directly related to the collision rate among the dispersed particles. The local accumulation of oblate/prolate spheroids serves as the major mechanism to promote the particle-particle collisions in dilute suspensions.