Numerical Study of the Sedimentation of Spheroidal Particles

TL;DR

This study uses numerical simulations to explore how non-spherical spheroidal particles settle in viscous fluids, revealing unique motion patterns and interactions that differ from spherical particles, with implications for sedimentation processes.

Contribution

It provides new insights into the sedimentation behavior of spheroidal particles, including critical thresholds and interaction dynamics, using the Immersed Boundary Method.

Findings

Critical Galileo number decreases with spheroid aspect ratio.

Oblate particles zigzag; prolate rotate around vertical axis.

Interaction time and clustering increase for spheroidal particles.

Abstract

The gravity-driven motion of rigid particles in a viscous fluid is relevant in many natural and industrial processes, yet this has mainly been investigated for spherical particles. We therefore consider the sedimentation of non-spherical (spheroidal) isolated and particle pairs in a viscous fluid via numerical simulations using the Immersed Boundary Method. The simulations performed here show that the critical Galileo number for the onset of secondary motions decreases as the spheroid aspect ratio departs from 1. Above this critical threshold, oblate particles perform a zigzagging motion whereas prolate particles rotate around the vertical axis while having their broad side facing the falling direction. Instabilities of the vortices in the wake follow when farther increasing the Galileo number. We also study the drafting-kissing-tumbling associated with the settling of particle pairs. We find that the interaction time increases significantly for non-spherical particles and, more interestingly, spheroidal particles are attracted from larger lateral displacements. This has important implications for the estimation of collision kernels and can result in increasing clustering in suspensions of sedimenting spheroids.