Inertial rotation of a small oblate spheroid in a simple shear flow

TL;DR

This study combines experiments and simulations to analyze how confinement and inertia affect the rotation and stability of a small oblate spheroid in shear flow, reconciling theoretical predictions with observed behaviors.

Contribution

It provides a comprehensive comparison of experimental, numerical, and theoretical results, highlighting the impact of confinement and inertia on spheroid rotation in shear flow.

Findings

Confinement reduces drift rate towards stable log-rolling orbit.

Inertia and confinement significantly influence spheroid orientation stability.

Results reconcile discrepancies between theory, experiments, and simulations.

Abstract

We compare experiments and fully-resolved particle simulations designed to match the experimental conditions of a weakly inertial, neutrally buoyant, moderately oblate spheroid in shear flow under confinement. Experimental and numerical results are benchmarked against theory valid for asymptotically small particle Reynolds numbers and for unconfined systems. By considering the combined effects of confinement and inertia, sensitivity to initial conditions, and the time span of observation, we reconcile the findings of theory, experiments, and numerical simulations. Furthermore, we demonstrate that confinement significantly influences the orientational stability of log-rolling spheroids compared to weak inertia, with the primary consequence being a reduced drift rate towards the stable log-rolling orbit.