Settling dynamics of an oloid: experiments and simulations

TL;DR

This paper investigates how oloid-shaped particles settle in fluids through experiments and simulations, revealing two distinct falling modes influenced by shape, orientation, and Galileo number, with good agreement between methods.

Contribution

It provides the first combined experimental and computational analysis of oloid settling dynamics, highlighting the influence of shape and initial orientation on falling modes.

Findings

Two distinct settling modes identified: stable and tumbling.

Good agreement between experimental and simulation results.

Initial orientation affects rotation dynamics at low Galileo numbers.

Abstract

This study presents a combined experimental and computational investigation of an oloid shaped particle settling in a quiescent fluid. The oloid, a unique convex shape with anisotropic geometry, provides a distinctive model for exploring how a particle's shape and orientation affect its settling dynamics. The settling oloids are tracked experimentally for Galileo numbers $48 \leq \text{Ga} \leq 5.4 \cdot 10^3$, using two particle sizes ($D_{\text{eq}}$ = 21.6 mm, and $D_{\text{eq}}$ = 10.8 mm). The density ratio between the particle and fluid $\Gamma$ = $\frac{\rho_p}{\rho_f}$ ranges from $1.11 \leq \Gamma \leq 1.30$ in the experiments. Computationally, the Galileo numbers $10 \leq \text{Ga} \leq 100$ are simulated, with $\Gamma = 2$. The experimental findings and numerical results are in good agreement, and give a consistent idea of the oloid settling dynamics. Our results indicate two distinct falling modes for the oloid, separated by Galileo number. The stable mode is characterised by a preferential orientation, with a rotation around the vertical axis, whereas the tumbling mode has randomly distributed orientation and rotation statistics. We characterise the falling velocity, orientation, and rotation dynamics of the oloids over a range of Galileo numbers. Additionally, the influence of the initial orientation is revealed to determine the rotation dynamics at low Galileo numbers.