## Physics

## Document Type

Article

## Abstract

Laboratory experiments and particle-resolved simulations are employed to investigate the settling dynamics of a pair of rigidly connected spherical particles of unequal size. They yield a detailed picture of the transient evolution and the terminal values of the aggregate's orientation angle and its settling and drift velocities as functions of the aspect ratio and the Galileo number, which denotes the ratio of buoyancy and viscous forces acting on the aggregate. At low to moderate values of, the aggregate's orientation and velocity converge to their terminal values monotonically, whereas for higher -values the aggregate tends to undergo a more complex motion. If the aggregate assumes an asymmetric terminal orientation, it displays a non-zero terminal drift velocity. For diameter ratios much larger than one and small, the terminal orientation of the aggregate becomes approximately vertical, whereas when is sufficiently large for flow separation to occur, the aggregate orients itself such that the smaller sphere is located at the separation line. Empirical scaling laws are obtained for the terminal settling velocity and orientation angle as functions of the aspect ratio and for diameter ratios from 1 to 4 and particle-to-fluid density ratios from 1.3 to 5. An analysis of the accompanying flow field shows the formation of vortical structures exhibiting complex topologies in the aggregate's wake, and indicates the formation of a horizontal pressure gradient across the larger sphere, which represents the main reason for the emergence of the drift velocity.

## Publication Title

Journal of Fluid Mechanics

## Publication Date

9-24-2024

## Volume

995

## ISSN

0022-1120

## DOI

10.1017/jfm.2024.711

## Keywords

particle/fluid flow, sediment transport, suspensions

## Repository Citation

Maches, Z. and Houssais, Morgane, "Settling of two rigidly connected spheres" (2024). *Physics*. 16.

https://commons.clarku.edu/faculty_physics/16

## Creative Commons License

This work is licensed under a Creative Commons Attribution 4.0 International License.

## Copyright Conditions

Original article must be properly cited: Maches, Z., Houssais, M., Sauret, A., & Meiburg, E. (2024). Settling of two rigidly connected spheres. arXiv preprint arXiv:2406.10381.