Break-up of suspension drops settling under gravity in a viscous fluid close to a vertical wall

TL;DR

This study investigates how suspension drops sedimenting near a vertical wall in a viscous fluid break up faster and travel shorter distances, using experiments and numerical simulations in the Stokes flow regime.

Contribution

It provides new insights into the destabilization process of sedimenting suspension drops near walls, combining experimental and numerical approaches with a point-force model.

Findings

Destabilization time and travel distance decrease as the drop gets closer to the wall.

Destabilization times and lengths vary significantly due to chaotic particle dynamics.

Linear dependence of destabilization metrics on D/h ratio for h ≥ D.

Abstract

The evolution of suspension drops sedimenting under gravity in a viscous fluid close to a vertical wall was studied experimentally and numerically with the use of the point-force model, in the Stokes flow regime. The fluid inside and outside the drop was identical. The initial distribution of the suspended solid heavy particles was uniform inside a spherical volume. In the experiments and in the simulations, the suspension drops evolved qualitatively in the same way as in an unbounded fluid. However, it was observed, both experimentally and numerically that, on the average, the destabilization time T and the distance L traveled by the drop until break-up were smaller for a closer distance h of the drop center from the wall, with approximately linear dependence of T and L on D/h, for h larger or comparable to the drop diameter D. Destabilization times and lengths of individual drops with different random configurations of the particles were shown to differ significantly from each other, owing to the chaotic nature of the particle dynamics.