Hydrodynamic irreversibility of non-Brownian suspensions in highly confined duct flow

TL;DR

This study investigates the irreversible behavior and particle migration in highly confined non-Brownian suspensions under oscillatory flow, combining experiments and simulations to reveal rapid wall migration and flow features.

Contribution

It provides new experimental and numerical insights into particle migration and irreversibility in highly confined suspensions, highlighting the effects of confinement on flow behavior.

Findings

Rapid particle migration to walls in confined flow

Correlation between particle proximity and migration

Agreement between experimental and simulation results

Abstract

The irreversible behavior of a highly confined non-Brownian suspension of spherical particles at low Reynolds number in a Newtonian fluid is studied experimentally and numerically. In experiment, the suspension is confined in a thin rectangular channel that prevents complete particle overlap in the narrow dimension and subjected to an oscillatory pressure-driven flow. In the small cross-sectional dimension particles rapidly separate to the walls, whereas in the large dimension features reminiscent of shear-induced migration in bulk suspensions are recovered. Furthermore, as a consequence of the channel geometry and the development and application of a single-camera particle tracking method, three-dimensional particle trajectories are obtained that allow us to directly associate relative particle proximity with the observed migration. Companion simulations of a steadily flowing suspension highly confined between parallel plates are conducted using the Force Coupling Method which also show rapid migration to the walls as well as other salient features observed in the experiment. While we consider relatively low volume fractions compared to most prior work in the area, we nevertheless observe significant and rapid migration which we attribute to the high degree of confinement.