Layering instability in a confined suspension flow

TL;DR

This paper investigates how layering instabilities, caused by swapping trajectories, influence the microstructure of confined suspension flows, potentially explaining layered formations across various densities.

Contribution

It demonstrates that swapping trajectories induce layering in confined suspension flows, extending previous work on collision prevention to microstructure formation.

Findings

Layering occurs near walls or across the entire channel.

Swapping trajectories significantly alter suspension microstructure.

The mechanism likely applies to a wide range of suspension densities.

Abstract

We have shown [J.\ Fluid Mech.\ {\bf 592}, 447 (2007)] that swapping (reversing) trajectories in confined suspension flows prevent collisions between particles approaching each other in adjacent streamlines. Here we demonstrate that by inducing layering this hydrodynamic mechanism changes the microstructure of suspensions in a confined Couette flow. Layers occur either in the near-wall regions or span the whole channel width, depending on the strength of the swapping-trajectory effect. While our theory focuses on dilute suspensions, we postulate that this new hydrodynamic mechanism controls formation of a layered microstructure in such flows in a wide range of densities.