Screening, Hyperuniformity, and Instability in the Sedimentation of Irregular Objects

TL;DR

This paper investigates how irregularly shaped objects sediment in a fluid, revealing that their anisotropic responses can suppress fluctuations and create hyperuniform structures, but may also cause instability depending on shape.

Contribution

It introduces a fluctuating hydrodynamics framework to analyze the sedimentation of irregular objects, highlighting the role of shape-induced anisotropy in fluctuation suppression and instability.

Findings

Irregular objects can suppress concentration fluctuations due to anisotropic responses.

Sedimentation can lead to hyperuniform structures in suspensions of irregular objects.

Certain shapes may destabilize uniform sedimentation due to anisotropic effects.

Abstract

We study the overdamped sedimentation of non-Brownian objects of irregular shape using fluctuating hydrodynamics. The anisotropic response of the objects to flow, caused by their tendency to align with gravity, directly suppresses concentration and velocity fluctuations. This allows the suspension to avoid the anomalous fluctuations predicted for suspensions of symmetric spheroids. The suppression of concentration fluctuations leads to a correlated, hyperuniform structure. For certain object shapes, the anisotropic response may act in the opposite direction, destabilizing uniform sedimentation.