Hydrodynamic and Brownian Fluctuations in Sedimenting Suspensions

TL;DR

This study uses mesoscopic simulations to explore how hydrodynamic and Brownian fluctuations influence sedimentation in suspensions, revealing that hydrodynamics significantly affect velocity reduction and fluctuations even when weaker than Brownian forces.

Contribution

It demonstrates the dominant role of hydrodynamic interactions in sedimentation velocity reduction and fluctuation behavior across a range of Peclet numbers.

Findings

Hydrodynamic interactions induce backflow effects.

Velocity fluctuations show nonequilibrium hydrodynamic behavior for Pe > 1.

Hydrodynamics influence sedimentation even when weaker than Brownian forces.

Abstract

We use a mesoscopic computer simulation method to study the interplay between hydrodynamic and Brownian fluctuations during steady-state sedimentation of hard sphere particles for Peclet numbers (Pe) ranging from 0.1 to 15. Even when the hydrodynamic interactions are an order of magnitude weaker than Brownian forces, they still induce backflow effects that dominate the reduction of the average sedimentation velocity with increasing particle packing fraction. Velocity fluctuations, on the other hand, begin to show nonequilibrium hydrodynamic character for Pe > 1