Three-dimensional pattern formation in suspensions of swimming micro-organisms

TL;DR

This paper presents a numerical simulation demonstrating how suspensions of swimming micro-organisms develop complex, chaotic flow patterns and density fluctuations, leading to efficient mixing, as predicted by linear stability analysis.

Contribution

It introduces a simulation based on a recent kinetic theory to explore three-dimensional pattern formation in micro-organism suspensions, revealing quasiperiodic density fluctuations and chaotic flows.

Findings

Density fluctuations merge and break up quasiperiodically

Fluctuations occur on the size of the simulation box

Flow fields are complex and chaotic, enhancing mixing

Abstract

Suspensions of self-propelled particles, such as swimming micro-organisms, are known to undergo complex dynamics as a result of hydrodynamic interactions. This fluid dynamics video presents a numerical simulation of such a suspension, based on a kinetic theory recently developed by Saintillan and Shelley (Physics of Fluids, 20, 123403, 2008). Starting from a nearly uniform and isotropic initial distribution, our simulations show the formation of strong density fluctuations, which merge and break up in time in a quasiperiodic fashion. These fluctuations are found to occur on the size of the simulation box, in agreement with a prediction from a linear stability analysis. In addition, the dynamics are characterized by complex chaotic flow fields, which result in efficient fluid mixing.