Hydrodynamic instabilities in a two-dimensional sheet of microswimmers embedded in a three-dimensional fluid

• DOI: 10.1017/jfm.2023.985
• Publication Date: 2024-02-02T08:14:58Z
• Authors: Viktor Škultéty; Dóra Bárdfalvy; Joakim Stenhammar; Cesare Nardini; Alexander Morozov
• Keywords: 0301 basic medicine; 03 medical and health sciences

A collection of microswimmers immersed in an incompressible fluid is characterised by strong interactions due to the long-range nature hydrodynamic fields generated individual organisms. As a result, suspensions rear-actuated ‘pusher’ swimmers such as bacteria exhibit collective motion state often referred ‘bacterial turbulence’, large-scale chaotic flows. The onset pusher classically understood within framework mean-field kinetic theories for dipolar swimmers. In bulk two and three dimensions, theory predicts that instability leading bacterial turbulence mutual swimmer reorientation sets at largest length scale available suspension. Here, we construct similar case microswimmer suspension restricted two-dimensional plane embedded three-dimensional fluid. This setting qualitatively mimics effect swimming close interface. We show in-plane flow are effectively compressible spite incompressibility fluid, on average act sources (pushers) or sinks (pullers). analyse stability homogeneous isotropic state, find types different from bulk, case: first, analogue orientational systems instead occurs smallest system. Second, associated with density variations arises puller generic consequence effective compressibility. Given these qualitative differences respect standard setting, conclude confinement can have crucial role determining behaviour suspensions.