Optimal Turbulent Transport in Microswimmer Suspensions

Abstract

Microswimmer suspensions self-organize into complex spatio-temporal flow patterns, including vortex lattices and mesoscale turbulence. Here we explore the consequences for the motion of passive tracers, based on a continuum model for the microswimmer velocity field. We observe two qualitatively different regimes distinguished via the dimensionless Kubo number $K$. At advection strengths right above the transition to turbulence, the flow field evolves very slowly ($K\gg 1$) and the spatial vortex structures lead to dominant trapping effects. In contrast, deep in the turbulent state, much faster dynamics ($K\ll 1$) consistent with the so-called sweeping hypothesis leads to transport properties completely determined by the temporal correlations. In between ($K\approx 1$), we observe a regime of optimal transport, signaled by a maximum of the diffusion coefficient.

References in corpus (5)

• Meso-scale turbulence in living fluids
• Diffusion and spatial correlations in suspensions of swimming particles
• Minimal continuum theories of structure formation in dense active fluids
• Oscillatory chiral flows in confined active fluids with obstacles
• Thermal conductivity changes across a structural phase transition: the case of high-pressure silica