Turbulence-Induced Fluctuating Interfaces in Heterogeneously-Active Suspensions

TL;DR

This study explores how spatial heterogeneity in activity influences turbulence and interface formation in dense bacterial suspensions, revealing complex flow behaviors and mixing dynamics.

Contribution

It demonstrates the emergence of hydrodynamic interfaces and multiscale fluctuations driven by activity heterogeneity in bacterial suspensions.

Findings

Hydrodynamic interfaces separate turbulence from jammed regions.

Heterogeneity affects mixing and residence times of tracers.

Complex flow configurations arise from natural activity heterogeneities.

Abstract

We investigate the effects of heterogeneous (spatially varying) activity in a hydrodynamical model for dense bacterial suspensions, confining ourselves to experimentally realizable, simple, quenched, activity patterns. We show that the evolution of the bacterial velocity field under such activity patterning leads to the emergence of hydrodynamic interfaces separating spatially localized turbulence from jammed frictional surroundings. We characterise the intermittent and multiscale fluctuations of this interface and also investigate how heterogeneity influences mixing via the residence times of Lagrangian tracers. This work reveals how naturally occurring heterogeneities could decisively steer active flows into more complex configurations than those typically studied, opening up parallels to droplet dynamics, front propagation and turbulent mixing layers.