Self-sustained patchy turbulence in shear-thinning active fluids

TL;DR

This paper investigates how shear-thinning non-Newtonian rheology influences active turbulence in bacterial suspensions, revealing a self-sustained heterogeneous state with unique velocity statistics and a hysteretic transition.

Contribution

It demonstrates the emergence of a self-sustained patchy turbulence state in shear-thinning active fluids, supported by numerical analysis and percolation transition insights.

Findings

Heterogeneous turbulent and quiescent regions coexist in shear-thinning active fluids.

The transition to this state is hysteretic and resembles directed percolation.

Velocity statistics are significantly altered in the patchy turbulence regime.

Abstract

Bacterial suspensions and other active fluids are known to develop highly dynamical vortex states, denoted as active or mesoscale turbulence. We reveal the pronounced effect of non-Newtonian rheological conditions on these turbulent states, concentrating on shear thinning. A self-sustained heterogeneous state of coexisting turbulent and quiescent areas develops, which results in anomalous velocity statistics. The heterogeneous state emerges in a hysteretic transition when varying activity. We provide an extensive numerical analysis and observe features consistent with a directed percolation transition. Our results are important, for instance, when addressing active objects in biological media with complex rheological properties.