Frustrating active flows

We address the degeneracy of active flows in fluidic networks. 

Over the past decade, by engineering soft materials from active units, physicists have learned how to drive fluids from within. The generic strategy consists in assembling orientationally ordered liquids from self-propelled particles. Their resulting mesmerizing flows are now understood in basic geometries such as linear channels or circular chambers. However, unlike flows of Newtonian viscous fluids, active flows are intrinsically multistable. This strongly nonlinear behavior can result in highly degenerated flow patterns, even in simple geometries.

Building on model experiments based on Quincke roller fluids and minimal model simulations, we reveal and elucidate two qualitatively different classes of flow degeneracy when active fluids explore periodic lattices. Our work explains how the local strategies used by active flows to resolve geometrical frustration determine the large scale morphology of their flow fields.