Active turbulence is one of the prominent features of active matter and occurs in diverse systems such as bacterial suspensions, biopolymeric assemblies, and tissues. One of the current challenges is to control these turbulent flow patterns for powering processes at small scales and to purposefully design them.
We rely on a continuum description of active paranematics, the Doi-Edwards theory supplemented by an active stress tensor [1], and characterize the occuring turbulent flow for extensile active stresses. Then, motivated by the possibility to control the activity of bacteria by light, we consider a square lattice of spots, where activity drops to zero. Depending on the lattice constant and the size of the spots, we identify a trapped-vortex and, most interestingly, a multi-lane flow state. The latter consists of lanes with opposite flow directions separated by a street of vortices. It displays multistability and can also appear transiently. In a further work, we can even generate a flow-vortex lattice with antiferromagnetic order. Finally, a different configuration, where we tune the size of a single activity spot, allows a controlled route towards active turbulence.
[1] A. Partovifard, J. Grawitter, and H. Stark, Soft Matter 20, 1800 (2024).