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BP: Fachverband Biologische Physik

BP 7: Active Fluids and Microswimmers (joint session DY/BP/CPP)

BP 7.1: Invited Talk

Monday, March 18, 2024, 15:00–15:30, BH-N 243

Control of active turbulence — •Holger Stark — Technische Universität Berlin, Institute of Theoretical Physics, Hardenbergstr. 36, 10623 Berlin, Germany

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.

In the first part of the talk we rely on a continuum description of active paranematics, the Doi-Edwards theory supplemented by an active stress tensor [1]. We 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.

Second, we perform hydrodynamic simulations of a collection of active or squirmer rods moving in their fluid environment [2]. We classify their dynamic states for the pusher/puller type as a function of density and aspect ratio of the rods and observe clustering and swarming. In particular, pusher rods show active turbulence as a compromise of disordering hydrodynamic and aligning steric interactions.

[1] A. Partovifard and H. Stark, submitted.

[2] A.W. Zantop and H. Stark, Soft Matter 18, 6179 (2022).

Keywords: active turbulence; active paranematics; squirmer rods; hydrodynamic simulations