Regensburg 2019 – scientific programme
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DY: Fachverband Dynamik und Statistische Physik
DY 38: Microswimmers (joint session DY/CPP)
DY 38.3: Talk
Wednesday, April 3, 2019, 16:00–16:15, H19
Stabilization of a square vortex lattice in microswimmer suspensions by periodic arrays of obstacles — •Henning Reinken1, Sebastian Heidenreich2, Igor S. Aranson3, Markus Bär2, and Sabine H.L. Klapp1 — 1Technische Universität Berlin, Berlin, Germany — 2Physikalisch-Technische Bundesanstalt, Berlin, Germany — 3Pennsylvania State University, University Park, PA 16802, USA
Bacterial suspensions, a paradigmatic example of an active fluid, are known to exhibit a state denoted as mesoscale turbulence which is characterized by chaotic dynamics of vortices of a characteristic size. In a recent experiment, these vortices have been stabilized into a square lattice with antiferromagnetic order by geometrically constraining the bacterial suspension using periodic arrays of obstacles with a spacing in the range of the unconstrained vortex size [1]. Interestingly, the vortices are consistently located in the gaps between the obstacles rather than forming around them [1]. We aim to reproduce the patterns observed in the experiment using a recently derived fourth-order field theory for a vectorial order parameter representing an effective microswimmer velocity [2]. In this continuum theoretical framework, we numerically explore different implementations of the constraints: Obstacles that favor negatively charged topological defects straightforwardly reproduce the observed vortex lattice configuration. For topologically neutral defects, higher order nonlinear effects are required to break the topological symmetry and stabilize a certain configuration.
[1] D. Nishiguchi et al., Nat Commun. 9, 4486 (2018).
[2] H. Reinken et al., Phys. Rev. E 97, 022613 (2018).