Dresden 2017 – scientific programme

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BP: Fachverband Biologische Physik

BP 17: Microswimmers II (Joint Session DY/BP)

BP 17.5: Talk

Tuesday, March 21, 2017, 15:30–15:45, HÜL 186

Collective Sedimentation of Squirmers under Gravity — •Jan-Timm Kuhr, Felix Rühle, Johannes Blaschke, and Holger Stark — Institut für Theoretische Physik, Technische Universität Berlin, Hardenbergstraße 36, 10623 Berlin, Germany

Biological microswimmers such as algae or plankton experience gravity. Recent theoretical studies on the sedimentation of microswimmers often explore the dilute case, where hydrodynamic and steric interactions between them can be neglected [1,2]. We apply parallelized MPCD simulations to study sedimentation of spherical squirmers under gravity and thereby explicitly include long-ranged hydrodynamic interactions also with bounding surfaces. We measure density profiles for systems of thousands of microswimmers and analyze how the ratio of active velocity to passive sedimentation velocity as well as the squirmer type (neutral, pusher, and puller) affect sedimentation.

Lower regions of the system are dominated by incomplete hexagonal layer formation with distinct orientation, whereas we recover an exponential density profile in the upper, less dense region. The average vertical orientation of the squirmers depends strongly on their vertical position as well as their type. Furthermore, we find that hydrodynamics organizes the microswimmers into convection cells, the strength of which changes with squirmer type and influences the sedimentation length.

[1] M. Enculescu and H. Stark, Phys. Rev. Lett. 107, 058301 (2011).
K. Wolff, A. Hahn, and H. Stark, Eur. Phys. J. E 36, 43 (2013).