Regensburg 2025 – scientific programme

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BP: Fachverband Biologische Physik

BP 17: Poster Session II

BP 17.9: Poster

Tuesday, March 18, 2025, 18:00–20:30, P4

Onset of bioconvection in a simple continuum model — •Marius M. Kaiser, Fabián Álvarez-Garrido, and Michael Wilczek — Universität Bayreuth

Dense suspensions of swimming micro-organisms show bioconvection, i.e.~the emergence of self-organized flow patterns much larger than the individual swimmers, under certain conditions. Here, we analyze the onset of bioconvection in a simple continuum model. The model is derived from the Fokker-Planck equation for the swimmer concentration field and the swimmer orientation field [Pedley, J. Fluid. Mech. 647, 335 (2010)] coupled to the Navier-Stokes equation, in which we only consider buoyancy effects (no cell stresses) and approximate higher-order moments in terms of the polar order parameter. A linear stability analysis in the idealized case of a prescribed polar orientation field shows that the system exhibits a type-II instability. The results of our linear stability analysis are in agreement with direct numerical simulations of our model. Simulations of the model, now with dynamically evolving polar orientation field, suggest that the type of spatial instability remains the same, albeit with shifted critical values. Our findings shed light on the mechanism driving pattern formation in this type of suspensions.

Keywords: bioconvection; hydrodynamic instability; pattern