Spontaneous Flows in Suspensions of Active Cyclic Swimmers
- 284 Downloads
Many swimming cells rely on periodic deformations to achieve locomotion. We introduce in this work a theoretical model and numerical simulations in order to elucidate the impact of these cyclic strokes on the emergence of mesoscale structures and collective motion in swimmer suspensions. The model extends previous kinetic theories for populations of identical swimmers to the case of self-propelled particles undergoing transitions between pusher and puller states, and is applied to quantify how the unsteadiness of the hydrodynamic velocity field, to which each swimmer population contributes, affects the onset and characteristics of spontaneous flows. A linear stability analysis reveals that the sign of the population-averaged dipole determines the stability of the uniform isotropic state, with suspensions dominated by pushers being subject to growing nematic bend fluctuations. Stochastic transitions, however, are also seen to provide an additional damping mechanism. To investigate the population dynamics above the instability threshold, we also perform direct particle simulations based on a slender-body model, where the growth or decay of the active power generated by the swimmers is found to be a robust measure of the structural and dynamical instability.
KeywordsActive suspensions Collective motion Kinetic theory Hydrodynamic stability
Mathematics Subject Classification92C05 92C17 76E99 76A05
D.S. gratefully acknowledges partial support from a Total-ESPCI ParisTech Chair.
- Baskaran, A., Marchetti, M. C.: Nonequilibrium statistical mechanics of self-propelled hard rods. J. Stat. Mech.: Theor. Exp. P04019 (2010)Google Scholar
- Bricard, A., Caussin, J.-B., Das, D., Savoie, C., Chikkadi, V., Shitara, K., Chepizhko, O., Peruani, F., Saintillan, D., Bartolo, D.: Emergent vortices in populations of colloidal rollers. Nature Comm. (2015, to appear)Google Scholar
- Gachelin, J., Miño, G., Berthet, H., Lindner, A., Rousselet, A., Clément, E.: Non-Newtonian viscosity of Escherichia coli suspensions. Phys. Rev. Lett. 110, 268103 (2013)Google Scholar
- Saintillan, D., Shelley, M.J.: Theory of active suspensions. In: Spagnolie, S.E. (ed.) Complex Fluids in Biological Systems: Experiment, Theory, and Computation, pp. 319–355. Springer, New York (2015)Google Scholar