Collective behavior of strongly confined suspensions of squirmers

¹ Institute for Cross-Disciplinary Physics and Complex Systems (CSIC-UIB), Campus Universitat Illes Balears E-07122 Palma de Mallorca, Spain
² Department of Chemical Engineering, Kyoto University - Kyoto 615-8510, Japan
³ Department of Physics, The University of Tokyo - 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

Received: 15 February 2016
Accepted: 28 April 2016

Abstract

We run numerical simulations of strongly confined suspensions of model spherical swimmers called “squirmers”. Because of the confinement, the Stokeslet dipoles generated by the particles are quickly screened and the far-field flow is dominated by the source dipole for all the different kinds of squirmers. However, we show that the collective behavior of the suspension still depends on the self-propelling mechanism of the swimmers as polar states can only be observed for neutral squirmers. We demonstrate that the near-field hydrodynamic interactions play a crucial role in the alignment of the orientation vectors of spherical particles. Moreover, we point out that the enstrophy and the fluid fluctuations of an active suspension also depend on the nature of the squirmers.