title: Hydrodynamic oscillations and variable swimming speed in squirmers close to repulsive walls.
abstract: We present a lattice Boltzmann study of the hydrodynamics of a fully resolved squirmer, confined in a slab of fluid between two no-slip walls. We show that the coupling between hydrodynamics and short-range repulsive interactions between the swimmer and the surface can lead to hydrodynamic trapping of both pushers and pullers at the wall, and to hydrodynamic oscillations in the case of a pusher. We further show that a pusher moves significantly faster when close to a surface than in the bulk, whereas a puller undergoes a transition between fast motion and a dynamical standstill according to the range of the repulsive interaction. Our results critically require near-field hydrodynamics and demonstrate that far-field hydrodynamics is insufficient to give even a qualitatively correct account of swimmer behaviour near walls. Finally our simulations suggest that it should be possible to control the density and speed of squirmers at a surface by tuning the range of steric and electrostatic swimmer-wall interactions.
authors.affiliation: Laboratoire de Physique des Solides, CNRS, Univ. Paris-Sud, Université Paris-Saclay, 91405 Orsay Cedex, France. juho.lintuvuori@u-psud.fr.
authors.forename: Juho S
authors.initials: JS
authors.lastname: Lintuvuori
authors.affiliation: SUPA, School of Physics and Astronomy, University of Edinburgh, UK. abrown20@staffmail.ed.ac.uk.
authors.forename: Aidan T
authors.initials: AT
authors.lastname: Brown
authors.affiliation: EPCC, School of Physics and Astronomy, University of Edinburgh, UK.
authors.forename: Kevin
authors.initials: K
authors.lastname: Stratford
authors.affiliation: SUPA, School of Physics and Astronomy, University of Edinburgh, UK. abrown20@staffmail.ed.ac.uk.
authors.forename: Davide
authors.initials: D
authors.lastname: Marenduzzo