# Flow properties and hydrodynamic interactions of rigid spherical microswimmers

## TL;DR

This paper investigates the flow and hydrodynamic interactions of rigid spherical microswimmers, highlighting how their extended surfaces influence collective behavior differently from idealized point-force models.

## Contribution

It introduces a minimal model for rigid spherical microswimmers, deriving their mobility matrices and revealing differences in hydrodynamic interactions compared to point-force dipoles.

## Key findings

- Flow fields differ from Stokeslet dipoles at finite distances.
- Hydrodynamic interactions among rigid microswimmers are significantly different.
- Derived mobility matrices enable better simulation of collective dynamics.

## Abstract

We analyze a minimal model for a rigid spherical microswimmer and explore the consequences of its extended surface on the interplay between its self-propulsion and flow properties. The model is the first order representation of microswimmers, such as bacteria and algae, with rigid bodies and flexible propelling appendages. The flow field of such a microswimmer at finite distances significantly differs from that of a point-force (Stokeslet) dipole. For a suspension of microswimmers, we derive the grand mobility matrix that connects the motion of an individual swimmer to the active and passive forces and torques acting on all the swimmers. Our investigation of the mobility tensors reveals that hydrodynamic interactions among rigid-bodied microswimmers differ considerably from those among the corresponding point-force dipoles. Our results are relevant for the study of collective behavior of hydrodynamically interacting microswimmers by means of Stokesian dynamics simulations at moderate concentrations.