Hydrodynamics of chiral squirmers

TL;DR

This paper investigates the hydrodynamic interactions of chiral squirmers, revealing complex behaviors such as helical trajectories, attraction, repulsion, and bounded orbits, which are relevant to microorganism collective motion.

Contribution

It introduces a model for chiral squirmers with asymmetrical slip velocities, analyzing their interactions and resulting complex swimming behaviors.

Findings

Chiral asymmetries induce helical swimming trajectories.

Hydrodynamic interactions can cause attraction, repulsion, or bounded orbits.

Bound states reflect the chiral nature of the swimmers.

Abstract

Many microorganisms take a chiral path while swimming in an ambient uid. In this paper, we study the combined behavior of two chiral swimmers using the well-known squirmer model taking into account chiral asymmetries. In contrast to the simple squirmer model, which has an axisymmetric distribution of slip velocity, the chiral squirmer has additional asymmetries in the surface slip, which contribute to both translations and rotations of the motion. As a result, swimming trajectories can become helical and chiral asymmetries arise in the ow patterns. We study the swimming trajectories of a pair of chiral squirmers that interact hydrodynamically. This interaction can lead to attraction and repulsion, and in some cases even to bounded states where the swimmers continue to periodically orbit around a common average trajectory. Such bound states are a signature of the chiral nature of the swimmers. Our study could be relevant to the collective movements of ciliated microorganisms.