Alignment-Induced Self-Organization of Autonomously Steering Microswimmers: Turbulence, Vortices, and Jets

TL;DR

This study uses mesoscale hydrodynamics simulations to explore how alignment influences the self-organization of microswimmers, revealing diverse collective behaviors like turbulence, clustering, and jets based on swimmer type.

Contribution

It demonstrates how hydrodynamic alignment leads to distinct collective phenomena in microswimmers, highlighting differences between pushers and pullers.

Findings

Pushers exhibit active turbulence with homogeneous density.

Pullers tend to cluster and form vortex rings.

Dynamics vary significantly between swimmer types.

Abstract

Systems of motile microorganisms exhibit a multitude of collective phenomena, including motility-induced phase separation and turbulence. Sensing of the environment and adaptation of movement plays an essential role in the emergent behavior. We study the collective motion of wet self-steering polar microswimmers, which align their propulsion direction hydrodynamically with that of their neighbors, by mesoscale hydrodynamics simulations. The simulations of the employed squirmer model reveal a distinct dependence on the swimmer flow field, i.e., pullers versus pushers. The collective motion of pushers is characterized by active turbulence, with nearly homogeneous density and a Gaussian velocity distribution. Pullers exhibit a strong tendency for clustering and display velocity and vorticity distributions with fat exponential tails; their dynamics is chaotic, with a temporal appearance of vortex rings and fluid jets. Our results show that the collective behavior of intelligent microswimmers is very diverse and still offers many surprises to be discovered.