Flocking turbulence of microswimmers in confined domains

TL;DR

This paper investigates a new active turbulence state called flocking turbulence in confined microswimmer systems, revealing its characteristics, energy spectrum, and stability conditions through numerical simulations of the Toner-Tu-Swift-Hohenberg model.

Contribution

It introduces and characterizes flocking turbulence in confined active matter, demonstrating its emergence, spectral properties, and transition to order with increased confinement.

Findings

Flocking turbulence features few strong vortices with coherent flocking islands.

The energy spectrum follows a power-law with a parameter-dependent exponent.

Increased confinement eventually destabilizes flocking turbulence, leading to a single vortex state.

Abstract

We extensively study the Toner-Tu-Swift-Hohenberg model of motile active matter by means of direct numerical simulations in a two-dimensional confined domain. By exploring the space of parameters of the model we investigate the emergence of a new state of active turbulence which occurs when the aligning interactions and the self-propulsion of the swimmers are strong. This regime of flocking turbulence is characterized by a population of few strong vortices, each surrounded by an island of coherent flocking motion. The energy spectrum of flocking turbulence displays a power-law scaling with an exponent which depends weakly on the model parameters. By increasing the confinement we observe that flocking turbulence becomes unstable: after a long transient, characterized by power-law distributed transition times, the system switches to the ordered state of a single giant vortex