Flocking and mesoscale turbulence in three-dimensional active fluids

TL;DR

This paper investigates three-dimensional active fluids, revealing a transition from bacterial turbulence to a novel turbulent flock with global order, supported by numerical simulations and a predictive closure model.

Contribution

It introduces a minimal model capturing the turbulent flock regime and explains the transition mechanism through a bifurcation analysis.

Findings

Identification of bacterial turbulence at low activity

Discovery of a turbulent flock with global order at high activity

Development of a closure model predicting the turbulent regimes

Abstract

We numerically study the three-dimensional turbulence in a minimal model of an active fluid--the Toner-Tu-Swift-Hohenburg equation. For small activity, we observe bacterial turbulence, while for large activity, we uncover hitherto unexplored regime of a turbulent flock where a global order coexists with turbulence. We present a simple closure model that predicts the turbulent flock and also qualitatively explains the transition to the bacterial turbulence regime via a transcritical bifurcation.