Onset of meso-scale turbulence in living fluids

TL;DR

This paper investigates how active biological fluids transition to meso-scale turbulence at zero Reynolds number, revealing a critical transition that aligns with directed percolation universality, bridging biological and classical turbulence theories.

Contribution

It demonstrates the transition to meso-scale turbulence in living fluids as a critical phenomenon in the directed percolation class, linking biological turbulence to classical turbulence models.

Findings

Transition to turbulence involves disordered patches called active puffs.

The critical behavior follows the directed percolation universality class.

This work connects biological turbulence onset to classical turbulence theories.

Abstract

Meso-scale turbulence is an innate phenomenon, distinct from inertial turbulence, that spontaneously occurs at zero-Reynolds number in fluidized biological systems. This spatio-temporal disordered flow radically changes nutrient and molecular transport in living fluids and can strongly affect the collective behaviour in prominent biological processes, including biofilm formation, morphogenesis and cancer invasion. Despite its crucial role in such physiological processes, understanding meso-scale turbulence and any relation to classical inertial turbulence remains obscure. Here, we show how the motion of active matter along a micro-channel transitions to meso-scale turbulence through the evolution of disordered patches (active puffs) from an absorbing state of flow vortex-lattices. We demonstrate that the critical behaviour of this transition to meso-scale turbulence in a channel belongs to the directed percolation universality class. This finding bridges our understanding of the onset of zero-Reynolds number meso-scale turbulence and traditional scale-invariant turbulence, therefore generalizing theories on the onset of turbulence in confinement to the distinct classes of incoherent flows observed in biological fluids.