51ÁÔÆæÈë¿Ú

Abstract:

Meso-scale turbulence is an innate phenomenon, distinct from inertial turbulence, that spontaneously occurs at low-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 mesoscale turbulence through the evolution of locally disordered patches (active puffs) from an ordered vortex-lattice flow state. We demonstrate that the stationary critical exponents of this transition to meso-scale turbulence in a channel coincide with the directed percolation universality class. This finding bridges our understanding of the onset of low-Reynolds number meso-scale turbulence and traditional scaleinvariant turbulence, therefore generalizing theories on the onset of turbulence in confinement to the distinct classes of incoherent flows observed in biological fluids.