Spontaneous mirror-symmetry breaking induces inverse energy cascade in 3D active fluids

Abstract

Classical turbulence theory assumes that energy transport in a 3D turbulent flow proceeds through a Richardson cascade whereby larger vortices successively decay into smaller ones. By contrast, an additional inverse cascade characterized by vortex growth exists in 2D fluids and gases, with profound implications for meteorological flows and fluid mixing. The possibility of a helicity-driven inverse cascade in 3D fluids had been rejected in the 1970s based on equilibrium-thermodynamic arguments. Recently, however, it was proposed that certain symmetry-breaking processes could potentially trigger a 3D inverse cascade, but no physical system exhibiting this phenomenon has been identified to date. Here, we present analytical and numerical evidence for the existence of an inverse energy cascade in an experimentally validated 3D active fluid model, describing microbial suspension flows that spontaneously break mirror symmetry. We show analytically that self-organized scale selection, a generic feature of many biological and engineered nonequilibrium fluids, can generate parity-violating Beltrami flows. Our simulations further demonstrate how active scale selection controls mirror-symmetry breaking and the emergence of a 3D inverse cascade.

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• Scaling regimes of active turbulence with external dissipation
• Helical Flow States in Active Nematics
• Topology, Vorticity and Limit Cycle in a Stabilized Kuramoto-Sivashinsky Equation
• Incompressible polar active fluids with quenched disorder in dimensions $d>2$
• An analytical and computational study of the incompressible Toner-Tu Equations
• Vortex pattern stabilization in thin films resulting from shear thickening of active suspensions
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• Spontaneous generation of helical flows by salt fingers
• Cascades and Kolmogorov's lognormal scaling in two-dimensional bacterial turbulence
• An optimal complexity spectral method for Navier--Stokes simulations in the ball
• Inverse Energy Cascade in Turbulent Taylor-Couette Flows
• Vortex line entanglement in active Beltrami flows