Emergent turbulence and coarsening arrest in active-spinner fluids

Abstract Turbulence in active fluids is a rapidly developing area in active-matter research. Yet the mechanisms and universal statistics of turbulence in a binary mixture of counter-rotating spinners remain unclear. We uncover activity-driven crossover from phase separation to a turbulent state in a two-dimensional system of counter-rotating spinners. This state exhibits spatiotemporal chaos with fluctuating vortex doublets that form, decay, and reappear. We study the statistical properties of this turbulence, using the active-rotor Cahn-Hilliard-Navier-Stokes model, and show that, as the activity increases, the vorticity ω ∝ ϕ , the scalar field that distinguishes regions with clockwise- and counter-clockwise rotation. Using direct numerical simulations, we characterize the power-law forms of fluid-energy spectra and show they are significantly different from those in fluid and bacterial turbulence. In addition to presenting evidence for small-scale intermittency in active-rotor turbulence, we characterize flow-topology statistics and contrast it with that in 2D fluid turbulence. Subsequently, we propose experimental tests for our predictions, and suggest biological implications of active-rotor turbulence.