Universal scaling in the turbulence of active flow-aligning nematics

Active nematic fluids, such as bacterial monolayers and microtubules-based suspensions, have been shown to exhibit two-dimensional turbulent-like flows at vanishing Reynolds number. However, it remains unclear whether these types of systems manifest universal scaling laws, akin to classic inertial turbulence [1]. Very recently, a q^-1 scaling of the kinetic energy spectrum has been established for long wavelengths in a minimal model of active liquid crystals (ALCs) [2]. This model takes a particularly simple form as it excludes i) topological defects and ii) the nonlinear flow alignment coupling ν. Here, we study an augmented nonlinear model of ALCs that adequately incorporates flow alignment [3]. We find that ν controls a number of important and non-trivial effects, including the energy transfer across scales. Our large-scale numerical simulations reveal, for the first time, that chaotic flows could emerge not only in the 'tumbling' (|ν|<1) limit but also in the 'flow-aligning' (|ν|>1) regime. Most importantly, the scaling exponent in the turbulence remains independent of ν—a result that serves as a crucial milestone towards establishing the existence of a broader 'active turbulence' universality class.