Abstract
Suspensions of active agents with nematic interactions exhibit complex spatiotemporal dynamics such as mesoscale turbulence. Since the Reynolds number of microscopic flows is very small on the scale of individual agents, inertial effects are typically excluded in continuum theories of active nematic turbulence. Whether active stresses can collectively excite inertial flows is currently unclear. To address this question, we investigate a two-dimensional continuum theory for active nematic turbulence. In particular, we compare mesoscale turbulence with and without the effects of advective inertia. We find that inertial effects can influence the flow already close to the onset of the turbulent state and, moreover, give rise to large-scale fluid motion for strong active driving. A detailed analysis of the kinetic energy budget reveals an energy transfer to large scales mediated by inertial advection. While this transfer is small in comparison to energy injection and dissipation, its effects accumulate over time. The inclusion of friction, which is typically present in experiments, can compensate for this effect. The findings suggest that the inclusion of inertia and friction may be necessary for dynamically consistent theories of active nematic turbulence.
Highlights
Role of Advective Inertia in Active Nematic TurbulenceSuspended densely in a liquid, they form so-called active fluids, in which the flow is driven on the scale of the agents [17]
Active matter on the microscale consists of motile agents, such as bacteria [1,2,3,4] and cells [5,6], filaments driven by motor proteins [7,8,9,10,11], motile algae [12,13,14], or colloids [15,16]
Principle, can excite flows in which inertial effects become apparent. We address this question with a detailed study on the impact of inertia on dense suspensions of active agents in the framework of an established two-dimensional continuum model of active nematic liquid crystals [28,29,30,31], which has been related to experimental results [32]
Summary
Suspended densely in a liquid, they form so-called active fluids, in which the flow is driven on the scale of the agents [17] Their collective behavior can lead to complex mesoscale phenomena, such as active turbulence, which is reminiscent of driven hydrodynamic flows and has been observed, e.g., in suspensions of bacteria [1,18,19] and in microtubule kinesin mixtures [11,20]. Principle, can excite flows in which inertial effects become apparent We address this question with a detailed study on the impact of inertia on dense suspensions of active agents in the framework of an established two-dimensional continuum model of active nematic liquid crystals [28,29,30,31], which has been related to experimental results [32]. The fluid flow is described by the incompressible (∇ · u 1⁄4 0) Navier-Stokes equation, which in nondimensional form reads
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