The role of advective inertia in active nematic turbulence

TL;DR

This study investigates how inertial effects influence active nematic turbulence, revealing that even small inertial contributions can significantly impact flow dynamics and large-scale motion, especially under strong activity.

Contribution

It demonstrates that inertial effects, often neglected, can alter turbulence onset and large-scale flows in active nematics, emphasizing the need to include inertia and friction in models.

Findings

Inertial effects influence flow near turbulence onset.

Inertia can generate large-scale fluid motion.

Friction can offset inertial effects in active nematics.

Abstract

Suspensions of active agents with nematic interactions exhibit complex spatio-temporal 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.