Nematic order condensation and topological defects in inertial active nematics

TL;DR

This study uses numerical simulations to explore how fluid inertia influences pattern formation, defect dynamics, and turbulence in active nematic materials, revealing a transition to vortex states and altered flow characteristics.

Contribution

It demonstrates the impact of inertia on active nematic order, defect density, and turbulence, highlighting a transition to vortex condensates and changes in flow spectra.

Findings

Increased inertia causes nematic order melting and defect proliferation.

A discontinuous transition to vortex-condensate states occurs at low viscosities.

Flow around defects and energy spectra are significantly affected by inertial effects.

Abstract

Living materials at different length scales manifest active nematic features such as orientational order, nematic topological defects, and active nematic turbulence. Using numerical simulations we investigate the impact of fluid inertia on the collective pattern formation in active nematics. We show that an incremental increase in inertial effects due to reduced viscosity results in gradual melting of nematic order with an increase in topological defect density before a discontinuous transition to a vortex-condensate state. The emergent vortex-condensate state at low enough viscosities coincides with nematic order condensation within the giant vortices and the drop in the density of topological defects. We further show flow field around topological defects is substantially affected by inertial effects. Moreover, we demonstrate the strong dependence of the kinetic energy spectrum on the inertial effects, recover the Kolmogorov scaling within the vortex-condensate phase, but find no evidence of universal scaling at higher viscosities. The findings reveal new complexities in active nematic turbulence and emphasize the important cross-talk between active and inertial effects in setting flow and orientational organization of active particles.