Symmetry, Invariant Manifolds and Flow Reversals in Active Nematic Turbulence

TL;DR

This paper explores how symmetry and invariant structures organize flow reversals in 2D active nematic turbulence, revealing a low-dimensional network of solutions that govern chaotic dynamics and flow switching.

Contribution

It identifies and characterizes exact coherent structures and their invariant manifolds that organize flow reversals in active nematic turbulence using equivariant bifurcation theory.

Findings

Invariant manifolds provide pathways for flow reversals.

Symmetry-dictated reversal mechanisms exist in preturbulent states.

ECSs persist in turbulent regimes and organize chaotic attractors.

Abstract

We investigate how symmetry, exact coherent structures (ECSs), and their invariant manifolds organize spontaneous flow reversals in a 2D active nematic confined to a periodic channel. In minimal flow units commensurate with the intrinsic active vortex scale, we use equivariant bifurcation theory to trace the origin of dynamically relevant ECSs via a sequence of symmetry-constrained local and global bifurcations. At low activity level, we identify relative periodic orbits, created via a sequence of SNIPER, homoclinic and heteroclinic bifurcations, whose invariant manifolds provide robust heteroclinic pathways between left- and right-flowing nearly uniaxial states. These result in several symmetry-dictated reversal mechanisms in the preturbulent regime, with and without vortex-lattice intermediate states. In the active turbulent regime, this ECS skeleton persists and organizes chaotic attractors exhibiting persistent two-way reversals. By classifying ECSs through their symmetry signatures, we relate a small set of ECSs embedded in turbulence back to the preturbulent branches, and show that typical turbulent trajectories repeatedly shadow these ECSs and their unstable manifolds, resulting in near-heteroclinic transitions between opposite-flow states. Our results establish that channel confined active nematic turbulence is organized by a low-dimensional, symmetry-governed network of invariant solutions and their manifolds, and identify dynamical mechanisms that could be exploited to design, promote, or suppress flow reversals in active matter microfluidic devices.