Self-sustainment of coherent structures in counter-rotating Taylor-Couette flow

TL;DR

This study explores the self-sustaining mechanisms of coherent structures in spiral turbulence within counter-rotating Taylor-Couette flow, revealing how drifting-rotating waves and localized vortices persist and resemble turbulence features.

Contribution

It identifies and analyzes the self-sustained drifting-rotating waves as key structures underlying spiral turbulence, using a novel small domain approach to replicate large-scale turbulence features.

Findings

Drifting-rotating waves capture main features of spiral turbulence.

Self-sustained vortices localize and resemble large-scale turbulence.

Flow properties persist beyond linear stability threshold.

Abstract

We investigate the local self-sustained process underlying spiral turbulence in counter-rotating Taylor-Couette flow using a periodic annular domain, shaped as a parallelogram, two of whose sides are aligned with the cylindrical helix described by the spiral pattern. The primary focus of the study is placed on the emergence of drifting-rotating waves ({\sc drw}) that capture, in a relatively small domain, the main features of coherent structures typically observed in developed turbulence. The transitional dynamics of the subcritical region, far below the first instability of the laminar circular Couette flow, is determined by the upper and lower branches of {\sc drw} solutions originated at saddle-node bifurcations. The mechanism whereby these solutions self-sustain, and the chaotic dynamics they induce, are conspicuously reminiscent of other subcritical shear flows. Remarkably, the flow properties of {\sc drw} persist even as the Reynolds number is increased beyond the linear stability threshold of the base flow. Simulations in a narrow parallelogram domain stretched in the azimuthal direction to revolve around the apparatus a full turn confirm that self-sustained vortices eventually concentrate into a localised pattern. The resulting statistical steady state satisfactorily reproduces qualitatively, and to a certain degree also quantitatively, the topology and properties of spiral turbulence as calculated in a large periodic domain of sufficient aspect ratio that is representative of the real system