A novel subcritical transition to turbulence in Taylor-Couette flow with counter-rotating cylinders

TL;DR

This paper reports a new subcritical transition to turbulence in counter-rotating Taylor-Couette flow, involving an unstable intermediate state with interpenetrating spirals, characterized through experiments and simulations.

Contribution

It identifies and characterizes a novel subcritical laminar-turbulent transition mediated by an unstable intermediate state in Taylor-Couette flow.

Findings

Discovery of a subcritical transition involving an unstable intermediate state.

Experimental and numerical evidence of interpenetrating spiral flows.

Reversible transition with the intermediate state acting as both unstable and stable.

Abstract

The transition to turbulence in Taylor-Couette flow often occurs via a sequence of supercritical bifurcations to progressively more complex, yet stable, flows. We describe a subcritical laminar-turbulent transition in the counter-rotating regime mediated by an unstable intermediate state in a system with an axial aspect ratio of $\Gamma=5.26$ and a radius ratio of $\eta=0.905$. In this regime, flow visualization experiments and numerical simulations indicate the intermediate state corresponds to an aperiodic flow featuring interpenetrating spirals. Furthermore, the reverse transition out of turbulence leads first to the same intermediate state, which is now stable, before returning to an azimuthally-symmetric laminar flow. Time-resolved tomographic particle image velocimetry is used to characterize the experimental flows; these measurements compare favorably to direct numerical simulations with axial boundary conditions matching those of the experiments.