Intermittent boundary layers and torque maxima in Taylor-Couette flow

TL;DR

This paper investigates the emergence of intermittent boundary layers in turbulent Taylor-Couette flow with counter-rotation, linking these phenomena to torque maxima through simulations, experiments, and a theoretical model.

Contribution

It introduces a theoretical model for the critical rotation ratio triggering intermittency and demonstrates its validity with numerical and experimental data.

Findings

Intermittent boundary layers occur at specific counter-rotation ratios.

Torque maxima coincide with the onset of boundary layer intermittency.

Mean Taylor vortex flow variations are correlated with torque changes.

Abstract

Turbulent Taylor-Couette flow between counter-rotating cylinders develops intermittently fluctuating boundary layers for sufficient counter-rotation. We demonstrate the phenomenon in direct numerical simulations for radius ratios \eta=0.5 and 0.71 and propose a theoretical model for the critical value in the rotation ratio. Numerical results as well as experiments show that the onset of this intermittency coincides with the maximum in torque. The variations in torque correlate with the variations in mean Taylor vortex flow which is first enhanced for weak counter-rotation, and then reduced as intermittency sets in. To support the model, we compare to numerical results, experiments at higher Reynolds numbers, and to Wendt's data.