Taylor-Couette turbulence at radius ratio $\eta=0.5$: scaling, flow structures and plumes

TL;DR

This study investigates turbulence in Taylor-Couette flow at a radius ratio of 0.5, revealing scaling laws, flow structures, and plume behaviors using high-resolution measurements, and compares findings to theoretical predictions and other radius ratios.

Contribution

It provides detailed experimental analysis of turbulence scaling, flow structures, and plume dynamics at a radius ratio of 0.5, extending understanding beyond previously studied ratios.

Findings

Wind Reynolds number scales with Taylor number as 3/7, matching theory.

Flow profiles follow a log-law more closely in angular velocity than azimuthal velocity.

Counter-rotation influences plume direction and boundary layer profiles.

Abstract

Using high-resolution particle image velocimetry we measure velocity profiles, the wind Reynolds number and characteristics of turbulent plumes in Taylor-Couette flow for a radius ratio of 0.5 and Taylor number of up to $6.2\cdot10^9$. The extracted angular velocity profiles follow a log-law more closely than the azimuthal velocity profiles due to the strong curvature of this $\eta=0.5$ setup. The scaling of the wind Reynolds number with the Taylor number agrees with the theoretically predicted 3/7-scaling for the classical turbulent regime, which is much more pronounced than for the well-explored $\eta=0.71$ case, for which the ultimate regime sets in at much lower Ta. By measuring at varying axial positions, roll structures are found for counter-rotation while no clear coherent structures are seen for pure inner cylinder rotation. In addition, turbulent plumes coming from the inner and outer cylinder are investigated. For pure inner cylinder rotation, the plumes in the radial velocity move away from the inner cylinder, while the plumes in the azimuthal velocity mainly move away from the outer cylinder. For counter-rotation, the mean radial flow in the roll structures strongly affects the direction and intensity of the turbulent plumes. Furthermore, it is experimentally confirmed that in regions where plumes are emitted, boundary layer profiles with a logarithmic signature are created.