Boundary layer dynamics at the transition between the classical and the ultimate regime of Taylor-Couette flow

TL;DR

This study uses direct numerical simulations to explore boundary layer dynamics and flow regime transitions in turbulent Taylor-Couette flow at high Reynolds numbers, revealing the coexistence of laminar and turbulent boundary layers.

Contribution

It provides detailed insights into the boundary layer behavior and flow regime transitions at high Reynolds numbers in Taylor-Couette flow, highlighting the coexistence of laminar and turbulent boundary layers.

Findings

Identification of three flow regimes with increasing Re_i

Coexistence of laminar and turbulent boundary layers in transitional regime

Flow becomes dominated by plumes at high Re_i

Abstract

Direct numerical simulations of turbulent Taylor-Couette flow are performed up to inner cylinder Reynolds numbers of {Re_i=10^5} for a radius ratio of {\eta=r_i/r_o=0.714} between the inner and outer cylinder. With increasing {Re_i}, the flow undergoes transitions between three different regimes: (i) a flow dominated by large coherent structures, (ii) an intermediate transitional regime, and (iii) a flow with developed turbulence. In the first regime the large--scale rolls completely drive the meridional flow while in the second one the coherent structures recover only on average. The presence of a mean flow allows for the coexistence of laminar and turbulent boundary layer dynamics. In the third regime the mean flow effects fade away and the flow becomes dominated by plumes. The effect of the local driving on the azimuthal and angular velocity profiles is quantified, in particular we show when and where those profiles develop.