The role of Stewartson and Ekman layers in turbulent rotating Rayleigh-B\'enard convection

TL;DR

This study investigates how Stewartson and Ekman boundary layers influence turbulent rotating Rayleigh-Bénard convection across different rotation regimes, revealing distinct temperature profile behaviors and boundary layer dynamics through experiments and simulations.

Contribution

It provides new insights into the boundary layer mechanisms and temperature profiles in rotating RB convection, highlighting the roles of Stewartson and Ekman layers across flow regimes.

Findings

Azimuthal temperature profiles change with rotation regimes.

Vertical temperature gradients have different origins in each regime.

Boundary layer dynamics drive secondary flows affecting temperature transport.

Abstract

When the classical Rayleigh-B\'enard (RB) system is rotated about its vertical axis roughly three regimes can be identified. In regime I (weak rotation) the large scale circulation (LSC) is the dominant feature of the flow. In regime II (moderate rotation) the LSC is replaced by vertically aligned vortices. Regime III (strong rotation) is characterized by suppression of the vertical velocity fluctuations. Using results from experiments and direct numerical simulations of RB convection for a cell with a diameter-to-height aspect ratio equal to one at $Ra \sim 10^8-10^9$ ($Pr=4-6$) and $0 \lesssim 1/Ro \lesssim 25$ we identified the characteristics of the azimuthal temperature profiles at the sidewall in the different regimes. In regime I the azimuthal wall temperature profile shows a cosine shape and a vertical temperature gradient due to plumes that travel with the LSC close to the sidewall. In regime II and III this cosine profile disappears, but the vertical wall temperature gradient is still observed. It turns out that the vertical wall temperature gradient in regimes II and III has a different origin than that observed in regime I. It is caused by boundary layer dynamics characteristic for rotating flows, which drives a secondary flow that transports hot fluid up the sidewall in the lower part of the container and cold fluid downwards along the sidewall in the top part.