Thermovelocimetric characterization of liquid metal convection in a rotating slender cylinder

Abstract

Rotating turbulent convection occurs ubiquitously in natural convective systems encompassing planetary cores, oceans and atmospheres, as well as in many industrial applications. While the global heat and mass transfer of water-like rotating Rayleigh–Bénard convection is well-documented, the dynamics in low-Prandtl-number liquid metals remain less understood. In this study, we experimentally investigate rotating Rayleigh-Bénard convection in liquid gallium (Prandtl number $Pr\approx 0.027$) within a slender cylinder (diameter-to-height aspect ratio $\Gamma =D/H=1/2$) using novel thermovelocimetric diagnostic techniques that integrate simultaneous multi-point thermometry and ultrasonic Doppler velocity measurements. Our results reveal the formation of a stable, global-scale azimuthal wavenumber $m=2$ quadrupolar vortex at low supercriticality. We propose that enhanced wall modes facilitated by the slender cylinder geometry interact with the bulk flow to create these large-scale axialized vortices. Furthermore, our findings imply a distinct scaling behavior for the wall-mode precession frequency in liquid metals, extending previous results obtained for moderate-$Pr$ fluids. This provides new insights into wall-bulk coupling mechanisms of low-$Pr$ rotating convective turbulence.