Diffusivity-Free Turbulence in Liquid Metal Rotating Rayleigh-B\'enard Convection Experiments

TL;DR

This study demonstrates the realization of diffusivity-free turbulence in rotating liquid metal convection experiments, validating theoretical models and enabling better understanding of geophysical and astrophysical flows.

Contribution

The paper introduces an experimental method to observe diffusivity-free turbulence in liquid metals, confirming theoretical predictions and overcoming boundary layer diffusion limitations.

Findings

Heat transfer efficiency $Nu$ matches theoretical scalings.

Flow velocities $Re$ are consistent with models.

Internal temperature anomalies $ heta$ agree with predictions.

Abstract

Convection in planets and stars is predicted to occur in the "ultimate regime'' of diffusivity-free, rapidly rotating turbulence, in which flows are characteristically unaffected by viscous and thermal diffusion. Boundary layer diffusion, however, has historically hindered experimental study of this regime. Here, we utilize the boundary-independent oscillatory thermal-inertial mode of rotating convection to realize the diffusivity-free scaling in liquid metal laboratory experiments. This oscillatory style of convection arises in rotating liquid metals (low Prandtl number fluids) and is driven by the temperature gradient in the fluid bulk, thus remaining independent of diffusive boundary dynamics. We triply verify the existence of the diffusivity-free regime via measurements of heat transfer efficiency $Nu$, dimensionless flow velocities $Re$, and internal temperature anomalies $\theta$, all of which are in quantitative agreement with planar asymptotically-reduced models. Achieving the theoretical diffusivity-free scalings in desktop-sized laboratory experiments provides the validation necessary to extrapolate and predict the convective flows in remote geophysical and astrophysical systems.