Magnetic modulation of flow reversals in liquid metal thermal convection

TL;DR

This study demonstrates that external magnetic fields can induce and control flow reversals in low-Prandtl-number liquid metal convection, revealing a transition from periodic to stochastic dynamics governed by buoyancy and Lorentz forces.

Contribution

The paper introduces a theoretical model and experimental evidence showing magnetic field modulation of flow reversals in low-Prandtl-number convection systems.

Findings

Magnetic fields induce flow reversals in liquid metal convection.

Transition from periodic to stochastic reversals with increasing $Ra/Ha$ ratio.

Linear scaling between Rayleigh and Hartmann numbers at critical points.

Abstract

Flow reversals are rarely observed in low-Prandtl-number liquid metal convection due to the fluid's exceptionally high thermal diffusivity. Here, we demonstrate that an external transverse magnetic field can induce such reversals in a quasi-two-dimensional (Q2D) rectangular cell with an aspect ratio ($\it\Gamma$) of $0.2$. Our experimental observations reveal that the system initially exhibits periodic dynamics at the onset of reversals before transitioning to stochastic behavior as the ratio of Rayleigh number ($Ra$) to Hartmann number ($Ha$) increases. This transition is governed by the competition between buoyancy and Lorentz forces, with experimental data showing a linear scaling relationship between $Ra$ and $Ha$ at critical points. We develop a theoretical model that incorporates magnetic field effects in low-Prandtl-number convection to predict the reversal frequencies. These findings provide new insights into how magnetic fields can modulate flow regimes in low-Prandtl-number convection, establishing a controlled framework for investigating reversal dynamics in magnetohydrodynamic systems.