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arXiv · 2607.21984

Flow Reversal in Low-Prandtl-Number Convection via Lateral Confinement

Zhi-Han Wu·Long Chen·Yan-Wu Cao·Liang Xue·Ming-Zhu Ai·Juan-Cheng Yang·Ming-Jiu Ni
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Abstract

A prevailing consensus holds that flow reversals of the large-scale circulation (LSC) are suppressed in low-Prandtl-number (Pr) fluids, as high thermal diffusivity rapidly dissipates the energy required to fuel the corner-vortex mechanisms. Here, we report Direct Numerical Simulations of liquid metal convection (Pr=0.029) revealing that strong lateral confinement defies this consensus, enabling sustained LSC reversals. We show that confinement triggers a ``plume condensation" transition, reorganizing chaotic thermal plumes into highly coherent, quasi-linear structures. A thermal dissipation analysis demonstrates that this coherence drastically reduces heat loss during transport, allowing plumes to deliver sufficient buoyancy to corner vortices to drive reversals. We map a distinct ``island of reversal" in the parameter space, establishing lateral confinement as a control parameter capable of overcoming the stabilizing effects of high thermal diffusivity.

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Zhi-Han Wu, Long Chen, Yan-Wu Cao, Liang Xue, Ming-Zhu Ai, Juan-Cheng Yang, Ming-Jiu Ni. 2026-07-24. Flow Reversal in Low-Prandtl-Number Convection via Lateral Confinement. https://arxiv.org/abs/2607.21984

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