The inverse Leidenfrost regime occurs when a heated object in relative motion with a liquid is surrounded by a stable vapour layer, drastically reducing the hydrodynamic drag at large Reynolds numbers due to a delayed separation of the flow. To elucidate the physical mechanisms that control separation, here we report a numerical study of the boundary-layer equations describing the liquid-vapour flow around a solid sphere whose surface temperature is above the Leidenfrost point. Our analysis reveals that the dynamics of the thin layer of vaporised liquid controls the downstream evolution of the flow, which cannot be properly described substituting the vapour layer by an effective slip length. In particular, the dominant mechanism responsible for the separation of the flow is the onset of vapour recirculation caused by the adverse pressure gradient in the rearward half of the sphere, leading to an explosive growth of the vapour-layer thickness due to the accumulation of vapour mass. Buoyancy forces are shown to have an important effect on the onset of recirculation, and thus on the separation angle. Our results compare favourably with previous experiments.

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关于逆莱顿弗罗斯特流域的流动分离机制

当与液体相对运动的受热物体被稳定的蒸汽层包围时，逆莱顿弗罗斯特状态发生，由于流动的延迟分离，在大雷诺数下大大降低了流体动力阻力。为了阐明控制分离的物理机制，我们在这里报告了边界层方程的数值研究，该方程描述了表面温度高于莱顿弗罗斯特点的固体球体周围的液-汽流动。我们的分析表明，汽化液体薄层的动力学控制着流动的下游演变，这无法用有效滑移长度代替蒸汽层来正确描述。特别是，造成流动分离的主要机制是由球体后半部分的不利压力梯度引起的蒸汽再循环的开始，由于蒸汽质量的积累导致蒸汽层厚度的爆炸性增长。浮力被证明对再循环的开始有重要影响，因此对分离角有重要影响。我们的结果与之前的实验相比毫不逊色。