In this article, we present direct numerical simulation results for the expansion of spherical cap bubbles attached to a rigid wall due to a sudden drop in the ambient pressure. The critical pressure drop beyond which the bubble growth becomes unstable is found to match well with the predictions from classical theory of heterogeneous nucleation imposing a quasi-static bubble evolution. When the pressure drop is significantly higher than the critical value, a liquid microlayer appears between the bubble and the wall. In this regime, the interface outside the microlayer grows at an asymptotic velocity that can be predicted from the Rayleigh–Plesset equation, while the contact line evolves with another asymptotic velocity that scales with a visco-capillary velocity that obeys the Cox–Voinov law. In general, three distinctive regions can be distinguished: the region very close to the contact line where dynamics is governed by visco-capillary effects, an intermediate region controlled by inertio-viscous effects away from the contact line yet inside the viscous boundary layer, and the region outside the boundary layer dominated by inertial effects. The microlayer forms in a regime where the capillary effects are confined in a region much smaller than the viscous boundary layer thickness. In this regime, the global capillary number takes values much larger then the critical capillary number for bubble nucleation, and the microlayer height is controlled by viscous effects and not surface tension.

中文翻译：

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异质气泡成核过程中微层形成的直接数值模拟

在本文中，我们提出了由于环境压力突然下降而导致附着在刚性壁上的球帽气泡膨胀的直接数值模拟结果。超过临界压降，气泡生长变得不稳定，结果与经典异质成核理论的预测相吻合，该理论强加准静态气泡演化。当压降明显高于临界值时，气泡和壁之间会出现液体微层。在这种情况下，微层外部的界面以可以从瑞利-普莱塞方程预测的渐近速度生长，而接触线以另一个渐近速度演化，该渐近速度与遵守考克斯-沃伊诺夫定律的粘毛细管速度成比例。一般来说，可以区分三个不同的区域：非常靠近接触线的区域，其中动力学受粘毛细管效应控制，中间区域由远离接触线但位于粘性边界层内部的惯性粘性效应控制，以及边界层以外的区域，以惯性效应为主。微层形成的区域中毛细管效应被限制在比粘性边界层厚度小得多的区域内。在这种情况下，整体毛细管数的值远大于气泡成核的临界毛细管数，并且微层高度由粘性效应而非表面张力控制。