When a drop impacts on a solid surface, a thin air film is entrapped first and later evolves into a spherical air bubble at the center inside the drop. The problem involves several complex physical processes, including two-phase fluid flow interactions, moving and deforming interfaces in space and time. In this paper, we dissect the whole air entrapment and evolution process from drop release at a certain height above the substrate to finally a spherical air bubble formation by direct numerical simulation. A detailed quantitative analysis of the various dynamic phenomena occurring at different stages is performed. The complex physical phenomena revealed by current high-fidelity numerical simulations are validated qualitatively against theoretical estimations and previous experimental observations, followed by quantitative comparisons with the theories and available experiments for the dimple, kink and air film. Finally, a new cognition of vortex ring evolution is proposed to explore further insights into the underlying physical mechanisms associated with the evolution of the entrapped air film in liquid-solid impact.

当液滴撞击固体表面时，首先会夹带一层薄薄的空气膜，然后在液滴内部的中心演变成球形气泡。该问题涉及几个复杂的物理过程，包括两相流体流动相互作用、空间和时间上的移动和变形界面。在本文中，我们通过直接数值模拟剖析了从基板上方一定高度的液滴释放到最终形成球形气泡的整个空气截留和演化过程。对发生在不同阶段的各种动态现象进行了详细的定量分析。当前高保真数值模拟揭示的复杂物理现象已根据理论估计和先前的实验观察进行定性验证，其次是与理论和可用实验的凹痕、扭结和空气膜的定量比较。最后，提出了对涡环演化的新认知，以进一步深入了解与液固撞击中夹带空气膜演化相关的潜在物理机制。