Although the impingement of droplets on superhydrophobic surfaces has been extensively studied, the critical role of the air is typically ignored, leading to some paradoxical conclusions. In this paper, a phase-field model with dynamic contact angles is implemented to simulate the impingement of droplets on a superhydrophobic surface. The simulation results agree well with the experimental data. The droplet's impact on the surface is observed and divided into four categories: contactless bouncing, wet bouncing, dry-out bouncing and non-bouncing. The role of air was emphasised by analysing pressure distribution and velocity field corresponding to the droplet evolution, revealing the mechanism behind the droplet impact. A non-monotonically varying trend of the non-dimensional maximum wetting diameter is observed by increasing Ohnesorge number (Oh). The value of dimensionless viscous extension first increased and then decreased with increasing impact number, and this counter-intuitively outcome has not been reported previously. Non-dimensional contact time of a bouncing droplet decreases rapidly with increasing Weber number (We), but approaches a plateau value if We is greater than 1. Additionally, for liquids with different viscosities, the non-dimensional contact time of bouncing droplets is independent of Oh. Moreover, regime maps of the dynamic behaviours of a droplet impact are developed to present an intuitive interpretation of different droplet fates.

尽管液滴对超疏水表面的冲击已得到广泛研究，但空气的关键作用通常被忽略，从而导致一些矛盾的结论。在本文中，采用具有动态接触角的相场模型来模拟液滴对超疏水表面的撞击。仿真结果与实验数据吻合良好。观察液滴对表面的影响，分为四类：非接触弹跳、湿弹跳、干弹跳和非弹跳。通过分析液滴演化对应的压力分布和速度场，强调了空气的作用，揭示了液滴撞击背后的机理。通过增加 Ohnesorge 数（哦）。随着冲击次数的增加，无量纲粘性延伸的值先增加后减少，这种违反直觉的结果以前没有报道过。弹跳液滴的无量纲接触时间随着韦伯数 ( We ) 的增加而迅速减小，但如果We大于 1，则接近平台值。此外，对于不同粘度的液体，弹跳液滴的无量纲接触时间是独立的哦。此外，还开发了液滴撞击动态行为的状态图，以呈现对不同液滴命运的直观解释。