Bouncing dynamics of a trailing drop off-center impacting a leading drop with varying time intervals and Weber numbers are investigated experimentally. Whether the trailing drop impacts during the spreading or receding process of the leading drop is determined by the time interval. For a short time interval of 0.15 ≤ Δt* ≤ 0.66, the trailing drop impacts during the spreading of the leading drop, and the drops completely coalesce and rebound; for a large time interval of 0.66 < Δt* ≤ 2.21, the trailing drop impacts during the receding process, and the drops partially coalesce and rebound. Whether the trailing drop directly impacts the surface or the liquid film of the leading drop is determined by the Weber number. The trailing drop impacts the surface directly at moderate Weber numbers of 16.22 ≤ We ≤ 45.42, while it impacts the liquid film at large Weber numbers of 45.42 < We ≤ 64.88. Intriguingly, when the trailing drop impacts the surface directly or the receding liquid film, the contact time increases linearly with the time interval but independent of the Weber number; when the trailing drop impacts the spreading liquid film, the contact time suddenly increases, showing that the force of the liquid film of the leading drop inhibits the receding of the trailing drop. Finally, a theoretical model of the contact time for the drops is established, which is suitable for different impact scenarios of the successive off-center impact. This study provides a quantitative relationship to calculate the contact time of drops successively impacting a superhydrophobic surface, facilitating the design of anti-icing surfaces.

中文翻译：

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水滴连续偏离中心冲击的弹跳动力学


通过实验研究了偏离中心的尾随水滴以不同的时间间隔和韦伯数撞击前水滴的弹跳动力学。尾随水滴是否在前导水滴的扩散或后退过程中发生影响由时间间隔决定。对于 0.15 ≤ Δt* ≤ 0.66 的短时间间隔，尾随液滴在前导液滴扩散期间发生冲击，并且液滴完全合并并反弹；对于 0.66 < Δt* ≤ 2.21 的大时间间隔，尾随液滴在后退过程中产生冲击，并且液滴部分合并并反弹。尾随液滴是否直接撞击前液滴的表面或液膜由韦伯数决定。尾随液滴以中等韦伯数 16.22 ≤ We ≤ 45.42 直接冲击表面，而以大韦伯数 45.42 < We ≤ 64.88 冲击液膜。有趣的是，当尾随液滴直接撞击表面或后退的液膜时，接触时间随时间间隔线性增加，但与韦伯数无关；当尾随液滴撞击铺展的液膜时，接触时间突然增加，表明前液滴液膜的力抑制了尾随液滴的后退。最后，建立了水滴接触时间的理论模型，该模型适用于连续偏心撞击的不同撞击场景。这项研究提供了一种定量关系来计算水滴连续撞击超疏水表面的接触时间，有助于防冰表面的设计。