Abstract The process of normal impingement of a single drop onto a quiescent liquid film was investigated experimentally to determine the thresholds of the early and late splashes. Seven liquids of different hydraulic properties were used and the liquid film thickness was varied within about 0.2−3 times the impacting drop diameter. It was found that the critical Weber number for the early splash to occur is dependent on the liquid properties (more specifically, the Ohnesorge number) but not on the liquid film thickness. On the other hand, the critical Weber number of the late splash was influenced by both the liquid properties and the liquid film thickness. It increased gradually with an increase in the liquid film thickness in a thin film range and jumped to a constant value when the critical film thickness was reached. The critical film thickness was 0.7 times the impacting drop diameter in average in the present experiments. Using the present experimental data, dimensionless correlations were developed for the thresholds of the early and late splashes. The predictive performances of the proposed correlations were tested against the experimental databases available in the literature. Due to the complexity of the drop impact process, noticeable disagreements remained between the experimental data and the predictions even in the simple situation explored in this work. Nonetheless, the present dimensionless correlations succeeded to express the overall trends of the splashing thresholds fairly well.

中文翻译：

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单滴撞击静止液膜时飞溅阈值的实验

摘要 通过实验研究单滴正常撞击静止液膜的过程，以确定早期和晚期飞溅的阈值。使用了七种不同水力特性的液体，液膜厚度在冲击液滴直径的 0.2-3 倍范围内变化。发现早期飞溅发生的临界韦伯数取决于液体性质（更具体地说，Ohnesorge 数），而不取决于液膜厚度。另一方面，晚期飞溅的临界韦伯数受液体性质和液膜厚度的影响。它在薄膜范围内随着液膜厚度的增加而逐渐增加，并在达到临界膜厚时跃升至恒定值。在本实验中，临界膜厚平均为冲击液滴直径的 0.7 倍。使用目前的实验数据，开发了早期和晚期飞溅阈值的无量纲相关性。针对文献中可用的实验数据库测试了所提出的相关性的预测性能。由于跌落撞击过程的复杂性，即使在这项工作中探索的简单情况下，实验数据和预测之间仍然存在明显的分歧。尽管如此，目前的无量纲相关性成功地很好地表达了飞溅阈值的整体趋势。为早期和晚期飞溅的阈值开发了无量纲相关性。针对文献中可用的实验数据库测试了所提出的相关性的预测性能。由于跌落撞击过程的复杂性，即使在这项工作中探索的简单情况下，实验数据和预测之间仍然存在明显的分歧。尽管如此，目前的无量纲相关成功地很好地表达了飞溅阈值的整体趋势。为早期和晚期飞溅的阈值开发了无量纲相关性。针对文献中可用的实验数据库测试了所提出的相关性的预测性能。由于跌落撞击过程的复杂性，即使在这项工作中探索的简单情况下，实验数据和预测之间仍然存在明显的分歧。尽管如此，目前的无量纲相关成功地很好地表达了飞溅阈值的整体趋势。即使在这项工作中探索的简单情况下，实验数据和预测之间仍然存在明显的分歧。尽管如此，目前的无量纲相关成功地很好地表达了飞溅阈值的整体趋势。即使在这项工作中探索的简单情况下，实验数据和预测之间仍然存在明显的分歧。尽管如此，目前的无量纲相关成功地很好地表达了飞溅阈值的整体趋势。