Experimental study on influence of liquid depth on morphological characteristics after droplet impact
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摘要: 用实验方法对液滴撞击液面后的形态特征及其机理进行了研究。用高速摄像机记录了不同液池深度下的液滴撞击液面过程，总结出了在不同阶段出现的液坑、液冠、中心射流和次生液滴等特征现象。基于计算机视觉算法开发了图像处理程序，实现了特征几何参数的自动提取。讨论了液池深度、韦伯数、初始液滴直径和液滴下落高度等因素对特征运动形态的影响。结果表明：在韦伯数一定的情况下，当液池深度跨越某个临界值时，液坑、液冠、中心射流和次生液滴等特征现象发生显著变化；液冠–液坑高度比随韦伯数的增大在一定范围内增大；中心射流能否分离出次生液滴与液池深度和初始液滴直径有密切的关系。Abstract: Characteristics and mechanism of a droplet impacting on the liquid surface were studied experimentally. The process of droplet impinging on the liquid surface with different depths of the liquid pool was recorded with a high-speed camera, and the characteristic phenomena such as liquid crater, liquid crown, central jet and secondary droplet that appeared at different stages were summarized. An image processing program was developed and the automatic extraction of geometric parameters was then realized. The influence of pool depth Weber number, droplet diameter, and falling height on droplet impacts was discussed. The results show that: under the condition of constant Weber number, when the pool depth crosses a certain critical value, the characteristic phenomena such as liquid crater, liquid crown, central jet and secondary droplet change significantly; the ratio of the liquid crown height to the liquid crater depth increases within a certain range with the increase of Weber number; whether the secondary droplet can be separated by the central jet is closely related to the depth of the liquid pool and the diameter of the initial droplet.
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Key words:
- droplet impact /
- liquid depth /
- liquid crater /
- central jet /
- Weber number /
- computer vision algorisms
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图 3 原始图像（左）与轮廓提取图像（右）
Figure 3. Original image (left) and contour-extractioned image (right)
图 5 不同液池深度下的液冠–液坑高度比与We的关系
Figure 5. Relationship between crown-pit height ratio and We for different liquid depths
图 7 不同液池深度下的中心液柱最大高度–液滴直径比与We的关系
Figure 7. Relationship of ratio of the maximum central jet height to droplet diameter and We for different liquid depths
图 8 本文实验与马慧敏等[22]的实验中液柱最大高度–液滴直径比与We的数据点分布及线性拟合
Figure 8. The data point distribution and linear fitting of the ratio of the maximum central jet height to droplet diameter and We in the experiment of this paper (deep liquid pool) and Ma's experiment
表 1 实验方案及参数
Table 1. Experimental scheme and parameters
实验参数 数值 密度ρ/(kg·m−3) 996.2 表面张力σ/(N·m−1) 0.0715 动力黏性系数μ/(N·s·m−2) 0.000836 液滴下落高度h/mm 400, 510, 640, 790, 940,
1110, 1300, 1500液池深度D/mm 3, 5, 7, 10, 13 初始液滴直径d/mm 2.67 ± 0.04, 3.16 ± 0.09,
3.71 ± 0.06We 290～1509 
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表 2 不同实验组次分离次生液滴的情况
Table 2. Separation of secondary droplets in different groups
液滴直径/mm 液池深度/mm 下落高度/mm 400 510 640 790 1110 1300 1500 3.71 13 是 是 是 是 是 是 是 10 是 是 是 是 是 是 是 7 是 是 是 是 是 是 是 5 否 1/3是 2/3是 是 是 是 是 3 否 否 否 否 否 是 是 3.16 13 是 是 是 是 是 是 是 10 是 是 是 是 是 是 是 7 是 是 是 是 是 是 是 5 否 否 否 否 否 1/3是 是 3 否 否 否 否 否 否 是 2.67 13 是 是 是 是 是 是 是 10 是 是 是 是 是 是 是 7 是 是 是 是 是 是 是 5 否 否 否 否 否 否 否 3 否 否 否 否 否 否 否 说明：“是”表示分离次生液滴；“否”表示不分离次生液滴；“1/3是”表示每组实验重复3次，其中1次会分离；“2/3是”表示每组实验重复3次，其中2次会分离。
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