INFLUENCE OF SURFACE WETTABILITY ON THE PROCESS OF OBLIQUE WATER ENTRY OF SPHERE
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摘要: 针对球体表面润湿性对倾斜入水空泡演化过程及球体动力特性的影响开展研究, 以便能够进一步理解润湿性对入水过程的影响并且能够为多种情况下的入水现象提供理论依据. 基于球体入水过程空泡形态观察、采集与测量实验平台, 分析了亲水性和疏水性球体入水过程中入水喷溅和空泡的演变规律, 并深入讨论了不同速度下球体表面润湿性对球体入水过程中动力特性的影响. 研究表明: 不同表面润湿性球体在入水过程中的喷溅及入水空泡演化与动力特性存在明显区别. 在相同入水速度下, 亲水性球体的三相接触点远高于疏水性球体, 而喷溅的高度却低于疏水性球体, 但该差异随入水速度的增加反而减小. 随着入水速度的增大, 亲水性球体依次经历了无空泡、浅闭合和面闭合3种闭合方式, 而疏水性球体先后只出现了深闭合和面闭合两种. 但是, 随着入水速度的增加, 球体表面润湿性对空泡演化过程的影响逐渐减弱, 当速度增加到11.25 m/s时, 二者不存在区别. 同时发现, 在入水过程中, 在相同速度下生成入水空泡较无入水空泡其总流动阻力系数降低49.94%; 亲水性球体生成空泡体积更小, 空泡带来的附加质量力也更小, 减阻效果更好.Abstract: The influence of surface wettability on the evolution process of inclined water entry cavitation and dynamic characteristics of the sphere is studied in order to further understand the influence of wettability on water entry process and provide theoretical basis for water entry phenomena in various cases. Based on the experimental platform of observation, acquisition and measurement of cavitation morphology and the numerical simulation method, the evolution laws of splashing and cavitation during water entry of hydrophilic and hydrophobic spheres are analyzed, and the influence of surface wettability of spheres on dynamic characteristics during water entry of spheres at different speeds is discussed. The results show that there are obvious differences in the evolution and dynamic characteristics of spatter and cavitation of different surface wettability spheres during water entry. At the same velocity, the three phase contact point of the hydrophilic sphere is much higher than that of the hydrophobic sphere, while the splashing height is lower than that of the hydrophobic sphere, but the difference decreases with the increase of the water entry speed. With the increase of water entry velocity, the hydrophilic sphere experiences three closure modes successively: no cavitation, shallow closure and surface closure, while the hydrophobic sphere only shows deep closure and surface closure. But, With the increase of water entry velocity, the influence of surface wettability on the cavity evolution process gradually decreases, and there is no difference between the two when the speed increases to 11.25 m/s. At the same time, it is found that the total flow resistance coefficient of the water entering cavity is 49.94% lower than that of the non-water entering cavity at the same velocity. The volume of the void generated by the hydrophilic sphere is smaller, the additional mass force brought by the void is also smaller, and the drag reduction effect is better.
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Key words:
- surface wettability /
- hydrophilic and hydrophobic /
- splash /
- cavity evolution /
- cavity closure /
- dynamic characteristic
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图 1 物体表面接触角与临界毛细数的关系图
Figure 1. Diagram of the relationship between the contact angle of a surface and the critical capillary number
图 2 球体入水观测平台示意图
Figure 2. Diagram of the observation platform for the sphere entering the water
图 4 不同表面润湿性球体入水喷溅演化过程
Figure 4. Water splashing evolution of spheres with different surface wettability
图 5 三相接触点及关键参数示意图
Figure 5. Schematic diagram of three phase contact points and key parameters
图 6 不同表面润湿性球体入水过程三相接触点变化曲线
Figure 6. Change curve of three phase contact point during water entry of different surface wettability spheres
图 8 不同润湿性球体水冠高度随时间变化曲线
Figure 8. Curve of water crown height with different surface wettability with time
图 9 不同润湿性球体水冠直径随时间变化曲线
Figure 9. Curve of water crown diameter with different surface wettability with time
图 10 不同表面润湿性球体入水空泡演化过程(v = 4 m/s Re = 19801)
Figure 10. Evolution of water-entering cavitation of spheres with different surface wettability (v = 4 m/s Re = 19801)
图 11 不同表面润湿性球体入水空泡演化过程(v = 5.6 m/s Re = 27722)
Figure 11. Evolution of water-entering cavitation of spheres with different surface wettability (v = 5.6 m/s Re = 27722)
图 12 不同表面润湿性球体入水空泡演化过程(v = 11.25 m/s Re = 55693)
Figure 12. Evolution of water-entering cavitation of spheres with different surface wettability (v = 11.25 m/s Re = 55693)
图 13 空泡图像处理过程及最大截面示意图
Figure 13. Cavitation image processing process and maximum interface diagram
图 14 不同表面润湿性球体入水空泡最大截面积随时间变化曲线
Figure 14. Curve of the maximum cross-sectional area of the water-entering cavity of the sphere with different surface wettability over time
图 15 不同表面润湿性球体速度随时间变化曲线
Figure 15. Velocity curve of different surface wettability spheres over time
图 16 相同速度下亲疏水性球体速度差最大值随速度变化曲线
Figure 16. The maximum velocity difference of hydrophilic sphere varies with the velocity at the same velocity
图 17 不同表面润湿性球体入水过程中加速度随时间变化曲线
Figure 17. Curve of the acceleration velocity of different surface wettability spheres during water entry with time
图 18 球体在水下运动过程中受力分析示意图
Figure 18. Schematic diagram of force analysis of sphere during underwater movement
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