Experimental investigation on the dynamic behaviors of droplets impacting on ultrasonically vibrating curve surfaces
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摘要: 通过实验研究了超声振动曲面上液滴碰撞的动力学行为。对边缘飞溅、表面飞溅以及毛细波、空化和子液滴回弹等复杂物理现象的产生机理和条件进行了分析，得到了超声振动曲面上发生边缘飞溅的临界曲线，并发现由于气动力的作用，超声振动曲面上发生边缘飞溅的临界超声振幅要小于平面情况。利用图像处理技术得到了不同条件下超声振动曲面对碰撞液滴的驱离效率以及飞溅液滴的尺寸分布。实验结果表明：碰撞液滴的驱离效率随振动曲面超声振幅的增大而增大，且呈线性增长；在高速碰撞中，碰撞速度几乎不影响超声振动曲面的液滴驱离效率；随着超声振幅的增加，飞溅液滴的平均尺寸增加。通过常温液滴与过冷液滴的碰撞实验对比，发现温度对超声振动曲面上液滴的动态碰撞过程影响较小。在过冷条件下，液滴驱离效率会略低于常温条件下，但仍能够持续有效地将液滴驱离表面，从而抑制冰层的增厚，说明超声振动曲面具有防水防冰的应用潜能。Abstract: The present work experimentally investigates the dynamic behaviors of droplets impacting on ultrasonically vibrating curve surfaces. The complicated experimental phenomena, including edge splash, surface splash, capillary wave, cavitation, and sub-droplet rebound, are observed, and the mechanisms behind each phenomenon are revealed. The critical curve of the edge splash is obtained, and the critical vibration amplitudes on curve surfaces are lower than that on flat surfaces due to the aerodynamic force. Using the image processing technique, the expelling efficiency of the ultrasonic vibrating curve surface and the size distribution of secondary droplets are elucidated and discussed. The expelling efficiency increases linearly with the increase of the ultrasonic vibration amplitude, and the impact velocity has almost no influence on the expelling efficiency. A higher excitation amplitude results in a wider secondary droplet size distribution and a larger average size. It is found that the temperature slightly affects the dynamic collision process of the droplets through comparing the experimental results under room temperature and supercooled conditions. Under the supercooled condition, the ultrasonic vibration could still effectively expel the impinging droplets, which shows the potential of the ultrasonic vibration on the waterproof and anti-icing fields.
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Key words:
- droplet /
- ultrasonic vibration /
- curve surface /
- splash /
- expelling efficiency
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图 1 不同条件下的实验装置示意图
Figure 1. Schematic diagrams of two sets of the experimental setup under different conditions
图 2 液滴在不同条件下碰撞超声振动曲面的动态过程(f=28 kHz)
Figure 2. Impact dynamics of droplets on ultrasonically vibrating curve surfaces
图 4 液滴在超声振动平面和曲面上发生边缘飞溅的临界曲线
Figure 4. The critical curves of the edge splash on the ultrasonically vibrating flat and curve surfaces
图 6 不同碰撞速度下驱离效率随超声振福的变化曲线
Figure 6. The expelling efficiency as a function of the ultrasonic amplitude at different impact velocities
图 7 不同超声振幅下驱离效率随碰撞速度的变化曲线
Figure 7. The expelling efficiency as a function of the impact velocity with different ultrasonic amplitudes
图 8 不同碰撞速度下飞溅液滴的尺寸随超声振幅的变化
Figure 8. The size distribution of the secondary droplets as a function of the ultrasonic amplitude at different impact velocities
图 9 液滴在不同温度条件下碰撞超声振动曲面的动态过程示意图(f=28 kHz，U0=2.80 m/s，A0=17 μm)
Figure 9. Impact dynamics of droplets with different temperatures on ultrasonically vibrating curve surfaces (f=28 kHz, U0=2.80 m/s, A0=17 μm)
图 10 不同温度条件下飞溅液滴的尺寸随超声振幅的变化规律(U0=2.80 m/s)
Figure 10. The size distribution of the secondary droplets as a function of the ultrasonic amplitude at different temperatures (U0=2.80 m/s)
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