This paper describes an experimental investigation of the cavity evolution and shedding wake behind a hydrophobic sphere during the water-entry process. Two distinct shedding phenomena are confirmed by varying the impact velocity and sphere size: regular air-bubble shedding and unstable air-cloud shedding. Both of these modes are highly dependent on the Weber and Bond numbers. Under the air-bubble shedding mode, approximately periodic big bubble shedding and low-frequency oscillation signals are observed. The relationship between big bubble shedding events and the corresponding acoustic signals is derived, and an empirical method for predicting the shedding period is proposed. The in-phase relationship between small bubble shedding and cavity rippling is confirmed, and we refer to the cavity shedding phenomenon as “acoustic” shedding. Unlike the observations of air-bubble shedding, the air-cloud shedding mode produces a group of disordered small bubbles from the rear of the cavity. Moreover, the cavity seal type has a significant effect on the cavity shedding mode. A deep seal always promotes the onset of air-cloud shedding, whereas surface seals with relatively low Bond numbers result in the air-bubble shedding mode. A surface seal suppresses resonance in the cavity volume. By observing the cavity motion, we find that air-cloud shedding is always accompanied by severe cavity resonance and a rapid decrease in cavity length. Under the air-bubble shedding mode, the cavity motion exhibits relatively weak oscillations.

中文翻译：

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疏水球后水进入腔内气泡演化的实验研究

本文介绍了在水进入过程中疏水球后面的空腔演化和脱落后流的实验研究。通过改变撞击速度和球体尺寸，可以确认两种明显的脱落现象：规则的气泡脱落和不稳定的气云脱落。这两种模式都高度依赖于韦伯和邦德数。在气泡脱落模式下，观察到大约周期性的大气泡脱落和低频振荡信号。推导了大气泡脱落事件与相应的声波信号之间的关系，提出了一种预测脱落周期的经验方法。确认了小气泡脱落与空腔波纹之间的同相关系，我们将空腔脱落现象称为“声学”脱落。与观察到气泡脱落不同，空气云脱落模式从腔体的后部产生了一组无序的小气泡。而且，型腔密封件类型对型腔脱落模式具有显着影响。深层密封总是会促进空气云的脱落，而邦德数相对较低的表面密封会导致气泡脱落。表面密封可抑制型腔体积中的共振。通过观察空腔运动，我们发现气云散发总是伴随着剧烈的空腔共振和空腔长度的迅速减小。在气泡脱落模式下，腔运动表现出相对较弱的振荡。空腔密封类型对空腔脱落模式有重大影响。深层密封总是会促进空气云的脱落，而邦德数相对较低的表面密封会导致气泡脱落。表面密封可抑制型腔体积中的共振。通过观察空腔运动，我们发现气云散发总是伴随着剧烈的空腔共振和空腔长度的迅速减小。在气泡脱落模式下，腔运动表现出相对较弱的振荡。空腔密封类型对空腔脱落模式有重大影响。深层密封总是会促进空气云的脱落，而邦德数相对较低的表面密封会导致气泡脱落。表面密封可抑制型腔体积中的共振。通过观察空腔运动，我们发现气云散发总是伴随着剧烈的空腔共振和空腔长度的迅速减小。在气泡脱落模式下，腔运动表现出相对较弱的振荡。我们发现，气云散发总是伴随着严重的空腔共振和空腔长度的迅速减小。在气泡脱落模式下，腔运动表现出相对较弱的振荡。我们发现，气云散发总是伴随着严重的空腔共振和空腔长度的迅速减小。在气泡脱落模式下，腔运动表现出相对较弱的振荡。