Mechanism and its application of bubble sounds induced by the drop impact in the irregular entrainment region

在弗劳德数Fr为300的范围内，研究了液滴撞击自由表面并诱发水声的表面破碎机理。文中还研究了这些声音在开口式水滴上的应用。(1)水滴的形状随韦伯数的变化而变化，然后撞击水面。当水滴撞击形状变长时，与扁平水滴撞击情况相比，产生的飞溅相对较弱。(2)单次水滴撞击产生三次水声。第一种声音是由于卫星落在收缩中的空腔底部而形成的单个气泡的振荡，第二种声音是由于水柱坍塌时产生的气泡的振荡。这些气泡的形成强烈地依赖于Fr数、We数(或键数)和IMPA…处液滴的纵横比更多的ct，尽管涉及概率特征。被困在水柱中的气泡在提高柱面与弯曲自由表面接触的概率方面起着重要作用。(3)一旦水罐内部产生跌落撞击，声音就会通过水面传播到罐子内的空气中，并在罐壁表面多次反射，产生持续时间长的回响声音，这是一种平静和治愈的声音。用平均直径分别为6.2、7.2和7.8 mm的水滴进行了实验，以考察水流量和水温对水声的影响。因此，为了发出强有力的水声，水温应保持在尽可能低的水平。上述结果已在各种会议上公布和发表。最近，我们关于表面破裂和气泡声音的论文已被《流体力学杂志》接受发表。较少

An experiment was carried out for investigating the mechanism of surface breakup due to drop impact on a free surface and induced underwater sounds for the range of Froude number Fr 300. Application of these sounds to an open-type Suikinkutsu was also examined.(1) A falling drop changes its shape oscillatory depending on the Weber number, then impacts onto a water surface. When a drop impacts with the shape being prolate the resultant splash is relatively weak compared to the oblate drop impact case.(2) Three times of underwater sounds were generated for a single shot of drop impact. The first sound resulted from the oscillation of a single air bubble formed as a result of the satellite drop impact on the bottom of a cavity under contracting, and the second sound was due to the oscillation of air bubbles generated during the collapse of a water column. The formation of these air bubbles strongly depends on the Fr number, We number (or Bond number) and the aspect ratio of a drop at impa … More ct, although involving probability characteristics. An air bubble entrapped into a water column plays an important role in elevating the probability of contact between the column surface and curved free surface.(3) Once drop impact is generated inside a water jar, the sounds propagate through the water surface into the air inside the jar and reflect many times on the wall surface of the jar, producing a reverberant sound with a long duration which is a peaceful and healing sound. An experiment was also performed by using drops with the average diameters of 6.2, 7.2 and 7.8mm in order to investigate the effects of water flow rate and water temperature on the Suikinkutsu sound. For generating a powerful sound of Suikinkutsu, therefore, water temperature should be maintained as low as possible.The results mentioned above have been presented and published at various meetings. More recently our paper associated with the surface breakup and bubble sounds has been accepted for publication in the Journal of Fluid Mechanics. Less