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

对佛汝德数Fr 300范围内的自由表面液滴撞击引起的表面破碎和水下声的机理进行了实验研究。这些声音的开放式Suikinkutsu的应用也进行了研究。(1)下落的水滴根据韦伯数改变其形状，然后撞击水面。当水滴以扁长的形状撞击时，与扁长的水滴撞击情况相比，所产生的飞溅相对较弱。(2)一次跌落冲击产生了三次水下声音。第一种声音是由于卫星水滴撞击在收缩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崩溃期间产生的气泡的振荡。这些气泡的形成在很大程度上取决于Fr数、We数（或Bond数）和撞击时液滴的纵横比。 ...更多信息 CT，虽然涉及概率特征。气泡在水柱中的滞留对提高水柱表面与弯曲自由表面接触的概率起着重要作用。(3)一旦在水罐内产生跌落冲击，声音通过水面传播到罐内的空气中，并在罐的壁表面上反射多次，产生持续时间长的混响声音，这是一种平静和治愈的声音。为了研究水流速度和水温对水金音的影响，还使用平均直径为6.2、7.2和7.8mm的水滴进行了实验。因此，为了产生强大的水金壶声，水温应保持尽可能低。上述结果已在各种会议上提出并发表。最近，我们关于表面破裂和气泡声的论文已被《流体力学杂志》接受发表。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