Measurement of cavitation bubble cluster downstream of sheet cavity

片材空腔下游空化气泡团的测量

基本信息

批准号：
10650899
负责人：
MAEDA Masatsugu
金额：
$ 2.24万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 1999
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-10650899/
关键词：
Cloud Cavitation Sheet Cavitation Foil Section Laser Holography Method Cavitation Bubble Cavitation Bubble Cluster Bubble Measurement Re-entrant Jet

项目摘要

A sheet cavity generated on a body such as hydrofoils begins to oscillate periodically when it attains a certain size, shedding harmful could cavities downstream. The collapse of cloud cavity is a collective collapse of cluster of numerous small bubbles, resulting in impulsive pressure fluctuations which leads to noise, high frequency vibration and erosion of the materials. In this study, we measured the number and spatial distribution of bubbles in cloud cavities downstream of sheet cavity.A laser holography method was applied to measure the bubbles in cloud cavities on a foil section. In the beginning, it took about 3 months to count the bubbles whose radii are more than 10 μm. Therefore, we measured the bubbles with radii of more than 35 μm mainly. As a result we succeeded in measuring bubbles in 9 cloud cavities for 3 cavitation numbers and 3 foil chord stations. The results can be summarized as follows :a) Bubbles in cloud exist around a U-shape vortex cavity near the center of cloud particularly downstream of it. Larger bubbles exist more closer to the vortex cavities. This suggests that the vortex cavities split into small bubbles, supplying bubbles around them, when they collapse. It is also seen that there are larger bubbles closer to the foil surface. It is considers that this is attributed to lower pressure close to the foil surface.b) The bubble number density function is inversely proportional to the bubble radius to power 5.1 when the bubble radius is larger than 35 μm. We obtained an empirical equation of the relation between the bubble number density function and bubble radius.We also measured evaporation rate at sheet cavity surface, which determines the total vapor volumes of the initial cloud cavity. Also measured are the characteristics of re-entrant jet, which tears off the sheet cavity resulting in could cavity shedding.

在氢油素等体内产生的片腔时，当它达到一定尺寸时会定期振荡，脱落有害的可能是下游的腔。云腔的崩溃是众多小气泡簇的集体崩溃，导致冲动压力波动，从而导致噪声，高频振动和材料的侵蚀。在这项研究中，我们测量了板腔下游云腔中气泡的数量和空间分布。应用激光全息方法来测量箔片上云腔中的气泡。一开始，大约花了3个月的时间来计算半径超过10μm的气泡。因此，我们用半径超过35μm测量了气泡。结果，我们成功地测量了9个云腔中的气泡，用于3个空穴数量和3个箔弦站。结果可以总结如下：a）云中的气泡在云中心附近的U形涡流腔周围，特别是在其下游。较大的气泡的存在更靠近涡流腔。这表明涡流腔分成小气泡，倒塌时供应周围的气泡。还可以看出，较大的气泡更靠近箔表面。它认为这归因于靠近箔表面的较低压力。B）当气泡半径大于35μm时，气泡数密度函数与气泡半径成反比为5.1。我们获得了气泡数密度函数与气泡半径之间关系的经验方程。我们还测量了板腔表面的经济速率，这决定了初始云腔的总蒸气量。还测量的是重入射流的特性，它从薄片腔中撕下，导致腔脱落。