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EROSION MECHANISM OF IMPULSIVE VORITEX CAVITATION BUBBLES AND VORTEX STRUCTURE OF GAS-LIQUID FLOW

脉冲涡流空化气泡的侵蚀机理及气液流涡结构

基本信息

批准号：
09650208
负责人：
SATO Keiichi
金额：
$ 2.11万
依托单位：
KANAZAWA INSTITUTE OF TECHNOLOGY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1999
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09650208/
关键词：
CAVITATION EROSION VORTEX TWO-PHASE FLOW BUBBLE UNSTEADYNESS IMPULSIVE FORCE HIGH SPEED LIQUID FLOW 発生制御

项目摘要

Vortex cavitation was investigated because of its possibility to cause high impulsive force compared with other types. It was tried to make clear the appearance of impact generation and the mechanism of impact. Especially, unsteady motions of vortex cavitation were examined as well as the role of gas-liquid two-phase state. The main results are as follows.First, it is found that an impulsive collapse of cavitation bubbles is caused by unsteady motion with the entrainment flow due to a pair of vortex cavitation in the separated shear layer behind a triangular or a circular cylinder. In addition it is experimentally proved that the axial-collapse pattern can cause erosion pits on the wall material. This collapse pattern which has a rotating axis perpendicular to the wall has been known as the strongest one of other patterns of vortex cavitations. It is also found that one attack generated by the collapse of vortex cavitation consists of a cluster of bubbles in gas-liquid two-phase state because the number of pits is two or up. A soft coated test-plate for erosion was used as a new one to catch directly the collapsing behavior of bubbles. Through experiments each erosion pit was investigated to find out the cluster-like behavior of vortex cavities. As the shedding type of vortex cavities make an important role in an impulsive character the cavitation characteristics about an axisymmetrical inside-flow were examined which had not been clear. Thus some results were obtained as follows ; the shedding cavities are also observed in this flow-type and closely connected to high impulsive force, a re-entrant motion occurs in the separation bubble of two-phase state and closely connected to the bubble shedding, and shedding two-phase vortices shows a ring-like appearance. Furthermore existing researching results were summarized under the present works.

涡空蚀是一种能产生较大冲击力的空蚀现象。试图弄清冲击产生的表象和冲击产生的机理。特别是，涡空化的非定常运动以及气液两相状态的作用进行了研究。主要研究结果如下：首先，发现空化泡的脉冲溃灭是由于三角柱或圆柱体后分离剪切层中的一对涡空泡与卷吸流的非定常运动引起的。此外，还通过实验证明了轴向塌陷模式会在壁面材料上产生冲蚀坑。这种具有垂直于壁的旋转轴的塌陷模式被认为是其他涡空化模式中最强的一种。研究还发现，由于涡空泡溃灭时的凹坑数为两个或两个以上，因此涡空泡溃灭时的一次冲击是由气液两相状态的气泡群组成的。采用一种新型的软涂层冲蚀试验板，直接捕捉气泡的溃灭行为。通过实验对每个蚀坑进行了研究，以了解涡腔的簇状行为。由于涡腔的脱落形式对脉冲特性起着重要作用，本文对轴对称内流的空化特性进行了研究。研究结果表明：在该流型中也观察到了脱落空腔，且与高冲击力密切相关;两相分离泡中出现了折返运动，且与气泡脱落密切相关;脱落两相涡呈环状。在此基础上，对现有的研究成果进行了总结.