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

与其他类型相比，涡流空化可能会产生较大的冲击力，因此被研究。试图弄清冲击产生的表现和冲击的机理。特别研究了涡流空化的非定常运动以及气液两相态的作用。主要研究结果如下：首先，研究发现，空化气泡的脉冲式崩塌是由于三角形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，试验还证明，轴向坍塌模式会在墙体材料上产生冲蚀坑。这种具有垂直于壁面的旋转轴的塌陷模式被认为是其他涡旋空化模式中最强的一种。研究还发现，由于凹坑数目为两个或两个以上，涡空化崩溃产生的一次冲击是由气液两相态的气泡簇组成的。采用软涂层冲蚀试验台作为一种新的冲蚀试验台，直接捕捉气泡的崩塌行为。通过实验，对每个侵蚀坑进行了考察，找出了涡穴的簇状行为。由于脱落类型的涡腔在冲击特性中起着重要的作用，本文对轴对称内流的空化特性进行了研究，但尚不清楚。结果表明：在这种流型中还观察到了与高冲击力密切相关的脱落空穴，在两相态的分离气泡中发生了再入运动，与气泡脱落紧密相连，脱落的两相涡呈环状。此外，本文还对已有的研究成果进行了总结。

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.