In this paper, the cavitating flow around a bluff body is studied both experimentally and numerically. The bluff body has a finite length with semi-circular cross section and is mounted on a surface in the throat of a converging-diverging channel. This set-up creates various 3D flow structures around the body, from cavitation inception to super cavities, at high Reynolds numbers (Re = 5.6*10^4 - 2.2*10^5) and low cavitation numbers (sigma = 0.56 - 1.69). Earlier studies have shown this flow to be erosive and the erosion pattern varies by changing the flow rate and w/o the cylinder; hence, this study is an attempt to understand different features of the cavitating flow due to the cylinder effect. In the experiments, high-speed imaging is used. Two of the test cases are investigated in more detail through numerical simulations using a homogeneous mixture model. Non-cavitating simulations have also been performed to study the effect of cavitation on the flow field. Based on the observed results, vortex shedding can have different patterns in cavitating flows. While at higher cavitation numbers the vortices are shed in a cyclic pattern, at very low cavitation numbers large fixed cavities are formed in the wake area. For mid-range cavitation numbers a transitional regime is seen in the shedding process. In addition, the vapour structures have a small effect on the flow behaviour for high cavitation numbers, while at lower cavitation numbers they have significant influence on the exerted forces on the bluff body as well as vortical structures and shedding mechanisms. Besides, at very low cavitation numbers, a reverse flow is observed that moves upstream and causes the detachment of the whole cavity from the cylinder. Such a disturbance is not seen in non-cavitating flows.

中文翻译：

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表面贴装半圆柱体空化流的实验与数值研究

在本文中，通过实验和数值方法研究了钝体周围的空化流动。钝体具有有限长度和半圆形横截面，并安装在收敛-发散通道喉部的表面上。这种设置在高雷诺数 (Re = 5.6*10^4 - 2.2*10^5) 和低空化数 (sigma = 0.56 - 1.69) 下在身体周围创建了各种 3D 流动结构，从空化开始到超级空腔. 早期的研究表明，这种流动具有侵蚀性，侵蚀模式会随着流速的变化和无气缸的变化而变化；因此，本研究试图了解由于圆柱效应引起的空化流的不同特征。在实验中，使用了高速成像。通过使用均匀混合模型的数值模拟，更详细地研究了两个测试案例。还进行了非空化模拟来研究空化对流场的影响。根据观察到的结果，涡旋脱落在空化流中可能具有不同的模式。当空化数较高时，涡流以循环模式脱落，而空化数非常低时，尾流区域会形成大的固定空腔。对于中等范围的空化数，在脱落过程中可以看到过渡状态。此外，蒸汽结构对高空化数的流动行为影响很小，而在低空化数时，它们对施加在钝体上的力以及涡流结构和脱落机制有显着影响。除了，在非常低的空化数下，观察到反向流动，向上游移动并导致整个空腔与气缸分离。这种扰动在非空化流动中是看不到的。