绕不同头型回转体初生空化的实验研究

为了研究绕不同头型回转体初生空穴的形成、发展过程和流场特性，采用流动显示技术分别观察了绕平头和锥头回转体初生空化的形态，并应用粒子图像测速系统（PIV）测量了相应工况下的速度分布。结果表明，绕回转体的头型对初生空化数和空穴形态有重大影响。实验中平头回转体的初生空化数为1．2，而45。锥角头型的初生空化数则为0．9。绕回转体的初生空穴形成于回转体肩部稍靠后的位置且没有附着在其表面，呈游离型发夹状，同时绕平头回转体的初生空穴的尺度较大，其初生位置距离肩部及回转体的壁面均较远。流场测试结果表明，空化初生和绕回转体头部流场的旋涡强度有关。与锥头回转体相比，同一雷诺数条件下，绕平头回转体的分离涡尺度较大、边界层离壁面较远、高涡量区域较大且离壁面较远，这是造成两种头型具有不同初生空化特性的主要原因。

Experimental study of inception cavitation around axisymmetric bodies with different headforms

A high-speed video camera was used to observe the process and structure of cavita- tion inception, flow characteristics and effects of headforms around two axisymmetric bodies with blunt and cone-shaped respectively. A particle image velocimetry （PIV） system was employed to measure the velocity and vorticity fields. The results show that the shape of headform has an effect on inception cavitation number and cavity shapes. In this work, the inception cavitation numbers of the blunt body and the fastigiate one are 1.2 and 0.9 respectively. Traveling bubbles with hairpin type at inception cavitation are incurred in the region downstream from the corner and the cavities are detached from the surface of bodies. Compared with the cone-shaped body, the bigger traveling bubbles forming around the blunt body are farther from the shoulder and body surface. In addition, the flow field shows inception cavitation is related to vortex intensity of the flow around heads. Compared to the cone-shaped body with the same value of Re, the scale of detached vortex around the blunt body is bigger, shear layer is farther from the body surface, and the area of high vorticity is larger and farther from the body surface. All of these probably cause the different characteristics of inception cavitation of the two bodies.