绕平头回转体空穴的发展及脱落特性研究

Study of Characteristics of Unsteady Cavitating Flow around an Axisymmetric Blunt Body

综合数值计算及实验技术研究了绕平头回转体的空穴发展及脱落特性。采用流动显示技术观察了绕平头回转体的空穴在不同空化数下的发展及脱落历程,并利用局部时均化湍流模型(PANS)进行了数值计算。研究结果表明:绕平头回转体空穴的发展过程和空泡的脱落细节均随空化数的不同而呈现出明显的差异;空化数较大时,空穴发展及脱落没有准周期性,空化数越小,空穴的发展周期越长,脱落空泡的尺度越小;绕平头回转体的空泡准周期性脱落过程主要包括空穴断裂与空泡脱落两个过程;空穴断裂的位置大约位于距回转体肩部0.3D(D为回转体直径)处,由于反向射流的作用使空穴的断裂呈U型涡状;在一定的空化条件下,绕平头回转体的空化由于断裂和融合两个过程的存在,将使空穴在发展过程中呈现更加稳定性的特征。

Cavitating flow around an axisymmetric blunt body is studied based on the experiments and nu- merical simulations. A high-speed video camera is used to observe the processes of cavity development and shedding. A partially-averaged Navier-Stokes （PANS） method which is a hybrid RANS/LES turbu- lent model is applied in numerical simulation. The results show that the characteristics of cavity develo- ping and shedding vary as cavitation number is changied. With the decrease in the cavitation number, the period of cavity developing increases and the shedding of small scale vortices occurs. Moreover, it is found that the shedding generally contains two processes ： cavity break-off and cavity shedding. The cavity break-off probably occurs at the location which is about 0.3D away from the shoulder. The cavity sheds with U-vortex type which is induced by the re-entrant flow. In addition, the cavity tends to be steady when the break-off cavity is in conjunction with the attached cavity.