带攻角轴对称体自然空泡流脉动特征的数值分析

Numerical Simulation of Flunctuating Characteristics of Cavitating Flow Around Axisymmetric Body at Angle of Attack

采用雷诺平均NS方程对轴对称体自然空泡流的脉动过程进行了数值模拟.采用通过降低两相过渡区域内湍流涡粘性系数的方法,实现了基于RANS方程的三维轴对称体自然空泡整体脱落过程的数值模拟.与1/4平头轴对称体自然空泡流实验结果比较,空泡大断裂的脱落频率计算值与实验数据基本一致.数值模拟结果表明,在空化数相同条件下,头型变化对空泡成长及脱落有着明显的影响,半球头模型的空泡长度较短,脱落频率较大,而平头模型的空泡长度更长,脱落频率较低.零攻角条件下,自然空泡在大断裂和脱落过程中也呈现非对称性的空泡形态.在小攻角条件下,攻角增大会使得背流侧空泡长度变大,脱落频率略有减小.当攻角大于8度时,空泡的整体脱落规律性受到抑制.

We numerically investigate the unsteady behavior of cavitating flow around an axisyrrmaetric body at small angle of attack. The Reynolds Averaged Navier-Stokes （RANS） equations are used to simulate the three dimensional cavitating flows. Adopted by modification of the eddy viscosity coefficient in the transition area of the two phase flow, the shedding process of cavitating flow is successfully captured. The computed frequency of shedding of cloud cavitation coincides with the measured frequency of the unsteady cavitating flow around an axisymmetric body. Given the cavitation number, the shedding process of the cavitating flow depends on the headform of the axisymmetric body significantly. Among four headforms, the cavity length on the hemisphere headform is shortest and its shedding frequency is greatest, and the cavity on the blunt headforrn is longest and the shedding frequency is smallest. For the case of zero angle of attack, the cavity shows asymmetric behavior of the cavity shedding. Increasing the angle of attach will make the length of cavity longer and shedding frequency slightly lower. As the angle of attack is greater than 8°, periodic shedding of cavity is depressed.