不同攻角下绕平头回转体初生空化流动特性研究

Study of Characteristics of Inception Cavitating Flows around an Axisymmetric Blunt Body at Different Angles of Attack

为了分析近壁面流场结构对附着型空化初生特性的影响规律,通过数值模拟方法开展不同来流攻角条件下绕平头回转体初生空化的形成及流动特性研究。采用均质两相流模型并耦合大涡模拟(LES)方法和Zwart空化模型,对绕平头回转体初生空化进行数值模拟。研究结果表明:LES方法可以较好地模拟绕平头回转体的初生空化流动,计算得到的空穴形态及其随时间的演变过程与实验结果基本一致;各攻角条件下的初生空穴均呈不规则的团泡状,不对称地分布在回转体肩部的分离涡区域内;随着攻角增大,回转体迎流区域的初生空穴分布范围逐渐减小,背流区域的初生空穴分布范围逐渐扩大;初生空穴的分布规律与时均分离涡结构紧密相关;随着攻角增大,迎流面分离涡尺度逐渐减小并向回转体头部及壁面移动,背流面分离涡尺度逐渐增大;大攻角条件下,在回转体背流面的分离再附着点附近出现二次分离现象,促使初生空化在此处形成。

The inception cavitating flows around an axisymmetric blunt body at different angles of attack are simulated to investigate the influence of near-wall flow structure on the characteristics of inception cavitation.The large eddy simulation(LES)method coupled with the Zwart cavitation model is applied based on the homogeneous flow model in the simulation of inception cavitation.The results show that the LES method gives good predictions of the incipient cavity shape and its time-evolution process.The inci-pient cavities exhibit irregularly bubble structures and are asymmetrically distributed in the separation vortex area at the shoulder of axisymmetric blunt body.As the angle of attack increases,the distribution area of incipient cavities in the incident flow region gradually decreases but increases in the backflow region.The distribution of incipient cavities is closely related to the time-averaged separation vortex structure.The vortex scale in the incident flow gradually decreases and tends to be close to the head and wall of axisymmetric blunt body.However,the separation vortex scale of the backflow gradually increases with the increase in the angle of attack.Especially for the larger angle of attack,a secondary separation phenomenon occurs near the reattachment point of the backflow,which induces the formation of inception cavitation.