绕三维扭曲水翼非定常空泡脱落特性的数值研究

Numerical Study of Unsteady Cavitating Shedding Structure around a Three-dimensional Twisted Hydrofoil

为了进一步探究绕三维扭曲水翼空化流动结构的非定常演变特性,基于均质流模型,采用大涡模拟(LES)方法,并耦合Zwart空化模型对绕扭曲水翼(NACA0009)的非定常空化流动进行了数值计算。结果表明:与试验结果对比发现,该数值计算方法可以很好地捕捉到绕NACA0009水翼的非定常空泡形态的演变过程,且计算得到的水翼升力系数的时均值及其特征频率均与实验值吻合较好。非定常空泡的脱落过程分为主脱落和二次脱落两个阶段,主脱落过程表现为大尺度空泡团的断裂,呈U型结构卷起并脱落,此时水翼表面的附着空泡呈凹形结构。随着时间的推移,附着空泡的两侧发生小尺度空泡团的二次脱落,产生局部高压,抑制了当地空泡的生长速度,从而使附着空泡由凹形结构逐渐发展为凸形结构。

In order to investigate the unsteady characteristics of cavitating flows,the simulation of the unsteady cavitating flow around a three-dimensional twisted hydrofoil called NACA0009 is carried out based on the homogeneous flow model,coupled with the large eddy simulation（LES） method and the Zwart cavitation model.The results show that compared with the experimental results,the numerical method can well predict the time-evolution process of unsteady cavitating flow structures as well as the mean value and the frequency of lift coefficient of the twisted hydrofoil.It is shown that the whole process of unsteady cavity shedding is divided into two stages named the primary shedding and the secondary shedding respectively.During the primary shedding process,there is the large scale of cavity breaking off,rolling up with U-type vortex structure and shedding,and then the remaining attached cavity seems like the concave structure.As time goes,the small-scale secondary shedding gradually generated at both sides of the attached cavity accompanied with the local high pressure which can restrain the growth rate of attached cavity.As a result,the attached cavity change again from the concave structure into convex structure.