绕不同扭曲水翼的空穴发展及其水动力特性的数值研究

Numerical Study of Cavity Development and Hydrodynamic Characteristics around Two Different Twisted Hydrofoils

针对水力机械叶片表面的空化问题,开展了绕不同扭曲水翼的空化流动特性的数值研究。采用均质流模型并耦合大涡模拟方法(LES)和Zwart空化模型,计算了绕NACA0009和Clark-Y两种扭曲水翼在不同空化数下的空化流动。结果表明:绕不同翼型的空穴发展随着空化数变化呈现明显不同的特性。相比于NACA0009翼型,绕Clark-Y翼型的空穴尺度随着空化数的减小而增大的幅度更明显,对空化数更为敏感。绕NACA0009翼型的空穴可以将翼型导边完全覆盖,而Clark-Y翼型导边的两侧并没有被空穴覆盖。另外,绕NACA0009翼型的空穴更容易出现准周期性变化和形成U形涡结构的脱落空泡团。不同翼型的升力系数的变化规律也显著不同,Clark-Y翼型的时均升力系数均显著大于NACA0009翼型。随着空化数的减小,相比于Clark-Y翼型,NACA0009翼型的升力系数更容易出现准周期性变化。

For the cavitation problem on the surface of hydraulic blade,numerical research was carried out on the cavitation flow characteristics around different twisted hydrofoils.The cavitation flow around two kinds of twisted hydrofoils known as NACA0009 and Clark-Y under different cavitation numbers was calculated by using homogeneous flow model and coupled with large eddy simulation(LES)and Zwart cavitation model.The results show that the development of cavitation around different hydrofoils shows obviously different characteristics with the change of cavitation number.With the decrease of cavitation number,the cavity size is gradually increasing.Compared with NACA0009 the increase of the cavity scale of Clark-Y is more obvious.The cavity around NACA0009 can completely cover the leading edge while the cavity around Clark-Y can just cover partially.In addition cavitation around NACA0009 is more prone to quasi-periodic changes and shedding in form of U-shaped vortex structure.The lift coefficient fluctuations for different hydrofoils are also significantly different.The time-averaged lift coefficient of Clark-Y is significantly larger than NACA0009.And with the decrease of cavitation number,the lift coefficient fluctuation of NACA0009 always presents quasi-periodic process.