前掠叶片流动分离特性的数值研究

Numerical Research on the Flow Separation Characteristics of Forward-swept Blades

实验与数值模拟同时表明,相比于常规叶片,前掠叶片在高流量工况区域有着更高的效率,然而在低流量工况下,叶片的前掠会使流动不稳定区域提前。本文通过分析表面极限流线构成的二维Jacobian矩阵,得到不同奇点形成规律与配合方式。采用拓扑分析预测轮毂与前掠叶片上奇点的分布,得到较为准确的流场信息,准确找到隐藏在叶片尾缘处的螺旋结点,并得到了前掠叶片在低流量工况下效率降低的原因。对于前掠叶片,流动分离主要出现在角区与叶顶处,并伴随着明显的压力波动,形成的脱落涡会破碎并扩散到主流中。随着流量的降低,脱落涡形成的位置将逐渐前移,湮灭速度逐渐减慢。

Compared with conventional blades,a forward-swept blade is more efficient at high flowrates.However,experiments and numerical simulations show that a forward-swept blade will cause an unstable region to occur ahead of it.This paper describes the flow separation behavior in separation line,shows the formation rules and matching modes of different singularities which are derived by analyzing the two-dimensional Jacobian matrix formed by the surface limit streamline equation.Through this theory,more accurate flow field information is obtained,and the focus hidden in the trailing edge of the blade is accurately located.For the forward-swept blade,flow separations mainly occur at the blade tip and corner,accompanied by clear pressure fluctuations,a breaking up of shed vortices and diffusion.With decreasing flow rate,the positions of the shedding vortices move forward and the speed of vortex annihilation slows down gradually.