A Study on the Relation between Stall Flutter and Rotating Stall

本研究的目的是通过数值模拟来了解失速颤振与旋转失速之间的关系。在第一年的研究中，扩展了分析刚性叶栅旋转失速的数值方法，使其可以处理叶栅叶片小振幅振荡的情况。以典型的NACA-65CA(30) 10叶片压气机叶栅为计算目标，分析了各叶片在不同振荡参数下绕各弧线中心旋转振荡时的非定常气动特性。当进口气流角较大时，叶栅也会发生旋转失速，且当叶片振动的相速度与旋转失速的传播速度重合时，两种现象同步，叶片振动被强烈激发，即发生失速颤振。第二年，围绕失速进口气流角逐步增大进气道气流角，对同一叶栅进行了一系列数值模拟，以观察失速颤振的发生与旋转失速的出现之间的关系。进口气流角较低时，既不发生失速颤振，也不发生旋转失速。当进口气流角略微增大时，根据叶片的振荡情况，有可能出现旋转失速。在这种情况下，虽然没有看到前面提到的两种现象的同步，但通过“更广泛意义上的失速颤振”激发叶片振荡是可能的。当进口气流角进一步增大时，发现情况继续与第一年的结果相同。

The aim of this study is to understand the relation between the stall flutter and the rotating stall by means of numerical simulations.In the first year of the study, the numerical method for the analysis of rotating stall in rigid cascades was extended so that it can treat the cases where the cascade blades oscillate with small amplitudes. A typical cascade of NACA-65CA (30) 10 compressor blades was selected as a calculation objective, and its unsteady aerodynamic characteristics were analyzed when each blade was oscillating rotationally around the center of each camber line with various oscillation parameters. Rotating stall occurred in these cascades as well if the inlet flow angle was large, and further, when the phase velocity of blade oscillation coincided with the propagation velocity of the rotating stall, the both phenomena synchronized and the blade oscillation was excited strongly, i.e., the stall flutter occurred.In the second year, a series of numerical simulation was carried out for the same cascade with increasing the inlet flow angle step by step around the stalling inlet flow angle, in order to see the relation between the occurrence of stall flutter and the appearance of rotating stall. When the inlet flow angle is comparatively low, neither the stall flutter nor the rotating stall occurred. When the inlet flow angle was increased slightly, it became possible for the rotating stall to appear depending on oscillation conditions of the blades. In this situation, although the synchronization of the both phenomena as mentioned before was not seen, the excitation of the blade oscillation by a "broader sense of stall flutter" became possible. When the inlet flow angle was increased further beyond, it was found the situation was continued to that described in the first years' result.