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。在研究的第一年，扩展了刚性叶栅旋转失速的数值分析方法，使其能够处理叶栅叶片小幅度振荡的情况。以典型的NACA-65CA(30)-10型压气机叶片叶栅为计算对象，分析了各叶片在不同振动参数下绕各弯曲线中心作旋转振动时的非定常气动特性。当进口气流角较大时，叶栅内也存在旋转失速现象，当叶片振动相速度与旋转失速传播速度一致时，两者同步，叶片振动强烈激发，即发生失速颤振。第二年，对同一叶栅进行了一系列数值模拟，分析了失速颤振的发生与旋转失速出现的关系。当进气角较小时，既不会发生失速颤振，也不会发生旋转失速。当进口气流角度略有增大时，根据叶片的振动条件，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这两种现象的同步，但有可能用更广泛的失速颤振来激发叶片振动。当进流角进一步增大时，发现这种情况延续到第一年的结果。

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.