Study on unstarted flutter and aerodynamic characteristics of supersonic compresser cascades.

在现代航空发动机的超音速叶栅中，高转速下存在弯曲模态颤振。在高背压下也就是在高负荷条件下。在这种类型的颤振中，压气机叶栅在未启动状态下运行，叶片伴随着分离的激波，因此称为“未启动颤振”。本研究旨在揭示未启动颤振的物理机制。实验在二维跨音速叶栅隧道中进行。叶栅的中央叶片是机械振荡的。叶栅的背压由下游位置流道面积的变化来控制。利用纹影技术对叶栅流场的激波进行了可视化，并测量了叶栅侧壁和叶片表面的压力分布。结果表明：(1)当背压较低时，激波更倾向于附着在叶片上，且前缘和后缘更多。随着背压的增大，激波转变为通道激波，最后转变为分离弓形激波。(2)低背压条件下，激波在非振荡叶片上的运动几乎不受叶片振荡的影响。另一方面，当背压变大时，叶片的振荡对其他叶片的激波运动产生非线性影响。采用半致动盘法对具有分离弓形激波的振动叶片进行了理论分析。结果表明，在超声速流动区，当流动马赫数接近1.0时，分离激波使叶片振荡更加危险。开发了一个欧拉程序来模拟二维振荡叶栅的流动。计算结果表明，在吸力侧运动模式下会发生叶栅颤振，且未启动工况比启动工况更不稳定。少

In the supersonic cascades of modern aeroengines, bending mode flutter is experienced at high rpm. and at high back pressure i.e., at high loading conditions. During this type of flutter the compressor cascade operates undee an unstarted condition, and the blades are accompanied by detached shock waves, and hence it is called "unstarted flutter. " The present study is aimed at revealing the physical mechanism of the unstarted flutter.The experiment was performed in a two-dimensional transonic cascade tunnel. The central bladd of the cascade was mechanically oscillated. The back pressure of the cascade was controlled by the change of the flow channel area at a downstream position. The shock waves in the cascade flow field ware visualized by schlieren technigue, and the pressure distributions on the side walls and blade surfaces were measured. The following conclusions were obtained from the results :(1) When the back pressure is low, the shock waves are obligue attaching to the blade le … More ading edge and trailing edge. With the increase of the back pressure the shock wave changes to a passage shock, and finally becomes a detached bow shock.(2) The movement of the shock waves on non-oscillatory blades are hardly influenced by the blade oscillation under the low back pressure condition. When the back pressure becomes high, on the other hand, the blade oscillation gives nonlinear effects on the shock movement of other blades.The oscillating blades with detached bow shocks were theoretically analyzed by the semi-actuator-disk method. The results predict that the detached shocks make the blade oscillation more dangerous when the flow Mach number approaches to 1.0 in the supersonic flow regime.An Euler code was developed to simulate the flow around a two-dimensional oscillating cascade. The computed results show that the cascade flutter can occur in the suction side traveling mode, and that the unstarted flow condition provides a more unstable situation than the started condition. Less