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

在现代航空发动机的超声速叶栅中，在高转速下会发生弯曲模态颤振。并且在高背压下即，在高负荷条件下。在这类颤振中，压气机叶栅处于未启动状态，叶片伴随着脱体激波，因此称为“未启动颤振”。“本研究旨在揭示未起动颤振的物理机制。实验是在二维跨音速叶栅风洞中进行的。叶栅的中心叶片是机械振动的。通过改变下游流道面积来控制叶栅的背压。用纹影技术显示了叶栅流场中的激波，测量了叶栅侧壁和叶片表面的压力分布。结果表明：（1）在低背压时，激波斜贴于叶片前缘，在低背压时，激波斜贴于叶片前缘; ...更多信息 上升沿和下降沿。随着背压的增加，激波转变为通道激波，最后转变为分离的弓形激波。(2)在低背压条件下，叶片振动对非振动叶片上激波的运动几乎没有影响。另一方面，当背压变高时，叶片振荡对其它叶片的激波运动产生非线性影响。计算结果表明，在超声速流场中，当马赫数接近1.0时，分离激波的存在使叶片振荡更加危险。计算结果表明，叶栅在吸力面移动模态下会发生颤振，未起动状态比起动状态更容易发生颤振。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