Study on Unsteady Flow Induced by Annular Cascade

为研究离心压气机进口导叶环形叶栅引起的非定常流动现象，进行了实验和数值分析。在实验中，用小型半导体压力传感器测量了脉动壁面压力分布，用热线风速仪测量了叶栅后10%弦长的瞬时速度分布，用氩离子剃刀片光和烟雾显示了叶栅周围的流纹线。结果发现：(1)当叶片与径向的安装角小于30度时，不会产生带噪声的非定常流，当叶片与径向的安装角大于50度时，会产生非定常流。(2)在管道中心加装芯，降低旋流的非定常，不影响带噪声的非定常的发生。(3)叶片宽度和弦长对非定常流的发生也没有影响。(4)非定常流场的基频与流速基本成线性关系。(5)在某些流动条件下，斯特罗哈尔数是常数，且与雷诺数无关。(6)认为非定常流的发生与叶片表面的流动分离有关。(7)在非定常流的发生下，叶片尾迹的流动方向有强烈的波动。(8)失稳性与旋涡式失速室的方向相反。(9)采用带噪声的非定常流保护片是有效的。此外，数值分析成功地模拟了与实验结果相对应的60度角压力波动。虽然计算精度还不够，但该数值计算为建立环形叶栅非定常流场模型开辟了道路。

To investigate phenomena of an unsteady flow induced by annular cascade of inlet guide vanes for a centrifugal compressor, experiments and numerical analysis were conducted. In experiments, fluctuating wall pressure distributions were measured by small semi-condustor pressure transducers and instantaneous velocity distributions at 10% chord length after the cascade were gotten by a hot-wire anemometer and flow streak lines around the vanes were visualized by sheet light of an argon ion razor and smoke. As a result, the followings are found : (1)In case that blade setting angle from radial direction is smaller than 30 degrees, the unsteady flow with noise is not induced, but in case that the angle is larger than 50 degrees, the unsteady flow is produced. (2)A core installed in center of a pipe passage to reduce unsteadiness of a swirling flow does not affect occurrence of the unsteady flow with noise. (3)Both blade width and chord length also have no influence for the occurrence of the unsteady flow. (4)Fundamental frequency of the unsteady flow almost has a linear relation to flow velocity. (5)Strouhal number is constant and independent of Reynolds number in some flow conditions. (6)The occurrence of the unsteady flow is considered to have a relation to flow separation from blade surface. (7)Flow direction of blade wake strongly fluctuates under the occurrence of the unsteady flow. (8)The unsteadiness travels counter direction of swirling stall cell. (9)A tab protecting the unsteady flow with noise is quit effective. Furthemore, numerical analysis was success in simulation of pressure fluctuations corresponding to be experimental results in 60 degrees of angle. Accuracy of calculation is not yet sufficient but it is say that the numerical opens the way to establish a flow model for the unsteady flow induced by annular cascade.