Three-Dimensional Separation in Complex Internal Flow Fields

研究了轴流压气机转子内旋转失速胞的演化和结构。为了捕获与转子和失速单元锁相的流场，发展了双锁相平均技术。用倾斜热线法获得了转子上下游三维速度分量随时间变化的系综平均值，用高响应压力传感器获得了机匣壁面压力分布，短尺度失速单元的特征是从转子前的机匣壁面到叶片吸力面之间存在一个集中涡。在长尺度失速单元中，前半部分叶片分离时，分离涡不规则地向上游移动，后半部分从轮毂侧重新进入转子，短尺度失速单元和长尺度失速单元对应的机匣壁压扰动行为随定转子间隙的不同而不同。对于大间隙和中间隙，失速起始由尖峰短尺度扰动检测，尖峰波的数量增加，产生高频波。大间隙时，它们在轻度失速时形成短尺度的部分跨失速胞元，而中间隙时，它们形成大尺度的增长失速胞元或长尺度扰动失速胞元。因此，在后一种情况下，失速过程被识别为“高频失速起始”。对于小的定子-转子间隙，失速过程被确定为“长波长失速起始”，并支持最近的计算模型的短波长失速起始显示，关闭转子-定子间隙抑制增长的短长度尺度的干扰。研究发现，短尺度扰动是由叶片表面的分离涡减少环量引起的。

Evolution and structure of rotating stall cells in an axial compressor rotor have been investigated. To capture the flow field phase-locked to both of the rotor and the stall cell, a double phase-locked averaging technique has been developed. Time-dependent ensemble averages of three-dimensional velocity components upstream and downstream of the rotor have been obtained with a slanted hot-wire, and pressure distributions on the casing wall with high response pressure transducers.The short length-scale stall cell is characterized by a concentrated vortex spanning from the casing wall ahead of the rotor to the blade suction surface. In the long length-scale stall cell, the separation vortices go upstream irregularly when blade separation develops in the front half of the cell, and reenter the rotor on the hub side in the rear half of it. Behavior of casing wall pressure disturbances corresponding to the short and long length-scale stall cells is different depending on the stator-rotor gap. For the large and middle gap, the stall inception is detected by a spiky short length-scale disturbance, and the number of spiky waves increases to generate the high frequency waves. They becomes the short length-scale part-span stall cells at the mild stall for the large gap, while they turn into a big stall cell with growth or a long length-scale disturbance for the middle gap. In the latter case, therefore, the stalling process was identified with 'high frequency stall inception'. For the small stator-rotor gap, the stalling process is identified with 'long wave-length stall inception', and supported the recent computational model for the short wave-length stall inception by showing that closing the rotor-stator gaps suppressed the growth of short length-scale disturbances. It is found that the short length-scale disturbance results from a separation vortex from a blade surface to reduce circulation.