Investigation on the Flow Structures in the Tip Region for a Transonic Axial Compressor Rotor

The effect of flow structures in the tip region on the stability of NASA Rotor 37 has been examined with numerical simulation. Stall inception mechanism of Rotor 37 is presented firstly with principal focus on the tip leakage flow behavior, passage shock wave and leakage flow vortex. Detailed survey reveals three features: (1) there exists an interface between the incoming main flow and the tip leakage flow;(2) in this rotor, the tip leakage flows along the blade chord can be divided into at least three parts, each part plays a different role in the tip region;(3) the combined interaction of the stagnated blockage due to breakdown of the leakage vortex and the leakage flow from the leading edge leads to the tip stall inception. When flow and tip leakage flow intersect with each other, there is great rivalry between the two flows. If the power of incoming flow is relatively large, the flow will be coerced a lot of tip clearance leakage flow smoothly into the passage. And vortex breakdown would not have happened to produce large numbers of low-energy groups. And after the "collision" of the incoming flow, the secondary tip clearance flow will be greatly reduced. The efficiency of compressor will rise. Conversely, if the power of incoming flow is relatively small, tip part of the clearance leakage flow will be enveloped into the blade passage by main flow. But this part is unable to be taken out of the blade passage, and the collision of the two weakens their respective power further more. Under the influence of reverse pressure gradient, the vortex breakdown and low energy mass blockage escalate. As a result of the gradually decreasing power of the incoming flow, the secondary tip clearance flow get emerging. Thus the interface moves forward and spill out of blade passage from leading edge.