Effect of discrete endwall recirculation on the stability of a high-speed compressor rotor

A numerical study has been carried out to understand the effect of discrete endwall recirculation on the performance of a transonic axial compressor rotor. Twenty-two recirculation passageways were designed and placed uniformly around the casing, and time-accurate simulations were performed with and without recirculation. The effect of recirculation on the rotor overall performance, tip flow structure and unsteady response of the leakage flow are presented and discussed. The amount of recirculation is not constant in this work, mostly owing to the injector-shock wave interaction. Results indicate that the tip leakage vortex and passage shock are periodically pushed rearwards due to recirculation. It is further found that at the near-stall point, with or without recirculation, the interface between the leakage and oncoming flows tends to become parallel to the leading-edge plane, and that recirculation increases stability by postponing this situation to lower mass flows. The flow field within recirculation passageway was also investigated, and the axial and circumferential components of the bled air were found to be mainly responsible for the total pressure loss.