Effect of self-recirculating casing treatment on the unsteady flow and stability of counter-rotating axial-flow compressor

Counter-rotating axial-flow compressor (CRAC) is a promising technology to enhance the thrust-to-weight ratio of aero-engines. Self-recirculating casing treatment (SRCT) is an efficient flow control technique for increasing stall margin in conventional compressors. With the purpose of investigating the applicability and mechanism of SRCT in the CRACs, a two-stage CRAC is selected to investigate the stability enhancement mechanism of SRCT and its effect on the unsteady flow near the rotor tip, and the effect of injector location on the stability improvement capacity of SRCT is also studied. Results show that about 7.73% stall margin improvement can be achieved by configuring the SRCT on the near rotor top, and the injector location also has a significant influence on the stability expansion potential of SRCT. The SRCT delays the stall occurrence by weakening the intensity of tip leakage flow (TLF) and restraining the leading-edge spillages of TLF. The SRCT reduces the unsteady interference between the adjacent rotors by receding the disturbance of the upstream wake and inhibiting the potential flow effect of the downstream. Furthermore, the SRCT reduces the self-excited oscillation frequency of TLF and damps its fluctuation amplitude.