Effect of axial slot casing treatment on a counter-rotating axial-flow compressor aerodynamic performance and stability

Counter-rotating axial-flow compressor (CRAC) technology is an important technical way to improve the thrust-to-weight ratio of aero-engines. To explore the stall margin improvement potential of axial slot casing treatment (ASCT) in the CRAC, a two-stage CRAC is selected to investigate the influence of axial position and radial deflection angle of slots on the stabilization capability of ASCT by numerical method. The paper also revealed the stability expansion mechanism of ASCT in the CRAC and the effect of casing treatment on the rotor/rotor interference effect between the front and rear rotors. Results show that the axial position of slots has little effect on stall margin improvement capacity of ASCT but has a great influence on peak efficiency. Increasing the radial deflection angle of slots to further improve the stabilization ability of ASCT is not remarkable, but it is beneficial to decline the efficiency penalty. The suppression of tip leakage flow by slots and the transport of low-energy fluid near the blade tip can delay the occurrence of the stall, and the maximum stall margin is improved by about 10.75%. Besides, the ASCT decreases the unsteady interference effect between the rotors and inhibits the potential flow effect of the downstream blade passage and improves the inlet flow field quality of the rear rotors.