The effect of TIP clearance on the first rotating stall stage in contra-rotating compressor

Numerical simulations are carried out to investigate the effect of tip clearance variation on the performance and first stall stage phenomenon. The results show that: the efficiency reduction with an increase in tip clearance is found to be approximately linear for both R1 and R2, and both the efficiency and stall margin change of the CRAC are more sensitive to the tip clearance variation in R2.At peak efficiency condition, the tip gap variation in R1 has significant impact on the tip leakage vortex onset point, trajectory and the location of interface between the incoming main flow and tip leakage flow in R1.However, the tip clearance variation in R2 has remarkable effect on those in both rotors. At near stall condition, the tip clearance variation in the two rotors has significant influence on the first rotating stall stage(FSS) phenomenon in CRAC, and the value of normalized tip blockage at leading edge can be used as a criterion to identify the FSS in CRAC.