Research on effects of tip clearance on performance of a contra-rotating compressor

In order to further understand the effects of the tip clearance variation of different rotors on the performance of a contra-rotating axial compressor (CRAC), numerical simulations are carried out for a contra-rotating axial compressor to investigate the tip clearance sensitivities of different rotors and the performance variation of this compressor. The results show that both the compressor total pressure ratio and efficiency decrease with the increase of tip gap, and the sensitivity curve in rotor peak efficiency for both rotors is found to be approximately linear with an increase in tip clearance. Compared with rotor1, the variations of peak efficiency and stall margin are more sensitive than those of rotor2 with the increase of tip clearance. There exists an optimum tip gap combination for this CRAC, i.e. 1.0 τ for rotor1 and 0.5 τ for rotor 2 (τ represents the design tip clearance), and the peak efficiency and stall margin are improved by about 0.62% and 6.9%, respectively. The onset location of tip leakage vortex is shifted downstream when the tip gap increased. For one of the rotors in this CRAC, the tip flow is influenced by the tip gap variation of the other rotor, and rotor2 shows a more significant impact on rotor1.Additionally, the first rotating stall stage is also influenced by the tip clearance variation of both the rotors.