Contra-rotating technology has been considered as an important approach to further improve the thrust-weight ratio of aircraft engine because of its structure and aerodynamic superiority. In the present work, the impact of tip clearance on the performance of a CRAC which consist of two counter-rotating rotors is investigated numerically. To detect the stall margin of CRAC exactly, the back pressure dichotomy method is developed, the grid indepence is verified and the performance is measured. A large number computation is carried out to explore the influence of tip clearance on the operating range of contra-rotating compressor. Finally the flow filed near the tip clearance is analyzed to find the relation between the tip clearance and the first stall rotor. The result shows: (1) Efficiency and pressure ratio decrease with the tip clearance size increased, but there is an optimal tip clearance size corresponding to a relative wide operating range. (2) The first stall stage of contra-rotating compressor varies with the tip clearance size increases. For the present CRAC, ROT2 is the first stall stage with the tip clearance size no greater than 0.5mm, while the ROT1 is the first stall stage if the tip clearance size greater than 0.5mm.

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