Effects of axial gap on stall characteristics of contra-rotating compressor

A numerical investigation about the effects of axial gap on the aerodynamic performance at stall inception of a high-speed contra-rotating axial flow compressor is reported, and the causes of performance change near stall condition are analyzed. The computation is carried out under several operating conditions with five different axial gap sizes. Full Non Matching Frozen Rotor method is used in rotor/rotor interface to ensure the accuracy of numerical simulation even with small axial clearance. The study shows that: (1) With the decreasing of the axial clearance size, the performance shows a downward trend, while the stable operation range is expended. Compared with the design axial gap (40%C), the peak efficiency is reduced by 2.2%, while the operation range is expended by 59.5% with small axial gap(20%C).(2) It is the main reason for the aerodynamic performance change in the compressor that the inlet distortion of downstream rotor varies with different axial gaps. (3) The flow field structure near the hub in the downstream rotor is influenced by the inlet distortion, which leads to the decrease of efficiency and pressure ratio. However, the stable operation range is expended due to the inlet distortion effects on the flow field in the tip gap.