Investigation of the casing groove location effect for a large tip clearance in a counter-rotating axial flow compressor

In the present work, the location effect of single grooved casing treatment (CT) on the compressor performance and flow stability are numerically studied at a large tip clearance in a two-stage counter-rotating axial flow compressor. The results show that the first stall stage is changed from the rear rotor (R2) to the front rotor (R1) as the tip clearance is increased from the normal design tip clearance (τ) to a large tip clearance of 2τ. The compressor stability can only be improved by the CT schemes in R1 without obvious change of compressor efficiency, while the compressor efficiency at near stall point can be increased remarkably for the effective CT configurations in R2 without stall margin improvement (SMI). The stall inception type may be changed for the least effective CT configuration in R1 due to the drastic change of flow structure of the tip leakage flow (TLF) released from near the blade leading edge. Detailed analysis of TLF structure shows that it is advisable to improve the compressor flow stability by controlling the TLF part which is released from the blade chord range away from the blade leading edge. After the application of effective CT schemes, the tip flow field is improved in the corresponding rotor and the interface is pushed further downwards to a different extent resulting in the reduction of the TLF intensity and loss generation.