Integrated Design of Axial Slot Casing Treatment and Blades in a Low-Speed Single Stage Axial Compressor

Casing treatment has been used to enhance the stability of axial-flow compressor by extending the stall margin; it also induces strong interaction with compressor blades, as demonstrated in the open literature. Revealing the mechanism of this interaction is a key to fully exploit the potential of the stability-enhancing capability of casing treatment without efficiency penalty. For this purpose, an integrated optimization design of rotor and axial slot casing treatment is implemented for a low-speed axial-flow compressor, and the stall margin is increased by 10.89% without penalty on the peak efficiency. Through detailed analysis, two important driving factors for the improvement of stall margin are illustrated: the suction effect that decreases the axial momentum of tip leakage flow, and the injection effect that increases the axial momentum of main flow. Meanwhile, it is found that the combination of forward-deflection axial slot casing treatment and forward-sweep rotor can maximize the enhancement of the momentum exchange, thereby adequately reducing the blockage region induced by tip leakage flow. More specially, the stator is then redesigned based on the matching mechanism between the stator and rotor with axial slot casing treatment in a stage. This redesign can considerably reduce entropy generation and flow separation in the passage and achieve an improvement of 0.87% in efficiency. The results hence demonstrate the superiority of integrated design of axial slot casing treatment and blades in improving both stall margin and efficiency.