Experimental Study on Hub Stall Instability Evolution in a Transonic Compressor with Arc-Shaped Slot Casing Treatment

Focusing on the hub-initiated stall inception partial surge in a transonic axial compressor, experimental investigations are carried out with a special designed arc-shaped slot casing treatment. With the comparison between solid casing and arc-shaped slot casing treatment, both the compressor performance and the instability evolution are analyzed. The stall margin is successfully enhanced by 19.88% with the specifically designed casing treatment, while the total pressure ratio only drops by 0.3% and the adiabatic efficiency does not quite change, which is compared with the original solid wall case. At the same time, there are two main findings: (1)With the solid casing, the compressor stalls with low-frequency partial surge and high-frequency stall cells. But the results of instability evolution with casing treatment present that partial surge still occurs at nearly the same mass flow rate as the stall point of the solid wall case, while the compressor is still on stable operation. It presents that the occurrence of partial surge is related to the hub region rather than the rotor tip region. (2) The formation of rotating stall cells in the rotor tip region is delayed by the casing treatment improving the tip flow situation, which can explain why the stall margin of this compressor is enhanced. Meanwhile, the formation of the high-frequency tip-initiated rotating stall cells induced by partial surge is necessary for substantial drop of the compressor performance in the hub stall evolution.