Impact of the ending position of controllable speed casing on the flow stability in a transonic compressor rotor

The structure of casing treatment has a significant influence on the stability expansion effect. The ending position of the rotatable ring is one of the important structural parameters in the controllable speed casing. The impact of ending position of the rotatable ring rotating at the same speed as the rotor on the stability expansion and stability expansion mechanism was studied in this paper. The results show that, when the ending position of rotatable ring expands downstream in the range of 20% to 60% axial chord length, because of the improvement in the tip leakage vortex trajectory and main flow/leakage flow interface, the stability expansion effect rises gradually. The further downstream expansion of ending position from 60% axial chord length, however, has a slight impact on tip flow, bringing out a steady stability expansion effect around 52.5%. The best stability expansion effect of ending position occurs at 60% axial chord length where the stable operating margin increases by 53.5%.