Momentum Transportation Analysis in Axial-slot Casing Treatment for Axial Compressors

In this paper, momentum transport analysis was proposed to investigate the effects of axial-slot casing treatment. The numerical simulation was performed on a transonic single rotor with and without casing treatment. The distribution of momentum in the tip region and slot opening was obtained. The result shows that casing treatments suppress the tip leakage flow and improve the axial momentum distribution near the tip. The decomposed momentum distribution demonstrates the flow interaction between casing treatment and tip region. The flow pumped into casing treatment is always with reverse axial momentum and the flow injected from casing treatment is always in positive axial momentum for these semi-circular slots. Furthermore, the influence of casing treatment axial position is also investigated by the analysis of momentum transportation. The numerical simulations were conducted in another two configurations with different axial positions. The results indicate that the axial momentum is not the only parameter that influences the stall margin. The strength of interaction between casing treatment and tip region should be neither too violent nor too weak. There might be an optimal momentum distribution that the demarcation point is just at the leading edge in axial momentum distribution.