Effect of different bleed slot positions and negative pre-swirl vanes on the performance of centrifugal compressor with recirculation casing treatment

The continuous advancement of aircraft engines requires centrifugal compressors with wider stability margins. This study investigates a centrifugal compressor with a total pressure ratio of 4.8, employed in a turboshaft engine. The static pressure characteristics indicate that the impeller is the primary source of instability within the compressor stage. To improve stability, various circulation casing treatments were applied, incorporating three distinct bleed slot positions and several configurations of negative pre-swirl vanes. By comparing the smooth-wall compressor with the numerical simulations of three circulation casing treatments featuring different bleed slot positions, it was found that the circulation casing treatment reduces the incident angle of the mainstream flow, thereby diminishing blade loading and mitigating the tip leakage vortex and passage vortex at the inducer. The most effective stabilization occurs when the treatment suppresses the interaction between the tip leakage vortex, passage vortex, and the shock wave, resulting in a 3.5%–6.6% increase in the map width. Optimal negative pre-swirl angles further improve the stable operating range while minimizing losses associated with the circulation casing treatment. The maximum map width increased by 7.6%, and the peak compression ratio was reduced by 0.8%.