Numerical investigation and comparison on the stall improvement mechanism of centrifugal compressor with inducer casing and bleeding

To enhance the stall margin, the performance of a centrifugal compressor with inducer bleeding, inlet recirculation and circumferential grooves casing treatment respectively is numerically simulated by using CFD software. The difference of the performance between solid casing and stall improvement techniques casing compressor are compared. The mechanisms of improved stability of the applied techniques are investigated. The results indicate that the interaction of tip-leakage and the separation flow at the leading edge of the inducer suction side leads to the compressor stall. With inducer bleeding, the low energy fluid formed in the flow separation flows out of the main flow channel. With inlet recirculation, the fluid from the recirculation channel adds negative pre-swirl to the inlet flow, which reduces the inlet tip incidence and restrains the flow separation on the suction side. Circumferential grooves casing treatment reduces the reverse flow of the tip-leakage to the impeller inlet. All the applied techniques can decrease the flow blockage near the inducer tip and delay the occurrence of stall, but inducer bleeding and inlet recirculation are more effective.