Stability Enhancement with Self-recirculating Injection in a Single-stage Axial Flow Compressor

Self-recirculating injection that was demonstrated to delay the occurrence of stall is experimentally studied in a single-stage axial flow compressor. It bleeds air from the downstream duct of the stator blade row and injects the air as a wall jet upstream of the rotor blade row. The bleed ports, injection ports and recirculating channels are circumferentially discrete and occupy only 38% of the circumference. The external injection and outlet bleed air are selected for comparison with the self-recirculating injection. Results show that the self-recirculating injection has an equivalent stabilizing ability compared to the external injection with the maximum injected mass flow under self-recirculating injection condition. It can improve the stall margin by 13.67% with no efficiency penalty compared with smooth casing; the re-circulated mass flow ratio near stall is accordingly generated by 0.48%. However, the outlet bleed air basically has no contribution on the stall margin improvement. It indicates that the upstream injection in the self-recirculating injection plays an important role in terms of stability-enhancement. The details of flow field are captured using a collection of high frequency pressure transducers on the casing with circumferential and chord-wise spatial resolution. The detailed comparative analysis of the characteristic flow in terms of endwall flow in the tip gap indicates that self-recirculating injection can postpone the occurrence of stalling in the proposed compressor through weakening the unsteadiness of tip leakage flow, delaying the forward movement of the interface between the tip leakage and main stream flow, and sharply declining the circumferentially propagatingspeed induced by tip leakage flow that triggers the spike-type stall inception. This study may be helpful to guide the design of self-recirculating injection in actual application.