Coupling stability-enhancing mechanism with compact self-recirculating injection in an axial flow compressor

Compact self-recirculating injection that bleeds air from the casing downstream of a rotor blade row and injects the air as a wall jet upstream of the same rotor blade row is experimentally studied after the elaborated design of its structure. The bleed ports, injection ports, and recirculating channels are circumferentially discrete and occupy only 38% of the circumference. Separate tip air injection and outlet bleed air are simultaneously selected for comparison with the self-recirculating injection. Results show that the compact self-recirculating injection can improve the most stall margin by 6.12% among all the three cases on the premise of no efficiency penalty and can also enhance the efficiency (maximum of 1%) for only 0.47% of the total injected momentum ratio recirculated near stall. The details of the flow field are obtained using a multihole probe, a time-resolved Kiel probe, and pressure transducers. The detailed comparative analysis of the characteristic flow in terms of tip leakage flow, blade load, rotor wake feature, and blockage indicates that the self-recirculating injection can postpone the occurrence of stalling in the proposed compressor through a coupling influencing mechanism. One mechanism is to weaken the self-induced unsteadiness of tip leakage flow and to delay the forward movement of the interface between the tip leakage flow and the main flow. The other mechanism is to unload the blade tip and to recover the rotor wake. All these responses can lead to improved stall margin in the self-recirculating injection. This study may be helpful to guide the design of self-recirculating injection in actual application.