Influence of Endwall Air Injection with Discrete Holes on Corner Separation of a Compressor Cascade

The aim of this study is to reveal the influence mechanism of endwall air injection with distributed holes on the corner separation of a highly loaded compressor cascade,so as to promote the application of injection in aero-engines.Single-hole and double-hole endwall injection schemes featuring different axial locations,pitchwise locations,injection mass rates and injection directions,were designed and investigated.Results showed that the corner separation was eliminated by endwall injection;the optimal single-hole injection scheme achieved an endwall loss coefficient reduction of 29.7%,with injection coefficient as low as 0.48%.The optimal axial location of single-hole endwall injection was at 82%axial chord,being the center of corner separation.However,as injection hole was located at upstream of it,endwall injection resulted in severer corner separation.The mid-span flow field was deteriorated after endwall injection,which was due to 3D flow effects,i.e.,AVDR(axial velocity density ratio)effect and low-momentum fluid spanwise migration effect.The optimal injection was achieved at low injection angle and from close to the suction surface on pitchwise.Double-hole injection exhibited inferior performance compared with single-hole,which was due to the interaction of the two injection streams and mixing of injection streams with the bulk stream.