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.