Performance enhancement and flow separation control in an S-duct by air injection

With the purpose of investigating the effect mechanism of injection on flow separation of the S-duct, different single-hole schemes were investigated and compared with double-hole schemes. Results show that, the performance of S-duct can be improved by using injection. The optimal scheme in this study is a double-hole injection scheme with two holes located at the same axial position. Flow separation reduction and a 16.9% reduction of loss coefficient were achieved by injection with an injection coefficient of 0.46% in each hole. The flow mechanisms are that, firstly, high momentum fluid is injected to separated flow by air injection; secondary, high momentum flow is transported to flow near downside wall by injection vortex. The position effect, injection flow rate effect and hole shape effect were also discussed. For double-hole scheme, the scheme with two holes located different axial positions generates a stronger vortex by mixing two injection vortexes and enhances secondary flow. Though the flow separation is reduced, a severe nonuniform flow field at outlet is formed. Due to the less swirling flow achieved at outlet of S-duct by Double-y scheme, it can offer a more uniform flow field for downstream compressor and has a better control effectiveness.