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An effective approach in suppressing stall is mass injection upstream of the tip of an axial flow compressor. Developing reliable injection systems for high pressure ratio compressors requires an understanding of the effects of injection parameters, for example, injection angle, on the compressor stability and performance. This paper reports on a numerical investigation of injection angle on the operability of a high-speed compressor rotor. The injection port is set to be choked for all of the injection cases. Simulations indicate that injection angle has a significant impact on stability improvement. Maximum range extension is obtained when an injection yaw angle equal to 30 deg is applied. At this injection angle, the stalling mass flow coefficient was reduced by 17.4% by using an injected mass flow equivalent to 1.55% of the baseline annulus flow. Results also indicate that the best injection case creates an incidence angle of about 0 deg over the tip of the blade and adds the highest momentum in the relative frame of reference.Nomenclature A = area a = annulus adb = adiabatic amb = ambient DF = diffusion factor in = blade inlet j = jet out = blade outlet P 0 = total pressure rel = relative frame of reference T 0 = total temperature t = tip U, V = velocity x = axial component y = nondimensional wall distance = efficiency = tangential component = momentum = density = solidity = flow coefficient

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The current paper presents numerical simulations for a high-speed axial-flow compressor rotor, NASA Rotor-67, with continuous air injection upstream of the rotor. A parametric study relating injection velocity to compressor stability is undertaken. The effects of injector exit velocity on blade loading and flow field are investigated and discussed. Results indicate that the injection velocity has major effects on compressor stability. The injector effectiveness is found to be maximized when the injector exit Mach number is equivalent to unity. Significant range extension in terms of reduction in stalling flow coefficient equivalent to 13.23 per cent is obtained for the case of choked injector, whereas the injection mass flow is only a small percentage of the main flowrate.

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