Parametric study of tip injection in a high-loaded axial compressor based on design of experiment

Parametric study of discrete tip injection on stall margin in a transonic compressor was presented with the method of three-dimensional unsteady numerical simulation. Combined with design of experiment and statistic analysis, the law of tip injection on stall margin was achieved and the mechanism of tip injection on enlargement of stall margin was also analyzed. The results show that tip injection is able to improve compressor performance and stability. Tip annulus wall boundary layer is encouraged by tip injection and tip leakage vortex blockage is depressed, which is the main reason of stability improvement. At the same time, tip injection can change the class of tip stall mechanisms in transonic compressor. The law of tip injection on stall margin varies with injection mass flow and there exists interaction between injection mass flow and throat height and between injection mass flow and injection angle. When injection mass flow is relatively less, throat height should be reduced and streamline is supposed to be aligned with rotor blade camber line at the leading edge in the rotating frame of reference. However, throat height should be increased to avoid blade tip stall and positive pre-whirl is suggested to reduce attack angle when injection mass flow is more. A certain distance between nozzle and blade tip leading edge should be kept.