Abstract: Tip air injection is a stability enhancement approach known to be effective in suppressing stall in axial compressor. Experiments were performed in a low speed axial compressor by using tip air injection, the injected momentum /free stream momentum is chosen as a measurement index, two critical injected momentum ratio is existed with the change of stall margin improvement(SMI), and the three stage of injected momentum below and above the two critical injected momentum is defined as micro injection, large injection and overlarge injection respectively. Then the inlet, outlet aerodynamic parameters and dynamic pressure on the casing wall are measured to analyze the stability enhancement mechanism under different injected momentum ratio. Experimental results demonstrate that micro injection can only to weaken the tip leakage vortex(TLV) and unsteadiness of tip leakage flow(UTLF) to enhance the stall margin; large injection can both decrease inlet flow angle-of-attack to delay the separation of suction surface and suppress the TLV, delay the generation of UTLF; overlarge injection can delay the generation of UTLF, but the effect area of tip air injection is shifted to the blade passage, and influencing the aerodynamic load seriously.

Key words: axial compressor, inlet flow angle-of-attack, power spectrum density(PSD), root of mean squares(RMS), unsteadiness of tip leakage flow