Numerical investigation of injector numbers on stability of an axial compressor with discrete tip injection

The effects of injector number on the aerodynamic performance of a transonic axial compressor with discrete tip injection were numerically studied using six-blade-passages three-dimensional unsteady simulations. The study on injector number was implemented at two levels of circumferential coverage percentage (CCP) of tip injection. This research focus on the mechanisms of injector number's influence on the stall margin and flow parameters' radial re-distributions. The results show that the interaction effect exits between the CCP and injector number, while they affect the stall range. When the CCP is 54%, the stall margin improvement is not affected by injector number. When the CCP is 27%, the stall margin improvement decreases from 3.5% to 2.5% as the injector number increases from 6 to 18. The effective depression on the tip blockage of tip injection, which should be guaranteed by a persistent interaction between the injected flow and tip reversed flow for each injector, is the main reason for the enhancement of compressor stability. The duration of the interaction for each injector is reduced by the increased number of injectors, leading to a less effective depression on the tip blockage. The discrete distributions of injectors make the flow at the outlet of the rotor tip region totally unsteady. The unsteady influence can be dampened by increasing the number of the injectors. To decide the best number, the effects of the tip injection on the stall margin and non-uniform flow should be considered.