Mechanism of unsteady influence of tip injection on a high-loaded axial compressor performance

Mechanism investigation on the unsteady influence of tip injection on a high-loaded compressor aerodynamic performance and stability margin was presented with the method of six-blade-passages three-dimensional unsteady numerical simulation in a transonic compressor. Quantitative analysis was made on the change of inner flow fields at different operating conditions with the application of two distinct injectors. The results show that tip injection is able to improve compressor total pressure ratio and stability, but it has little impact on compressor efficiency. The degree of the influence on compressor performance is determined by injected mass flow. Tip injection induces asynchronously periodic fluctuation of mass flow at compressor inlet and outlet of tip region. Blade tip loading will not be unloaded until the injected flow arrives at blade trailing edge, and blade tip loading varies periodically accordingly. The stability gain of 3.3% and 3.6%, respectively, is achieved by circumferential coverage percentage of 27.3% and 54.6%, respectively, with the identical injector throat height. It is proved that the effect on stability improvement of tip injection depends on the impact that tip injection makes at blade passage outlet by depressing tip blockage. The delay of injected flow in blade passage makes the blockage depression duration at passage outlet longer than that at passage inlet, so a small width injector is sufficient to depress tip blockage effectively and extending injector width contributes little to stability improvement.