Experimental Study of Blade Hub Loading Effects on Instability Evolution in a Low-Speed Compressor

Based on the previous results of a single-stage low-speed axial compressor showing that a stall inception can be changed from modal wave to spike with the blade tip loading increasing, a hypothesis is further proposed that the type of stall inceptions is related to the radial loading distributions. A series of experiments are designed to examine the effects of hub loading to the stall inception and its evolution. Well-designed hub distortion screen installed at the inlet of the compressor induces various radial distributions of blade loading for compressor operating. The uniform inflow situation, i.e. without screen, shows the modal type stall inception of the compressor's final instability. With hub distortion screen, the hub loading is keeping to be increased, however, the compressor still shows modal type of stall inception. After detailed examining the data, it is found that the period between linear growth of modal wave and the formation of a large amplitude stall cell is growing longer. In that transition period, the tip pressure signal does not show any complete traveling disturbances in circumferential direction. Meanwhile, there are large disturbances formed in the hub region during this period. With further increasing the hub loading, the large amplitude disturbances in hub region appear stronger and stronger. It makes flow unstable in hub region and intensifies the flow mixing in radial direction and further lengthens the transition period between stall inception and final instability. At the same time, there are three main findings: (1)With hub loading increasing, the compressor instability evolution will be changed and the transition period between stall inception and final instability is prolonged. (2)The pressure fluctuations in the hub region become stronger as hub loading changing. (3)The radial load distributions do have significant effects on the compressor instability evolution.