Effects of increasing blade hub loading on instability evolution in a low-speed compressor

Based on previous results showing that a compressor stall can be initiated from hub region, a hypothesis is further proposed: The type of stall inceptions is related to the loading distributions. A series of experiments are designed to examine the effects of radial loading to the stall inception and its evolution. Well-designed distortion screens installed at the inlet of a single-stage low-speed axial compressor induce various radial distributions of blade loading. The uniform inflow situation, i.e. without screen, is defined as the baseline, in which case the compressor shows the modal type stall inception. With hub distortion screens, the hub loading is keeping to be increased, however, the compressor still shows modal type of stall inception. After further data processing, it is found that there is a period between linear growth of modal wave and the formation of a large amplitude stall cell. In that period, the tip pressure signal does not show any clear traveling disturbances. In further investigation, it is found that there are large disturbances formed in the hub region during this period. With increasing the hub loading, the large amplitude disturbances in hub region appear earlier and earlier. In our previous work, the compressor showed spike type stall inception with a tip distortion screen. Combining these observations, it is proposed that radial loading of the blade does have significant effects on both the type of stall inception and the evolution which is in particular corresponding to transient process from small linear disturbance to final formation of stall cell in our compressor.