Experimental investigation of instability inception on a transonic compressor under various radial distributions of loading

The radial distribution of blade loading could be various due to the inlet distortion, the change of rotor speed or mismatching between stages, which is a key factor affecting the flow stability. In this paper, the instability inceptions under the various radial distribution of loading are experimentally investigated on a transonic compressor. The research subject is chosen as a 1.5-stage transonic axial flow compressor in which three types of instability inceptions were previously detected, including spike-type inception initiated at the rotor tip under the low speed, partial surge initiated at the stator hub under the high speed, and hub instability when the slot casing treatment was mounted. In order to facilitate the conversion of the compressor instability inception, the rotating speed is selected (17,160 r/min in this study) at which the blade loading at both the stator hub and rotor tip reach the critical value near the rotating stall. Furthermore, the variation of radial distribution of loading is induced by the radial non-uniformity of total pressure. Meanwhile, the high-response dynamic test points are mounted to measure static pressures at rotor tips and total pressures at stator trailing edges during the experiments. To detect the system response, an additional high response sensor is installed on the plenum inner wall. As demonstrated by the WFT and filtering methods, the results indicate that the instability evolution varies gradually with the radial distribution of loading at the inlet. The partial surge instability converts into the spike with the increase of tip loading intensity. With the increase of hub loading intensity, the partial surge instability converts into the hub instability. For the hub instability, a special process is that a sudden decrease of total pressure occurs at the stator hub. Furthermore, the short-length scale disturbance occurs at the rotor tip, and leads to the final compressor stall.