Experiments on stall initial disturbance characteristics of contra-rotating compressor with distorted inflow

A high frequency dynamic pressure sensor array arranged at the tip of the frontand rear rotors is utilized to capture the stall initial disturbance characteristics of a low-speed axial contra-rotating compressor with different speed configurationsand distortion conditions. The results obtained by analyzing the pressure waves collected at stall conditions show that the stall type at the design speed is rotating stall when the inlet flow is uniform, and the stall propagation direction is consistent with the rotation direction of the rear rotor. The maturely developed stall is fixed at a circumferential positionand does not rotate circumferentially when the speed ratio is 1.40. With further increase of speed difference in the frontand rear rotors, the type of stall disturbance changes again to rotating stall at the speed ratio of 1.52, and the stall disturbance propagates in the same direction as the front rotor rotation due to the reduced suction effect of the rear rotor on the front rotor wake. The stall disturbance characteristics at different speed ratios are all consistent with a uniform inlet when the compressor incoming flow is changed to be circumferential inlet distortion. However, the distortion will cause different amplitude fluctuations in the pre-stall pressure sequence at different circumferential positions. The Empirical Mode Decomposition-Local Mean Decomposition (EMD-LMD) method is employed to capture the small pre-stall perturbations that gradually accumulate energy over time.