Effect of differential tip clearance on the performance and noise of an axial compressor

Rotor tip clearance (TC) shows significant effects on the stability and performance of aero-engine compressors. TC is also related to the producing of noise and tip leakage flow which is an indicator of critical operating conditions for rotating stall or surge. In this paper, the effect of TC on stall evolution process under different TC values is studied on a single-stage compressor with low speed and high load, and a frequency-domain interferometer diastimeter for high-resolution measurements is applied to accurately measure the TC value. In the present study, a soft-wall casing made of grindable material is applied to achieve the “zero clearance” condition, and casings with different diameters are adopted to reach different clearance values. Experimental results show that pressure rise and efficiency are improved with a small TC. With the TC varying from zero to a certain large scale, experimental results have proved that there is an optimal TC with the presence of maximum flow margin. In addition, eighty measurement points are evenly distributed around the casing circumferentially at the leading edge of the blade to analyze the circumferential flow characteristics of the tip flow field. And twenty wall-flush mounted microphones are evenly distributed circumferentially to monitor the induct sound field of the compressor, and the experimental results show that the sound pressure level (SPL) of the compressor is lowest at a relatively small TC rather than zero. The influence of different TC values on compressor is discussed based on the analysis of the pressure fields, stall process, and the acoustic signal. Furthermore, a detailed discussion of rotating instability (RI) brought about by large clearances is provided.