Effects of circumferentially non-uniform clearance on the spanwise flow characteristics in a transonic compressor rotor

Abstract

The circumferentially non-uniform clearance has significant effect on the overall performance and operation safety of high loading compressor rotors. However, both the variation rules and mechanism of flow characteristic in the circumferential, radial and streamwise directions caused by the asymmetric clearance are not fully clarified, which restricts the performance degradation assessment and rubust design of high loading compressors. Therefore, different types of asymmetric tip clearance were designed in this paper to reveal the circumferential fluctuation laws and induced mechanism of key characteristic parameters in full-channel domains of compressor rotor with circumferentially non-uniform clearance. It is shown that the circumferentially non-uniform clearance has less effect on the total pressure ratio and efficiency of compressor rotor, while it causes an obvious deterioration of the stall margin. Furthermore, the circumferentially non-uniform clearance causes the circumferential fluctuations of performance parameters, and the fluctuation amplitude has been affected by the eccentricity ratio and operating condition of rotor directly. In addition, the leakage flow originated from a single channel may pass through about three adjacent channels in rotor with uniform clearance, while it covers almost seven adjacent channels in the rotor with circumferentially non-uniform clearance. In consequence, it is precisely the difference of strength variation of leakage flow in tip region caused by the circumferential distributions of tip clearance that produces an alternated variation of low-velocity zone in rotor prototype and a concentrated distribution of low-velocity zone in the range of 270° to 360° of rotor with non-uniform clearance. Due to the serious blockage appearing in this range, the rotating stall of transonic rotor with circumferentially non-uniform clearance has occurred in advance, even with a maximum drop of 35.94% in stall margin.