Attenuation of leakage flow using axially nonuniform tip clearance in high loading transonic compressor rotor

Abstract

Several linearly nonuniform clearances have been designed to explore a novel strategy for attenuation of leakage flow in tip region of high loading transonic rotor and the effects of axially nonuniform clearance on detailed tip flow structure and stable operating range of rotor have been discussed as well. The results showed that the tip flow characteristic of rotor is affected mainly by the combined effects of two parts of low-velocity flow, which are produced by interaction of leakage flow with passage shock and boundary layer separation near suction side, respectively. However, the stall margin of rotor and isentropic efficiency near tip region is dominated significantly by the former part, and the local changes of size and shape of tip clearance have a large influence on it. Once the strength of leakage flow decreases due to clearance size variation, the boundary layer separation near suction side of blade tip worsens gradually and increases additional aerodynamic losses in passage. Both the mass flow rate and mixing losses of the tip leakage flow can be reduced due to a smaller size of clearance existing in front part of clearance of rotor with a linearly divergent clearance shape, and the area of low-velocity region near pressure side has reduced accordingly. By contrast, a linearly convergent shape of tip clearance can increase both the area of low-velocity region and the mixing loss of leakage flow as a result of a larger size of clearance existing over the front part of blade tip of rotor. Eventually, a divergent shape of tip clearance with a reasonable minimum size near leading edge of blade tip is preferred for transonic rotor in consideration of the benefit in stall margin improvement with nearly no penalty in efficiency.