Effect of tip clearance variation in the transonic axial compressor of a miniature gas turbine at different Reynolds numbers

Abstract

Degradation in the service or manufacturing tolerances can cause tip clearance variation, which adversely affects the stability and performance of compressors. In particular, for a miniature gas turbine, the size of the tip clearance ratio (the ratio of tip clearance to the tip chord length) is relatively large, thus it is more likely to operate at low Reynolds number. This study, therefore, numerically investigated the effect of tip clearance variation on the aerodynamic performance of a 1.5-stage transonic compressor at high and low Reynolds numbers using a 3D Reynolds averaged Navier-Stokes (RANS) solver that incorporates the SST k-ω turbulence model coupled with the γ-θ transition model. The results show that the aerodynamic performance and the tip flow field structure of the compressor change significantly with varying tip clearance.At high Reynolds number, the performance curves are essentially negatively linear with tip clearance, but the slopes sharply increase at medium tip clearance (0.9% C, C represents the tip chord length). At low Reynolds number, the varying trends of the sensitive curves for large tip clearances (0.9% C–1.8% C) are basically the same as that at high Reynolds number. However, for small tip clearances (0.3% C–0.9% C), the aerodynamic performance parameters fluctuate, namely, there is a peak aerodynamic performance at low Reynolds number. When considering the performance and surge margin of the compressor comprehensively, the best tip clearance is 0.6% C at high Reynolds number, but 0.9% C at low Reynolds number.