Tip clearance effects on multistage axial compressor performance and flow structure for small core application

Abstract

This thesis describes the effect of increasing multistage axial compressor rotor blade tip clearance on embedded stage performance and flow structure for clearance-to-span ratios ranging from 1.4% to 5.6% using steady and unsteady three-dimensional viscous flow multistage computations. Embedded stage efficiency displays decreased sensitivity as rotor tip clearance increases with two flow regimes. For clearance-to-span ratios less than 3.6%, a nearly linear decrease in stage efficiency of 1.6 points per 1% increase in clearance-to-span is identified, in agreement with published literature. For clearance-to-span ratios greater than 3.6%, the computed stage efficiency decreases at a rate of 0.5 points per 1% increase in clearance-to-span. A parameter is developed that correlates with rotor tip section loss generation over a range of rotor tip clearance-to-span ratios and flow coefficients. The blade row relative streamwise tip section blockage increases in both rotor and stator passages and follows trends in rotor and stator tip section loss generation with rotor tip clearance. The tip section velocity deficit into the stator increases with tip clearance resulting in stator suction side corner flow separation, creating a challenge to design a high efficiency stage with larger tip clearance.