Demonstrating Multistage Compressor Blockage Calculations Using Pressure Measurements for Large Tip Clearances

Abstract

With future gas turbine designs seeking increased overall pressure ratios, blade heights in the rear stages of high-pressure compressors are expected to decrease. As this will lead to an increase of relative tip-clearance height, detailed knowledge of the associated rotor tip-leakage flows becomes increasingly important. In particular, the development of blockage due to large tip-leakage flows can be a key component leading to an understanding of stage matching for multistage machines. To assess blockage related to increased tip clearance, a series of measurements are presented here from a three-stage axial compressor at two loading conditions on the 100% corrected speed line. These data correspond to three tip-clearance configurations, up to 4% span. Three-component velocity measurements are used to validate a new blockage calculation technique based on measured steady and time-resolved pressures, and instrumentation techniques that are more robust and require fewer resources than multicomponent velocity tests. Ultimately, these simplified pressure-based blockage calculation techniques yield results that compare well with the velocity-based results, within 2% flow area or better.