Demonstrating multistage compressor blockage calculations using pressure measurements for large tip clearances

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.