Quantifying blockage in a multistage compressor for different tip clearances using steady and unsteady pressure measurements

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, a 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 an 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 compressor at two loading conditions on the 100% corrected speedline. These data correspond to three tip clearance configurations, up to 4% span. Initially, three-component velocities measured using hot-wire anemometry are analyzed. Following these initial calculations, a blockage definition technique related to gradient identification is introduced, by which the tip leakage flow size downstream of the rotors is directly related to the blockage in the tip region of the compressor. Further, steady pressures are used to calculate an approximate blockage downstream of the stators. Ultimately, these simplified pressure-based blockage calculation techniques reveal results which compare well with the velocity-based results, within three percent or better.