Effect of specific heat ratio, impeller tip running clearance, and compressor insulation on high-pressure-ratio centrifugal compressor modeling

Results are displayed which show the effect of gas specific heat ratio, impeller tip running clearance, and compressor insulation on modeling of a high-pressure-ratio compressor's performance. The data were obtained using a low-speed-of-sound gas and a compressor previously tested extensively in air. Duplication of the air inlet specific heat ratio was found to be essential to modeling of the air-equivalent flow rate accurately. Stage pressure ratio and stage efficiency were found to be less sensitive to the accurate replication of the air specific heat ratio. For the compressor tested, stage isentropic efficiency increased as impeller-to-shroud tip running clearance was reduced from 15% to 5% of the impeller tip axial depth. The measured stage efficiency was found to depend strongly on the heat transfer between the compressor and surroundings.