Centrifugal compressor stages are widely used in a variety of turbomachinery applications including power generation, turbochargers,refrigeration processes, oil and gas industry, and
aeronautics. For centrifugal compressors with high pressure ratio, an unshrouded impeller is generally used. It is wellknown that impeller performance deteriorates as the tip leakage
flow increases. The leakage occurs through the clearance between the impeller blade tip and the stationary casing surface. The performance of unshrouded impellers suffers from the pressure loss over the tip clearance and the formation of secondary flows.