Operating range enhancement by tip leakage vortex breakdown control of a centrifugal compressor

Centrifugal compressor applied to turbochargers is required to operate stably in wide range from choking to surging. In our past research, it was suggested that impellers which induced tip leakage vortex breakdown at relatively high flow rate might stabilize internal flow by generating circumferential uniform blockage region near blade tip at low flow rate. In this study, authors investigated whether modifying a given impeller to induce the tip leakage vortex breakdown could reduce the surging flow rate or not. Pressure measurement of the conventional impeller showed that unstable pressure fluctuation occurred at smaller flow rate side than the peak pressure point. Furthermore, it was clarified by unsteady numerical calculation that the rotating stall occurred with circumferentially non-uniform reverse flow. On the other hand, in the new impeller increasing its inducer loading, unsteady numerical calculation showed that the blade tip leakage flow was strengthened and generated a circumferentially uniform blockage region, which could stabilize its internal flow. As a result of performance test of the new impeller, considering that the surging flow rate at the same shaft speed was reduced by 3% and the pressure ratio at the surging point had been improved from 2.8 to 2.9, the surging flow rate at the pressure ratio of 2.8 could be reduced by 8%. In this way, it was found that the tip leakage flow was dominant with the stall phenomenon of the centrifugal compressor, and it was also confirmed that the tip leakage vortex control was one of the effective means for the operation range enhancement.