ROLE OF THE INDUCER IN FLOW INSTABILITY OF A HIGH-SPEED CENTRIFUGAL COMPRESSOR IMPELLER

The performance of a high-speed centrifugal compressor has been numerically studied in this paper. The flow instability of the centrifugal compressor impeller, in the inlet blade tip Mach number range of 0.57 to 0.92, is reviewed from the different perspectives of the inducer and centrifuge. The results show that the roles of the inducer and the centrifuge in the evolution of impeller flow instability are fickle. At the large mass flow rate far away from the onset of impeller flow instability, the inducer has been unstable, and the flow field analysis indicates that the leading-edge flow spillage can be used as the criterion for the onset of inducer flow instability. As the mass flow decreases further, the flow stability of the inducer worsens first and then becomes neutral. However, the flow stability of the centrifuge worsens continually and finally results in impeller flow instability. The back flow relates closely to the flow instability of the inducer and the centrifuge, and the detailed blade-to-blade flow field and the back flow loss are investigated. The results imply that the design of a new device to control the back flow in the centrifuge may obtain a wider stable flow range than the traditional recirculation casing treatment on the inducer casing.