Centrifugal Compressor, Fillets, Impeller, CFD
In most cases of aerodynamic design of centrifugal compressors, the effects of impeller blade fillets on performance are not considered in the process, but could be estimated later from some limited studies. As one of numerical investigations for the effects in centrifugal compressors, the Krain backswept impeller was modeled with and without blade fillets on the hub. A vaneless diffuser and impeller tip clearances were included in the steady state analysis using a commercial CFD code. Over the range of flows at design speed, the case with blade fillets showed a slight drop in the pressure ratio, the efficiency, the choke flow and the range of operation, relative to the case of clean blades. A more detailed look into three-dimensional flow structure inside the impeller shows that a small scraping vortex, developed in the case of clean blades at the corner of the hub pressure surface, disappears in the case with blade fillets due to a local flow acceleration produced by the fillet. As a result of balancing forces acting in the impeller passage, it was observed that the shroud passage vortex in the case with blade fillets grows toward the impeller exit with a higher vortex core than that in the case of clean blades, which means that there are more wake flows with blade fillets, leading to aerodynamic performance drops.