Performance Improvement of a Highly Loaded Transonic Centrifugal Compressor with Tandem Impeller and Freeform Blade Configuration

A highly loaded transonic centrifugal compressor is aerodynamically designed and numerically investigated. The objectives are to improve the compressor efficiency by using tandem impeller configuration and 3D free-formed blade design concepts. This approach has the potential to control both the transonic and distorted flows within impeller passages. The results suggest that employing the tandem impeller configuration can significantly improve the compressor efficiency by 1.4%. The efficiency gain is mainly contributed by the improved uniformity of the impeller discharge flow achieved when the newly generated inducer-shed vortices rearrange the secondary flow pattern. In addition, the location of the impeller passage shock moves downstream due to the potential effect within the tandem impeller and locally changes the back pressure of the inducer. These factors mitigate flow losses in the impeller and diffuser. Furthermore, the 3D design concepts of forward blade sweep and negative lean are employed in the tandem impeller configuration. The forward sweep design of the inducer weakens flow acceleration before the passage shock, and the negative lean design optimizes the secondary flow pattern, which yield an additional compressor efficiency improvement of 0.7%. The study conducted in this paper provides a valuable reference for future advanced transonic centrifugal compressor designs.