It is a known fact that machined impellers result in improved compressor performance compared to cast impellers of the same design. The performance improvements can be attributed to better surface finish, more accurate geometric definition (tighter dimensional tolerances), well-defined edges, and the lack of blade tip fillet on shrouded impellers. In addition, it has been observed through experimental investigations that the construction method of the impellers has an impact on performance. This paper presents computational fluid dynamic investigations of two types of impellers, with blade surfaces generated using straightline elements (SLEs) and CAD arbitrary definitions. Because there are many different mathematical definitions that CAD tools employ for curves, the resulting arbitrary blade surface is not unique. The numerical results will help understand the causes of the performance differences as well as the effects of SLE blades on the flow through the impeller. Input conditions for computational dynamic simulations are based on experimental results. All references to experimental data in the present paper are for cast impellers. Therefore, the differences in performance are attributed to blade definition (SLE versus other) and not to differences resulting from manufacturing methods.

One of the major concerns of the centrifugal compressor designer is the trade-off between the compressor’s efficiency and its range. The compressors equipped with vaneless diffusers benefit from a broader operational range than conventional vaned diffusers, but with decreased compression efficiency. One solution found in recent years is the Low Solidity Diffuser, which displays a range greater than conventional vaned diffusers, by preventing rotating stall, and efficiency higher than vaneless diffusers. The study focuses on the impact of geometry elements on the flow field through the vanes’ passages, and on the change of performance with the location of the vanes relative to the scroll tongue. This paper presents results of experimental and Computational Fluid Dynamics (CFD) investigations — for centrifugal compressors with low solidity cascade diffusers. The vanes are based on a NACA airfoil profile and have been designed using commercial software from ConceptsNREC: Compal and AxCent. The analysis part was performed using CFX software from Ansys, Inc. The performance parameters recorded are pressure ratios, isentropic efficiency, flow angles and velocity field profiles.

It is a known fact that machined impellers result in improved compressor performance compared to cast impellers of the same design. The performance improvements can be attributed to better surface finish, more accurate geometric definition (tighter dimensional tolerances), well-defined edges, and the lack of blade tip fillet on shrouded impellers. In addition, it has been observed through experimental investigations that the construction method of the impellers has an impact on performance. This paper presents computational fluid dynamic investigations of two types of impellers, with blade surfaces generated using straightline elements (SLEs) and CAD arbitrary definitions. Because there are many different mathematical definitions that CAD tools employ for curves, the resulting arbitrary blade surface is not unique. The numerical results will help understand the causes of the performance differences as well as the effects of SLE blades on the flow through the impeller. Input conditions for computational dynamic simulations are based on experimental results. All references to experimental data in the present paper are for cast impellers. Therefore, the differences in performance are attributed to blade definition (SLE versus other) and not to differences resulting from manufacturing methods.