Impeller-Diffuser Interaction in Centrifugal Compressors: Numerical Analysis of the "Radiver" Test Case

In the present work, a numerical analysis of the Radiver test case was carried out using computational fluid dynamics techniques. Radiver is a centrifugal compressor stage for which a large amount of experimental data are available for ten diffuser configurations. Two diffuser geometries, differing in the radial gap between impeller exit and diffuser inlet, were compared to investigate the impact of impeller–diffuser interaction on the stage performance and the flowfield. Both steady and unsteady computations were carried out with the aim of separating unsteady effects from steady ones. As a result, flow unsteadiness turned out to have a positive impact on the sole lower radial gap configuration, especially in terms of the flow structure, in agreement with experimental indications. Moreover, physical mechanisms responsible for this behavior were identified and discussed.