Experimental and Numerical Analysis of the Flow Field in the Impeller of a Centrifugal Compressor Stage at Design Point Available to Purchase

The design of high efficiency modern centrifugal compressor stages with a wide operating range is challenging and demanding. To achieving the best design, numerical tools and test equipments for performance prediction and validation need to be at the state-of-the-art. Test data are also necessary to validate and continuously improve the numerical techniques used for performance prediction during the design phase. This paper presents the experimental and computational analysis of the flow field in a modern high flow, high Mach centrifugal compressor stage at the design point. Phase-resolved flow measurements for total pressure, static pressure and flow angle were carried out at the exit section of the centrifugal impeller. The measurements were performed using a Fast Response Aerodynamic Pressure Probe (FRAPP), traversed from the impeller hub up to the shroud; the key experimental results are presented as two-dimensional distributions as well as hub-to-shroud profiles. A CFD analysis was also carried out using an in-house CFD code to compare the results of the computational models with the FRAPP. In particular two different approaches, which combined accuracy and reasonable computational time, were used for the CFD computations: one is the standard methodology with only the flow-path modeled; the second also includes modeling of the leakage cavities. In fact the correct prediction of the flow profiles at the impeller exit and downstream, at the diffuser exit, is fundamental for the accurate design of the non-rotating downstream parts. Historically, the standard CFD approach has been found to be weak in capturing these profiles, especially close to the hub wall. Instead the CFD model including cavities was able to match to within a good approximation the profiles from the FRAPP probe.