FLUENT CFD Steady State Predictions of Single Stage Centrifugal Compressor with Supercritical CO2 Working Fluid

by T. A. Munroe1, M. A. Zaccaria1, W. H. Flaspohler1, R. J. Pelton2, K. D. Wygant2, & O. B. Dubitsky2
1Knolls Atomic Power Laboratory
2Concepts NREC

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This paper presents preliminary results of a study to assess, by means of Computational Fluid Dynamics (CFD) analyses, the steady state performance characteristics of a supercritical CO2 (S-CO2) single stage centrifugal compressor with a vaneless, unpinched diffuser. The real gas CO2 properties were generated by the NIST REFPROP database. The inlet flow conditions were kept constant at an inlet total temperature of 308.7 K and inlet total pressure of 9.2 MPa. The impeller was evaluated at an off-design speed of 10,400 rpm, while the pressure ratio of the impeller was allowed to vary between a pressure ratio corresponding to stall and a higher pressure ratio corresponding to the limit of the model. The FLUENT results were compared against meanline results generated by Concepts NREC. The Fluent results showed a higher rate of change than the meanline results probably as a consequence of the steep change in properties near the critical point. Because of the potential for subcritical operation, the range of operation for the compressor predicted by FLUENT is less than that predicted by the meanline code. At the lowest pressure ratio, a maximum difference of 5% exists between the CFD and meanline predictions. Future experiments will be needed to verify the meanline and CFD predictions.