CFD investigation of a centrifugal compressor derived from pump technology for supercritical carbon dioxide as a working fluid

Due to the pressing needs to develop and improve compressors to be used in supercritical carbon dioxide Brayton (S-CO₂) cycle, a 3D numerical study has been carried out for the full S-CO₂ compressor geometry including diffuser and volute. The predictions were compared with measurements obtained from the recently constructed S-CO₂ compressor test facility called SCO₂PE (Supercritical CO₂ Pressurizing Experiment), based on existing liquid water technology. The objective of the experimental and numerical work is to obtain fundamental data for the design optimization of compressor and to measure the overall performance near the critical point and in the supercritical state. To simulate nonlinear behavior near the critical point of CO₂, the fluid properties were implemented, via property table, in the computational analysis code. Before embarking in the CFD approach evaluation, a number of parametric runs were conducted to examine the order of errors induced by the property table resolution and to achieve grid convergence. The steady-state numerical predictions using the k-ω SST model were found to return satisfactory results for liquid water and in the case of S-CO₂ operating condition, quite far from the critical point. However, as the compressor operating condition approaches more toward the critical point; deviation from the reference data start to become more apparent. In the more challenging case, the disagreement with experimental data might be partially due to the modeling limitations but is also attributed to the subcritical region observed in the contour plot of the static pressure.