Numerical Investigations on the Aerodynamic Performance of Supercritical Carbon Dioxide Centrifugal Compressor

Study on steady and unsteady aerodynamic performance of supercritical carbon dioxide (SCO2) has great significant on improving SCO2 centrifugal compressor performance. In this paper, the SCO2 centrifugal compressor volute has been designed under the assumption of equal density. The effects of the asymmetric volute structure on the upstream flow and flow characteristics in the volute are studied. The unsteady flow structures of pressure and radial velocity at the impeller-diffuser interface are captured. The results show that under the steady calculation the total-static isentropic efficiency of the SCO2 centrifugal compressor is 71.0%, and the total-static pressure ratio is 2.190 at the design condition; The uneven pressure distribution caused by the volute tongue will affect the pressure distribution at the diffuser outlet. While at the diffuser inlet, the periodic distribution of pressure is basically unaffected by the volute; Under the unsteady calculation, the time-average total-static isentropic efficiency is 71.7% and time-average total-static pressure ratio is 2.227 at the design condition; The different relative positions between the impeller blades and diffuser blades are the main causes for the unsteady flow structures of the impeller-diffuser interface. When the impeller blade and diffuser blade are at the same position, under the effects of the impeller blade wake and flow acceleration near the diffuser blade leading edge, the pressure is the lowest and the back flow at the impeller tip clearance is the most obvious; The overprediction of the blade tip clearance back flow causes the efficiency under the steady calculation lower than the time-average total-static efficiency under the unsteady calculation. This paper can provide reference for the aerodynamic performance analysis for SCO2 centrifugal compressor.