Aerodynamic design considerations for supercritical CO2 centrifugal compressor with real-gas effects

The optimal supercritical carbon dioxide (SCO2) Brayton cycle requires the SCO2 compressor to operate near the critical point, where strong real-gas effects make the aerodynamic design much more challenging. Conventional semi-empirical aerodynamic design guidelines developed for air compressors are no longer applicable because CO2 flows undergo significant changes in thermophysical properties when inlet conditions of the SCO2 compressor change, when different design parameters are chosen, and when the phase change occurs. This paper proposed a set of new design guidelines for SCO2 compressors from zero-dimensional (0D), one-dimensional (1D), and three-dimensional (3D) perspectives. At 0D level, the concept of similitude is introduced to derive new performance correlations independent of inlet conditions. At 1D level, the coupling effect of thermophysical properties and design parameters is considered and new guidelines for preliminary design are proposed. At 3D level, detailed blade modeling procedures are discussed in order to improve compressor performance and suppress phase changes. All these design considerations are validated by redesigning and comparing several well-designed SCO2 compressors from open literature. The results show that for the compressor operating near the pseudo-critical line, an efficiency increment of about 0.7% can be obtained by adopting the proposed design considerations, while phase change can also be well suppressed at the same time.