Influence of Real Gas Properties on Aerodynamic Losses in a Supercritical CO2 Centrifugal Compressor

Supercritical carbon dioxide (SCO2) centrifugal compressor is a key component of a closed Brayton cycle system based on SCO2. A comprehensive understanding of the loss mechanism within the compressor is vital for its optimized design. However, the physical properties of SCO2 are highly nonlinear near the critical point, and the internal flow of the compressor is closely related to its properties, which inevitably influences the generation of aerodynamic losses within the compressor. This paper presents a comprehensive investigation of the compressor's loss mechanism with an experimentally validated numerical method. The real gas model of CO(2)embodied in the Reynolds-Averaged Navier-Stokes (RANS) model was used for the study. Firstly, the numerical simulation method was validated against the experimental results of Sandia SCO2 compressor. Secondly, performance and loss distribution of the compressor were compared among three fluids including SCO2, ideal CO2 (ICO2) and ideal air (IAir). The results showed that the performance of SCO2 was comparable to IAir under low flow coefficient, however markedly inferior to the other two fluids at near choke condition. Loss distribution among the three fluids was distinctive. In the impeller, SCO2 was the most inefficient, followed by ICO2 and IAir. The discrepancies were magnified as the flow coefficient increased. This is due to a stronger Blade-to-Blade pressure gradient that intensifies boundary layer accumulation on walls of the shroud/hub. Furthermore, owing to the reduced sonic speed of SCO2, a shock wave appears earlier at the throat region and SCO2 encounters more intense boundary layer separation.