DESIGN AND AERODYNAMIC PERFORMANCE INVESTIGATIONS OF CENTRIFUGAL COMPRESSOR FOR 150KW CLASS SUPERCRITICAL CARBON DIOXIDE SIMPLE BRAYTON CYCLE

摘要

The centrifugal compressor is the key component to improve the SCO_2 cycle efficiency. In this paper, according to 150kW class supercritical carbon dioxide (SCO_2) simple Brayton cycle. a centrifugal compressor with rotating speed 60000r/min is designed. For the small-scale SCO_2 centrifugal compressor, the impeller tip clearance loss accounts for most of the aerodynamic loss. Therefore, the designed compressor performance is numerically studied by the three-dimensional Reynolds-Averaged Navier-Stokes (RANS) and k-e (Extended Wall Function) turbulence model. The large variations in physical properties for SCO2 near the critical make simulation be difficult to convergence. To keep the numerical stability and accuracy, 400×400 resolution physical properties tables are adopted by the physical properties tables verification. The designed SCO_2 centrifugal compressor is with the isentropic efficiency of 73.2% and the pressure ratio of 2.207 under the design flow condition, and good off-design conditions performance are obtained. Compared to the flow condition without the impeller tip clearance, the isentropic efficiency of designed compressor decreases by 14%. For the impeller tip clearance leakage flow, the flow can be divided into three regions, the separation flow region which is along the mainstream flow direction, the back flow region which occupies the top of the impeller tip clearance and the downstream flow region which occupies the bottom of the impeller tip clearance. These flow phenomena and their causes are analyzed. The obtained results reveal that the designed centrifugal compressor meets the requirement of the aerodynamic performance for the 150kW class simple Brayton cycle. The detailed flow pattern of the designed SCO_2 centrifugal compressor with consideration of the impeller tip leakage flow is also illustrated.