THE INFLUENCE OF TIP CLEARANCE ON SUPERCRITICAL CO2 CENTRIFUGAL COMPRESSOR PERFORMANCE

The supercritical CO2 (SCO2) compressor is the key component of the SCO2 Brayton cycle. It is considered as one of the most promising power conversion systems, because the compressor could consume small compression work as operating condition near the critical point. In this paper, a researched SCO2 compressor was designed to operate with slightly above the vapor-liquid critical point of CO2. The flow characteristics were investigated by NUMECA FINE/Turbo, coupled with the thermophysical properties of CO2 in REFPROP database. Particular attention was paid on the blade tip clearance flow characteristics. The formation and development mechanism of the blade tip low pressure regions and the parameters distributional difference were studied. Then, the effects of different blade tip clearance types on the low pressure regions of the blade leading edge tip and the aerodynamic performance of SCO2 compressor stage were compared and discussed. The combined effects of the injecting action, the blade leading edge tip shedding vortex, and the flow acceleration can lead the fluid thermodynamic state to enter the low pressure and low temperature regions at the leading edge of both the main blade and splitter blade tip. Especially, the condensation maybe exist at sharp corner of the blade tip leading edge. However, the tip clearance leakage vortex can significantly inhibit and weaken the low pressure regions. With the increase of tip clearance, the distribution and development tendency of the static pressure and temperature on the main blade leading edge tip are similar, but there is a significant influence for the splitter blades tip. Furthermore, because the tip clearance increases, the SCO2 compressor stage pressure ratio and isentropic efficiency have degraded in whole operating range, but the stable operation range is expanded. Therefore, the above comprehensive factors should be considered during the design process in order to select the suitable tip clearance shape.