| Compared with the existing power cycle,the supercritical C02 Brayton cycle has obvious advantages of small volume,high energy density and comparable efficiency at significantly low heat source temperature(550℃).It is a new kind of power cycle layout which is expected to be one powerful competitor of next generation cycle.However,research about SCO2 compressor-one of the core components of SCO2 Bryton cycle-is still in its initial stage,especially in numerical instability caused by CO2 property change and condensation and compressor performance improvement within design process.In this paper,the numerical method was verified and effects of CO2 property tables resolution were investigated.Design and numerical investigation of main compressor of a 5MWth supercritical CO2 Brayton cycle were completed.The effects of geometry factors such as tip clearance and back-sweep angles on the numerical results were studied.The main work of this paper is shown as follows:(1)Based on the NUMECA software platform,the numerical simulation method of supercritical CO2 compressor was verified.The main compressor in the compression experiment circuit built by Sandia laboratory was used as the research object.The NIST property library was selected to make CO2 property tables which contains properties of supercritical,liquid,gas and two-phase region.The reliability and accuracy of the numerical method are verified by comparing the experimental and numerical results of the design point and the non-design point.(2)Based on the Sandia geometric model,the influence of the resolution of CO2 properties tables on the numerical simulations was studied.The results show that the resolution of the table has a great influence on the numerical results,especially in areas where static parameters are below the critical point due to local acceleration of the flow.With low-resolution tables,condensation areas at suction side of main blade and regions near top of the blades can not be simulated accurately,while high-resolution tables requires much more computing resources and time consuming.The appropriate CO2 properties tables are selected to carry out follow-up work based on the results of the study ahead.(3)According to the parameters of a 5MWth supercritical CO2 Brayton cycle,the design of the main compressor,one-dimensional calculation and three-dimensional numerical simulation are completed.Both one-dimensional calculation and three-dimensional results are shown and meet the requirements.The mechanism of the form of condensation and the relationship between tip clearance and condensation areas were analyzed.The results show that with the existence of tip clearance,flow was mixed and more uniform,which would reduce the fluid temperature and pressure gradient.It was found that increasing back-sweep angle and supplemented by fine-tuning other geometric parameters like axial length within a certain range had positive impact on total pressure ratio and surge margin without decreasing efficiency and reduce the volume of condensation zone on the suction side. |
