Parametric Design Optimization And Performance Analysis Of Supercritical Carbon Dioxide Axial Flow Turbines

The Brayton cycle system with supercritical carbon dioxide（S-CO₂）as the working fluid has attracted more and more attention and development around the world due to its compact structure,good environmental protection and high efficiency.As the main power generation component in the Brayton cycle system,axial flow turbine plays a vital role in the whole cycle system.Therefore,it is of great significance to conduct in-depth research on supercritical carbon dioxide axial flow turbine.In this paper,one-dimensional aerodynamic analysis,one-dimensional optimization design,off design performance analysis and different clearances of supercritical carbon dioxide axial flow turbines are studied.The one-dimensional aerodynamic analysis of the axial flow turbine was carried out,and the one-dimensional optimization design program of the S-CO₂ axial flow turbine was independently developed,and the optimization design of the S-CO₂ axial flow turbine was completed.In the program,the maximum total static efficiency is taken as the optimization objective,six important parameters are selected as optimization variables,and the optimization algorithm is combined to optimize the axial flow turbine design.Based on the results of one-dimensional optimization design,a three-dimensional model of the axial flow turbine is established,and NUMECA software is used for numerical simulation.The three-dimensional flow field analysis and performance analysis under design conditions and off design conditions are completed.The results show that the total static efficiency of the optimized S-CO₂ axial flow turbine has been significantly improved,and it has good performance under both design and off design conditions.In order to explore the influence of different clearances on the performance of S-CO₂ axial flow turbine,take the 10MW axial flow turbine designed in this paper is taken as an example,and different radial clearance dimensions and axial clearance dimensions are set for numerical simulation calculation and analysis.The results show that the effect of radial clearance on total static efficiency is almost linear,the clearance blade height ratio increases by 0.5%,and the total static efficiency decreases by about 1.2%;There is always an axial clearance value that makes the axial flow turbine perform best.For S-CO₂ axial flow turbines,15～35%of the average axial chord length is recommended for the clearance between the moving and stationary blades in the same stage,and 35～50%of the average axial chord length is recommended for the axial clearance between two stages.The change of the axial clearance size has no obvious effect on the flow field in the flow passage of the stationary blade and the moving blade,and has a significant impact on the flow field distribution in the clearance.