Thermodynamic Calculation And Aerodynamic Analysis Of Supercritical Carbon Dioxide Axial Turbine

Supercritical carbon dioxide Brayton cycle has many advantages,such as high efficiency,compact structure,simple layout,safety and environmental friendly and so on,which is regarded as one of the most promising power cycles in the future.Turbine is the core power component of the supercritical carbon dioxide power cycle.The aerodynamic design and performance of turbine have an important influence on the performance of the whole cycle system.Besides,supercritical carbon dioxide is featured as high density and lower viscosity leading to very compact turbine and lower flow loss with the same power scale.This paper adopts supercritical carbon dioxide axial flow turbine as the research object.Then discuss characteristic of s-CO2 turbine by comparing thermal design results between air turbine,vapor turbine and CO2 turbine.And verify the one-dimentional thermal design results by numerical solution of computational fluid dynamics software and analyze the difference between the results.The main work of this paper is as follows:Firstly,according to mean line flow analysis method,a one-dimensional thermal calculation program for axial flow turbines was developed.On the basis of verifying the accuracy of the program through engineering examples,the one-dimensional thermal design of the two-stage supercritical carbon dioxide axial flow turbine was carried out.In the program,the properties of carbon dioxide were invoked from the NIST database.Combined with the experimental data of HQ series blade profile,the through-flow size of the turbine is preliminarily selected for the one-dimensional thermal design of the supercritical carbon dioxide axial flow turbine.Under design conditions,the turbine inlet total pressure is 18MPa and inlet total temperature is 550OC and the turbine outlet static pressure is 9MPa.Optimize the supercritical carbon dioxide axial flow turbine one-dimensional thermal design by change of root diameter and flow angle.The turbine is designed with 2 stages with flow rate of 606kg/s and the rotational speed of 4800r/min.The turbine total-static efficiency of the wheel periphery is 90.1%and the power is 56.2MW.The turbine relative internal efficiency is 86.9%and reduces about 3.2%compared with the turbine total-static efficiency of the wheel periphery when considering wheel friction loss and leakage loss.Under the same inlet and outlet condition and same through-flow parameter,s-CO2 turbine has lower enthalpy drop,lower power,lower reheat factor,higher mass flow rate and higher relative leakage percentage.Secondly,the computational fluid dynamics software was used to conduct numerical simulation analysis on the one-dimensional determined turbine,and the straight blade modeling and structured grid were adopted to solve the n-s equation under steady state.Obtain the radial distribution of aerodynamic parameters and the performance parameters of the turbine.The mass flow rate is 631kg/s,the turbine total-static efficiency of the wheel periphery is 91.8%,and the turbine power is 59.8MW,which is higher than the one-dimensional result.The reason is due to the fact that the velocity coefficient and flow angle at the outlet of the cascade in the three-dimensional solution are higher than those in the one-dimensional thermodynamic calculation.The velocity coefficient and flow angle values obtained in the three-dimensional solution are modified as the input values in the one-dimensional thermodynamic calculation.The recalculated results are basically consistent with the results in the three-dimensional solution with a relative error of less than 1%.Finally,the flow field and loss at the flow passage section of the supercritical carbon dioxide turbine blade are analyzed.The distribution of flow velocity and Mach number at the flow passage section of the blade are reasonable,which are all in subsonic flow.The streamlines in most of the middle part of the four-row cascade blade span are evenly distributed without separation,and have good aerodynamic performance.At the trailing edge of each cascade and the suction surface near the trailing edge,the entropy increases obviously,which shows large loss.