Design And Flow Characteristics Analysis Of Supercritical Carbon Dioxide Single Stage Axial Flow Turbine

Supercritical carbon dioxide(SCO2)is considered as a potential working medium in energy conversion system.In supercritical carbon dioxide(TC = 304 K,PC = 7.38 MPa),viscosity is close to gas,density is close to liquid,flow density is high,and heat transfer performance is good.Therefore,the supercritical carbon dioxide Brayton cycle system has the advantages of small equipment size,high power generation efficiency and low cost.The axial flow turbine technology is mature,suitable for large flow of working medium,high efficiency,convenient for multistage treatment,and can meet the requirements of high expansion ratio and high power.In this paper,the design,modeling,simulation and flow analysis of SCO2 Brayton cycle axial-flow turbine are studied.The thermal design of 10 MW axial-flow turbine with SCO2 as working fluid was completed.The impeller start-up parameters and size parameters derived from onedimensional design were used to model the turbine with bladegen,and the numerical simulation was carried out with CFX.Considering that the physical property equation could not accurately represent the supercritical physical properties,NIST real physical property data was used.After analyzing the simulation data,the one-dimensional thermal performance was verified The results of force design are accurate,the error is obviously less than the expected value,and the design standard is reached,which can better reflect the turbine performance.At the same time,the variable condition performance of the turbine is analyzed.The data of inlet pressure,outlet pressure,inlet temperature and rotation speed which deviate from the design condition by 5%-20% are taken to simulate and analyze the impeller.The flow,efficiency,power generation and other parameters of each non design condition are given,and the position of loss in different conditions is analyzed.When the parameters change within 10%,the maximum effect of inlet pressure change on turbine efficiency is2.5%,the maximum effect of outlet pressure change on turbine efficiency is 1.6%,and the effect of inlet temperature and rotation speed change on efficiency is 0.17% and 0.77%,respectively.When the pressure and temperature produced in the working fluid flow are lower than the critical point,the nozzle model is constructed.In the model,the expansion process in the impeller is simulated by using the zoom nozzle.It is found that there is a sudden change of physical parameters,such as density,in the throat of the nozzle,while in the simulation of the flow channel,when the temperature drops close to 400 k,there is also a sudden change of physical parameters With the flow separation and reflux,the turbine efficiency decreased to about 0.74.In the change of pressure and speed,there is also a transcortical region.Although it causes a certain degree of flow separation,there is no mutation of biological parameters,and the change gradient of density is maintained at a level consistent with the design condition.The detailed causes of transcritical region in flow are given,and the modification measures are given for the points where pressure drop is easy to occur,such as widening the nozzle trailing edge,changing the airfoil profile and other methods,so that the efficiency can rise by about 0.6%.As a whole,the design requirements of the turbine load and the adaptability to the variable condition environment can be met.By adjusting the inlet and outlet parameters or changing the airfoil,the effect of the lower transcritical phenomenon on the efficiency can be reduced to a certain extent.