Numerical Study Of LES In Methane Turbulent Combustion Based On OpenFOAM

The research on gas turbine combustion technology has always been one of the hot issues in the field of combustion.Combustion chemical reaction is a very complex process.Many intermediate products,such as active radicals,atoms and ions in different states,are produced when the reaction takes place.These intermediate products are closely related to ignition delay time,flame development,flame structure,combustion stability and pollutant generation.This interaction has an important influence on combustion process.However,the mechanism of this interaction has not been fully clarified.Therefore,based on OpenFOAM open source computing platform,numerical simulation of methane turbulent diffusion combustion in coaxial jet combustor is carried out.Firstly,the simplified coaxial jet combustor was studied.Smagorinsky turbulence model was used to capture the flow of methane in the turbulent combustion process,and PaSR combustion model was used to simulate the combustion of methane in the combustor and air.The numerical simulation of the turbulent combustion of methane in a coaxial jet combustor was carried out,and the numerical simulation results were compared with the experimental data.It was found that the simulation values were in good agreement with the experimental values.The correctness of the solver and the accuracy of the mathematical model are verified.Secondly,the combustion characteristics of methane turbulent diffusion flame in combustor are studied by using the one-step reaction mechanism of methane.The effects of initial pressure and inlet velocity on the combustion process and the concentration distribution characteristics of each component are emphatically studied.The results show that when the inlet velocity is the same,the initial pressure increases from 1atm to 2atm,the number of vortices increases,and the peak temperature increases.When the initial pressure is 1atm,the effects of methane velocity and air velocity on combustion process are studied.The results show that the mixture of fuel and air is better and the combustion stability is better when the methane velocity is 1m/s and the air velocity is 20m/s.The concentration of CO₂ and H₂O decreases the fastest at y/R=0.8 and the smallest at y/R=0.9.Finally,the detailed reaction mechanism of methane was selected to simulate the turbulent diffusion flame of methane in the combustor.The effects of different initial pressures and inlet velocities on ignition delay time and concentration distribution were emphatically studied.The calculation results of one-step reaction mechanism and detailed reaction mechanism were compared and analyzed.The results show that the ignition delay time increases from 0.0017s to0.0018s when the initial pressure increases from 1atm to 2atm,and the influence of air and fuel speed on the ignition delay time is also investigated.It is found that the influence of fuel speed on the ignition delay time is more obvious.The results show that the simulated peak temperature is about 200 K higher than that of the detailed reaction mechanism,because the one-step reaction mechanism does not take into account the heat absorption during the formation of intermediate products.The radial methane concentration at the exit section decreases to zero at y/R=0.8 and the O₂ concentration increases gradually along the radial direction at y/R=0.75,indicating that y/R=0.75⁰.8 is the reaction zone.The distribution of the concentration of H₂O is basically the same as that of the temperature field.In the high temperature region,the concentration of H₂O reaches the highest level and distributes more downstream of the combustor.NO_X is mainly distributed near the flame surface,because the highest temperature in the reaction zone is conducive to the formation of NO_X.