Large Eddy Simulations Of Turbulent Partially Premixed Flames In The Sydney Burner With Inhomogeneous Inlets

Generally,fuel and air do not have enough time to mix completely in practical combustion devices,thus there is partially premixed combustion phenomenon basically in practical combustion devices.Over the past 10 years,academic research is focused mainly on the study of fully premixed flame and non-premixed flame.Therefore,it is needed to conduct deeper research on partially premixed flame.However,LES of partially premixed combustion still constitutes an open challenge.In the present work,the REDIM-PFDF sub-grid combustion model,based on the reaction-diffusion manifold?REDIM?and presumed filtered density function?PFDF?,is used to calculate the partially premixed flames with inhomogeneous inlets,measured jointly by the University of Sydney and Sandia Laboratory.This study simplified the detailed methane-air reaction mechanism into a two-dimensional lookup table with CO₂ and N₂ mass fractions as reduced coordinates.The PFDF method gives a random distribution of the CO₂ and N₂ mass fractions in the sub-grid control body.The distribution of CO₂ and N₂ mass fractions in the PFDF model is assumed to be the Clipped Gaussian distribution and the Top-hat distribution,respectively.This study simulate the two cases FJ200-5GP-Lr75-57?U57?and FJ200-5GP-Lr75-103?U103?.The inlet jet velocity of U57 and U103 are both lower than the blowoff velocity,blowoff does not occur in these two cases.In order to obtain a fully developed turbulence in the inflow pipe to match the experimental state,a periodic inlet boundary condition is set in the upstream of the inflow pipes.In the present study,the flow field structure,flame modality,and local extinction of U57 and U103 were analyzed.Detailed comparative analysis between the LES statistical data and experimental data of temperature,mixture fraction,mass fraction of CO₂ and CO,and other thermodynamic variables under the two cases are performed.Analysis shows that,under the studied partially premixed flame cases,fully developed turbulence is obtained by using periodic boundary conditions in the upstream of the inflow pipe.The LES predicts local extinction in both of the two operating cases well.The Top-hat distribution assumed for the distribution of N₂ mass fractions does adjust its distribution range automatically,therefore,Top-hat distribution can be used to solve the multi-stream mixing phenomenon.The mixture fraction,temperature,mass fractionof CO₂ and CO,and other thermodynamic variables obtained from the LES flow field agree well with experimental data.This validates the ability of the REDIM-PFDF model to simulate partially premixed combustion further.