Large Eddy Simulations Of Lean Premixed Flames Based On DTF And REDIM Methods

As a new great promising combustion technology,lean premixed combustion plays an important role in improving combustion efficiency and reducing pollution emissions.It is increasingly applied to actual industrial combustion.However,lean premixed combustion also has a series of safety issues,such as autoignition,flashback,thermoacoustic oscillation and so on.Nowadays,a large number of experiments and numerical simulations on lean premixed flames have been carried out in academia.Among these,the numerical simulation method has the advantages of low cost,high reliability,and can effectively reduce the workload.At the same time,the numerical simulation results can also be used to guide the experiment and design work,which can shorten the research and development cycle.As a result,more and more people pay attention to and use it.Among the three numerical simulation methods currently used,the large eddy simulation?LES?method,as a compromise method,has higher simulation accuracy than the traditional Reynolds average?RANS?method,and its calculation amount is much less than that of the direct numerical simulation?DNS?method.Meanwhile,it can describe unsteady combustion phenomena,so it is increasingly used in combustion simulation.In LES of turbulent combustion,a suitable sub-grid scale combustion model is necessary.In this study,a sub-grid scale combustion model based on Dynamically Thickened-Flame?DTF?model and Reaction-Diffusion Manifold?REDIM?method is proposed for lean premixed flame.The REDIM method is used to simplify the detailed reaction mechanism,and a low-dimensional reduced manifold is generated.Then the interaction between turbulence and chemical reactions is dealed with the DTF modeling strategy,which couples the low-dimensional manifold with turbulent flow field.So that a new REDIM-DTF sub-grid scale combustion model is developed,which can improve the computational efficiency while maintaining a high simulation accuracy.In order to assess the performance of the REDIM-DTF model,two lean premixed swirling flames in the well-known PRECCINSTA gas turbine model combustor were calculated by it via large eddy simulation,with equivalence ratios0.75 and 0.83,respectively.The calculated results were analyzed and compared qualitatively and quantitatively with the experimental data and those of the original DTF model in terms of velocity,temperature,major species,intermediate species,as well as instantaneous flame surface area and so on.Through comparative analysis,it can be found that the results of REDIM-DTF model are generally consistent with the experimental data,and are very close to those of the original DTF model,indicating that it is completely feasible to use the REDIM-DTF model to calculate the lean premixed flames.The results of the REDIM-DTF model agree well with the experimental results when predicting the statistics of velocity,temperature and major species.However,when it comes to the simulation accuracy of minor species CO,there is a large difference between the results of the REDIM-DTF and original DTF model,which may be related to the different reaction mechanisms used by these two models.Since less species transport equations are solved in REDIM-DTF model,the computational efficiency of it is about 15%higher than the original DTF model.In the simulation of lean premixed flames,as long as the two basic conditions of monotonic variation and single value function are met,the effect of which species mass fraction is used as the reaction process variable in one-dimensional REDIM table is not significant.In theory,the REDIM-DTF model can be easily applied to calculate partially premixed flames,and only needs to increase the dimension of the REDIM table accordingly,such as introducing the N₂ mass fraction to describe the change of equivalence ratio.