Pore-Scale Simulation Of Turbulent Premixed Combustion In Randomly Packed Porous Media

Porous media combustion refers to the inflammable gas or fuel vapor through solid porous media during combustion by using porous materials instead of free space,similar to the combustion occurring under conditions of filtration,which widely exists in nature and engineering practice.Turbulent combustion in porous structure is an important branch of combustion science.The main difference between turbulent combustion and other combustion processes is that the complex porous structures have an effect on turbulent characteristics,heat transfer characteristics,combustion process and turbulent-flame interactionTo analyze the turbulent premixed combustion characteristics in porous media deeply,a random packed model which is close to the actual structure was used in this work and combined with turbulence and combustion model based on large eddy simulation(LES)method,the flow,heat transfer and combustion process in porous structure under pore scales were studied.In this paper,the work completed as follows:Firstly,two different simulation methods were used to establish the geometric structure model similar to the actual random porous media structure.The random packed model,which can give a random packed structure similar to the actual packed bed structure by simulating the free fall,collision and stacking process of pellets;and a seed growth structure similar to the foamed ceramics structure by simulating the foaming agent random distribution,gas core expansion,bubble breaking and stop growth process.The above two models have simulated main processes in the actual production of porous media materials,and combined with the batch modeling order output by software MATLAB,so both of them meet the basic requirement that high similarity with the actual structure and building fast.Secondly,based on the packed model,the pore-scale numerical simulation of fluid flow and heat transfer processes in the packed structure are given.By comparing the simulation results with the corresponding experimental data,the validity of the structure model,turbulence model and heat transfer model are verified comprehensively.On this basis,the macro analysis is given,it is found that the mean porosity,various flow scalars and heat transfer scalars in the packed structure are all periodically distributed,and the influence of inlet velocities,pellets size and other parameters on the turbulence and temperature field in porous media is described in detail;The large eddy simulation(LES)method is used to study the flow and temperature field under pore-scale in the local porous structure,the distribution characteristic of eddies in porous structure was obtained,and the time scale range of the series evolution process of eddies,and the change regulation of isothermal surface shape and the shape sophisticates with heating were also given.Reynolds averaging simulation(RANS)method was used to simulate the turbulent flow and temperature field under the same working condition.The results are compared with those simulated by large eddy simulation(LES)method,then the differences and advantages between the two methods were analyzed and discussed.Thirdly,on the basis of the above random packed structure,the premixed combustion process of methane/air in packed bed was simulated by large eddy method combined with the double-temperature model and EBU-Arrhenius combustion model.The validity of the model was verified by comparing with the experimental data;the distribution of temperature and flame,the correlation characteristic of flame surface in packed beds under various conditions were analyzed,the effects of inlet velocity,gas equivalence ratio and packed structure on combustion process and important flame parameters were studied;through the quantitative analysis of turbulent-flame interaction in porous media,the zoning law of turbulent flame under various working conditions is determined.At last,a spherical enclosure was used to cut the random packed structure to obtain a geometric structure for pore-scale study.Large eddy simulation(LES)method combined with power-law flame wrinkling model were used to simulate the premixed combustion process of hydrogen-air in enclosed space with random porous structure.And the validity of the model is verified by comparing the simulation results with the experimental data under different turbulent intensity;then the change rules of thickness,propagation velocity,flame surface radius,area and average vorticity of spherical flame in different structures at different time points were analyzed;based on the distribution of Karlovitz number on the flame surface,the quantitative analysis of turbulent-flame interaction in the porous structures was carried out,the zoning law of turbulent flame under various working conditions was determined;some results are compared with those simulated by EBU-Arrhenius model under the same working condition,which shows the advantages of the power-law flame wrinkling model and the necessity of applying this model.