Numerical Simulation Of Fluid Flow,Heat Transfer And Combustion In Porous Media By Chebyshev Collocation Spectral Method

Compared with the traditional combustion technology,porous media combustion technology as a new type of clean combustion technology has the huge development potential,especially in the field of low calorific value gas combustion.However,porous media combustion technology for medium and high temperature field has some problems such as unstable combustion and short service life of materials.The study of premixed gas combustion characteristics in porous media has important practical significance for the development of porous media combustion technology.At present,porous media combustion is mainly studied by experiment and numerical method.Most numerical methods simplify the problem of porous media combustion by the assumption of "volume average",adopt the finite volume method to discrete the governing equation,and iteratively solve the governing equation.In this paper,the fluid flow heat transfer and combustion in porous media are numerically simulated,the governing equation is spatially discretized based on Chebyshev collocation spectrum method(CCSM),the differential equation is matrixed and solved.First,a one-step complete reaction model is used to simulate the combustion reaction of the double-layer porous medium.To ensure the convergence of the numerical results,the projection function g(x,?,?) is used to move the Chebyshev-Gauss-Lobatto(CGL)grid refinement.A one-dimensional transient two-temperature mathematical model is established,which can be solved directly after the coefficient matrix of each equation is determined.Secondly,a two-dimensional transient two-temperature mathematical model was established by simulating porous media combustion with a constant heat release region,and the improved projection scheme(IPS)was adopted to process the coupling process of velocity and pressure.Solve the matrix equation with a two-step method.Through Matlab software programming to realize the numerical calculation,and complete the grid independence and the validity verification of numerical method.The influence of porous media material,structural parameters,thermal conductivities,volumetric heat transfer coefficient,extinction coefficient and gas inlet velocity on gas and solid temperature distribution was analyzed in the one-dimensional model.The results show that the influence of porosity and pore size on the temperature of gas and solid should be taken into account by volumetric heat transfer coefficient and extinction coefficient.Increase the combustion zone the coefficient of thermal conductivity of porous media,the porous media to the downstream thermal conductivity enhancement,will decrease the temperature of gas and solid,downstream of the flame front to moving.The temperature and velocity distributions of gas and solid in porous media were investigated under a two-dimensional model.The results show that the temperature of the gas and the solid do not show obvious two-dimensional structure,and the temperature of the gas has obvious high temperature area.The velocity of mixed gas changed dramatically at the entrance section,which was manifested by the thickening of velocity boundary layer and the decrease of velocity gradient.