Dynamic Second-order Moment Closure Model For Turbulent Combustion With Detailed Chemistry

Combustion is a main way to obtain energy in modern society.It is widely used in engineering applications,such as internal-combustion engine,gas turbine,power station boiler,etc.At present,large eddy simulation(LES)has become a popular approach for turbulent combustion.Studies have shown that there may be multiple modes of combustion at the same time in actual burners.Premixed and non-premixed combustion are exist in both conventional premixed and diffused flame.Up to now,most of the combustion models can not predict and calculate the flame well.To solve this problem,our group has proposed and developed a dynamic second-order moment(DSOM)closure model for turbulent combustion.In order to further improve this model,we develop a dynamic second-order moment closure model with detailed chemical mechanism in the present paper.The new model is applied to premixed flame and non-premixed flame with multiple modes of combustion to verify its capability.To deepen the understanding of turbulent combustion,the characteriscs of flame structure and the interaction between flame and turbulence are studied.The first part introduces the mathematical theory of dynamic second-order moment closure model with detailed chemistry.For different species of elementary reaction,the transport equations for the second variance correlation terms are derived.Those transport equations are simplified in analogy to the method of the Reynolds stress model and their non-dimensional coefficients are determined by a dynamic procedure.The DSOM model is improved and developed,which sets a theoretical basis for the large-eddy simulation program of dynamic second-moment model with detailed chemistry.The second part studies the accuracy and capability of DSOM turbulent combustion model with detailed chemistry for premixed combustion.The DSOM model with multi-step reaction mechanism of CH4 is applied to Sydney Piloted Premixed Jet Burner(PPJB).The velocity field,temperature field and composition field of the premixed flame with different inlet velocities have been compared with the experiment results.It is found that the results obtained by the DSOM model with detailed chemistry agree well with the experiment.The flame structure is well captured.It has been proved that the DSOM model can accurately predict the premixed flame.The third part studies the accuracy and capability of the dynamic second-order moment closure model for the non-premixed piloted turbulent jet flame with multiple modes of combustion.Besides,the flame structure and combustion stability are investigated.The DSOM model is applied to Sydney piloted burner with inhomogeneous inlets.By comparison with the experimental data,the model's capability in simulating the non-premixed flame with multiple modes of combustion has been examined,and the flame structure has been analyzed.The results show that the location of high temperature gradients are different from that of high mixture fraction gradients at x/D=1 and x/D=5,whereas the reacting shear layer at the edge of the main jet in the flame with near-homogenous inlets is characterized by high gradients in both temperature and mixture fraction.At x/D=15 and further downstream,local extinction occurs.The DSOM model can also predict local extinction.The probability of local extinction increases with the increase of the inlet velocity.