Numerical Simulation Of Turbulence-radiation Interaction In Diffusion Flame

To compute the radiation heat transfer in turbulent reacting flows, the conventional simulation method base on the average temperature and average mass fraction. Yet various experimental data and numerical simulations indicate that the conventional method proves to be less accurate in predicting the radiation heat transfer in turbulent reacting flows. During last two decades, turbulent-radiation coupled simulations have been extensively studied. Those results showed that the turbulence and radiation coupled with each other and such coupling is called turbulence-radiation interaction(TRI). Hence, it is necessary to develop one model to simulate TRI for engineering applications.This work simulates TRI with user defined scalar method. Firstly, the mean square value of the regional temperature is obtained by solving the transport equation firstly, and the related term of the turbulence radiation is constructed. Then the UDF function of FLUENT software is used to reconstruct the radiative transfer equation, and the simulation of interaction between turbulence and radiation is completed. By comparing the simulated results of user defined scalar method with those of conventional method, it shows that the average temperature is relatively lower than that of conventional method, and the average mass fraction is different. Moreover, the simulated time-averaged radiation source terms of those two methods are compared. It shows that the calculated radiation source term by user defined scalar method is higher than that of the conventional method, which is caused by that the conventional radiation simulation method ignores the fluctuation of temperature.Moreover, this work simulates TRI with the probability density function(PDF) model. Assume that the instantaneous temperature and instantaneous components of mass fraction of the pulsation obey Gauss distribution. According to the k-ε-g combustion model, the fluctuation of mixture fraction is obtained from the mean mixture fraction and its mean square value. According to the linear relationship between the mixture fraction and temperature, the mass fraction and PDF is obtained. Then, by using the method of numerical value and replacing integral, the radiation source term and time-averaged absorption coefficient are constructed, and the radiation source term and the time-averaged absorption coefficient are modified using the UDF function. The calculated results show that the mean temperature is lower than that of the conventional simulation method, and the radiation source term is relatively higher.