DNS of incompressible turbulent reacting flows and validation of the RANS turbulence-chemistry model

The direct numerical simulation(DNS) of well-developed three-dimensional incompressible turbulent reacting channel flows was carried out by using a spectral method.The instantaneous turbulence fluctuation database with the coupling of temperature and mass fraction was gained.The instantaneous results show that both the temperature fluctuation and the mass fraction fluctuation have strip structures in the near wall region.Exact transport equations of the correlations for the second order moment reaction model in the Reynolds averaged Navier-Stokes equations(RANS-SOM) are deducted.As for the correction of the reaction rate coefficient and mass fraction,the dissipation term is key to model closure,and consideration of reaction for the dissipation term of the model equation is necessary.Based on the statistical results of the DNSdatabase,a priori study on the budget of each term in the RANS-SOMmodel correlations transport equations was carried out.It is found that the contributions from the production and dissipation terms are most important,whereas the contributions from the diffusion and reaction terms are rather small.The chemical reaction has obvious influence on the magnitude and distribution of all the terms.Moreover,in the studied cases in this paper,the correlation of reaction rate coefficient and mass fraction which is obtained by DNSdatabase statistical results is close to the value obtained by the algebra second order moment(ASOM) model prediction,affirming reasonableness of ASOMmodel.