不可压湍流反应流直接模拟和RANS反应模型检验

用谱方法对三维不可压槽道湍流反应流动进行了直接数值模拟,得到了温度和质量分数耦合的瞬态数据库.结果显示温度与质量分数脉动在近壁区都有条带结构.推导了雷诺平均方法中湍流二阶矩反应模型中所求关联量的精确输运方程,发现耗散项是化学反应率系数-质量分数关联量封闭的关键,耗散项需要考虑化学反应影响.基于数据库的统计结果,对关联量模型方程中各项进行了先验研究,发现产生项和耗散项的贡献最大,扩散项和反应项的贡献较小,化学反应对各项大小和分布形状有明显影响.在算例中,直接模拟统计得到的化学反应率系数-质量分数关联和用代数二阶矩模型的模拟值很接近,说明ASOM模型具有一定的合理性.

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 DNS database,a priori study on the budget of each term in the RANS-SOM model 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 DNS database statistical results is close to the value obtained by the algebra second order moment(ASOM) model prediction,affirming reasonableness of ASOM model.