条件矩模型模拟湍流扩散燃烧  

CONDITIONAL MOMENT CLOSURE MODEL FOR SIMULATION OF TURBULENT DIFFUSION COMBUSTION AND NITRIC OXIDES FORMATION

作　　者：邹春[1] 郑楚光[1] 周力行[2] 

机构地区：[1]华中科技大学煤燃烧国家重点实验室,武汉430074 [2]清华大学工程力学系煤的清洁燃烧国家重点实验室,北京100084

出　　处：《力学学报》2002年第6期969-977,共9页Chinese Journal of Theoretical and Applied Mechanics

基　　金：国家重大基础研究发展规划(G19990222-07)资助项目。

摘　　要：对条件矩模型模拟湍流扩散燃烧进行了初步的研究.在条件矩模型中,标量的统计是以混合分数为条件的,条件平均使得非线性化学反应源项可以在一阶条件下被封闭.模拟结果和美国Sandia国家实验室的实验结果对比表明:对温度、主要组分浓度的预报结果是令人满意的,NO浓度的预报在趋势上也符合实验结果.误差分析表明,提高标量耗散率的预报精度和二阶条件矩模型都将有助于推动条件矩模型的发展.Modeling turbulent combustion is a formidable task, since there is a strong interaction between turbulent mixing and chemical reaction, which results in the difficulties to express the averaged reaction rates in terms of the averaged values of the scalars. Most of presently developed engineering models in the commercial CFD codes are highly simplified and cannot accurately simulate chemical reactions in turbulent flows, such as NOX formation in turbulent flows. The PDF transport equation method can exactly simulate the chemistry-turbulence interaction, but computationally is very expensive. The conditional moment closure model (CMC) proposed by Klimenko and Bilger makes the reaction source term closed at the first conditional moment level, since the conditional averaging in terms of the mixture fraction suppresses fluctuations of most interesting scalar quantities (composition, temperature, enthalpy, etc.), which means that the fluctuations about the conditional average are so small that the covariance can be neglected. The CMC method is directly derived from the conservation equations for the mass fraction of species treated in a purely stochastic manner without any simplifications. Therefore, the CMC model has a rather sound basis and can be applicable to turbulent reacting flows in which species formation time scales are of the same order as that of local mixing times.A primary study of the simulation of turbulent diffusion combustion with conditional moment closure (CMC) model is presened in this paper. Experimental results show that the conditional averages have a very weak dependence on the across stream position in a steady axisymmetric jet flame. And Klimenko also proves it by asymptotic analysis. This weak dependence allows us to simplify the CMC equations by integrating them across the flow. The comparison of simulation results with experimental data given by Sandia laboratories, USA, shows that the performances of the prediction of temperature and main species concentrations are satisfactory, while the

关 键 词：氮氧化物 条件矩模型 扩散燃烧 数值模拟 湍流 

分 类 号：O357.5[理学—流体力学]