基于FGM和附加输运方程的NO数值模拟方法研究

Numerical Study of NO Formation with FGM and an Additional Transport Equation

关键词:  FGM  辐射  绝热  非绝热  NO排放  光学薄模型

Key words:  FGM  Radiation  Adiabatic  Non-adiabatic  NO emission  Optically thin model

摘要:

为研究污染物NO的数值计算方法，对Sandia Flame D火焰的燃烧流场和NO排放进行了数值模拟研究。采用Realizable κ-ε模型捕捉湍流特征，分别采用绝热和非绝热FGM(Flamelet Generated Manifold)模型模拟热力化学特性，辐射模型采用光学薄模型(OTM)。由于NO的生成过程是慢反应过程，FGM模型的控制变量的时间尺度没有包含NO的时间尺度，因此通过求解NO的输运方程进行NO预测，其化学反应源项由FGM数据库直接插值得到。模拟结果与试验进行对比表明:FGM模型能够很好地捕捉燃烧流场的热力化学特征，但在上游富油区会过高地预测CO；辐射对温度、NO及其化学反应源项分布有非常强的影响，但对H2O，CO₂，CO的影响较小；采用求解NO输运方程的NO质量分数模拟精度明显高于直接由FGM数据库插值得到的NO质量分数，而且非绝热FGM模型得到的NO质量分数的模拟精度明显高于绝热FGM模型的，为精确模拟NO需要考虑NO的动力学特性和辐射效应。

Abstract:

In order to study the numerical method of NO formation，the reactive flow and NO emission of Sandia Flame D were studied numerically. The turbulent characteristics was captured with Realizable κ-ε model and the thermal chemical property was modeled with adiabatic and non-adiabatic FGM(Flamelet Generated Manifold) model respectively in which the optically thin model(OTM) was adopted as radiation model. As the formation of NO was a slow process，and moreover the time scale of progress variable in FGM model did not cover the time scale of NO，thereby NO distribution was simulated with a NO additional transport equation of which the chemical source term was interpolated from FGM look-table. The comparison between the numerical results and experiments shows that FGM model can capture the thermal chemical property of reactive flow well，while CO mass fraction is overestimated in the rich zone upstream. Radiation has a quite strong effect on the temperature，NO and NO chemical source term distribution，but has little effect on the H2O，CO₂，CO. The accuracy of NO mass fraction modeling with the additional transport equation is significantly higher than that directly interpolated from FGM look-table，and then the accuracy of NO mass fraction modeling with non-adiabatic FGM model is higher than that with adiabatic FGM model，hence the kinetics characteristics of NO and radiation effect should be considered in the simulation of NO for higher accuracy.