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Modeling extinction and reignition in turbulent flames

机译：模拟湍流火焰中的灭绝和重燃

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The conditional moment closure method (CMC) has been extended to improve reactive species predictions in flames with significant local extinction and reignition. Simple first-order closure of the conditionally averaged reaction rate term does not give satisfactory results due to large fluctuations around the conditional mean and an alternative closure is suggested here. The new closure is based on a precomputed parameterized reference field that maps reactive species mass fractions as functions of mixture fraction and sensible enthalpy. During the computations, the reference field is continuously adjusted to ensure consistency with the CMC solution and doubly conditioned chemical source terms that are functions of time, space, mixture fraction, and sensible enthalpy can thus be obtained. Integration over sensible enthalpy space yields the improved singly conditioned chemical source term that can be used for the solution of the CMC equations. Full closure can be achieved by assuming a ?-PDF for the probability distribution in sensible enthalpy space and an additional conditional variance equation needs to be solved. The overall agreement between the measured and the computed variance is satisfactory and the extended CMC model is applied to Sandia Flames D, E, and F. Excellent predictions of temperature, major species, intermediates, and NO are obtained in Flames D and E while temperature predictions can be significantly improved in Sandia Flame F.
机译：有条件的力矩闭合方法（CMC）已得到扩展，以改善具有明显的局部熄灭和重燃的火焰中反应物种的预测。由于条件均值周围存在较大波动，因此条件平均反应速率项的简单一阶闭合无法给出令人满意的结果，因此建议在此处提出一种替代闭合。新的封闭基于预先计算的参数化参考字段，该字段将反应性物质的质量分数映射为混合物分数和显热焓的函数。在计算过程中，不断调整参考场以确保与CMC解决方案的一致性，并因此获得了作为时间，空间，混合物分数和显热函的函数的双条件化学源项。在有意义的焓空间上积分产生了改进的单条件化学源项，该项可用于解决CMC方程。完全封闭可以通过假设-PDF表示在感性焓空间中的概率分布来实现，并且需要求解一个附加的条件方差方程。测量和计算的方差之间的总体一致性令人满意，并且将扩展的CMC模型应用于Sandia Flames D，E和F。在温度升高的情况下，Flames D和E对温度，主要物种，中间产物和NO的预测非常好Sandia Flame F可以大大改善预测。

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