Differential diffusion effects in a turbulent H2-O2 nonpremixed flame are investigated using DNS. A generalized Burke-Schumann formulation 1 that allows for differing mass and thermal diffusivities as well as finite-rate chemistry is used. The formulation is based on a three-step reduced mechanism with H as the only intermediate species. Preferential diffusion of H2 and the intermediate species H are considered. Heat release is assumed small such that there is no feed back on the flow field. The flow field is incompressible decaying isotropic turbulence. The objectives are to study the effect of differential diffusion of both fuel and intermediate species, and the effects of reaction rate, dilution and turbulence on differential diffusion. The effects of differential diffusion are characterized by the difference in element mixture fractions, Δ = ξH − ξO. Comparisons are made with the limiting cases of no reaction and a single step, infinite rate reaction. An evolution equation for Δ is derived for each of the three cases.; With LeH2 ≠ 1 and LeH = 1, the peak conditional average temperature increases over the unity Lewis number case. But with LeH 2 ≠ 1 and LeH ≠ 1, the peak conditional temperature decreases below the unity Lewis number case, but increases on the oxidizer side. The effects of H2 and H differentially diffusing are found to be counteracting.; For the nonreacting case, conditional Δ has a reverse “ S” shape that is characteristic of differential diffusion. With reaction, the flame modifies the shape so a peak appears at the stoichiometric position. Varying the reaction rate is found to have little effect on Δ though reacting scalars that are used in the calculation of Δ are affected.; With increasing dilution, the peak of the conditional average of Δ also increases. The shape of the conditional average of Δ for the lowest dilution was found to approach the reverse “ S” shape of the nonreacting case. With more dilution, Δ exhibits more of a peak at the stoichiometric position.; Increasing turbulence was found to reduce the conditional average of Δ while increasing the fluctuations of Δ.; 1Sanchez, Liñan, and Williams, Combust. Sci. and Tech., 1997
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机译：使用DNS研究了湍流H2-O2非预混火焰中的差异扩散效应。使用广义Burke-Schumann公式 1 ，它允许不同的质量和热扩散率以及有限速率化学反应。该配方基于三步还原机理，其中 H 是唯一的中间物种。考虑了 H 2 和中间物种 H 的优先扩散。假设热量释放很小，以至于流场上没有反馈。流场是不可压缩的衰减各向同性湍流。目的是研究燃料和中间物质的差异扩散的影响，以及反应速率，稀释度和湍流对差异扩散的影响。微分扩散的影响通过元素混合分数的差异来表征，Δ=ξ H -ξ O 。比较了无反应和单步无限速率反应的极限情况。对于这三种情况，分别推导了Δ的演化方程。当 Le H 2 ≠1且 Le H = 1时，峰值条件平均温度在统一的路易斯数情况下升高。但是当 Le H 2 ≠1和 Le H ≠1时，峰值条件温度降低到统一的Lewis数以下，但在氧化剂侧升高。发现 H 2 和 H 差异扩散的作用相互抵消。对于非反应情况，条件Δ具有反向“ S ”形状，这是微分扩散的特征。通过反应，火焰会改变形状，因此在化学计量位置会出现一个峰。虽然改变反应速率对Δ几乎没有影响，尽管影响Δ计算的反应标量受到影响。随着稀释度的增加，Δ条件平均值的峰值也会增加。发现最低稀释度的条件条件Δ的形状接近未反应情况的反向“ S ”形状。随着更多的稀释，Δ在化学计量位置上显示出更多的峰。发现增加湍流可以降低Δ的条件平均值，同时增加Δ的波动。 1 Sanchez，Liñan和Williams， Combust。科学和技术。，1997年
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