Assessment of the constant non-unity Lewis number assumption in chemically-reacting flows
Assessment of the constant non-unity Lewis number assumption in chemically-reacting flows
复制标题
化学反应流中恒定非统一路易斯数假设的评估
DOI：
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发表时间：
2016
期刊：
影响因子：
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通讯作者：
Y. Xuan
中科院分区：
文献类型：
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作者：
N. Burali;S. Lapointe;B. Bobbitt;G. Blanquart;Y. Xuan
精确计算化学反应流中的分子扩散系数是一个昂贵的过程，而使用常数非统一的刘易斯数往往被认为是一种较便宜的替代方法。目前的工作的目标是探讨的有效性和限制的常数非统一刘易斯数的方法在层流和湍流火焰中的分子混合的描述。为了进行这一分析，三个测试案例已被选定，包括一个贫，高度不稳定，预混氢/空气火焰，一个贫湍流预混正庚烷/空气火焰，和一个层流乙烯/空气同向流扩散火焰。对于氢火焰，层流和湍流配置已被认为是。这三种火焰的特征分别是小于1、大于1和接近1的刘易斯数。对于每个火焰，混合物平均运输模拟进行，并作为参考数据。目前的分析表明，对于许多燃烧配置，恒定的非统一刘易斯数近似导致小的误差时，适当地选择刘易斯数的集合。对于选定的测试用例和我们的数值框架，计算成本的减少被发现是最小的。
Accurate computation of molecular diffusion coefficients in chemically reacting flows can be an expensive procedure, and the use of constant non-unity Lewis numbers has been adopted often as a cheaper alternative. The goal of the current work is to explore the validity and the limitations of the constant non-unity Lewis number approach in the description of molecular mixing in laminar and turbulent flames. To carry out this analysis, three test cases have been selected, including a lean, highly unstable, premixed hydrogen/air flame, a lean turbulent premixed n-heptane/air flame, and a laminar ethylene/air coflow diffusion flame. For the hydrogen flame, both a laminar and a turbulent configuration have been considered. The three flames are characterised by Lewis numbers which are less than unity, greater than unity, and close to unity, respectively. For each flame, mixture-averaged transport simulations are carried out and used as reference data. The current analysis suggests that, for numerous combustion configurations, the constant non-unity Lewis number approximation leads to small errors when the set of Lewis numbers is chosen properly. For the selected test cases and our numerical framework, the reduction of computational cost is found to be minimal.