Abstract Complex-chemistry direct numerical simulation (DNS) data obtained earlier from lean hydrogen-air flames associated with corrugated flame (case A), thin reaction zone (case B), and broken reaction zone (case C) regimes of turbulent burning are analysed to directly assess capabilities of the flamelet approach to predict mean concentrations of species in a premixed turbulent flame. The approach consists in averaging dependencies of mole fractions, reaction rates, temperature, and density on a single combustion progress variable c, which are all obtained from the unperturbed laminar flame. For this purpose, four alternative definitions of c are probed and two probability density functions (PDFs) are adopted, i.e. either an actual PDF extracted directly from the DNS data or a presumed β-function PDF obtained using the DNS data on the first two moments of the c(x, t)-field. Results show that the mean density and mean mole fractions of H2, O2, and H2O are well predicted using both PDFs for each c, although the predictive capabilities are little worse in case C. In cases A and B, the use of the actual PDF and the fuel-based c also offers an opportunity to well predict mean mole fractions of O and H, whereas the mean mole fraction of OH is slightly underestimated. In the highly turbulent case C, the same approach performs worse, but still appears to be acceptable for evaluating the mean radical concentrations. The use of the β-function PDFs or another combustion progress variable yields substantially worse results for these radicals. When compared to the mean mole fractions, the mean rate of product creation, i.e. the source term in the transport equation for the mean combustion progress variable, is worse predicted even for a quantity (species concentration or temperature) adopted to define c and using the actual PDF. Consequently, turbulent burning velocity is not predicted either.

中文翻译：

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小火焰概念适用性的先验 DNS 研究，用于预测各种卡洛维茨数下湍流预混火焰中物种的平均浓度

摘要 分析了较早前从与波纹火焰（案例 A）、薄反应区（案例 B）和破碎反应区（案例 C）相关的稀薄氢气-空气火焰中获得的复杂化学直接数值模拟 (DNS) 数据。直接评估火焰法预测预混湍流火焰中物种平均浓度的能力。该方法包括平均摩尔分数、反应速率、温度和密度对单个燃烧进程变量 c 的依赖性，这些变量都从未受干扰的层流火焰中获得。为此，探讨了 c 的四个替代定义，并采用了两个概率密度函数 (PDF)，即 直接从 DNS 数据中提取的实际 PDF 或使用 c(x, t) 字段的前两个矩的 DNS 数据获得的假定 β 函数 PDF。结果表明，使用每个 c 的两种 PDF 可以很好地预测 H2、O2 和 H2O 的平均密度和平均摩尔分数，尽管在情况 C 中预测能力稍差。在情况 A 和 B 中，使用实际 PDF并且基于燃料的 c 也提供了一个机会来很好地预测 O 和 H 的平均摩尔分数，而 OH 的平均摩尔分数被稍微低估了。在高度湍流的情况 C 中，相同的方法表现更差，但对于评估平均自由基浓度似乎仍然可以接受。对于这些自由基，使用 β 函数 PDF 或其他燃烧进程变量会产生更糟糕的结果。与平均摩尔分数相比，产物生成的平均速率，即平均燃烧进程变量的传输方程中的源项，即使对于用于定义 c 的量（物质浓度或温度）并使用实际的PDF。因此，也没有预测湍流燃烧速度。