AI 中文总结
研究贫氢火焰RANS模拟中优先和差异扩散问题，基于表格化学模型扩展到RANS框架，考虑混合平均扩散等因素，通过假定PDF方法纳入湍流-化学相互作用，能正确再现火焰相关特性，证明模型在模拟中纳入相关效应的能力。
AI 中文摘要
贫氢火焰由于优先和差异扩散效应容易出现热扩散不稳定性，给计算流体动力学模拟中的建模带来重大挑战。本文将包含优先和差异扩散效应的表格化学（TC）模型扩展到雷诺平均Navier-Stokes（RANS）框架，并以直接数值模拟（DNS）为参考，评估其在两个雷诺数（Re = 5500和11000）下对贫预混H₂-空气狭缝燃烧器的性能。该方法基于从考虑混合平均扩散和索雷特效应的物种质量传输方程导出的进展变量和混合分数的传输方程，并通过假定概率密度函数（PDF）方法纳入湍流-化学相互作用。包括优先-差异扩散的RANS模拟能够正确再现DNS火焰长度、热释放分布以及狭缝火焰的特征当量比和超绝热温度分支。与（i）统一刘易斯数变体和（ii）仅在小火焰表中包括热扩散效应的模型的比较显示了优先和差异扩散在热化学和传输水平上对TC模型的影响。最后，评估了湍流扩散、标量耗散率和雷诺应力的湍流封闭的影响。本文结果证明了该模型在贫氢火焰的经济高效RANS模拟中纳入优先和差异扩散效应的能力。
英文摘要
Lean hydrogen flames are prone to thermo-diffusive instabilities due to preferential and differential diffusion effects, posing significant challenges for their modeling in computational fluid dynamics simulations. This work extends a tabulated-chemistry (TC) model that includes preferential and differential diffusion effects to a Reynolds-averaged Navier-Stokes (RANS) framework and assesses its performance for a lean premixed $\mathrm{H_2}$-air slot burner at two Reynolds numbers ($\mathrm{Re}=5500$ and $11000$) using direct numerical simulation (DNS) as a reference. The approach is based on transport equations for the progress variable and mixture fraction derived from the species mass transport equations considering mixture-averaged diffusion and Soret effect, and incorporates turbulence--chemistry interaction via a presumed probability density function (PDF) approach. RANS simulations including preferential-differential diffusion are able to correctly reproduce the DNS flame length, heat-release distribution, and the characteristic equivalence-ratio and super-adiabatic temperature branches of the slot flame. Comparisons with (i) a unity-Lewis-number variant and (ii) a model including thermo-diffusive effects only in the flamelet table show the impact of preferential and differential diffusion on the TC model at both the thermochemical and transport levels. Finally, the impact of the turbulence closures for turbulent diffusion, scalar dissipation rate, and Reynolds stresses is assessed. The results presented in this paper demonstrate the capability of the model to include preferential and differential diffusion effects in cost-effective RANS simulations of lean hydrogen flames.
