The present work describes the numerical study of unconfined turbulent premixed methane/air flames stabilized on an axisymmetric conical baffle under lean and ultra-lean, close to blow-off conditions. A finite-volume-based LES method, using the dynamic Smagorinsky subgrid model in combination with two turbulent combustion methodologies, the thickened flame model and the implicit LES (ILES) laminar reaction rate approach were employed in the investigation. Methane–air oxidation was modeled with a 14-species reduced scheme. OH* chemiluminescent species levels were also evaluated by post-processing quasi-steady-state-derived algebraic expressions, exploiting directly simulated species thus enabling direct comparisons with experimental images. The quality of the simulations was appraised against experimental data for velocity, turbulence, temperature, species mass fractions, heat release profiles as well as chemiluminescence images for conditions far and close to blow-off. Both turbulent combustion models followed closely several intrinsic trends and variations of the flame front anchoring and disposition close to the burner rim shear layers and along the reverse flow region as the fuel level was reduced toward the lean limit. The interaction of the bluff-body recirculation with the adjacent toroidal reacting shear layer and the impact of combustion and heat release on the development of the turbulent velocity and species fields in the near-wake recovery zone were adequately reproduced for both mixtures. Quantitative deviations between simulations and measurements, regarding heat release and OH species, increased for the near-LBO flame with an attendant extrapolated underprediction of the blow-off event by about 8% in terms of equivalence ratio.

中文翻译：

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使用准全局化学和代数化学发光模型对接近贫燃极限的预混 CH $$_{{\mathbf {4}}}$$ 4 钝体火焰进行大涡模拟

目前的工作描述了在贫和超贫、接近吹气条件下稳定在轴对称锥形挡板上的无侧限湍流预混甲烷/空气火焰的数值研究。在研究中采用了基于有限体积的 LES 方法，使用动态 Smagorinsky 子网格模型结合两种湍流燃烧方法、增厚火焰模型和隐式 LES (ILES) 层流反应速率方法。甲烷-空气氧化采用 14 种简化方案建模。OH* 化学发光物质水平也通过后处理准稳态衍生代数表达式进行评估，利用直接模拟的物质，从​​而能够与实验图像进行直接比较。模拟的质量根据速度、湍流、温度、物种质量分数、热释放曲线以及远和接近吹气条件下的化学发光图像。两种湍流燃烧模型都密切关注火焰前缘锚定和靠近燃烧器边缘剪切层并沿着反向流动区域的几个内在趋势和变化，因为燃料水平降低到稀薄极限。两种混合物都充分再现了钝体再循环与相邻环形反应剪切层的相互作用以及燃烧和放热对近尾流恢复区湍流速度和物种场发展的影响。模拟和测量之间的定量偏差，关于放热和 OH 物质，