Modeling turbulent non-premixed combustion remains a challenge in the context of Large Eddy Simulation (LES) in complex geometries and for realistic conditions, taking into account all physical phenomena impacting the flame such as heat loss, dilution, or liquid fuel atomization and evaporation. In this work, the Thickened Flame concept, which allows to resolve the flame front on the LES grid while preserving the consumption speed, and initially derived for premixed combustion, is adapted to diffusion flames. It is demonstrated that the concept holds for these flames, with however, a different formulation of the model due to but their specific nature and properties. In particular, in the high-Damköhler regime, the thickening factor is applied only to the diffusion coefficients. The behavior of thickened diffusion flames is illustrated on laminar steady strained flames for both simple and complex chemistry, showing how the Thickened Flame concept applies. Based on these results, an expression for the thickening factor related to mesh coarsening is derived. For a complete turbulent combustion model, the thickening factor should also describe the sub-grid scale flame-turbulence interaction, which is left for future work.

在复杂几何形状和现实条件下的大涡流模拟 (LES) 环境中，模拟湍流非预混燃烧仍然是一个挑战，考虑到影响火焰的所有物理现象，例如热损失、稀释或液体燃料雾化和蒸发。在这项工作中，加厚火焰概念允许在保持消耗速度的同时解决 LES 网格上的火焰前沿，最初用于预混燃烧，适用于扩散火焰。事实证明，该概念适用于这些火焰，但是由于它们的特定性质和特性，模型的公式不同。特别是，在高 Damköhler 状态下，增稠因子仅适用于扩散系数。在简单和复杂化学的层流稳定应变火焰上说明了增厚扩散火焰的行为，展示了增厚火焰概念的应用。基于这些结果，推导出与网格粗化相关的加厚因子的表达式。对于完整的湍流燃烧模型，增稠因子还应描述亚网格尺度的火焰-湍流相互作用，这留待以后的工作。