任祝寅, 解青, 杨天威, 周华. 输运概率密度函数中的小尺度标量混合建模[J]. 空气动力学学报, 2020, 38(3): 501-514. DOI: 10.7638/kqdlxxb-2019.0093
引用本文: 任祝寅, 解青, 杨天威, 周华. 输运概率密度函数中的小尺度标量混合建模[J]. 空气动力学学报, 2020, 38(3): 501-514. DOI: 10.7638/kqdlxxb-2019.0093
REN Zhuyin, XIE Qing, YANG Tianwei, ZHOU Hua. Micromixing models for transported PDF simulation of turbulent combustion[J]. ACTA AERODYNAMICA SINICA, 2020, 38(3): 501-514. DOI: 10.7638/kqdlxxb-2019.0093
Citation: REN Zhuyin, XIE Qing, YANG Tianwei, ZHOU Hua. Micromixing models for transported PDF simulation of turbulent combustion[J]. ACTA AERODYNAMICA SINICA, 2020, 38(3): 501-514. DOI: 10.7638/kqdlxxb-2019.0093

输运概率密度函数中的小尺度标量混合建模

Micromixing models for transported PDF simulation of turbulent combustion

  • 摘要: 输运概率密度函数方法能精确地求解湍流燃烧中的有限化学反应速率,但小尺度上分子扩散引起的组分变化则需要通过标量小尺度混合模型来模拟。论文综述了当前湍流预混燃烧中混合模型研究的最新进展。首先介绍了现有标量混合模型在不同预混燃烧模式下的表现:对于火焰面燃烧模式,保持组分空间的临近性对于标量混合模型非常重要,标量混合频率受火焰结构影响显著;对于破碎反应区模式,组分空间保持临近性的重要性有所减弱,标量混合频率由湍流主导。接着介绍了最新基于直接数值模拟数据的标量小尺度混合机制和建模研究,包括湍流预混燃烧中反应标量小尺度耗散机制、反应标量混合时间尺度在不同燃烧模式下的演化规律、依据线性混合思路构建的标量混合时间尺度模型。针对不同湍流预混燃烧模式的模型验证表明:相比于已有湍流混合时间尺度模型,新模型显著提升了对湍流预混火焰中的标量耗散率和燃烧特性的预测精度。最后介绍了大涡模拟/输运概率密度函数方法在近极限湍流预混火焰,如甲烷预混值班火焰和湍流对冲预混火焰中的应用,验证了其对贫燃、高湍流度条件下的湍流-化学反应相互作用及局部熄火/再燃现象的预测能力。

     

    Abstract: Transported probability density function (TPDF) methods are attractive for modeling turbulent flames as the highly nonlinear chemical reactions appear in closed form. However, challenges remain when applying TPDF methods to turbulent premixed flames, for which modeling molecular diffusion is difficult because the species local gradients are governed both by turbulence and chemical reactions. In this paper, recent progress on micromixing modelling for turbulent premixed flames is reviewed with particular focus on the model performance in different combustion regimes, the analysis and modelling of the scalar mixing timescales using direct numerical simulation (DNS) datasets, and the LES/TPDF simulations of near-limit premixed flames. For flames in the flamelet regime, localness in composition space for scalar mixing is essential and the mixing rate of reactive scalar is dominantly controlled by flame structure; for flames in the broken reaction zone regime, reactive scalar mixing is controlled by turbulent mixing. Then models for the mixing timescale of progress variable are discussed, with a focus on the recently developed hybrid mixing timescale model, which is applicable to different combustion regimes and has significant advantages over the existing constant mechanical-to-scalar timescale model. This work concludes with a discussion on the effects of grid resolution on LES/TPDF modelling of near-limit premixed flames.

     

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