Scalar gradient and flame propagation statistics of a flame-resolved laboratory-scale turbulent stratified burner simulation
Scalar gradient and flame propagation statistics of a flame-resolved laboratory-scale turbulent stratified burner simulation
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DOI：
10.1016/j.combustflame.2021.111917
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发表时间：
2022
影响因子：
4.4
通讯作者：
E. Inanc;Achim Kempf;N. Chakraborty
中科院分区：
文献类型：
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作者：
E. Inanc;Achim Kempf;N. Chakraborty
采用火焰分辨数值模拟方法研究了甲烷/空气贫燃混合气分层燃烧中钝体稳定湍流射流火焰的燃烧特性。基于预混小火焰生成歧管（PFGM）的列表化学方法解释了热化学。计算的网格分辨率为100 µm，足以解决热火焰厚度。该查找表生成与混合平均扩散率的假设和优先扩散通量包括在模拟中，使用一种有效的方法，而不增加流形的维数。预测的平均值和RMS量与实验结果非常一致。研究的重点是比较靠近进口的上游位置的燃烧行为与弱混合物分数梯度的下游位置远离进口的强混合物分数梯度。对火焰内扩散项的统计分析表明，在钝体上方的回流区，在入口附近，优先扩散仍然很明显。分层火焰在下游位置的结构进行了统计分析的位移速度和标量梯度的条件下，通过比较对上游位置的相应数量与弱混合分数梯度。结果表明，由于分子扩散和反应速率分量的影响，在弱或强混合分数梯度下的火焰之间的位移速度是统计上不同的。然而，增加的曲率效应和交叉耗散分量也起作用。最后，研究了火焰刷内混合分数脉动和反应进程变量脉动的标量耗散率和交叉耗散率，并讨论了它们的封闭方法。
A bluff-body stabilised turbulent jet flame burning in a stratified mode of combustion for fuel-lean methane/air mixtures is investigated by a flame-resolved simulation. A tabulated chemistry approach based on premixed flamelet generated manifolds (PFGM) accounts for thermochemistry. The computations are performed for a grid-resolution of 100 µm, sufficient to resolve the thermal flame thickness. The look-up table is generated with a mixture-averaged diffusivity assumption and the preferential diffusion fluxes are included in the simulation, using an efficient method without increasing the dimensionality of the manifold. The predicted mean and RMS quantities are found to be in good agreement with the experiment. The investigation focuses on the comparison of the combustion behaviour of the upstream locations close to the inlet with weak mixture fraction gradients to the downstream locations away from the inlet with strong mixture fraction gradients. Statistical analysis of the diffusion terms within the flame revealed that the preferential diffusion remains significant near the inlet, in the recirculation zone over the bluff-body. The structure of the stratified flame in downstream locations is statistically analysed in terms of displacement speed and scalar gradients by comparing against the corresponding quantities in upstream locations with weak mixture fraction gradients. It is shown that the displacement speed is statistically different between the flames under weak or strong mixture fraction gradients due to the influence of molecular diffusion and reaction rate components. However, increased curvature effects and cross-dissipation component also play a role. Finally, scalar dissipation and cross-dissipation rates of the mixture fraction fluctuation and the reaction progress variable fluctuation within the flame-brush are investigated, and their closure approaches are discussed.