In this paper, the mixing and combustion at low-heat release in a turbulent mixing layer are studied numerically using large eddy simulation. The primary aim of this paper is to successfully replicate the flow physics observed in experiments of low-heat release reacting mixing layers, where a duty cycle of hot structures and cool braid regions was observed. The nature of the imposed inflow condition shows a dramatic influence on the mechanisms governing entrainment, and mixing, in the shear layer. An inflow condition perturbed by Gaussian white noise produces a shear layer which entrains fluid through a nibbling mechanism, which has a marching scalar probability density function where the most probable scalar value varies across the layer, and where the mean-temperature rise is substantially over-predicted. A more sophisticated inflow condition produced by a recycling and rescaling method results in a shear layer which entrains fluid through an engulfment mechanism, which has a non-marching scalar probability density function where a preferred scalar concentration is present across the thickness of the layer, and where the mean-temperature rise is predicted to a good degree of accuracy. The latter simulation type replicates all of the flow physics observed in the experiment. Extensive testing of subgrid-scale models, and simple combustion models, shows that the WALE model coupled with the Steady Laminar Flamelet model produces reliable predictions of mixing layer diffusion flames undergoing with fast chemistry.

本文利用大涡模拟对湍流混合层中低放热时的混合和燃烧进行了数值研究。本文的主要目的是成功复制在低放热反应混合层实验中观察到的流动物理，其中观察到热结构和冷编织区域的占空比。强加的流入条件的性质显示出对剪切层中控制夹带和混合的机制的显着影响。高斯白噪声扰动的流入条件会产生一个剪切层，它通过一个咬动机制夹带流体，它具有一个行进的标量概率密度函数，其中最可能的标量值在整个层中变化，并且平均温度上升显着超过预料到的。由循环和重新缩放方法产生的更复杂的流入条件导致剪切层通过吞没机制夹带流体，其具有非行进标量概率密度函数，其中优选的标量浓度存在于整个层的厚度，并且其中平均温度上升的预测精度很高。后一种模拟类型复制了实验中观察到的所有流动物理。对亚网格尺度模型和简单燃烧模型的广泛测试表明，WALE 模型与稳态层流火焰模型相结合，可以对经历快速化学反应的混合层扩散火焰产生可靠的预测。它具有非行进标量概率密度函数，其中优选的标量浓度存在于整个层的厚度，并且平均温升被预测到了很好的准确度。后一种模拟类型复制了实验中观察到的所有流动物理。对亚网格尺度模型和简单燃烧模型的广泛测试表明，WALE 模型与稳态层流火焰模型相结合，可以对经历快速化学反应的混合层扩散火焰产生可靠的预测。它具有非行进标量概率密度函数，其中优选的标量浓度存在于整个层的厚度，并且平均温升被预测到了很好的准确度。后一种模拟类型复制了实验中观察到的所有流动物理。对亚网格尺度模型和简单燃烧模型的广泛测试表明，WALE 模型与稳态层流火焰模型相结合，可以对经历快速化学反应的混合层扩散火焰产生可靠的预测。