Accurate prediction of nitrogen oxides (NOX) emissions is of great importance in combustion simulations. This work proposes an improved model to predict NO distributions in turbulent flames, based on the large eddy simulation approach and flamelet-progress-variable turbulence combustion model. A separate table for NO reaction rate is constructed to account for both unsteady and nonadiabatic effects on NO production. Different from the existing models, the nonadiabatic effect is considered by specifying different enthalpy defects by a scaling factor in the flamelet calculations. Additionally, it is observed that the transient variation of NO reaction rate with NO concentration exhibits two linear stages. As a result, only three flamelet databases are included to describe the NO reaction rate in a transient process, thereby simplifying the flamelet table while maintaining model accuracy. The proposed NO prediction model is validated in large eddy simulations of turbulent combustion, including the classic Sandia D and the Sydney swirling SM1 flames. The calculated NO variations show good agreement with experimental data, demonstrating the applicability and accuracy of the proposed model.

中文翻译：

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一种改进的湍流燃烧大涡模拟NO预测模型

准确预测氮氧化物 (NOX) 排放量在燃烧模拟中非常重要。这项工作基于大涡模拟方法和小火焰进程变量湍流燃烧模型，提出了一种改进的模型来预测湍流火焰中的 NO 分布。构建了一个单独的 NO 反应速率表，以说明对 NO 生成的不稳定和非绝热效应。与现有模型不同，非绝热效应是通过在小火焰计算中通过比例因子指定不同的焓缺陷来考虑的。此外，观察到 NO 反应速率随 NO 浓度的瞬态变化表现出两个线性阶段。因此，仅包含三个火焰数据库来描述瞬态过程中的 NO 反应速率，从而在保持模型精度的同时简化小火焰表。提议的 NO 预测模型在湍流燃烧的大涡模拟中得到验证，包括经典的桑迪亚 D 和悉尼漩涡 SM1 火焰。计算出的 NO 变化与实验数据显示出良好的一致性，证明了所提出模型的适用性和准确性。