采用不同建表方法的火焰面模型在燃烧室中的应用研究

Study of the Application of Flamelet Models in Combustorwith Different Tabulation Methods

关键词:  航空发动机燃烧室  火焰面/进度变量  火焰面生成流形  反应进度变量  概率密度函数  建表方法

Key words:  Aeroengine combustor  Flamelet/progress variable  Flamelet generated manifolds  Reaction progress variable  Probability density function  Tabulation method

摘要:

为加深对航空发动机燃烧室中湍流燃烧过程的理解，采用不同建表方法的火焰面模型对航空发动机模型燃烧室内的湍流燃烧过程进行数值模拟，包括层流火焰面数据库的构建和反应进度变量的PDF类型两个方面。其中，层流火焰面数据库的构造方法包括基于扩散火焰的FPV和基于预混火焰的FGM模型，反应进度变量的PDF类型包括δ和β分布。LISA和KHRT模型分别用于模拟液膜和液滴的破碎过程，非平衡Langmuir-Knudsen模型用于模拟液滴的蒸发过程。LISA模型得到的液膜破碎距离约为4.6mm，液滴直径在文氏管出口下游迅速减小到10μm左右，并在头部出口下游附近完全蒸发。通过与相干反斯托克斯喇曼散射(CARS)和可调谐二极管激光吸收光谱(TDLAS)测量温度的对比，验证了FPV和FGM模型的精度，并表明在流动变化较大的位置FPV模型具有更高的精度，而其他位置FGM模型具有更高的精度，采用β分布作为反应进度变量PDF的模型，可以有效提高温度的预测进度，而且主燃区内的误差基本都在5%以内。此外采用β分布作为反应进度变量PDF的FGM模型，可以更好地描述未燃混合物被回流燃气点火的过程，而且反应进度变量的PDF类型比层流火焰面数据库构建方法的影响更为显著。

Abstract:

In order to improve the knowledge and understanding of the turbulent combustion in aeroengine combustor， flamelet models with different tabulation methods are used to simulate the turbulent combustion in an aeroengine model combustor. The tabulation methods include two sections: One is the construction method of laminar flamelet library that means Flamelet/Progress Variable (FPV) based on diffusion flame and Flamelet Generated Manifolds (FGM) based on premixed flame; the other is the Probability Density Function (PDF) type of reaction progress variable that means δ and β distribution. LISA and KHRT models are employed to model the breakup of liquid film and droplets respectively， and non-equilibrium Langmuir-Knudsen model is employed to model the evaporation of droplets. The breakup distance of liquid film from LISA model is about 4.6 mm， and the droplets diameter decreases rapidly to about 10μm in the downstream of venturi exit and are completely evaporated close to the downstream of dome exit. Compared with the temperature from Coherent Anti-Stokes Raman Scattering (CARS) and Tunable Diode Laser Absorption Spectroscopy (TDLAS)， the accuracy of FPV and FGM models is verified， and FPV model has higher accuracy in the locations where flow changes violently and moreover FGM model has higher accuracy in the rest locations. Models adopting β distribution as the PDF of reaction progress variable can improve the accuracy of temperature， and the error of temperature is almost below 5% in primary zone. In addition， it can be described better that the unburned mixture is ignited by the recirculated burned gas by FGM with β distribution， and the PDF type of reaction progress variable has a more important effect than construction method of laminar flamelet library.