详细化学反应机理对预混丙烷钝体熄火模拟影响

Effects of Detailed Chemical Mechanism on Premixed Propane Bluff Body Blow-Off Simulation

关键词:  概率密度函数输运方程湍流燃烧模型（TPDF）  大涡模拟（LES）  钝体熄火  反应机理  AECSC程序

Key words:  Transported probability density function  Large eddy simulation  Bluff body blowoff  Reaction mechanism  Aero engine combustor simulation code

摘要:

航空发动机熄火预测是重要关键问题之一，湍流和化学反应的非线性相互作用使预测非常困难。本文采用大涡模拟（LES）对湍流进行高精度模拟，采用概率密度函数输运方程湍流燃烧模型（TPDF）耦合JL4，Z66和H73三种化学反应机理，对预混丙烷钝体熄火现象和规律进行研究。JL4的反应机理最简单，反应释热快，局部放热高，火焰宽度大，火焰两侧温度梯度大，燃烧更加趋于稳定，无法模拟出熄火状态。H73机理绝热火焰温度低，火焰温度低，回流区中部OH含量高；在近熄火状态，大量CO被氧化，释放热量过高导致无法模拟出熄火现象。Z66机理可以模拟出火焰正常状态，在低当量比下也可以模拟出熄火状态。算例中，局部Da>1的区域超过35%则会发生熄火。

Abstract:

The prediction of aero engine flameout is a crucial problem. The nonlinear interaction of turbulence and chemical reactions increases the difficulty of prediction. The phenomenon and law of premixed propane bluff body blow-off were investigated by analyzing turbulence and combustion. The large eddy simulation was used to simulate turbulence with high accuracy. Three chemical mechanisms， JL4， Z66 and H73， were coupled by the transported probability density function to describe combustion process. JL4’s reaction is the simplest of the three， leading to the larger rate of exothermic reaction， wider flame width， higher temperature gradient on both sides of the flame and more stable combustion， and is unable to simulate the blowoff state. The lower adiabatic flame temperature of H73 mechanism results in the lower simulated flame temperature， and the content of OH in the middle of the simulated recirculation zone is very high. In the blowoff state， a large amount of CO is oxidized， and excessive heat is released， which makes it impossible to simulate the flameout state. The mechanism of Z66 can simulate the normal state of flame， and the flameout state can be correctly simulated under low equivalence ratio. In this bluff body example， if the flame region where the local Da number is greater than 1 exceeds 35%， the extinction will occur.