管道内甲烷/空气层流火焰向湍流转捩的微观特性研究

Microscopic Characteristics of Transition From Laminar to Turbulent Flame of Premixed Methane/air in the Duct

为揭示障碍物对火焰的加速特性,本文运用高速摄影技术和压力传感器分别对空管道和置障管道内甲烷/空气预混火焰的形状变化、火焰传播速度及升压特性进行了实验研究,利用Power-law火焰褶皱模型对管道内流场结构进行了大涡模拟分析。结果表明:空管道和置障管道内甲烷/空气预混火焰传播过程都经历了层流火焰向湍流的转变,且置障管道内的湍流强度明显高于空管道的;障碍物未对前期火焰传播过程产生影响,23ms之前,空管道和置障管道内火焰形态完全一致;障碍物能显著提高管道内的压力上升速率,相比于空管道,障碍物对管道内火焰传播速度提升501%;空管道内涡旋出现在管道的近壁侧,置障管道内涡旋出现在障碍物的背风侧,管道内出现的涡旋结构是火焰形态不断变化的根本原因;空管道湍流燃烧机制始终处于薄火焰区域,而置障管道内湍流火焰机制由薄火焰区域转变到破碎火焰区域;基于大涡模拟的Power-law火焰褶皱模型成功再现了实验中观察到的火焰形状、火焰前锋速度及流场结构,说明该模型适用于置障管道内预混火焰传播特性的研究.

To reveal the acceleration characteristics of premixed methane/air flame propagating in blank and obstructed ducts,high-speed video photography and pressure transducer are used to study the flame shape changes,flame front speed and pressure build-up in the experiment.The power-law flame wrinkling mode based on the large eddy simulation（LES） is applied to investigate the flow structure.The results demonstrate that premixed methane/air flame undergoes transition from laminal to turbulent combustion both in blank and obstructed ducts,the turbulent intensity in obstructed duct is more larger while obstacles have little influence on the initial stage of flame propagation as the observed phenomena are the same in the blank duct and in the obstructed duct before 23 ms.Obstacles have a pronounced effect on the flame velocity and pressure rising rate,particularly,compared to the flame speed obtained in the blank duct,the flame velocity has increased by 501% in obstructed duct.Vortices which are observed on the leeside of obstacle and close to the side wall in obstructed and blank duct,respectively,play the dominant role in the evolution of flame shape.Furthermore,the turbulent combustion regime differently with different configurations due to it appears in the thin reaction zones in obstructed duct and observed in the broken reaction zones in the smooth duct.The flame shape changes and flow structure observed in the experiments can be reproducible in the numerical simulations using LES model which indicates the LES model can be used in premixed flame propagating in an obstructed duct.