基于火焰面密度的湍流分层燃烧大涡模拟

Large Eddy Simulation of Turbulent Stratified Combustion Using Flame Surface Density

关键词:  大涡模拟  火焰面密度  化学热力学建表  分层燃烧

Key words:  Large eddy simulation  Flame surface density  Thermo-chemistry tabulation  Stratified combustion

摘要:

为了研究分层燃烧火焰结构、发展适用于分层条件的亚格子燃烧模型，采用火焰面密度模型描述燃烧过程，通过化学热力学建表方法确定主要标量信息，对剑桥分层旋流燃烧器SwB5工况进行大涡模拟研究。模拟结果表明，该亚格子燃烧模型可以很好地满足流场上游的计算，但是在下游存在偏差，这可能与所采用的皱褶因子模型低估了湍流对火焰的形变作用有关。由于燃烧放热引起的再层流化现象明显，钝体后回流区近似稳态。瞬时Q函数云图表明，流动在管口附近发生Kelvin-Helmholtz不稳定性并形成环状涡结构。瞬时、统计火焰因子云图表明SwB5的燃烧机制主要由预混燃烧主导。

Abstract:

Large eddy simulation was applied to investigate operating condition SwB5 of Cambridge stratified swirl burner， using flame surface density model to describe combustion process and thermo-chemsitry tabulation to determine major scalars， with the purpose to research flame structure of stratified combustion and develop suitable subgrid scale (sgs) combustion models for the stratified condition. The LES results show that the sgs model is well suit for the calculation of upstream， while it exists deviation in downstream， which may be caused by the wrinkling model adapted underestimate the shape change of turbulent to flame. The recirculation zone formed behind the bluff body is closed to stable owe to the re-laminarisation caused by heat release of combustion. As seen from the snapshot of Q function， a ring vortex formed near the pipe orifice by the Kelvin-Helmholtz flow instability. It can be confirmed from the snapshots of flame index that the premixed mode is dominant in SwB5.