基于动态火焰增厚模型气氧/气甲烷剪切火焰燃烧不稳定性的LES研究

LES Investigation of Combustion Instability on GO2/GCH4 Shear Flame Based on Dynamic Thickened Flame Model

关键词:  液体火箭发动机  DTF燃烧模型  大涡模拟  燃烧不稳定性  POD分解

Key words:  Liquid rocket engine  DTF combustion model  Large eddy simulation  Combustion instability  POD decomposition

摘要:

为提升对液体火箭发动机中流动诱导燃烧不稳定机制的理解，使用动态火焰增厚模型（DTF）对气氧/气甲烷同轴剪切喷射燃烧试验进行了大涡模拟（LES），考虑了在相同氧燃混合比下的两种燃氧速度比工况，模拟的OH分布与PLIF试验结果吻合良好。燃氧速度比为0.5时，沿流向方向火焰从层流向湍流转变，同时剪切层厚度与褶皱程度均有明显增大。速度比为1.5时，火焰伴随着周期性熄灭和重燃而变得不稳定，通过联合OH与速度分布序列进行本征正交分解（POD），获得了对熄火起主导作用的大尺度相干结构，进一步将重构流场与火焰动态演化联系起来，揭示了流动因素对火焰不稳定性的影响过程。

Abstract:

In order to improve the understanding of flow-induced combustion instability mechanism in liquid rocket engines， Large Eddy Simulation （LES） was carried out for gas-oxygen/gas-methane coaxial shear injection combustion test using the Dynamic Thickened Flame （DTF） model. Two cases with different fuel-oxygen velocity ratio under the same oxygen-fuel mixing ratio were simulated. The predicted OH distribution is in good agreement with the PLIF results. When the fuel-oxygen velocity ratio is 0.5， the flame transits from laminar to turbulent along the flow direction， while the thickness of shear layer and the level of wrinkle increase significantly. When the velocity ratio is 1.5， the flame becomes unstable with periodic quenching and reignition. The large-scale coherent structure that plays a dominant role in quenching was obtained by Proper Orthogonal Decomposition （POD） associating OH with velocity distribution sequences， which further linked the reconstructed flow with the dynamic evolution of flame and revealed the influence process of flow factors on flame instability.