氢燃料双模态冲压发动机火焰结构及其稳定机制的LES研究

Flame structure and stability mechanism in a hydrogen- fueled dual-mode ramjet engine using LES

关键词:  双模态冲压发动机  超声速燃烧  火焰结构  火焰稳定机制  大涡模拟

Key words:  Dual-mode ramjet engine  Supersonic combustion  Flame structure  Flame stabilization mechanism  Large-eddy simulation

摘要:

为深入理解双模态冲压发动机内流场结构和燃烧特性，本文采用精细的有限速率化学反应模型，对凹腔内氢气直喷式超声速燃烧室火焰进行了大涡模拟研究。发动机隔离段入口马赫数为2.0，滞止温度和压力分别为950 K和0.82 MPa。定性和定量的验证分析表明，计算结果良好符合试验所反映的物理规律，再现了两种典型的工作模态及其稳焰模式。当量比为0.1时，发动机处于超燃模态，为凹腔剪切层稳焰模式；当量比为0.3时，发动机处于亚燃模态，为凹腔辅助射流尾迹稳焰模式，分离涡的大尺度脉动及凹腔回流区的缺失致使火焰剧烈振荡。同时采用改进的火焰因子和过滤函数详细分析了局部火焰特征和流动模式，观察到了不同规律的局部熄火现象，并且剧烈的流动振荡对于局部火焰结构的稳定性有着不利影响。

Abstract:

In order to obtain an improved understanding of the flow structure and combustion characteristics in a dual-mode ramjet engine， investigation on the supersonic combustor with hydrogen direct-injection on the cavity-floor was carried out， via detailed finite-rate chemistry large-eddy simulation. The inflow conditions of isolator entrance were Ma=2.0， T₀=950 K， and p₀=0.82 MPa. The qualitative and quantitative validation showed that， the calculated results accorded with the physical laws of experiment well， reproducing two typical operating modes and their flame stabilization modes. When the equivalence-ratio is 0.1， the engine is at scramjet mode corresponding to cavity shear-layer stabilized flame. When the equivalence-ratio is 0.3， the engine is at ramjet mode corresponding to cavity assisted jet-wake stabilized flame. The large-scale fluctuation of separation vortexes and the absence of cavity recirculation zone make the flame oscillate violently. Furthermore， the modified flame index and filter functions were used to analyse the local flame features and flow regimes in detail. Different phenomena about local quenching were observed， and the severe flow oscillation has adverse effect on the stability of local flame structure.