Very-large eddy simulation of hydrogen flames in strut-based supersonic combustor
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摘要:
采用超大涡模拟（VLES）方法对德国宇航中心（DLR）支板燃烧室中的超声速火焰进行了数值模拟，并使用基于守恒变量的爆炸模态分析方法（CCEMA）对火焰的稳定机理进行了分析。研究中采用了基于
k -ω 切应力输运（SST）模型的VLES湍流模型，以及基于Ingenito超声速燃烧模型（ISCM）和部分搅拌反应器（PaSR）模型的混合湍流燃烧模型。数值模拟方法预测的时间平均温度和流向速度分布与实验数据的吻合度较高。离散方法方面，提出了一种改进的低耗散激波捕捉格式，拥有更好激波分辨能力。相比原始格式，改进的格式进一步提高了燃烧室支板下游点火区内湍流/火焰结构的模拟保真度。火焰诊断结果表明：在着火点前，组分扩散、化学反应和激波压缩效应都对爆炸模态（CEM）起到正面促进作用。另外热爆炸效应相比自由基爆炸更为剧烈，说明了DLR燃烧室内的火焰稳定模式为扩散和压缩效应协助点火模式。Abstract:The very-large eddy simulation (VLES) method was used to simulate the supersonic flames in the strut-injection hydrogen combustor of Germany’s Aerospace Centre (DLR), and the flame stabilization mechanism was analyzed by the conservative representation of chemical explosive mode analysis (CCEMA) method. The VLES turbulent model based on the
k -ω shear stress transport (SST) model and the hybrid turbulent combustion model based on the Ingenito supersonic combustion model (ISCM) along with the partially stirred reactor (PaSR) model were adopted in this study. The time-averaged temperature and streamwise velocity profiles predicted by the numerical methods were in good agreement with the experiment. In terms of discretization method, a modified low dissipation shock-capturing scheme with better shock-capturing ability was proposed. Compared with the original scheme, the simulation fidelity of turbulence/flame structures in the ignition zone was further improved by the modified shock-capturing scheme. The flame diagnostic also showed that the component diffusion, chemical reaction and shock compression effects played positive roles in promoting the explosion mode before the flame onset location. In addition, the thermal explosion effect was more intensive than the radical explosion, indicating that the flame stability mode in the DLR combustor is a diffusion and compression effects assisted-ignition mode. -
图 1 不同截面处的平均温度和流向速度分布曲线
Figure 1. Averaged temperature and streamwise velocity profiles at different locations
图 6 着火区温度和释热率分布图
Figure 6. Distributions of temperature and heat release rate in the ignition region
图 7 瞬时分辨率控制函数分布图
Figure 7. Distributions of the instantaneous resolution control function
图 8 着火区爆炸模态分布图以及组分OH、H、H2O的爆炸指标分布图
Figure 8. Distributions of chemical explosive mode and explosive indexes of species OH, H, H2O in the ignition region
图 9 着火区温度分布图以及化学反应投影项、扩散投影项、可压缩性投影项分布图
Figure 9. Distributions of temperature and projection terms of chemical reaction, diffusion, compressibility in the ignition region
表 1 自由来流及燃料入口条件
Table 1. Free stream and fuel inlet conditions
参数 空气 燃料 U/（m/s） 730 1200 T/K 340 250 p/Pa 101325 101325 $w_{{\rm{O}}_2} $ 0.232 0 $w_{{\rm{N}}_2} $ 0.736 0 $w_{{\rm{H}}_2} $ 0 1 $w_{{\rm{H}}_2{\rm{O}}} $ 0.032 0 注：表中U表示来流速度。 
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