Impact of Combustion Modeling on the Spectral Response of Heat Release in LES
Impact of Combustion Modeling on the Spectral Response of Heat Release in LES
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DOI：
10.1080/00102202.2018.1558218
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发表时间：
2019-09
影响因子：
1.9
通讯作者：
Feichi Zhang;T. Zirwes;P. Habisreuther;H. Bockhorn;D. Trimis;H. Nawroth;C. Paschereit
中科院分区：
文献类型：
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作者：
Feichi Zhang;T. Zirwes;P. Habisreuther;H. Bockhorn;D. Trimis;H. Nawroth;C. Paschereit
摘要本文评估了在大涡模拟中，采用不同的空间滤波平均反应率封闭概念对湍流热释放分辨谱响应的影响。两个著名的燃烧模型，湍流火焰速度闭合（TFC）和动态增厚火焰（DTF）模型已被应用到预混湍流射流火焰，否则相同的数值设置。虽然在DTF模型中火焰前缘被人为地加厚，但与TFC模型相比，它再现了更薄的火焰，因此，更强的火焰-湍流相互作用。由于两种方法的时间平均量相当，DTF方法显示出与TFC模型相比，局部和积分热释放率在谱域中的总体波动更高，特别是在高频范围内。一个更好的协议与测得的声压密度观察TFC在低频范围内和DTF在高频范围内。TFC模拟与不同的源配方，也就是说，表现出可比的火焰厚度和光谱的热释放，但计算的平均流量，但是，偏离很大程度上从测量数据为当前的设置。在第二步中，相同的配方的平均速率被应用到一个受激平面射流火焰（二维（2D））使用等距网格单元和强制流入的条件，从而排除了不同的网格分辨率和宽带湍流波动的影响。这种设置是专门为详细分析火焰对流动不稳定性和网格分辨率的响应而定制的。与DTF模型和直接数值模拟的结果相比，即使在足够细的网格上，根据TFC方法的反应速率的制剂也会导致相当厚的火焰。因此，DTF配方的反应速率显示出整体更强的热释放速率的响应，强制波动比TFC配方。在低频范围内的差异较小，表明TFC制剂随着频率的增加对热释放波动的阻尼更强。粗网格导致一个更强的阻尼的热释放波动的DTF配方相比，TFC配方，使DTF配方的好处随着网格分辨率的降低而降低。这反映了这些模型对非定常流动和网格分辨率的不同敏感性行为，这对于用LES计算热声问题（例如燃烧噪声）非常重要。
ABSTRACT This work assesses the effect of using different closure concepts for the spatially filtered mean reaction rate on the resolved spectral response of turbulent heat release in large eddy simulations (LESs). Two well-known combustion models, the turbulent flame speed closure (TFC) and the dynamically thickened flame (DTF) models have been applied to a premixed turbulent jet flame with otherwise identical numerical setups. Although the flame front is artificially thickened in the DTF model, it reproduces a thinner flame and, hence, stronger flame–turbulence interactions compared to the TFC model. As the time-averaged quantities from both methods are comparable, the DTF approach shows overall higher fluctuations of local and integral heat release rates in the spectral domain compared to the TFC model, particularly in the high-frequency range. A better agreement with measured sound pressure density is observed for TFC in the low-frequency range and for DTF in the high-frequency range. TFC simulations with different source formulations, that is, , showed comparable flame thicknesses and spectra of heat release, but the averaged flow quantities calculated with , however, deviate largely from measured data for the current setup. In the second step, the same formulations for the mean rate are applied to an excited plane-jet flame (two-dimensional (2D)) using equidistant grid cells and forced inflow conditions, thereby excluding the influence of varying grid resolution and broadband turbulent fluctuations. This setup is specifically tailored for a detailed analysis of flame response to flow unsteadiness and grid resolution. The formulation of the reaction rate according to the TFC approach again results in a considerably thicker flame compared to results obtained from the DTF model and direct numerical simulation, even on a sufficiently fine mesh. Therefore, the DTF formulation of the reaction rate shows overall stronger responses of heat release rates to forced fluctuations than the TFC formulation. Differences are smaller in the low-frequency range, indicating a stronger damping of heat release fluctuations with increasing frequency for the TFC formulation. Coarsening the grid leads to a much stronger damping of heat release fluctuations in the DTF formulation compared with the TFC formulation, so that the benefit of the DTF formulation decreases with decreasing grid resolution. This reflects the different sensitivity behavior of these models with respect to unsteady flows and grid resolutions, which is of great importance for computing thermoacoustic problems with LES, for example, combustion noise.