Abstract Features of the flame transfer function (FTF) are characterized for turbulent, non-swirled, bluff body stabilized “M” flames for different hydrogen and methane blends including pure hydrogen flames. An increase in the cut-off frequency of the FTF is observed for increasing hydrogen concentration. Modulations in the form of peaks and troughs in the gain and the phase were also observed and are shown to be caused by the interaction of two different flow disturbances, acoustic and convective, originating upstream of the flame. The first mechanism is due to the acoustic velocity fluctuations imposed at the base of the flame. A Strouhal number scaling based on the flame height and bulk velocity is shown to collapse the phase slopes and the cut-off frequencies. The second mechanism is shown to be due to vortex shedding from the grub screws used to align the bluff body in the inlet pipe. The associated convective time-delay is used to define a second Strouhal number which collapses the modulations in the gain and phase. A model is developed that separately considers the impulse response of each mechanism and is interpreted as a distribution of time lags between velocity fluctuations and the unsteady heat release rate. The distributed time lag (DTL) model consists of two distributions that are shown to capture all the features of the FTFs. The distributions show that the acoustic and convective mechanisms behave as a low pass filter and band pass filter, respectively. This results in a band of frequencies where they interact through superposition driving fluctuations of heat release rate. Similar interactions are shown to exist in the forced cold flow revealing that they are of hydrodynamic origin. Further, the band of frequencies are shown to be centered around the natural shedding frequency of the grub screws appearing as peaks in the unforced energy spectra of the velocity at the dump plane. Finally, a generalized model which takes as an input the bulk velocity, flame height and a geometric parameter is derived assuming a linear dependency of the DTL parameters. The model is shown to predict the behavior of the FTFs relatively well and can potentially be used to analyse regions in the operating conditions map which have not been experimentally tested.

中文翻译：

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贫预混 H2/CH4 火焰中传递函数的标度和预测

摘要 火焰传递函数 (FTF) 的特征是针对包括纯氢火焰在内的不同氢和甲烷混合物的湍流、非涡流、钝体稳定的“M”火焰进行表征。随着氢浓度的增加，观察到 FTF 的截止频率增加。还观察到增益和相位中以波峰和波谷形式出现的调制，并且表明是由源自火焰上游的两种不同流动扰动（声学和对流）的相互作用引起的。第一种机制是由于施加在火焰底部的声速波动。显示了基于火焰高度和体积速度的 Strouhal 数缩放，以折叠相位斜率和截止频率。第二种机制是由于用于对齐入口管中的钝体的平头螺钉产生的涡流脱落。相关的对流时间延迟用于定义第二个 Strouhal 数，该数使增益和相位中的调制崩溃。开发了一个模型，该模型分别考虑每个机构的脉冲响应，并将其解释为速度波动和不稳定热释放率之间的时间滞后分布。分布式时间滞后 (DTL) 模型由两个分布组成，显示为捕获 FTF 的所有特征。分布显示声学和对流机制分别表现为低通滤波器和带通滤波器。这导致它们通过叠加驱动放热率波动而相互作用的频率带。在强制冷流中显示出类似的相互作用，表明它们是流体动力学起源的。此外，频率带显示为以平头螺钉的自然脱落频率为中心，表现为倾卸平面速度的非受力能谱中的峰值。最后，假设 DTL 参数的线性相关性，推导出将体积速度、火焰高度和几何参数作为输入的广义模型。该模型可以相对较好地预测 FTF 的行为，并且有可能用于分析操作条件图中尚未经过实验测试的区域。频率带显示为以平头螺钉的自然脱落频率为中心，表现为倾卸平面速度的非受力能谱中的峰值。最后，假设 DTL 参数的线性相关性，推导出将体积速度、火焰高度和几何参数作为输入的广义模型。该模型可以相对较好地预测 FTF 的行为，并且有可能用于分析操作条件图中尚未经过实验测试的区域。频率带显示为以平头螺钉的自然脱落频率为中心，表现为倾卸平面速度的非受力能谱中的峰值。最后，假设 DTL 参数的线性相关性，推导出将体积速度、火焰高度和几何参数作为输入的广义模型。该模型可以相对较好地预测 FTF 的行为，并且有可能用于分析操作条件图中尚未经过实验测试的区域。