Non-linear Response of Turbulent Premixed Flames to Imposed Inlet Velocity Oscillations of Two Frequencies
Non-linear Response of Turbulent Premixed Flames to Imposed Inlet Velocity Oscillations of Two Frequencies
复制标题
湍流预混火焰对两种频率的入口速度振荡的非线性响应
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
E. Mastorakos
中科院分区：
文献类型：
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作者：
R. Balachandran;A. Dowling;E. Mastorakos
本文描述了一个实验研究稀薄预混空气/乙烯火焰的非线性响应的两个频率的强进口速度扰动。燃烧室有一个中心放置的海崖体和一个短的石英段。海崖体和流管之间的环形空间，也容纳了声压传感器，允许反应物进入燃烧室。使用扬声器扰动入口流。高速激光层析成像、OH* 化学发光和OH平面激光诱导荧光（PLIF）分别用于流动显示、放热和火焰表面密度（FSD）测量。热释放波动最初线性增加与入口速度振幅为一个单一的频率强迫，饱和后发生强迫振幅约15%的体积速度，这是发现发生由于涡流卷起和随后的火焰湮灭。在第二频率（即谐波）的能量的引入被发现改变涡的形成和脱落频率，这取决于强迫的水平。这导致非线性火焰响应传递函数（定义为不稳定热释放的振幅除以基波处速度扰动的振幅），其振幅极大地取决于扰动中存在的谐波含量的量。高次谐波的引入减少了导致饱和的火焰湮灭事件，从而减少了火焰响应的振幅依赖性中的非线性。这些结果进一步验证了使用顺序的时间分辨OH PLIF测量。从这项研究的结果表明，火焰的声学响应主要是由于火焰面积的变化所影响的调制的环形射流和剪切层的演变。
This paper describes an experimental study investigating the non-linear response of lean premixed air/ethylene flames to strong inlet velocity perturbations of two frequencies. The combustor has a centrally-placed bluff body and a short quartz section. The annulus between the bluff body and the flow tube, which also housed the acoustic pressure transducers, allowed the reactants into the combustor. The inlet flow was perturbed using loudspeakers. High speed laser tomography, OH* chemiluminescence and OH Planar Laser Induced Fluorescence (PLIF) have been used for flow visualization, heat release and flame surface density (FSD) measurements respectively. The heat release fluctuations increased initially linearly with inlet velocity amplitude for a single frequency forcing, with saturation occurring after forcing amplitudes of around 15% of the bulk velocity, which was found to occur due to vortex roll up and subsequent flame annihilation. The introduction of energy at the second frequency (i.e, the harmonic) was found to change the vortex formation and shedding frequency, depending on the level of forcing. This resulted in a non-linear flame response transfer function (defined as the amplitude of unsteady heat release divided by the amplitude of velocity perturbation at the fundamental) whose amplitude depended greatly on the amount of harmonic content present in the perturbations. The introduction of higher harmonics reduced the flame annihilation events, which are responsible for saturation, thus reducing non-linearity in the amplitude dependence of the flame response. These results were further verified using sequential time-resolved OH PLIF measurements. The findings from this study suggest that the acoustic response of the flame was mostly due to flame area variation effected by modulation of the annular jet and evolution of the shear layers.