Flame Leading Edge and Flow Dynamics in a Swirling, Lifted Flame
Flame Leading Edge and Flow Dynamics in a Swirling, Lifted Flame
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DOI：
10.1080/00102202.2014.923410
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发表时间：
2012-06
影响因子：
1.9
通讯作者：
M. Malanoski;Michael Aguilar;D. Shin;T. Lieuwen
中科院分区：
文献类型：
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作者：
M. Malanoski;Michael Aguilar;D. Shin;T. Lieuwen
在高旋流场中，旋涡破裂的火焰往往在内部流动驻点前气动稳定。与具有几乎固定的、明确定义的火焰附着点的剪切层稳定火焰相比，空气动力学稳定火焰的前缘可以基本上由于涡流破裂区域的固有动力学和外部施加的振荡两者而四处移动。该火焰稳定点相对于流场的运动在燃烧不稳定期间可能具有重要的动力学作用，因为它产生火焰前缘褶皱和热释放波动。例如，先前的研究表明，在高强迫振幅下火焰响应的非线性动力学与这些前缘动力学有关。这种放热机制与其他火焰湍流过程一起存在，这些过程由剪切层卷起和旋流波动等过程引起。本文描述了流动强迫对旋流稳定火焰前缘动力学影响的实验研究。火焰和流动动力学的特点是使用高速粒子图像测速（PIV）和CH* 化学发光成像。通过改变强迫频率、振幅和声场对称性来实现一系列强迫条件。这些结果表明，火焰前缘的运动是由自然流动不稳定性，特别是绕中心线的回流区的进动。在激励频率的前缘运动的波动比这些自然运动小得多，但仍然是与外部激励相关联的流体颗粒位移的顺序，这表明它们表现出对局部火焰燃烧和热释放的重要影响。火焰响应模型表明，全球，空间集成的热释放响应是由三个因素控制的涡扰动，声流扰动，火焰前缘运动。涡流运动主导了火焰响应，火焰前缘运动对整个放热响应的贡献较小。这是一个重要的结果，因为它表明火焰前缘的显著运动实际上对于理解火焰的空间积分的强制响应几乎没有动力学意义。
Flames in high swirl flow fields with vortex breakdown often stabilize aerodynamically in front of interior flow stagnation points. In contrast to shear layer stabilized flames with a nearly fixed, well-defined flame attachment point, the leading edge of aerodynamically stabilized flames can move around substantially as a result of both the inherent dynamics of the vortex breakdown region and externally imposed oscillations. Motion of this flame stabilization point relative to the flow field may have an important dynamical role during combustion instabilities, as it creates flame front wrinkles and heat release fluctuations. For example, a prior study has shown that nonlinear dynamics of the flame response at high forcing amplitudes were related to these leading edge dynamics. This heat release mechanism exists alongside other flame wrinkling processes, arising from such processes as shear layer rollup and swirl fluctuations. This article describes an experimental investigation of flow forcing effects on the dynamics of the leading edge of a swirl stabilized flame. Flame and flow dynamics were characterized using high-speed particle image velocimetry (PIV) and CH* chemiluminescence imaging. A range of forcing conditions was achieved by varying the forcing frequency, amplitude, and acoustic field symmetry. These results show that the flame leading edge motion is dominated by the natural flow instabilities, particularly the precession of the recirculation zone around the centerline. The fluctuations in leading edge motion at the excitation frequency are much smaller than these natural motions, but are still on the order of the fluid particle displacement associated with the external excitation, indicating that they exhibit an important influence on local flame wrinkling and heat release. Flame response modeling shows that the global, spatially integrated heat release response is controlled by three factors—vortical disturbances, acoustic flow disturbances, and flame leading edge motion. The vortical flow motions dominate the flame response, and the flame leading edge motion is a minor contributor to the overall heat release response. This is an important result, as it shows that the significant motions of the flame leading edge actually have little dynamical significance for understanding the spatially integrated, forced response of the flame.