Flow Field and Flame Dynamics of Swirling Methane and Hydrogen Flames at Dry and Steam Diluted Conditions
Flow Field and Flame Dynamics of Swirling Methane and Hydrogen Flames at Dry and Steam Diluted Conditions
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DOI：
10.1115/1.4028392
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发表时间：
2015-04-01
影响因子：
1.5
通讯作者：
Paschereit, Christian Oliver
中科院分区：
文献类型：
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作者：
Terhaar, Steffen;Krueger, Oliver;Paschereit, Christian Oliver
大多数最近的固定燃气涡轮机燃烧室采用旋流来稳定火焰。旋流发生涡破裂（VB），并表现出复杂的流场，包括区域的再循环流体和高剪切强度的区域。通常，在这些流动中发现自激螺旋流不稳定性，其表现在涡核的进动中，并且可能以有利和不利的方式影响燃烧过程。在本研究中，我们调查的发生和形状的自激流体动力学不稳定性和它们的影响，在很宽的操作条件下的热释放波动和混合特性。我们采用高速立体粒子图像测速（S-PIV）和同步OH*-化学发光成像来解决流速和热释放分布，分别。结果表明，火焰形状有四种：分离环形火焰、长喇叭形火焰、V形火焰和锚定在燃烧室入口附近的非常短的火焰。火焰形状被发现与混合物的反应性密切相关。高度蒸汽稀释或非常稀薄的火焰会导致分离，而氢燃料会导致非常短的火焰。分离火焰具有螺旋不稳定性，其在频率和形状方面与等温情况相似。一个完全抑制的螺旋结构被发现为V火焰。喇叭形火焰和超短火焰都具有不同频率和形态的螺旋不稳定性。相位平均OH*-化学发光图像表明，螺旋不稳定性导致大规模的放热波动。利用波动的螺旋结构来使用层析重建技术。此外，它示出的螺旋不稳定性显着增强之间的混合发出的射流和中央回流区。
The majority of recent stationary gas turbine combustors employ swirling flows for flame stabilization. The swirling flow undergoes vortex breakdown (VB) and exhibits a complex flow field including zones of recirculating fluid and regions of high shear intensities. Often, self-excited helical flow instabilities, which manifest in a precession of the vortex core, are found in these flows and may influence the combustion process in beneficial and adverse ways. In the present study, we investigate the occurrence and shape of self-excited hydrodynamic instabilities and their impact on heat release fluctuations and mixing characteristics over a wide range of operating conditions. We employ high-speed stereoscopic particle image velocimetry (S-PIV) and simultaneous OH*-chemiluminescence imaging to resolve the flow velocities and heat release distribution, respectively. The results reveal four different flame shapes: A detached annular flame, a long trumpet shaped flame, a V flame, and a very short flame anchored near the combustor inlet. The flame shapes were found to closely correlate with the reactivity of the mixture. Highly steam-diluted or very lean flames cause a detachment, whereas hydrogen fuel leads to very short flames. The detached flames feature a helical instability, which, in terms of frequency and shape, is similar to the isothermal case. A complete suppression of the helical structure is found for the V flame. Both the trumpet shaped flame and the very short flame feature helical instabilities of different frequencies and appearances. The phase-averaged OH*-chemiluminescence images show that the helical instabilities cause large-scale heat release fluctuations. The helical structure of the fluctuations is exploited to use a tomographic reconstruction technique. Furthermore, it is shown that the helical instability significantly enhances the mixing between the emanating jet and the central recirculation zone.