Correspondence Between “Stable” Flame Macrostructure and Thermo-acoustic Instability in Premixed Swirl-Stabilized Turbulent Combustion-猫眼课题宝

DOI：

10.1115/1.4029173

发表时间：

2014-12

期刊：

影响因子：

通讯作者：

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其他

文献类型：

作者：

M. Habib;Soufien Taamallah;Z. LaBry;A. Ghoniem;Santosh J. Shanbhogue

本文对预混旋流稳定突扩燃烧室中的突扩宏观结构--或突扩刷空间分布--与热声不稳定性之间的联系进行了实验研究。我们用预混甲烷-空气在当量比（f）从贫熄火极限到f/4 0：75的范围内操作燃烧室。首先，我们观察到随着f升高，在该稀燃范围内的不同动态模式。我们还记录了/对相同宏观结构的影响。接下来，我们将研究动态模式转换和相同宏观结构变化之间的对应关系。为此，我们通过下游截短来修改燃烧室长度，而不改变上游的基本气流。因此，几何形状的谐振频率被改变，从而允许解耦热释放速率波动和声反馈。按照相同的实验方案，对改进的艾德燃烧室和相同当量比范围内的平均燃烧室构型进行了检验。结果发现，不仅在两种燃烧室中观察到相同序列的相同宏观结构，而且在相似的当量比下发生转变。特别是，在长燃烧室的外回流区（ORZ）中，与基频不稳定性的开始同时出现的热声不稳定性的出现与短燃烧室相似，但在后一种情况下不会伴随着向热声不稳定性的转变。然后，我们通过分析非反应湍流和不同湍流类型的流线、平均速度和均方根速度来询问湍流场。最后，我们专注于在声学解耦的情况下的ORZ的的的过渡的AQUAME。我们对这种转变的分析表明，它是逐渐发生的，在ORZ中间歇性地出现一个小的，并且随着/的增加概率增加。这种现象的频谱分析，我们称之为“ORZ的不稳定现象”-显示存在的不稳定事件发生在两个不同的低频范围。在与内部回流区（IRZ）的膨胀和收缩相关的范围（cid：2）（1 Hz-10 Hz）内的极低频率的宽带和中心在28 Hz附近的窄带，这是当由ORZ平流输送时，卫星的旋转频率。10.1115/1.4029173]

In this paper, we conduct an experimental investigation to study the link between the ﬂame macroscale structure—or ﬂame brush spatial distribution—and thermo-acoustic instabilities, in a premixed swirl-stabilized dump combustor. We operate the combustor with premixed methane–air in the range of equivalence ratio ( / ) from the lean blowout limit to / ¼ 0 : 75. First, we observe the different dynamic modes in this lean range as / is raised. We also document the effect of / on the ﬂame macrostructure. Next, we examine the correspondence between dynamic mode transitions and changes in ﬂame macrostructure. To do so, we modify the combustor length—by downstream truncation— without changing the underlying ﬂow upstream. Thus, the resonant frequencies of the ge- ometry are altered allowing for decoupling the heat release rate ﬂuctuations and the acoustic feedback. Mean ﬂame conﬁgurations in the modiﬁed combustor and for the same range of equivalence ratio are examined, following the same experimental protocol. It is found that not only the same sequence of ﬂame macrostructures is observed in both combustors but also that the transitions occur at a similar set of equivalence ratio. In particu- lar, the appearance of the ﬂame in the outside recirculation zone (ORZ) in the long combustor—which occurs simultaneously with the onset of instability at the fundamental frequency—happens at similar / when compared to the short combustor, but without being in latter case accompanied by a transition to thermo-acoustic instability. Then, we interrogate the ﬂow ﬁeld by analyzing the streamlines, mean, and rms velocities for the nonreacting ﬂow and the different ﬂame types. Finally, we focus on the transition of the ﬂame to the ORZ in the acoustically decoupled case. Our analysis of this transition shows that it occurs gradually with an intermittent appearance of a ﬂame in the ORZ and an increasing probability with / . The spectral analysis of this phenomenon—we refer to as “ORZ ﬂame ﬂickering”—shows the presence of unsteady events occurring at two distinct low frequency ranges. A broad band at very low frequency in the range (cid:2) (1 Hz–10Hz) associated with the expansion and contraction of the inner recirculation zone (IRZ) and a narrow band centered around 28Hz which is the frequency of rotation of the ﬂame as it is advected by the ORZ ﬂow. 10.1115/1.4029173]

Correspondence Between “Stable” Flame Macrostructure and Thermo-acoustic Instability in Premixed Swirl-Stabilized Turbulent Combustion

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