Modal dynamics of self-excited azimuthal instabilities in an annular combustion chamber
Modal dynamics of self-excited azimuthal instabilities in an annular combustion chamber
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DOI：
10.1016/j.combustflame.2013.04.031
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发表时间：
2013-11
影响因子：
4.4
通讯作者：
N. Worth;J. Dawson
中科院分区：
文献类型：
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作者：
N. Worth;J. Dawson
本文描述了在大气条件下工作的简单环形燃烧室中自激方位不稳定性的时变幅度及其与总放热率的关系。燃烧室的结构是模块化的，由12个、15个或18个等间距的预混钝体火焰围绕固定的圆周组成，能够研究相邻火焰之间的大规模相互作用的影响。从环上方获得的高速OH∗化学发光成像和在环周围多个位置获得的压力测量表明，模式的极限环在很大程度上是简并的，因为它们经历了驻留模式和自旋模式之间顺时针和逆时针方向的连续跃迁，但具有相同的共振频率。在大涡模拟中也观察到了类似的行为，这表明简并模式可能是环形燃烧室中自激方位不稳定性的一个特征。通过将不稳定性模拟为两个沿相反方向传播的振幅随时间变化的声波，我们证明了存在与火焰间距、当量比和旋涡构型有关的站立m=1或自旋m=1±1模的统计盛行。位相平均的OH-∗化学发光揭示了均匀旋涡构型在极限环条件下驱动自旋模式方向的可能机制。通过将环空划分为内环区和外环区，发现自旋方向与峰值放热率相对于沿环壁诱导的整体涡流方向的空间分布的变化相一致。对于驻波模式，热释放率的全局积分起伏沿声学模式的形状变化，压力节点处的贡献可以忽略不计，而压力反节点处的贡献最大。
In this paper we describe the time-varying amplitude and its relation to the global heat release rate of self-excited azimuthal instabilities in a simple annular combustor operating under atmospheric conditions. The combustor was modular in construction consisting of either 12, 15 or 18 equally spaced premixed bluff-body flames around a fixed circumference, enabling the effect of large-scale interactions between adjacent flames to be investigated. High-speed OH∗chemiluminescence imaged from above the annulus and pressure measurements obtained at multiple locations around the annulus revealed that the limit cycles of the modes are degenerate in so much as they undergo continuous transitions between standing and spinning modes in both clockwise (CW) and anti-clockwise (ACW) directions but with the same resonant frequency. Similar behaviour has been observed in LES simulations which suggests that degenerate modes may be a characteristic feature of self-excited azimuthal instabilities in annular combustion chambers. By modelling the instabilities as two acoustic waves of time-varying amplitude travelling in opposite directions we demonstrate that there is a statistical prevalence for either standingm= 1 or spinningm= ±1 modes depending on flame spacing, equivalence ratio, and swirl configuration. Phase-averaged OH∗chemiluminescence revealed a possible mechanism that drives the direction of the spinning modes under limit-cycle conditions for configurations with uniform swirl. By dividing the annulus into inner and outer annular regions it was found that the spin direction coincided with changes in the spatial distribution of the peak heat release rate relative to the direction of the bulk swirl induced along the annular walls. For standing wave modes it is shown that the globally integrated fluctuations in heat release rate vary in magnitude along the acoustic mode shape with negligible contributions at the pressure nodes and maximum contributions at the pressure anti-nodes.