The effect of baffles on self-excited azimuthal modes in an annular combustor
The effect of baffles on self-excited azimuthal modes in an annular combustor
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DOI：
10.1016/j.proci.2014.07.011
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发表时间：
2015
期刊：
影响因子：
--
通讯作者：
J. Dawson;N. Worth
中科院分区：
文献类型：
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作者：
J. Dawson;N. Worth
本文通过实验研究了在环形燃烧室中插入挡板对燃烧室自激方位角模态和非定常放热率的影响。特别注意了它们对方位角模时变行为的影响，这些时变行为是在方位角对称环形腔中最近的实验和大涡模拟（LES）中观察到的。这种时变行为导致方位角模式在自旋和驻波模式之间来回切换。随着单个挡板的加入，腔室的方位角对称性被打破，导致顺时针（CW）和逆时针（ACW）方位角声波之间的耦合。这消除了时变行为并促进了驻波模式。研究发现，需要三个或更多的挡板来实现模态的显著阻尼。由于几乎完美的驻波模式发生在添加单个挡板的情况下，因此获得了高速化学发光测量来表征压力节点和反节点的非定常热释放率。以往的研究表明，最大和最小的热释放率分别在反节点和节点产生。如前所述，反节点处的峰值波动是由压力波动驱动燃烧器进口轴向质量流量波动引起的放热率的轴对称波动引起的。然而，在压力节点处，观察到一个反对称结构通过抵消机制产生可以忽略不计的放热速率。后一个结果表明，横向速度波动在确保在节点产生可忽略不计的热释放率方面起着重要的机制作用。
In this paper the effect of inserting baffles on the self-excited azimuthal modes and unsteady heat release rate in an annular combustor are investigated experimentally. Particular attention is given to their effect on the time-varying behaviour of azimuthal modes observed in recent experiments and Large Eddy Simulations (LES) in azimuthally symmetric annular chambers. This time-varying behaviour causes the azimuthal modes to switch back and forth between spinning and standing wave modes. With the addition of a single baffle, the azimuthal symmetry of the chamber was broken leading to a coupling between the clockwise (CW) and anticlockwise (ACW) azimuthal acoustic waves. This eliminated the time-varying behaviour and promoted standing wave modes. It was found that three or more baffles were required to achieve significant damping of the modes. Since almost perfect standing wave modes occurred with the addition of a single baffle, high-speed chemiluminescence measurements were obtained to characterise the unsteady heat release rate at the pressure node and anti-node. Previous studies have shown that maximum and minimum heat release rate is produced at the anti-nodes and nodes respectively. As found previously, peak fluctuations at the anti-nodes result from axisymmetric fluctuations in heat release rate caused by pressure fluctuations driving axial mass flow fluctuations at the burner inlet. However, at the pressure nodes, an anti-symmetric structure was observed producing negligible heat release rate via the mechanism of cancellation. This latter result suggests that transverse velocity fluctuations play an important mechanistic role in ensuring that negligible heat release rate is produced at the node.