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Impact of swirl and bluff-body on the transfer function of premixed flames
Proceedings of the Combustion Institute ( IF 3.4 ) Pub Date : 2018-09-11 , DOI: 10.1016/j.proci.2018.06.148
M. Gatti , R. Gaudron , C. Mirat , L. Zimmer , T. Schuller

The frequency response of three lean methane/air flames submitted to flowrate perturbations is analyzed for flames featuring the same equivalence ratio and thermal power, but a different stabilization mechanism. The first flame is stabilized by a central bluff body without swirl, the second one by the same bluff body with the addition of swirl and the last one only by swirl without central insert. In the two last cases, the swirl level is roughly the same. These three flames feature different shapes and heat release distributions, but their Flame Transfer Function (FTF) feature about the same phase lag at low frequencies. The gain of the FTF also shows the same behavior for the flame stabilized by the central insert without swirl and the one fully aerodynamically stabilized by swirl. Shedding of vortical structures from the injector nozzle that grow and rollup the flame tip controls the FTF of these flames. The flame stabilized by the swirler-plus-bluff-body system features a peculiar response with a large drop of the FTF gain around a frequency at which large swirl number oscillations are observed. Velocity measurements in cold flow conditions reveal a strong reduction of the size of the vortical structures shed from the injector lip at this forcing condition. The flame stabilized aerodynamically only by swirl and the one stabilized by the bluff body without swirl do not exhibit any FTF gain drop at low frequencies. In the former case, large swirl number oscillations are still identified, but large vortical structures shed from the nozzle also persist at the same forcing frequency in the cold flow response. These different flame responses are found to be intimately related to the dynamics of the internal recirculation region, which response strongly differs depending upon the injector used to stabilize the flame.



中文翻译:

旋流和钝体对预混火焰传递函数的影响

对于具有相同当量比和热功率,但稳定机制不同的火焰,分析了三个经受流量扰动的贫甲烷/空气火焰的频率响应。第一个火焰由不带涡流的中央钝体稳定,第二个由不带涡流的同一个钝体稳定,最后一个仅由不带中心插入件的涡流稳定。在最后两种情况下,涡旋水平大致相同。这三个火焰具有不同的形状和热量释放分布,但是它们的火焰传递函数(FTF)在低频下具有大约相同的相位滞后。FTF的增益对于中央插入物稳定而没有涡旋的火焰表现出相同的行为,而通过涡旋完全空气动力学稳定的火焰表现出相同的行为。从喷嘴喷出的旋涡结构脱落会扩大并聚集火焰尖端,从而控制这些火焰的FTF。由旋流器加吹液器体系统稳定的火焰具有独特的响应,在观察到大涡旋数振荡的频率附近,FTF增益大幅下降。在冷流条件下的速度测量表明,在这种强迫条件下,从喷油嘴喷出的旋涡结构的尺寸大大减小。仅通过涡流在空气动力学上稳定的火焰和通过没有涡流的钝体稳定的火焰在低频下不会表现出任何FTF增益下降。在前一种情况下,仍然可以识别出大的旋流数振荡,但是在冷流响应中,从喷嘴喷出的大型旋涡结构也以相同的强迫频率持续存在。

更新日期:2018-09-11
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