Relative Effects of Velocity- and Mixture-Coupling in a Thermoacoustically Unstable, Partially Premixed Flame
Relative Effects of Velocity- and Mixture-Coupling in a Thermoacoustically Unstable, Partially Premixed Flame
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热声不稳定、部分预混火焰中速度耦合和混合耦合的相对效应
DOI：
10.1115/1.4052262
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
O'Connor, Jacqueline
中科院分区：
文献类型：
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作者：
Karmarkar, Ashwini;Boxx, Isaac;O'Connor, Jacqueline
燃烧不稳定性是现代燃气轮机运行和性能的严重制约因素，燃烧不稳定性是燃烧室声学模式和非定常火焰热释放速率耦合的结果。这种耦合可以通过不同的途径发生，例如流场波动或当量比波动。在实际的燃烧室系统中，涉及到复杂的流体力学和热化学过程，这可能导致多个耦合路径。为了理解和预测实际燃气轮机中燃烧不稳定性的机理，我们考虑了这些耦合路径对部分预混涡流稳定火焰的稳定性和动力学的影响。在这项研究中，我们使用了一个模型燃气轮机燃烧室，有两个同心旋转的空气喷嘴，由一圈喷油器隔开，在5 bar的加压下运行。系统地改变了两股气流之间的分流，以观察其对流动和火焰动力学的影响。用高速立体粒子图像测速仪、OH平面激光诱导荧光和丙酮平面激光诱导荧光分别获得了速度场、火焰和燃料流动行为的信息。根据流动条件的不同，存在热声振荡模式或流体动力模式，被识别为进动涡核。研究的重点是描述这种部分预混火焰中的混合气耦合过程，以及速度振荡对混合气耦合的影响。结果表明，对于这种燃烧室系统，改变两个同心喷嘴之间的流量分配可以改变系统中的主谐振荡模式，从而显著影响燃料在空气中的扩散，从而调节火焰的局部当量比。这一认识可用于实际燃气轮机失稳控制机构的设计。
Combustion instability, which is the result of a coupling between combustor acoustic modes and unsteady flame heat release rate, is a severely limiting factor in the operability and performance of modern gas turbine engines. This coupling can occur through different pathways, such as flow-field fluctuations or equivalence ratio fluctuations. In realistic combustor systems, there are complex hydrodynamic and thermo-chemical processes involved, which can lead to multiple coupling pathways. In order to understand and predict the mechanisms that govern the onset of combustion instability in real gas turbine engines, we consider the influences that each of these coupling pathways can have on the stability and dynamics of a partially premixed, swirl-stabilized flame. In this study, we use a model gas turbine combustor with two concentric swirling nozzles of air, separated by a ring of fuel injectors, operating at an elevated pressure of 5 bar. The flow split between the two streams is systematically varied to observe the impact on the flow and flame dynamics. High-speed stereoscopic particle image velocimetry, OH planar laser-induced fluorescence, and acetone planar laser-induced fluorescence are used to obtain information about the velocity field, flame, and fuel-flow behavior, respectively. Depending on the flow conditions, a thermoacoustic oscillation mode or a hydrodynamic mode, identified as the precessing vortex core, is present. The focus of this study is to characterize the mixture coupling processes in this partially premixed flame as well as the impact that the velocity oscillations have on mixture coupling. Our results show that, for this combustor system, changing the flow split between the two concentric nozzles can alter the dominant harmonic oscillation modes in the system, which can significantly impact the dispersion of fuel into air, thereby modulating the local equivalence ratio of the flame. This insight can be used to design instability control mechanisms in real gas turbine engines.