Impact of Swirling Flow Structure on Shear Layer Vorticity Fluctuation Mechanisms
Impact of Swirling Flow Structure on Shear Layer Vorticity Fluctuation Mechanisms
复制标题
旋流结构对剪切层涡度脉动机制的影响
DOI：
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发表时间：
2016
期刊：
影响因子：
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通讯作者：
J. O’Connor
中科院分区：
文献类型：
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作者：
Benjamin M. Mathews;S. Hansford;J. O’Connor
涡量波动是旋流稳定火焰中速度耦合燃烧不稳定性的重要耦合机制。燃烧室中的声振荡可引起涡量的所有分量振荡，特别是在剪切层卷起时激发的横流或方位角涡量，以及在涡流波动期间激发的流向或轴向涡量。这些波动可由在火焰上游的旋流器和倾卸平面上振荡的纵向声波动引起。虽然这些波动已被确定在一些配置，该机制的流动配置和边界条件的敏感性还没有被参数化研究。在这项研究中，我们调查的影响，时间平均的旋流水平，禁闭，和强迫的频率和振幅的涡度波动动力学的方位角方向的非反应旋转射流。这项工作的目标是更好地了解涡度波动对这些参数的依赖性，以及涡度转换过程中发生的流动。我们已经表明，涡度波动水平随时间平均涡流数而变化，特别是在存在自激旋进涡核的情况下，这会抑制大多数声学驱动运动。此外，强制频率的变化在流动的不同部分中激发流动响应，特别是对于不同的涡流数。最后，限制急剧改变的流动拓扑结构和非受迫动力学，导致显着不同的响应强迫和生成的旋涡波动。
Vorticity fluctuations have been identified as an important coupling mechanism during velocity-coupled combustion instability in swirl-stabilized flames. Acoustic oscillations in the combustor can cause all components of vorticity to oscillate, particularly the cross-stream, or azimuthal, vorticity that is excited in shear layer roll-up, and streamwise, or axial, vorticity that is excited during swirl fluctuations. These fluctuations can be induced by longitudinal acoustic fluctuations that oscillate across the swirler and dump plane upstream of the flame. While these fluctuations have been identified in a number of configurations, the sensitivity of this mechanism to flow configuration and boundary conditions has not been studied parametrically. In this study, we investigate the impact of time-averaged swirl level, confinement, and forcing frequency and amplitude on vorticity fluctuation dynamics in the azimuthal direction of a non-reacting swirling jet. The goal of this work is to better understand the dependence of vorticity fluctuations on these parameters as well as the vorticity conversion processes that occur in the flow. We have shown that vorticity fluctuation levels vary with time-averaged swirl number, particularly in the presence of a self-excited precessing vortex core, which dampens most acoustically-driven motion. Additionally, variations in forcing frequency excite flow response in different portions of the flow, particularly for different swirl numbers. Finally, confinement drastically changes the flow topology and unforced dynamics, resulting in significantly different response to forcing and generation of vortical fluctuations.