Impact of turbulence on the coherent flame dynamics in a bluff-body stabilized flame
Impact of turbulence on the coherent flame dynamics in a bluff-body stabilized flame
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DOI：
10.1016/j.proci.2020.08.059
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发表时间：
2021-04-10
影响因子：
3.4
通讯作者：
O'Connor, Jacqueline
中科院分区：
文献类型：
--
作者：
Karmarkar, Ashwini;Tyagi, Ankit;O'Connor, Jacqueline
大规模流动不稳定性产生的相干火焰振荡已被证明会显着影响燃烧器性能和热声不稳定性。本研究探讨了湍流强度对棒稳定火焰大尺度动力学的影响。钝体稳定火焰流场的不稳定性是流场中的平均剪切、传入流的湍流强度以及火焰相对于剪切层的位置的函数，表现为相干涡流脱落。然而，如果流动是全局稳定的，则这种涡流脱落就不会自激，这在反应流中通常是这种情况。在本实验中，在三种湍流入口流条件和三种总体流速下，通过高速立体粒子图像测速仪进行时间分辨三分量速度测量。为了确定是否发生这些不稳定性，使用围绕选定谱带的小波变换对速度场进行滤波，然后使用适当的正交分解进行分解，以提取流中最具能量的运动；此过滤方法保留任何依赖于时间的间歇性行为。结果表明，涡旋脱落是间歇性的，间歇性的程度取决于流入的湍流水平。尽管所有测试的情况都被确定为全局稳定，但流速的变化会改变火焰和流动的结构，从而改变流动对湍流扰动的接受能力。因此，涡旋脱落的强度和规律性随着湍流水平的增加和接收能力的增加而增加，表明该系统是一个噪声驱动的全局稳定振荡器。(c) 2020 The Combustion Institute。由爱思唯尔公司出版。保留所有权利。
Coherent flame oscillations generated by large-scale flow instabilities have been shown to significantly influence combustor performance and thermoacoustic instability. This study examines the influence of turbulence intensity on the large-scale dynamics of rod-stabilized flames. Instability in the flow field of a bluff-body stabilized flame, which is a function of mean shear in the flow field, turbulence intensity of the incoming flow, and the location of the flame with respect to the shear layer, manifests as coherent vortex shedding. However, this vortex shedding is not self-excited if the flow is globally stable, as is often the case in reacting flows. In this experiment, time-resolved, three-component velocity measurements from high-speed stereoscopic particle image velocimetry are taken at three turbulent inlet flow conditions and at three bulk flow velocities. To identify whether these instabilities occur, the velocities fields are filtered using a wavelet transform around select spectral bands and then decomposed using proper orthogonal decomposition to extract the most energetic motion in the flow; this filtering method retains any time-dependent, intermittent behavior. The results show that vortex shedding is intermittent and the degree of intermittency is dependent on the in-flow turbulence level. Although all the cases tested were determined to be globally stable, variations in the flow velocity change the structure of the flame and flow, which alters the receptivity of the flow to turbulent perturbations. As a result, the strength and regularity of vortex shedding increase with increasing turbulence level and increased receptivity, indicating that the system is a noise-forced globally-stable oscillator.(c) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.