Influence of momentum ratio on heat release rate and noise of co/counter-swirl non-premixed diluted CO/H2 flames

IF 2.8 2区 工程技术 Q2 ENGINEERING, MECHANICAL Experimental Thermal and Fluid Science Pub Date : 2024-10-18 DOI:10.1016/j.expthermflusci.2024.111336
Atanu Dolai , R.V. Ravikrishna
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Abstract

Understanding co/counter-swirl or twin-swirl flames remains challenging due to the complex interaction of two swirling streams. In the present study, we investigate the heat release features of non-premixed co/counter-swirl syngas/air flames and their’ influence on combustor noise in a ∼20 kW combustor using simultaneous high-speed OH*-chemiluminescence (5 kHz) and microphone measurement (50 kHz) by varying the momentum ratio (M) from 0.4 to 0.95. Furthermore, the velocity field is examined using a low-speed two-dimensional particle image velocimetry (2D-PIV, frequency = 7 Hz). For all studied momentum ratios, the frequency spectra of noise measurements for both co/counter-swirl flames consistently exhibit a dominant frequency (∼285 Hz), close to the fundamental axial mode of the combustor. A further analysis using spectrograms, phase spaces, and recurrence plots reveals intermittent patterns in noise measurements, featuring periodic (P) and aperiodic regions (A). In periodic regions (P), noise synchronizes with the global fluctuation of the heat release rate as observed in chemiluminescence. Along with global fluctuation, the chemiluminescence also reveals a rotational component of heat release rate with distinct frequencies for co and counter-swirl configurations. This rotational motion possibly originated from a precessing vortex core (PVC) as indicated by the zig-zag arrangements of vortices in the inner shear layer. Furthermore, the impact of M on global fluctuation and rotational motion has been investigated using the frequency spectrum of OH*-intensity and the distribution of peaks in noise measurement. The global fluctuation is found to be suppressed when M increases while the rotational component becomes prominent at higher M. Therefore, the study elucidates the co-existence of global fluctuation and rotational motion and how these motions evolve with the varying momentum ratio (M), thus enhancing the understanding of combustion characteristics of the complex twin-swirl (co/counter-swirl) flames.
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动量比对同向/逆向非预混稀释 CO/H2 火焰热释放率和噪声的影响
由于两个漩涡流之间的相互作用非常复杂,因此了解共/逆漩涡或双漩涡火焰仍然具有挑战性。在本研究中,我们通过同时使用高速 OH* 化学发光(5 kHz)和麦克风测量(50 kHz),在动量比(M)从 0.4 到 0.95 的变化范围内,研究了非预混合同/反漩涡合成气/空气火焰的热释放特征及其对 20 kW 燃烧器噪声的影响。此外,还使用低速二维粒子图像测速仪(2D-PIV,频率 = 7 Hz)对速度场进行了检测。对于所有研究的动量比,同向/反向漩涡火焰的噪声测量频谱始终显示出一个主频(∼285 Hz),接近燃烧器的基本轴向模式。利用频谱图、相位空间和递推图进行的进一步分析表明,噪声测量中存在间歇模式,包括周期性区域(P)和非周期性区域(A)。在周期性区域(P)中,噪声与化学发光中观察到的热释放率的整体波动同步。除了全局波动外,化学发光还显示了热释放率的旋转成分,其频率在同涡和反涡构型中截然不同。正如内部剪切层中涡旋的之字形排列所显示的那样,这种旋转运动可能源于前冲涡旋核心(PVC)。此外,还利用 OH* 强度的频谱和噪声测量的峰值分布研究了 M 对全局波动和旋转运动的影响。因此,该研究阐明了全局波动和旋转运动的共存,以及这些运动如何随动量比(M)的变化而演变,从而加深了对复杂双漩涡(共/反漩涡)火焰燃烧特性的理解。
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来源期刊
Experimental Thermal and Fluid Science
Experimental Thermal and Fluid Science 工程技术-工程:机械
CiteScore
6.70
自引率
3.10%
发文量
159
审稿时长
34 days
期刊介绍: Experimental Thermal and Fluid Science provides a forum for research emphasizing experimental work that enhances fundamental understanding of heat transfer, thermodynamics, and fluid mechanics. In addition to the principal areas of research, the journal covers research results in related fields, including combined heat and mass transfer, flows with phase transition, micro- and nano-scale systems, multiphase flow, combustion, radiative transfer, porous media, cryogenics, turbulence, and novel experimental techniques.
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