Large-eddy simulation analysis of turbulent flame periodic flashbacks in a backward-facing step (BFS) combustor

IF 5.8 2区工程技术 Q2 ENERGY & FUELS

Combustion and Flame Pub Date : 2025-07-22 DOI:10.1016/j.combustflame.2025.114335

Jean-Michel Klein , Aurelien Genot , Axel Vincent-Randonnier , Arnaud Mura

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引用次数: 0

Abstract

Highly turbulent premixed flame dynamics is studied in a backward-facing step combustor. Large-eddy simulations are performed for two operating conditions: (i) a stable case with the flame anchored in the vicinity of the sudden expansion and (ii) an unstable case with massive periodic flashbacks. This set of computational results is first assessed through comparisons with experimental data. Then, it is used to conduct a detailed analysis of the flashback process. Pressure and velocity fluctuations signals display (i) high frequency fluctuations associated to turbulence with similar amplitudes in both the stable and unstable cases, and (ii) a low frequency fluctuation, of acoustic origin, the amplitude of which is significantly higher in the unstable case. The occurrence of flame flashback is found to be closely related to the structure of the first longitudinal acoustic mode, which can be modified thanks to a throttling plug used to modulate the area of the combustor exit cross-section. In the unstable case, this corresponds to an axial-velocity anti-node at the backward-facing step location. Pressure variations are synchronized with the motions of the flame toward the combustor upper wall and the cross-correlation between pressure and heat-release rate oscillations is relevant to a thermoacoustic feedback.

Novelty and significance statement

The present computational study is devoted to the analysis of highly turbulent flame periodic flashbacks in a BFS combustor. It includes three principal contributions. First of all, it demonstrates the capability of the retained computational approach to satisfactorily retrieve flame dynamics and complex phenomena, as observed in experiments, for both conditions (i.e., stable and unstable). Then, it confirms that the presence of the needle at the outlet nozzle leads to the birth of a velocity anti-node in the BFS direct vicinity (i.e., at the flame location). Finally, it provides a detailed characterization of the thermoacoustic behavior of the combustor, putting into evidence the coupling of turbulence and acoustic-induced oscillations with the unsteady motion of the flame and the structure of the acoustic field.

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后台阶燃烧室湍流火焰周期性闪回的大涡模拟分析

研究了后台阶燃烧室高湍流预混火焰动力学。在两种工况下进行了大涡模拟：(i)稳定工况下火焰锚定在突然膨胀附近；（ii）不稳定工况下有大量周期性闪回。这组计算结果首先通过与实验数据的比较来评估。然后，对闪回过程进行了详细的分析。压力和速度波动信号显示：(i)稳定和不稳定情况下与湍流相关的高频波动，振幅相似；（ii）声波来源的低频波动，在不稳定情况下，其振幅明显更高。发现火焰闪回的发生与第一纵声模的结构密切相关，这可以通过使用节流塞来调节燃烧室出口截面的面积来改变。在不稳定的情况下，这对应于一个轴向速度反节点在面向后的步骤位置。压力变化与火焰向燃烧室上壁的运动同步，压力和放热率振荡之间的相互关系与热声反馈有关。新颖性和意义声明：本文对BFS燃烧室中高湍流火焰周期性闪回现象进行了计算分析。它包括三个主要贡献。首先，它证明了保留计算方法在两种条件下（即稳定和不稳定）都能令人满意地检索火焰动力学和复杂现象，正如实验中观察到的那样。然后，它证实了出口喷嘴处针头的存在导致BFS直接附近（即火焰位置）的速度反节点的诞生。最后，详细描述了燃烧室的热声特性，证明了湍流和声激振荡与火焰的非定常运动和声场结构的耦合。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Combustion and Flame 工程技术-工程：化工

CiteScore

9.50

自引率

20.50%

发文量

631

审稿时长

3.8 months

期刊介绍： The mission of the journal is to publish high quality work from experimental, theoretical, and computational investigations on the fundamentals of combustion phenomena and closely allied matters. While submissions in all pertinent areas are welcomed, past and recent focus of the journal has been on: Development and validation of reaction kinetics, reduction of reaction mechanisms and modeling of combustion systems, including: Conventional, alternative and surrogate fuels; Pollutants; Particulate and aerosol formation and abatement; Heterogeneous processes. Experimental, theoretical, and computational studies of laminar and turbulent combustion phenomena, including: Premixed and non-premixed flames; Ignition and extinction phenomena; Flame propagation; Flame structure; Instabilities and swirl; Flame spread; Multi-phase reactants. Advances in diagnostic and computational methods in combustion, including: Measurement and simulation of scalar and vector properties; Novel techniques; State-of-the art applications. Fundamental investigations of combustion technologies and systems, including: Internal combustion engines; Gas turbines; Small- and large-scale stationary combustion and power generation; Catalytic combustion; Combustion synthesis; Combustion under extreme conditions; New concepts.