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Modelling of pulsating inverted conical flames: a numerical instability analysis
Combustion Theory and Modelling ( IF 1.3 ) Pub Date : 2021-12-14 , DOI: 10.1080/13647830.2021.2011961
Louise da Costa Ramos 1, 2 , Luís Fernando Figueira da Silva 3 , Florent Di Meglio 2 , Valery Morgenthaler 1
Affiliation  

The study of combustion-thermoacoustic instabilities is a topic of interest in the development of engines. However, the modelling of these systems involves a high computational burden. This paper focuses on a simpler class of systems that still features such instabilities: inverted conical flames anchored on a central bluff-body. Here these flames are modelled by solving species mass, momentum and energy transport equations, coupled with a skeletal methane/air chemical kinetic mechanism. The aim is to characterise the dynamic behaviour of inverted conical flames, both due to their natural dynamics and to external incoming velocity fluctuations. The main contribution is the detailed model of the flames, including the smallest scales. The analysis of the impact of the mesh adaption on the flame response shows a trade-off between model accuracy and computational burden that can be adjusted by changing the temperature gradient threshold. The flame response analysis in terms of the temperature and OH mass fraction gives a detailed characterisation of the flame front behaviour in its different scales, both in time and space. The analysis of the flame front dynamic response employing a spectral analysis shows that these have a natural frequency of 35 Hz, and this frequency interacts with the flame response due to incoming velocity excitations. More specifically, when forcing the flame with low frequencies (f 125 Hz) the flame responds only to the forcing and some harmonics, whereas when forcing between 125<f172 Hz the flame response comprises both the natural and forced behaviour. Forcing beyond 200 Hz shows the natural flame response only.



中文翻译:

脉动倒锥形火焰的建模:数值不稳定性分析

燃烧-热声不稳定性的研究是发动机开发中的一个热门话题。然而,这些系统的建模涉及很高的计算负担。本文重点关注仍然具有这种不稳定性的一类更简单的系统:锚定在中央钝体上的倒锥形火焰。在这里,这些火焰是通过求解物种质量、动量和能量传输方程以及骨骼甲烷/空气化学动力学机制来模拟的。目的是描述倒锥形火焰的动态行为,这归因于它们的自然动力学和外部传入速度波动。主要贡献是火焰的详细模型,包括最小的尺度。网格自适应对火焰响应影响的分析显示了模型精度和计算负担之间的权衡,可以通过改变温度梯度阈值进行调整。根据温度和 OH 质量分数进行的火焰响应分析详细描述了火焰前锋行为在不同尺度上的时间和空间特性。使用光谱分析对火焰前缘动态响应的分析表明,它们具有 35 Hz 的固有频率,并且由于传入的速度激励,该频率与火焰响应相互作用。更具体地说,当以低频(根据温度和 OH 质量分数进行的火焰响应分析详细描述了火焰前锋行为在不同尺度上的时间和空间特性。使用光谱分析对火焰前缘动态响应的分析表明,它们具有 35 Hz 的固有频率,并且由于传入的速度激励,该频率与火焰响应相互作用。更具体地说,当以低频(根据温度和 OH 质量分数进行的火焰响应分析详细描述了火焰前锋行为在不同尺度上的时间和空间特性。使用光谱分析对火焰前缘动态响应的分析表明,它们具有 35 Hz 的固有频率,并且由于传入的速度激励,该频率与火焰响应相互作用。更具体地说,当以低频(F 125 Hz)火焰只对强迫和一些谐波做出反应,而当强迫之间125<F172 Hz 火焰响应包括自然行为和强制行为。强制超过 200 Hz 仅显示自然火焰响应。

更新日期:2021-12-14
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