Period-2 Thermoacoustics in a Swirl-Stabilised Partially Premixed Flame Computed Using Large Eddy Simulation

IF 2 3区工程技术 Q3 MECHANICS

Flow, Turbulence and Combustion Pub Date : 2023-07-10 DOI:10.1007/s10494-023-00452-z

Ankit D. Kumar, James C. Massey, Michael Stöhr, Wolfgang Meier, Nedunchezhian Swaminathan

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引用次数: 1

Abstract

A partially premixed swirl-stabilised flame under thermoacoustically unstable conditions is studied using large eddy simulation with an unstrained flamelet model for the filtered reaction rate. The simulation results agree well with measured statistics of velocity, temperature and mixture fraction. Two thermoacoustic modes at approximately 300 and 590 Hz are excited for the case studied. The second mode pressure amplitude is comparable to that of the first mode. However, the second mode of heat release rate fluctuations is not as significant as for the pressure which results in a 2:1 frequency locking behaviour. The analysis offers insights into the physical mechanism involved in the excitation of the two modes and the 2:1 frequency locking behaviour. The index based on the Rayleigh Criterion in frequency domain is analysed to understand the coupling between the heat release rate and pressure fluctuations. It is observed that there is a nonlinear interaction between the two modes resulting in energy exchange across the two modes. The conventional Rayleigh Index has limitations in explaining the observed dynamics and therefore, a modified Rayleigh Index is defined to understand the effects of nonlinear mode interactions on thermoacoustic characteristics. A mode shape analysis using LES and acoustic-modelling reveals that the first mode may be a Helmholtz mode with internal damping that is excited by an acoustic source, and the second mode has the characteristic shape of a chamber mode.

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用大涡模拟计算旋流稳定部分预混火焰的周期-2热声学

对热声不稳定条件下的部分预混旋流稳定火焰进行了大涡模拟，采用无应变火焰模型计算了过滤反应速率。模拟结果与速度、温度和混合分数的实测数据吻合较好。在研究的案例中，激发了大约300和590 Hz的两种热声模态。第二模态压力幅值与第一模态压力幅值相当。然而，热释放率波动的第二种模式不如导致2:1频率锁定行为的压力那么重要。该分析提供了对两种模式的激发和2:1频率锁定行为所涉及的物理机制的见解。分析了基于瑞利准则的频域指标，了解了放热率与压力波动之间的耦合关系。观察到两模之间存在非线性相互作用，导致两模之间的能量交换。传统的瑞利指数在解释观测到的动力学方面有局限性，因此，定义了一个改进的瑞利指数来理解非线性模态相互作用对热声特性的影响。利用LES和声学模型进行的模态振型分析表明，第一模态可能是由声源激发的具有内阻尼的亥姆霍兹模态，第二模态具有腔室模态的特征形状。

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来源期刊

Flow, Turbulence and Combustion 工程技术-力学

CiteScore

5.70

自引率

8.30%

发文量

审稿时长

2 months

期刊介绍： Flow, Turbulence and Combustion provides a global forum for the publication of original and innovative research results that contribute to the solution of fundamental and applied problems encountered in single-phase, multi-phase and reacting flows, in both idealized and real systems. The scope of coverage encompasses topics in fluid dynamics, scalar transport, multi-physics interactions and flow control. From time to time the journal publishes Special or Theme Issues featuring invited articles. Contributions may report research that falls within the broad spectrum of analytical, computational and experimental methods. This includes research conducted in academia, industry and a variety of environmental and geophysical sectors. Turbulence, transition and associated phenomena are expected to play a significant role in the majority of studies reported, although non-turbulent flows, typical of those in micro-devices, would be regarded as falling within the scope covered. The emphasis is on originality, timeliness, quality and thematic fit, as exemplified by the title of the journal and the qualifications described above. Relevance to real-world problems and industrial applications are regarded as strengths.