Interference mechanisms of acoustic/convective disturbances in a swirl-stabilized lean-premixed combustor

Kim, Kyu Tae; Santavicca, D. A.

doi:10.1016/j.combustflame.2013.02.022

Cited by 81 publications

(23 citation statements)

References 53 publications

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“…Straub and Richards [8] firstly described the influence of the swirler position on self-sustained combustion instabilities in a gas turbine combustor. Komarek and Polifke [9] and later Kim and Santavicca [10] observed a strong dependence of the Flame Transfer Function (FTF) upon the distance from the swirler to the injector outlet. It has been shown that an acoustic pulsation impinging on a swirler generates a vorticity wave, convected downstream at the local flow velocity [9,11].…”

Section: Introductionmentioning

confidence: 99%

A Comparison of the Transfer Functions and Flow Fields of Flames With Increasing Swirl Number

Gatti

Gaudron

Mirat

et al. 2018

Volume 4B: Combustion, Fuels, and Emissions

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The frequency response of premixed swirled flames is investigated by comparing their Transfer Function (FTF) between velocity and heat release rate fluctuations. The equivalence ratio and flow velocity are kept constant and four different swirling injectors are tested with increasing swirl numbers. The first injector features a vanishing low swirl number S = 0.20 and produces a flame anchored by the recirculating flow in the wake of a central bluff body. The three other swirling injectors produce highly swirled flows (S > 0.6) leading to a much larger internal recirculation region, which size increases with the swirl level. When operating the burner at S = 0.20, the FTF gain curve smoothly increases to reach a maximum and then smoothly decreases towards zero. For the highly swirled flames (S > 0.6), the FTF gain curve shows a succession of valleys and peaks attributed to interferences between axial and azimuthal velocity fluctuations at the injector outlet. The FTF phase-lag curves from the vanishing low and highly swirled flames are the same at low frequencies despite their large differences in flame length and flame aspect ratio. Deviations between the FTF phase lag curves of the different swirled flames start above the frequency corresponding to the first valley in the FTF gain of the highly swirled flames. Phase averaged images of the axial flow fields and of the flame chemiluminescence are used to interpret these features. At forcing frequencies corresponding to peak FTF gain values, the cold flow response of all flames investigated is dominated by large coherent vortical structures shed from the injector lip. At forcing frequencies corresponding to a valley in the FTF gain curve of the highly swirled flames, the formation of large coherent structures is strongly hindered in the cold flow response. These observations contrast with previous interpretations of the mechanisms associated to the low FTF response of swirled flames. It is finally found that for flames stabilized with a large swirl number, heat release rate fluctuations result both from large flame luminosity oscillations and large flame volume oscillations. For conditions leading to a small FTF gain value, both the flame luminosity and flame volume fluctuations are suppressed confirming the absence of strong perturbations within the flow at these frequencies. The experiments made in this work reveal a purely hydrodynamic mechanism at the origin of the low response of swirling flames at certain specific frequencies.

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Section: Introductionmentioning

confidence: 99%

A Comparison of the Transfer Functions and Flow Fields of Flames With Increasing Swirl Number

Gatti

Gaudron

Mirat

et al. 2018

Volume 4B: Combustion, Fuels, and Emissions

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“…Previous theoretical studies suggest that vortex shedding may be at the origin of ITA modes [3], while others mention a possible counter-reaction of the flame to its own production of acoustics [2]. This section shows that mode conversion [17,[37][38][39][40], i.e. the transformation of an acoustic wave into a convective wave is the mechanism that must be introduced into the analysis to understand the instability loop.…”

Section: Description Of Physical Phenomena Responsible For Ita Modesmentioning

confidence: 99%

DNS of Intrinsic ThermoAcoustic modes in laminar premixed flames

Courtine

Selle

Poinsot

2015

Combustion and Flame

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OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. , Emmert et al. 2015 suggest that thermoacoustic modes can appear in combustors with anechoic terminations, which have no acoustic eigenmodes. These modes, called here Intrinsic ThermoAcoustic (ITA), can be predicted with simple theoretical arguments, but have been ignored for a long time. They are reproduced in this paper using Direct Numerical Simulation (DNS) of a laminar premixed Bunsen type flame. DNS results and theory are compared showing very good agreement in terms of both frequency and mode structure. DNS confirms that the frequency of ITA modes does not depend on any acoustic characteristic of the burner. Based on a numerical evaluation of the Flame Transfer Function, stability limits of ITA modes predicted by theory are also recovered in the DNS with reasonable accuracy. Finally, DNS is used to analyze the mechanisms of ITA modes.

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“…vortex core (PVC) [7,8], interference between acoustic and convective disturbances [9], and the temporal fluctuation in swirl strength [10][11][12]. However, it is almost impossible to derive a universal mechanism for interpreting and predicting complex nonlinear combustion instability phenomena [13,14] because the governing mechanisms differ in combustor geometry, fuel specification, and air-supplying conditions.…”

Section: Introductionmentioning

confidence: 99%

Effects of High-harmonic Components on the Rayleigh Indices in Multi-mode Thermo-acoustic Combustion Instability

Song¹,

Yoon²,

Yoon³

et al. 2016

International Journal of Aeronautical and Space Sciences

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This paper presents the characteristics of non-fundamental multi-mode combustion instability and the effects of highharmonic components on the Rayleigh criterion. Phenomenological observations of multi-harmonic-mode dynamic pressure waves regarding the intensity of harmonic components and the source of wave distortion have been explained by introducing examples of second-and third-order harmonics at various amplitudes. The amplitude and order of the harmonic components distorted the wave shapes, including the peak and the amplitude, of the dynamic pressure and heat release, and consequently the temporal Rayleigh index and its integrals. A cause-and-effect analysis was used to identify the root causes of the phase delay and the amplification of the Rayleigh index. From this analysis, the skewness of the dynamic pressure turned out to be a major source in determining whether multi-mode instability is driving or damping, as well as in optimizing the combustor design, such as the mixing length and the combustor length, to avoid unstable regions. The results can be used to minimize errors in predicting combustion instability in cases of high multi-mode combustion instability. In the future, the amount of research and the number of applications will increase because new fuels, such as fast-burning syngases, are prone to generating multi-mode instabilities.

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Interference mechanisms of acoustic/convective disturbances in a swirl-stabilized lean-premixed combustor

Cited by 81 publications

References 53 publications

A Comparison of the Transfer Functions and Flow Fields of Flames With Increasing Swirl Number

A Comparison of the Transfer Functions and Flow Fields of Flames With Increasing Swirl Number

DNS of Intrinsic ThermoAcoustic modes in laminar premixed flames

Effects of High-harmonic Components on the Rayleigh Indices in Multi-mode Thermo-acoustic Combustion Instability

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