Experimental and Numerical Investigation of Thermoacoustic Sources Related to High-Frequency Instabilities

Zellhuber, Mathieu; Schwing, Joachim; Schuermans, Bruno; Sattelmayer, Thomas; Polifke, Wolfgang

doi:10.1260/1756-8277.6.1.1

Cited by 35 publications

(14 citation statements)

References 45 publications

(92 reference statements)

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“…Another type of sequential combustor [1] features a flame that is stabilized substantially downstream of the fuel injector in order to ensure good mixing of the fuel with the vitiated flow before the former is consumed, and it falls into the category of partially-premixed combustion. The response of these flames to different types of perturbation, such as acoustic velocity [16,17] or temperature fluctuations [18][19][20] have been investigated numerically in the context of thermoacoustic instabilities in sequential combustors [21,22].…”

Section: Introductionmentioning

confidence: 99%

Combustion regimes in sequential combustors: Flame propagation and autoignition at elevated temperature and pressure

Schulz

Noiray

2019

Combustion and Flame

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This numerical study investigates the combustion modes in the second stage of a sequential combustor at atmospheric and high pressure. The sequential burner (SB) features a mixing section with fuel injection into a hot vitiated crossflow. Depending on the dominant combustion mode, a recirculation zone assists flame anchoring in the combustion chamber. The flame is located sufficiently downstream of the injector resulting in partially premixed conditions. First, combustion regime maps are obtained from 0-D and 1-D simulations showing the co-existence of three combustion modes: autoignition, flame propagation and flame propagation assisted by autoignition. These regime maps can be used to understand the combustion modes at play in turbulent sequential combustors, as shown with 3-D large eddy simulations (LES) with semi-detailed chemistry. In addition to the simulation of steady-state combustion at three different operating conditions, transient simulations are performed: (i) ignition of the combustor with autoignition as the dominant mode, (ii) ignition that is initiated by autoignition and that is followed by a transition to a propagation stabilized flame, and (iii) a transient change of the inlet temperature (decrease by 150 K) resulting into a change of the combustion regime. These results show the importance of the recirculation zone for the ignition and the anchoring of a propagating type flame. On the contrary, the autoignition flame stabilizes due to continuous self-ignition of the mixture and the recirculation zone does not play an important role for the flame anchoring.

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Section: Introductionmentioning

confidence: 99%

Combustion regimes in sequential combustors: Flame propagation and autoignition at elevated temperature and pressure

Schulz

Noiray

2019

Combustion and Flame

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“…The second stage fuel is injected into the vitiated hot-gas flowing from the first stage, leading to a reaction zone stabilised by mixture autoignition and flame propagation. One can refer to previous numerical studies [19,29,27] and experimental work [27,25,1]. The thermoacoustic stability is one of the main challenges in gas turbine combustor engineering, especially in lean conditions [14].…”

Section: Introductionmentioning

confidence: 99%

Autoignition flame dynamics in sequential combustors

Schulz

Noiray

2018

Combustion and Flame

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This numerical study deals with the heat release rate response of a sequential combustor flame to temperature perturbations. These flames are found in the new generation of gas turbine combustors, which are based on sequential combustion technologies. It is shown that the temperature perturbations T upstream of the fuel injection induce mixture fraction oscillations Z which also propagate toward the reaction zone, and that the combination of these two perturbations yields a strongly nonlinear heat release rate response Q . Large Eddy Simulation (LES) were performed using an Analytically Reduced Chemistry (ARC) mechanism, which includes 22 transported species in combination with the Dynamic Thickened Flame model (DTF). The burner flame transfer function (BFTF) giving the flame response with respect to T is obtained using a broadbandexcitation-based system identification (SI) as well as harmonic single frequency excitations. A simplified configuration with perfectly premixed conditions is considered to quantify the respective contributions of the different types of perturbation. These simulations highlight (i) the strong nonlinearity of the flame response to temperature perturbations, and (ii) the difficulty to break down the global flame response into independent driving mechanisms by making use of "simplified" configurations.

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“…The combustion chamber has a radius R of 80 mm and length L of 200 mm. Afterwards, the burnt gas enters the exhaust (7). Different swirl configurations -specified by the width b of the slots inside the swirl generator -are investigated in this study, similar to Schwing.…”

Section: Methodsmentioning

confidence: 99%

“…The gradient of the mean heat release, which can be positive or negative, is responsible for this negative result. The comparison of the Rayleigh-Indices shows significant differences, although they should be equal according to equation (7). Recalling equation (5), integration by parts is performed in general, while the computation of the Rayleigh-Index is only performed in the direction of r and y, as mentioned in equation (8).…”

Section: Comparison Of the Two Rayleigh-indicesmentioning

confidence: 99%

“…A numerical study by Zellhuber 6 deals with high-frequency, transversal instabilities in autoignition-stabilized gas turbine combustion systems and provides equations to compute the RayleighIndex with contributions of flame displacement, density fluctuations, and pressure sensitivity, the latter of which is only relevant for auto-ignition flames. Zellhuber et al 7 determine that Schwing's displacement model can be derived from Zellhuber's feedback formulation for a thin flame in the direction of the fluctuation of the mode. The direction of the fluctuation of the mode is the transverse direction of the oscillation, orthogonal to the burner axis.…”

Section: Introductionmentioning

confidence: 99%

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Impact of the heat release distribution on high-frequency transverse thermoacoustic driving in premixed swirl flames

Hertweck

Berger

Hummel

et al. 2016

International Journal of Spray and Combustion Dynamics

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Self-excited, high-frequency first transversal thermoacoustic instabilities in a cylindrical combustion chamber equipped with a premixed swirl-stabilized flame are investigated. Phase-locked image analysis of the phenomena shows the displacement of the flame and a higher burning rate in the region of elevated pressure. The impact of diffuser angle and fuel composition on the stability limits and the flame position is investigated. The Rayleigh-Index is computed for a threedimensional domain based on analytical flame transfer functions for experimentally obtained data of OH*-chemiluminescence as measure for the spatial heat release. Two models from different sources are applied, which describe the interaction between flame and acoustic locally. The axial dependence of the amplitude of the transversal mode is computed by a numerical model, which takes the temperature distribution inside the combustion chamber into account. The comparison of the Rayleigh-Index of different operation points shows a correlation with the stability limits for some, but not for all investigated configurations.

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Experimental and Numerical Investigation of Thermoacoustic Sources Related to High-Frequency Instabilities

Cited by 35 publications

References 45 publications

Combustion regimes in sequential combustors: Flame propagation and autoignition at elevated temperature and pressure

Combustion regimes in sequential combustors: Flame propagation and autoignition at elevated temperature and pressure

Autoignition flame dynamics in sequential combustors

Impact of the heat release distribution on high-frequency transverse thermoacoustic driving in premixed swirl flames

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