Numerical Simulation of the Dynamics of Turbulent Swirling Flames

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Response of Premixed Flames to Velocity Disturbances a strong mutual interaction (leading to annihilation) between the flames stabilized on both shear layers, causing an amplification behavior (amplitudes higher than 1) on the flame transfer function for a frequency range. Durox et al. [44] investigated the same burner to measure the Flame Describing Functions (FDF) of the different flame geometries mentioned before. The investigation included an additional configuration consisting on a Collection of Small Conical Flames (CSCF) stabilized on a perforated plate. The compared cases were performed at slightly rich conditions (φ=1.08) for a methane-air mixture. Under these conditions, it was possible to obtain all flame shapes mentioned before with the same incoming flow and equivalence ratio. The flame response was different between cases, concluding that the steady-state flame geometry has a strong influence on the flame response. The CSCF, V-shape and M-shape flames showed similar behavior with amplitudes higher than 1 for low frequencies, followed by a decay in amplitude at higher frequencies. Additionally, the M-flame exhibited a broader frequency response (with amplitudes higher than 1) than the other flames. This different flame response can lead also to a varied production of combustion noise [19] and stability behavior [82, 96]. Variation of the flame shape and length in premixed cases can be obtained using the same burner by modifying operational conditions such as: • Fuel and mixture conditions: Kim et al. [97] investigated the flame response in a lean-premixed axial swirl burner with various equivalence ratios and methane-hydrogen-air mixture compositions at atmospheric conditions. It was observed that for the same inlet velocity and mixture temperature, a V-flame stabilized initially at certain methane-air equivalence ratio can change to a M-flame by the increase of equivalence ratio or by hydrogen enrichment. With the increase in these parameters, the flame speed and reaction rate are increased, and flame stabilization can be achieved in both shear layers. • Inlet pre-heat temperature: Huang and Yang [81] analyzed experimentally and numerically the transition of flame structure from a stable to an unstable state in a lean-premixed axial swirl burner. It was observed that with the increase of the inlet mixture temperature, a stable system with 42
3.3 Additional Parameters Influencing the Flame Response in Premixed Flames a V-flame shape shifted to an unstable system with a M-flame. The transition appears due to the increase of flame speed by the increase of inlet temperature. Then, the flame flashes back, penetrating in the outer recirculation zone and stabilizing in the outer shear layer. Foley et al. [55] investigated also the influence of variation of equivalence ratios and inlet temperature on the flame shape, observing similar transition behavior as in the previously cited study. In their work, additional flame shapes, as a lifted flame or a flame with stabilization only in the outer shear layer, were observed. • Operating Pressure: The increase of pressure has an influence on the flame length [17, 59, 60]. By increasing the operating pressure on the burner and keeping the same equivalence ratio, inlet pre-heating temperature and inlet velocity, the output power increases due to the higher total mass flow produced by the higher density at this condition. Furthermore, the chemical kinetics and reaction rate changes [115] with the increase of pressure. It was observed on references [17, 59, 60] that the flame length is reduced with the increase of operating pressure. Change of the flame topology due to the increase in pressure was not observed on the previous cited investigations. This investigation has a special emphasis on the influence of thermal boundary conditions at the combustor wall, confinement ratio and swirler position on the flame dynamics. Previous studies related with these variations on conditions are reviewed in the following. 3.3.1 Influence of Combustor Thermal Boundary Conditions Heat losses can modify the flame structure as the flame reaction has a strong dependence on the temperature [115]. In combustion systems, the burnt gases approach temperatures between 1500 and 2500 K, while the combustor walls have temperatures between 400 and 600 K [152] because of the cooling to protect the material. Under nonadiabatic conditions, the heat losses can lead to the extinction of the flame [35, 127, 187]. The influence of thermal 43
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Technische Universität München In
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gas turbine combustion during my in
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Zusammenfassung Die Dynamik von per
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CONTENTS 3.3.3 Influence of Swirler
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CONTENTS A.7.4 Inlet . . . . . . .
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LIST OF FIGURES 3.2 Scheme of deter
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LIST OF FIGURES 5.21 Instantaneous
Page 16 and 17: LIST OF FIGURES 5.47 FTFs from expe
Page 18 and 19: List of Tables 2.1 LES Combustion M
Page 20 and 21: Nomenclature R i j Two-point veloci
Page 22 and 23: Nomenclature M MF O prop r stoich S
Page 24 and 25: xxiv Nomenclature
Page 26 and 27: Introduction Figure 1.1: Left: Worl
Page 28 and 29: Introduction Figure 1.4: Illustrati
Page 30 and 31: Introduction fluctuations of the he
Page 32 and 33: Introduction tor walls, increasing
Page 34 and 35: Turbulent Reacting Flows Figure 2.1
Page 38 and 39: Turbulent Reacting Flows time scale
Page 40 and 41: Turbulent Reacting Flows instantane
Page 42 and 43: Turbulent Reacting Flows as the pro
Page 44 and 45: Turbulent Reacting Flows where s L
Page 48 and 49: Turbulent Reacting Flows 2.4.2 Fund
Page 50 and 51: Turbulent Reacting Flows 2.4.2.1 Mo
Page 52 and 53: Turbulent Reacting Flows Some of th
Page 54 and 55: Turbulent Reacting Flows Table 2.1:
Page 56 and 57: Turbulent Reacting Flows port equat
Page 58 and 59: 3 Response of Premixed Flames to Ve
Page 60 and 61: Response of Premixed Flames to Velo
Page 76 and 77: System Identification put, the heat
Page 78 and 79: System Identification Figure 4.2: U
Page 80 and 81: System Identification 4.2 The Wiene
Page 82 and 83: System Identification Figure 4.3: S
Page 84 and 85: System Identification 4.3 The LES/S
Page 86 and 87: System Identification A flow chart
Page 88 and 89: Identification of Flame Transfer Fu
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Identification of Flame Transfer Fu
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6 Stability Analysis with Low-Order
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Stability Analysis with Low-Order N
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Summary and Conclusions series gene
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Summary and Conclusions • The ide
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Outlook tion. The system identifica
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BIBLIOGRAPHY [8] H. Büchner, C. Hi
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BIBLIOGRAPHY [28] P.J. Colucci, F.A
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BIBLIOGRAPHY [48] D. Fanaca. Influe
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BIBLIOGRAPHY [65] M. Germano, U. Pi
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BIBLIOGRAPHY [83] A. Huber. Impact
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BIBLIOGRAPHY [102] T. Komarek. Priv
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BIBLIOGRAPHY [122] L. Ljung. System
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BIBLIOGRAPHY [141] P. Palies, T. Sc
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BIBLIOGRAPHY [163] S.B. Pope. Compu
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BIBLIOGRAPHY [183] F. Selimefendigi
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BIBLIOGRAPHY [200] L. Tay Wo Chong,
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BIBLIOGRAPHY [223] B.T. Zinn and T.
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Appendices Figure A.1: Evaluation o
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Appendices Table A.1: One Step Reac
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Appendices and isotropic, the energ
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Appendices Figure A.2: DRBS Input s
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Appendices (a) The flow is homentro
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Appendices ends of the duct, the fo
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Appendices Figure A.6: Scheme for f
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Appendices Expressing Eqs. (A.59) a
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Appendices Figure A.7: Scattering M
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Appendices ping [45] is used. The i
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Appendices 4. Load in TECPLOT only
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Numerical Simulation of the Dynamics of Turbulent Swirling Flames

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