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Linear Response of Laminar Premixed Flames to Flow Oscillations: Unsteady Stretch Effects

Published on May 1, 2010in Journal of Propulsion and Power1.803
· DOI :10.2514/1.41559
Sai Kumar Thumuluru5
Estimated H-index: 5
,
H. Santosh2
Estimated H-index: 2
,
Tim Lieuwen43
Estimated H-index: 43
Abstract
�c and � � s ,forcurvatureand hydrodynamic strain, respectively. Unsteady curvature effects on the flame surface area become significant when j� � c jSt 2 2 � O� 1� and are responsible for the experimentally observed reduction in the flame front wrinkle size in the flow direction [referred to as “filtering” by Bourehla and Baillot (Bourehla, A., and Baillot, F., “Appearance and Stability of a Laminar Conical Premixed Flame Subjected to an Acoustic Perturbation,” Combustion and Flame,
  • References (34)
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#2Vishal Acharya (Georgia Institute of Technology)H-Index: 10
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This paper presents a comparative study of the global responses of heat release and chemiluminescence emissions of a laminar premixed flame excited by oscillations in fuel/air ratio. Chemiluminescence fluctuations are a commonly used marker of heat release oscillations in unsteady flames. While there is strong evidence of a good correlation between these two quantities in situations where the flame is excited by velocity oscillations, the situation is less well understood for cases where the exc...
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This paper describes the dynamics of non-premixed flames responding to bulk velocity fluctuations, and compares the dynamics of the flame sheet position and spatially integrated heat release to that of a premixed flame. The space–time dynamics of the non-premixed flame sheet in the fast chemistry limit is described by the stoichiometric mixture fraction surface, extracted from the solution of the -equation. This procedure has some analogies to premixed flames, where the premixed flame sheet loca...
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#1Dong-Hyuk Shin (Georgia Institute of Technology)H-Index: 11
#2Tim Lieuwen (Georgia Institute of Technology)H-Index: 43
Abstract This paper describes numerical and theoretical analyses of the nonlinear dynamics of harmonically forced, stretch-sensitive premixed flames. A key objective of this work is to analyze the relative contributions of kinematic restoration and flame stretch upon the rate at which flame wrinkles, excited by harmonic forcing, are smoothed out. Kinematic restoration is an intrinsically nonlinear process with a two spatial-zone structure, whose amplitude dependence is fundamentally different ne...
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The objective of the study is to investigate the impact of curvature on the kinematic response of an axisymmetric curved laminar premixed flame, utilizing a phenomenological relationship between the curvature and the laminar burning velocity. The reference and the perturbed flame shapes are obtained by numerically or analytically integrating the flame kinematics equations. The steady reference flame shape deviates gradually from that obtained without the curvature effect as the effect of curvatu...
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Abstract The linear response of 2D wedge-shaped premixed flames to harmonic velocity disturbances was studied, allowing for the influence of flame stretch manifested as variations in the local flame speed along the wrinkled flame front. Results obtained from analyzing the G-equation show that the flame response is mainly characterized by a Markstein number σ ˆ C , which measures the curvature effect of the wrinkles, and a Strouhal number, St f , defined as the angular frequency of the disturbanc...
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An inverted conical flame anchored on a central bluff-body in an unconfined burner configuration features a distinctive acoustic response. This configuration typifies more complex situations in which the thermo-acoustic instability is driven by the interaction of a flame with a convective vorticity mode. The axisymmetric geometry investigated in this article features a shear region between the reactive jet and the surrounding atmosphere. It exhibits self-sustained oscillations for certain operat...
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#1Ju Hyeong Cho (Georgia Institute of Technology)H-Index: 3
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Self-excited oscillations in low emission, premixed combustion systems are often caused by feedback between unsteady heat release rates and reactive mixture equivalence ratio perturbations. This paper presents an analysis of the flame response to equivalence ratio perturbations, showing that the heat release response is controlled by the superposition of three disturbances: heat of reaction, flame speed, and flame area. The first two disturbances are directly generated by equivalence ratio oscil...
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Funding Sources : This work is funded by the King Abdullah University of Science and Technology,the Deutsche Forschungsgemeinschaft ,and the Agence Nationale de la Recherche, through the GECCO project.
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Abstract This study investigates the consequences of flame geometry for the linear response of laminar premixed flames to acoustic perturbations, as expressed by the flame transfer function (FTF). Analytical G-equation-based response models are derived for Slit, Bunsen and Wedge type flames; their respective characteristics are analyzed and validated against data obtained from high fidelity numerical simulations. Motivated by the poor agreement between numerical and analytical flame response pre...
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