Academic literature on the topic 'Instabilités de front de flamme'
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Journal articles on the topic "Instabilités de front de flamme"
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Ayoobi, Mohsen, and Ingmar Schoegl. "Numerical analysis of flame instabilities in narrow channels: Laminar premixed methane/air combustion." International Journal of Spray and Combustion Dynamics 9, no. 3 (June 5, 2017): 155–71. http://dx.doi.org/10.1177/1756827717706009.
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Premixed flames propagating within small channels show complex combustion phenomena that differ from flame propagation at conventional scales. Available experimental and numerical studies have documented stationary, non-stationary, or asymmetric modes that depend on properties of the incoming reactant flow as well as channel geometry and wall temperatures. This work seeks to illuminate mechanisms leading to symmetry breaking and limit cycle behavior that are fundamental to these combustion modes. Specifically, four cases of lean premixed methane/air combustion—two equivalence ratios (0.53 and 0.7) and two channel widths (2 mm and 5 mm)—are investigated in a 2D configuration with constant channel length and bulk inlet velocity, where numerical simulations are performed using detailed chemistry. External wall heating is simulated by imposing a linear temperature gradient as a boundary condition on both walls. In the 2 mm channel, both equivalence ratios produce flames that stabilize with symmetric flame fronts after propagating upstream. In the 5 mm channel, flame fronts start symmetrically, although symmetry is broken almost immediately after ignition. Further, 5 mm channels produce non-stationary combustion modes with dramatically different limit cycles: in the leaner case ( φ = 0.53), the asymmetric flame front flops periodically, whereas in the richer case ( φ = 0.7), flames with repetitive extinctions and ignitions (FREI) are observed. To further understand the flame dynamics, reaction fronts and flame fronts are captured and differentiated. Results show that the loss of flame front symmetry originates in a region close to the flame cusp, where flow and chemical characteristics exhibit large gradients and curvatures. Limit cycle behavior is illuminated by investigating flame edges that are formed along the wall, and accompany local or global ignition and extinction processes. In the flopping mode ( φ = 0.53), local ignition and extinction in regions adjacent to the wall result in oblique fronts that advance and recede along the wall and redirect the flow ahead of the flame. In the FREI mode, asymmetric flames propagate much farther upstream, where they experience global extinction due to heat losses, and re-ignite far downstream with opposite flame front orientation. In both cases, an interaction of flow and chemical effects drives the asymmetric limit cycles. The lack of instabilities and asymmetries for the 2mm cases is attributed to insufficient wall separation, which is of the same order of magnitude as the flame thickness.
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Xia, Yongfang, Tingyong Fang, Haitao Wang, Erbao Guo, and Jinwei Ma. "Numerical investigation of low-velocity filtration combustion instability based on the initial preheating non-uniformity." E3S Web of Conferences 136 (2019): 02040. http://dx.doi.org/10.1051/e3sconf/201913602040.
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The effects of the initial preheating perturbation on the dynamical behaviors of FGC wave propagation instability for low-velocity FGC in packed bed are studied numerically. The behaviors of the flame front inclination, break, and shrinking instabilities are always observed in experiments. Based on the experimental phenomena, an initial thermal perturbation model is numerically proposed as to predict the deformation behaviors of the flame front instabilities. The typical flame shapes are obtained depending on filtration velocity, equivalence ratio, and initial preheating temperature difference. It is demonstrated that the development of flame front inclination instability is proportional to the magnitude of initial preheating perturbation. At a lower equivalence ratio, the initial thermal perturbation of 300 K leads to the evolution of flame front break. Increasing filtration velocity leads to the appearance of flame front break, due to the intensification of the hydrodynamic instability. In addition, a perculiar instability of flame front shifting is also confirmed with the initial thermal perturbation of 400 K, which results in a fuel leakage of incomplete combustion.
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Yang, Sheng, Abhishek Saha, Zirui Liu, and Chung K. Law. "Role of Darrieus–Landau instability in propagation of expanding turbulent flames." Journal of Fluid Mechanics 850 (July 10, 2018): 784–802. http://dx.doi.org/10.1017/jfm.2018.426.
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In this paper we study the essential role of Darrieus–Landau (DL), hydrodynamic, cellular flame-front instability in the propagation of expanding turbulent flames. First, we analyse and compare the characteristic time scales of flame wrinkling under the simultaneous actions of DL instability and turbulent eddies, based on which three turbulent flame propagation regimes are identified, namely, instability dominated, instability–turbulence interaction and turbulence dominated regimes. We then perform experiments over an extensive range of conditions, including high pressures, to promote and manipulate the DL instability. The results clearly demonstrate the increase in the acceleration exponent of the turbulent flame propagation as these three regimes are traversed from the weakest to the strongest, which are respectively similar to those of the laminar cellularly unstable flame and the turbulent flame without flame-front instability, and thus validating the scaling analysis. Finally, based on the scaling analysis and the experimental results, we propose a modification of the conventional turbulent flame regime diagram to account for the effects of DL instability.
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Palies, Paul, Milos Ilak, and Robert Cheng. "Transient and limit cycle combustion dynamics analysis of turbulent premixed swirling flames." Journal of Fluid Mechanics 830 (October 5, 2017): 681–707. http://dx.doi.org/10.1017/jfm.2017.575.
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Premixed low swirling flames (methane–air and hydrogen–methane–air) are experimentally investigated for three different regimes. Stable, local transient to instability and limit cycle regimes corresponding to three distinct equivalence ratios are considered. Dynamic mode decomposition is applied to the hydrogen–air–methane flame to retrieve the modes frequencies, growth rates and spatial distributions for each regime. The results indicate that a vortical wave propagating along the flame front is associated with the transition from stability to instability. In addition, it is shown that a key effect on stability is the location of the non-oscillating (0 Hz) flame component. The phase-averaged unsteady motion of the flames over one cycle of oscillation shows the vortical wave rolling up the flame front. The Rayleigh index maps are formed to identify the region of driving and damping of the self-sustained oscillation, while the flame transfer function phase leads to the propagation mode of the perturbations along the flame front. The second mechanism identified concerns the swirl number fluctuation induced by the mode conversion. By utilizing hypotheses for the flow field and the flame structure, it is pointed out that those mechanisms are at work for both flames (methane–air and hydrogen–methane–air) and their effects on the unsteady heat release are determined. Both unsteady heat release contributions, the vortical wave induces flame surface fluctuations and swirl number oscillation induces unsteady turbulent burning velocity, are in phase opposition and of similar amplitudes.
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Yu, Rixin. "Deep learning of nonlinear flame fronts development due to Darrieus–Landau instability." APL Machine Learning 1, no. 2 (June 1, 2023): 026106. http://dx.doi.org/10.1063/5.0139857.
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The Darrieus–Landau instability is studied using a data-driven, deep neural network approach. The task is set up to learn a time-advancement operator mapping any given flame front to a future time. A recurrent application of such an operator rolls out a long sequence of predicted flame fronts, and a learned operator is required to not only make accurate short-term predictions but also reproduce characteristic nonlinear behavior, such as fractal front structures and detached flame pockets. Using two datasets of flame front solutions obtained from a heavy-duty direct numerical simulation and a light-duty modeling equation, we compare the performance of three state-of-art operator-regression network methods: convolutional neural networks, Fourier neural operator (FNO), and deep operator network. We show that, for learning complicated front evolution, FNO gives the best recurrent predictions in both the short and long term. A consistent extension allowing the operator-regression networks to handle complicated flame front shape is achieved by representing the latter as an implicit curve.
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JOULIN, GUY, HAZEM EL-RABII, and KIRILI A. KAZAKOV. "On-shell description of unsteady flames." Journal of Fluid Mechanics 608 (July 11, 2008): 217–42. http://dx.doi.org/10.1017/s0022112008002140.
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The problem of a non-perturbative description of unsteady premixed flames with arbitrary gas expansion is addressed in the two-dimensional case. Considering the flame as a surface of discontinuity with arbitrary local burning rate and gas velocity jumps, we show that the flame-front dynamics can be determined without having to solve the flow equations in the bulk. On the basis of the Thomson circulation theorem, an implicit integral representation of the downstream gas velocity is constructed. It is then simplified by a successive stripping of the potential contributions to obtain an explicit expression for the rotational component near the flame front. We prove that the unknown potential component is left bounded and divergence-free by this procedure, and hence can be eliminated using the dispersion relation for its on-shell value (i.e. the value along the flame front). The resulting system of integro-differential equations relates the on-shell fresh-gas velocity and the front position. As limiting cases, these equations contain all the theoretical results on flame dynamics established so far, including the linear equation describing the Darrieus–Landau instability of planar flames, and the nonlinear Sivashinsky–Clavin equation for flames with weak gas expansion.
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Hicks, E. P. "A shear instability mechanism for the pulsations of Rayleigh–Taylor unstable model flames." Journal of Fluid Mechanics 748 (May 6, 2014): 618–40. http://dx.doi.org/10.1017/jfm.2014.198.
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AbstractPrevious studies have shown that the behaviour of Rayleigh–Taylor (RT) unstable flames depends on the boundary conditions. If the boundary conditions at the domain walls are impermeable/adiabatic or reflecting then the flame assumes a stable parabolic shape. On the other hand, periodic boundary conditions can produce unstable pulsating solutions. In this paper, we explore why periodic boundary conditions allow unstable solutions by showing the results of two-dimensional direct numerical simulations of model flames. We show that RT unstable premixed model flames pulsate at low gravity because of a shear instability of the vorticity layers behind the flame front. The resulting vortex shedding is controlled by a region of absolute-like instability which moves closer to the flame front as gravity is increased, ultimately disturbing the flame and leading to pulsations. We demonstrate that this region is ‘absolutely unstable’ by showing that the wake is dominated by pure frequency oscillations. In addition, the shear instability can be described by the Landau equation and can be represented dynamically by a Hopf bifurcation. The applicability of the Landau equation allows the apparently complex spatio-temporal behaviour of the vortex shedding to be described by a simple temporal model with only a secondary spatial dependence. We show that the flame behaviour is analogous to the initial instability downstream of a circular cylinder, which leads to the von Kármán vortex street for large enough values of the Reynolds number.
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Altantzis, C., C. E. Frouzakis, A. G. Tomboulides, M. Matalon, and K. Boulouchos. "Hydrodynamic and thermodiffusive instability effects on the evolution of laminar planar lean premixed hydrogen flames." Journal of Fluid Mechanics 700 (May 18, 2012): 329–61. http://dx.doi.org/10.1017/jfm.2012.136.
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AbstractNumerical simulations with single-step chemistry and detailed transport are used to study premixed hydrogen/air flames in two-dimensional channel-like domains with periodic boundary conditions along the horizontal boundaries as a function of the domain height. Both unity Lewis number, where only hydrodynamic instability appears, and subunity Lewis number, where the flame propagation is strongly affected by the combined effect of hydrodynamic and thermodiffusive instabilities are considered. The simulations aim at studying the initial linear growth of perturbations superimposed on the planar flame front as well as the long-term nonlinear evolution. The dispersion relation between the growth rate and the wavelength of the perturbation characterizing the linear regime is extracted from the simulations and compared with linear stability theory. The dynamics observed during the nonlinear evolution depend strongly on the domain size and on the Lewis number. As predicted by the theory, unity Lewis number flames are found to form a single cusp structure which propagates unchanged with constant speed. The long-term dynamics of the subunity Lewis number flames include steady cell propagation, lateral flame movement, oscillations and regular as well as chaotic cell splitting and merging.
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Jiang, Xiaozhen, Jingxuan Li, and Lijun Yang. "Nonlinear response of laminar premixed flames to dual-input harmonic disturbances." INTER-NOISE and NOISE-CON Congress and Conference Proceedings 265, no. 4 (February 1, 2023): 3408–19. http://dx.doi.org/10.3397/in_2022_0484.
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In gas turbines, aero-engines and rocket engines, flames are always disturbed by perturbations of dual or multiple harmonic frequencies, resulting in corresponding combustion instability. This paper analyses the nonlinear response of laminar premixed flames to dual-input harmonic disturbances to further understand those associated combustion instability. Nonlinear results of flame dynamics were derived from analytical and numerical solutions of the G-equation. The spatial front-tracking of premixed flames was obtained, where types of nonlinear behaviors were classified and related mechanisms of that were elucidated. A dual-input flame description function (DIFDF) was proposed to separately determine global nonlinearities of flame responses of fundamental and higher harmonics frequencies under dual-input disturbances. The fundamental frequency response consists of linear and nonlinear components, and the higher harmonic frequency one is purely nonlinear. The DIFDF properties of conical and "V" flames were compared, with particular emphasis on their differences in nonlinear behavior. The spatial and global effects of the second input frequency on the flame kinematics perturbed by the first frequency were also clarified. Furthermore, the roles of perturbation amplitude and flame height in spatial flame dynamics and DIFDF were quantified.
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Mokrin, Sergey, R. V. Fursenko, and S. S. Minaev. "Thermal-Diffusive Stability of Counterflow Premixed Flames at Low Lewis Numbers." Advanced Materials Research 1040 (September 2014): 608–13. http://dx.doi.org/10.4028/www.scientific.net/amr.1040.608.
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Dynamics of radiative, near-limit, stretched premixed flames is investigated analytically and numerically. Investigation of counterflow premixed flames stability is important for the development of new combustion technologies such as those associated with low-NOx emission, lean burn and material synthesis. Emphasis is paid on the linear stability of multiple flame regimes. The present analysis, for the first time, gives out a dispersion equation describing growth rate of small spatial perturbations of the flame front. The stability diagram is obtained and the region of instability is distinguished.
Dissertations / Theses on the topic "Instabilités de front de flamme"
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Hok, Jean-Jacques. "Stratégie de modélisation pour la simulation aux grandes échelles d'explosions de mélanges hydrogène-air pauvres." Electronic Thesis or Diss., Université de Toulouse (2023-....), 2024. http://www.theses.fr/2024TLSEP065.
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La crise climatique à laquelle le monde est confronté aujourd'hui exige des actions immédiates pour réduire les émissions de carbone. En particulier, une transition énergétique rapide vers des sources plus propres est nécessaire. Parmi de nombreux candidats, l'hydrogène se distingue en tant que vecteur d'énergie décarboné. Cependant, son stockage et son transport en grandes quantités posent des problèmes de sécurité. Dans le cas d'une fuite accidentelle d'hydrogène, un mélange hautement inflammable peut se former. En cas d'allumage, différents scénarios et régimes de combustion sont possibles, en fonction de différents facteurs tels que la géométrie (dimensions, confinement, présence d'obstacles), la composition du mélange, la température, la pression ou le niveau de turbulence. Ces régimes vont de la déflagration lente à la transition vers la détonation dans le pire des cas. Pour prédire les dommages consécutifs à une explosion, la Mécanique des Fluides Numérique présente l'avantage d'être plus sûre que les expériences et de donner accès à des quantités difficiles ou impossibles à mesurer empiriquement. Cette thèse traite de la prédiction des explosions de mélanges d'hydrogène-air pauvres en utilisant l'approche de Simulation aux Grandes Échelles (SGE ou LES en anglais). Les mélanges pauvres d'H2-air sont caractérisés par leur nombre de Lewis subunitaire, qui traduit un déséquilibre entre les processus de diffusion moléculaire et thermique avec des conséquences majeures : (1) les flammes H2-air pauvres sont très sensibles à l'étirement ; (2) elles sont enclines à développer des cellules sur le front de flamme dues à l'instabilité thermo-diffusive. Les deux constituent des mécanismes d'accélération qui impactent la surpression générée lors de l'explosion. Dans ce travail, nous montrons que l'utilisation du modèle de Flamme Épaissie (TF en anglais) pour simuler les flammes à nombre de Lewis subunitaire : (1) induit une amplification de l'effet d'étirement sur la flamme ; (2) combinée à la faible résolution de maillage en LES, filtre les instabilités de front de flamme. Le couplage de ces mécanismes indésirables peut générer une propagation erronée de la flamme qui remet en question la capacité de prédiction de la LES pour les explosions de mélanges H2-air pauvres. Dans le cadre de cette thèse, une stratégie de modélisation est proposée afin de prédire de manière fiable et précise les explosions d'hydrogène-air pauvre. Un nouveau paradigme est envisagé pour corriger séparément l'amplification des effets d'étirement et modéliser les phénomènes de sous-maille dus à l'instabilité thermo-diffusive. Ces deux corrections sont d'abord développées sur des configurations canoniques, puis étendues et validées sur des configurations d'explosion plus réalistesThe climate crisis the world faces today calls for immediate actions to curb down carbon emissions. In particular, a rapid energy transition towards cleaner sources is necessary. Among many candidates, hydrogen stands out as a carbon-free energy vector. However, its storage and transport in big quantities raise safety concerns. Following a leakage, mixed with the surrounding air, this hydrogen can form a highly flammable mixture. In case of accidental ignition of this mixture, different combustion scenarios and regimes are possible, depending on factors such as geometry (dimensions, confinement, presence of obstacles), mixture composition, temperature, pressure or turbulence level. These regimes range from slow deflagration to the transition to detonation in the worst case. To predict the damage induced by an explosion, Computational Fluid Dynamics has the advantage of being safer than experiments and gives access to quantities hard or impossible to measure empirically. This thesis deals with the prediction of lean hydrogen-air explosions using Large-Eddy Simulation (LES). Lean H2-air mixtures are known for their distinctive sub-unity Lewis number, which characterises an unbalance between molecular and heat diffusion processes with major consequences: (1) lean H2-air flames are strongly sensitive to stretch; (2) they are prone to develop flame front cells due to the thermo-diffusive instability. Both constitute accelerating mechanisms which impact the overpressure generated during the explosion. In this work, we show that the Thickened Flame (TF) approach to simulate sub-unity Lewis number flames: (1) induces an amplification of stretch on the flame; (2) combined with the low grid resolution in LES, filters out flame front instabilities. The coupling of these undesired mechanisms can generate an erroneous flame propagation which questions the predictability of LES for lean H2-air explosions. In this thesis, a modelling strategy is proposed to reliably and accurately predict lean hydrogen-air explosions. A new paradigm is considered to separately correct the amplification of stretch effects and model subgrid phenomena due to the thermo-diffusive instability. These two corrections are first developed on canonical configurations and then extended and validated on more realistic explosion configurations
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Radisson, Basile. "Dynamique non linéaire de fronts de flammes : expériences et modélisation." Thesis, Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0124.
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Les flammes de prémélange sont souvent minces devant les échelles de l’écoulement dans lequel elles évoluent. La description de leur dynamique peut alors se réduire à des équations d’évolution pour leur front. Ce manuscrit présente une série d’expériences de laboratoire qui visent à valider la pertinence de telles modélisations. Les expériences sont menées dans une configuration quasi-2D (brûleur de Hele-Shaw) permettant une analyse fine de la dynamique de l’interface. Dans une première partie, l’évolution d’une flamme initialement plane et se propageant dans un écoulement au repos est étudiée. Pour la première fois, une comparaison quantitative de l’évolution non-linéaire avec une équation de type Michelson-Sivashinsky est obtenue. Par ailleurs, on montre que les solutions analytiques de cette équation permettent de prédire certaines propriétés statistiques du front. Ces prédictions restent valables même aux temps longs lorsque le bruit joue un rôle important dans la dynamique. Dans une deuxième partie, l’influence de l’enceinte du brûleur est étudiée. Un nouveau mécanisme de couplage vibroacoustique, propre à cette géométrie confinée,est identifié. Les propriétés de ces modes de structure sont ensuite exploitées pour étudier l’interaction d’une flamme avec un forçage périodique. Enfin, ces flammes quasi-2D, planes en moyenne, sont soumises à un écoulement faiblement turbulent. L’évolution de la vitesse de flamme avec l’intensité du forçage transite d’un régime super-linéaire aux très faibles forçages vers un régime sous-linéaire quand l’intensité turbulente s’approche de la vitesse de flamme laminaireIn many applications where premixed combustion is involved, the flame thickness is weak compared to the scales of the flow. This property allows to describe the flame frontevolution as an interface dynamics. In this manuscript some experiments are performed in order to check the validity of such models. The experiments are carried out in a Hele-Shaw burner. This quasi-bidimensional configuration allows for an accurate analysis ofthe flame front evolution. First, the dynamics of an initially flat flame propagating in aquiescent flow are analyzed. A quantitative comparison of an experimental flame evolution with the one predicted by a Michelson-Sivashinsky type equation is obtained for the firsttime. Moreover, the analytic pole solutions of this model allows us to predict some statisticproperties of the flame front. These predictions are shown to still be valid at large time,where the external noise plays an important role in the observed dynamics. In a second part, flame/burner interactions are investigated. A new vibroacoustic coupling mechanismis identified. Then, harnessing the properties of this vibroacoustic coupling, the flame issubmitted to an oscillating flow. It allows us to explore some characteristics of the flame response to a time dependent external forcing. Finally, the flame is submitted to a weaklyturbulent flow. The influence of the flow fluctuations intensity on the turbulent flamespeed is explored. The flame speed increase is shown to switch from a sublinear regime atsmall forcing to a superlinear one when the forcing intensity is approaching the laminar flame speed value
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LACHAUX, Thierry. "Etude des effets de la haute pression sur la structure et la dynamique des flammes turbulentes de prémélange pauvre de méthane-air." Phd thesis, Université d'Orléans, 2004. http://tel.archives-ouvertes.fr/tel-00010401.
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L'étude expérimentale porte sur l'influence de la haute-pression jusqu'à 0.9 MPa pour la combustion d'une flamme de prémélange méthane-air, pauvre, turbulente stabilisée sur un brûleur de type Bunsen. La vitesse débitante et la richesse sont fixées à 2.1 m/s et 0.6. Le champ de vitesses et les échelles de la turbulence sont déterminés à l'aide de l'anémométrie Laser Doppler. Les mesures de diffusion Rayleigh renseignent sur la fluctuation du scalaire. De l'imagerie de Mie deux dimensions sont obtenus la courbure, l'angle d'orientation, les longueurs de plissement et enfin, la densité de surface de flamme et l'intensité de combustion qui sont comparées avec les valeurs données par le modèle BML. Lorsque la pression augmente les échelles de Taylor et de Kolmogorov diminuent avec la viscosité cinématique, l'échelle intégrale et la vitesse fluctuante restent constantes, les structures du front de flamme deviennent plus petites et plus pointues, augmentant la densité de surface de flamme.
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Denet, Bruno. "Simulations numériques d'instabilités de front de flamme." Aix-Marseille 1, 1988. http://www.theses.fr/1988AIX11155.
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Simulation d'oscillations de relaxation dans un modele de retrocombustion dans un solide poreux, de l'instabilite thermodiffusive, et de l'instabilite hydrodynamique de darrieus-landau. Etude de l'extinction par pertes de chaleur a la paroi d'un tube et de l'interaction entre une flamme courbee et du bruit dans l'ecoulement
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Trouvé, Arnaud. "Instabilités hydrodynamiques et instabilités de combustion de flammes turbulentes prémélangées." Châtenay-Malabry, Ecole centrale de Paris, 1989. http://www.theses.fr/1989ECAP0097.
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Etude des modes de combustion instable observes sur une maquette de statoréacteur ou l'instabilité est le résultat d'interactions complexes entre la dynamique de l'écoulement dans la zone de réaction, les processus de dégagement de chaleur et le comportement acoustique du système confine. Etude des modes hydrodynamiques au cours d'un régime de combustion stable
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Boury, Gaël. "Etudes théoriques et numériques de fronts de flammes plissées : dynamiques non-linéaires libres ou bruitées." Poitiers, 2003. http://www.theses.fr/2003POIT2255.
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Les flammes de prémélange, souvent minces, sont assimilées à des interfaces actives. Des équations d'évolution pour leur front sont obtenues par développement asymptotique en contraste de densité. Selon ces dernières, la dynamique de flamme devrait être correctement gouvernée par les seules interactions entre hydrodynamique non visqueuse, non linéarité géométrique liée à la propagation (Huygens), changement de densité et géométrie d'ensemble, si certaines symétries globales soient respectées (invariances Galiléenne, par translation ou rotation) ou leur brisure prise en compte. Cette thèse est confortée par l'examen de 3 configurations : flammes accrochées soumises à un écoulement tangentiel fort et des stimuli externes, influence de gravités faibles, expansion 3-D. Les méthodes mises en œuvre sont analytiques et pseudo-spectrales. Dans chaque cas des lois d'échelle simples pour leur plissement sont identifiées. Celles-ci sont en accord au moins qualitatif avec les expériences disponibles. Pour chaque cas, des problèmes ouverts sont mentionnésUsually, premixed flames are thin. We view them as active interfaces. Evolution Equations for their front are obtained from asymptotic expansions in the density-contrast. Flame dynamics seems accurately controlled only by the interplay amongst elliptic hydrodynamics, a geometric non-linearity coming from the flame normal propagation (Huygens), the change in density, and the overall geometry, provided minimal symmetries (Galilean, translation, rotation) are fulfilled, or explicitly broken. Examining three configurations confirms the thesis, namely: flames anchored in the presence of a strong tangential blowing and external forcing, influence of a weak gravity field, 3-Dimensional expansions. Our methods are analytical and pseudo-spectral. In each case, scaling laws for wrinkling are identified. These are in good agreement with available experiments. Open problems are also evoked
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Clanet, Christophe. "Instabilités de propagation de flammes monophasiques et diphasiques dans une enceinte semi-ouverte." Aix-Marseille 1, 1995. http://www.theses.fr/1995AIX11071.
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Cette these traite des instabilites de propagation de flammes dans une enceinte semi-ouverte et plus precisement des instabilites thermo-acoustiques et de l'effet tulipe. Concernant les instabilites acoustiques, l'etude porte essentiellement sur l'origine physique de l'instabilite primaire et sur sa saturation. Cette etude est menee pour des melanges monophasiques et diphasiques, en tenant compte des pertes et en s'apuyant sur des theories recentes. Dans le cas monophasique, on montre que l'instabilite primaire resulte d'un couplage entre les cellules de landau et le champ d'acceleration acoustique. Dans le cas diphasique, l'instabilite est liee au dephasage de viteses entre les gouttes et l'air. Concernant l'effet tulipe, les differentes phases de la propagation sont identifiees puis etudiees de facon quantitative. Les resultats obtenus sont interpretes a partir d'un modele geometrique et compares a ceux, deja publies, obtenus dans une enceinte fermee aux deux extremites
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Rego, Rui. "Sur un modèle non linéaire d'interaction entre flamme et acoustique." Poitiers, 2006. http://www.theses.fr/2006POIT2304.
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Les flammes prémélangées peuvent être représentées comme des interfaces minces et actives, un point de vue qu'on adopte ici. Alors qu'existent des approches asymptotiques, fournissant des Equations d'Evolution (EE) du 1er-order-en temps qui soient précises, elles cessent d'être applicables lorsque les accélérations sont non négligeables. Pourtant, on peut bâtir quelques EE, capables de prendre en compte les effets les à l'accélération : celles-ci liés à découlent d'arguments de symétrie, de la phénoménologie disponible et leur consistance avec des cas-limite connus. De telles EE peuvent prendre en compte des effets d'accélération, externes ou induites, et de la non-linéarité d'Huygens, pourvu que la invariance Galiléen fût vérifie. Ce modèle couple la dynamique de la forme de flamme (méthode Fourier pseudo-spectrale) et l'acoustique externe, elle-même linéaire en moyenne. Tous les tests portant sur la réponse de notre modèle de flamme à une accélération imposée ont étés validés, même en régime non-linéaire. Ce système-modèle, global et non-linéaire, est résolu numériquement dans le cas de flammes se propageant le long d'un tube, par exemple. Des extensions sont aussi envisagéesPremixed flames may be considered as thin active interfaces, a point of view that we adopt here. Whereas accurate asymptotic expansions methods exist to obtain first-order-in-time Evolution Equations, whenever flow-field accelerations intervene those methods fail to provide an unambiguous answer. Still, suitable designed Evolution Equations that are able to handle with flow accelerations are tailored, based on phenomenological grounds, symmetry arguments, and consistency with known limiting cases. Those describe flame dynamics by a second-order-in-time Evolution Equation, with a geometrical non-linearity stemming from normal (Huygens) propagation, the density change, the overall geometry, and the inertia-induced gravitational forcing, provided that Galilean invariance is fulfilled. This flame EE model is numerically coupled with its self-induced acceleration field, where linear acoustics is shown to prevail on transverse average. The flame-shape evolution is handled via a Fourier pseudo-spectral method, which is checked against flame responses to prescribed accelerations successfully, even in the nonlinear regime. This nonlinear, global, system model is solved for flames in tubes as an example. Follow-on studies are also envisaged
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Palies, Paul. "Dynamique et instabilités de combustion des flammes swirlées." Phd thesis, Ecole Centrale Paris, 2010. http://tel.archives-ouvertes.fr/tel-00545421.
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Ce travail traite de la dynamique des flammes turbulentes prémélangées confinées et swirlées soumises à des perturbations de vitesses acoustiques. L'objectif général est d'acquérir une compréhension des mécanismes régissant la réponse de ces flammes et d'en tirer des méthodes de prévision des instabilités de combustion. Les écoulements swirlés sont d'abord examinés en termes de nombre de swirl et de nouvelles expressions sont données pour cette quantité. On traite notamment des effets de perturbations de vitesse et une expression est proposée qui tient compte des fluctuations de vitesses dans l'écoulement. Le système utilisé pour l'étude expérimentale comprend une cavité amont, un injecteur équipé d'un swirler et un tube à flamme transparent permettant la visualisation directe du mouvement de la flamme. Deux points de fonctionnement sont étudiés correspondant à des vitesses débitantes différentes. La cavité amont et le tube à flamme du brûleur peuvent être facilement changés pour étudier plusieurs configurations différentes. L'acoustique du brûleur est également analysée au moyen d'une approche de cavités couplées pour déterminer les fréquences de résonance du système en configuration non-réactive. Des expériences sont menées pour mesurer les fréquences propres du système et l'estimation du coefficient d'amortissement est réalisée à partir de la réponse du système à une modulation externe. Un critère de découplage des mode acoustiques est proposé. La dynamique de l'écoulement est examinée en termes de conversion de modes au niveau de la vrille (swirler) ou dans une grille d'aubes. Cette partie du travail, effectuée au moyen de simulations numériques montre que lorsqu'une grille ou une vrille sont soumis à une onde acoustique, le swirler donne naissance à une onde azimutale convective en plus de l'onde acoustique axiale transmise. Les deux types de swirlers, axial et radial, donnent lieu à ce mécanisme, un fait confirmé par des expériences. Il est montré que ce processus de conversion de mode a un impact important sur la dynamique de la flamme swirlée. La dynamique de la combustion est ensuite analysée en mesurant la fonction de transfert généralisée ainsi que les distributions de taux de dégagement de chaleur au cours du cycle d'oscillation. La fonction de transfert est utilisée pour déterminer la réponse de la flamme à des perturbations acoustiques se propageant dans l'écoulement en amont de la flamme. Il est aussi montré que le nombre de Strouhal est un groupe sans dimensions qui permet de caractériser la réponse de la flamme. La dynamique est également analysée au moyen d'un ensemble de diagnostics comprenant des sondes de pression, un photomultiplicateur et un vélocimètre laser Doppler. Un modèle pour la fonction de transfert linéaire de la flamme est dérivé théoriquement à partir d'une description de la flamme au moyen de l'équation pour une variable de champ G. Les mécanismes physiques de la réponse de la flamme sont identifiés : enroulement tourbillonnaire et fluctuations du nombre de swirl. L'enroulement tourbillonnaire est associé à l'onde acoustique transmise en aval du swirler et qui pénètre dans la chambre de combustion. Tandis que les fluctuations du nombre de swirl sont directement liées aux mécanismes de conversion de mode au swirler qui induit différentes vitesses pour les perturbations axiales et azimutales. L'enroulement tourbillonnaire enroule l'extrémité de la flamme tandis que les fluctuations du nombre de swirl agissent sur l'angle de la flamme. Ces deux mécanismes en compétition se combinent de manière constructive ou destructive conduisant à des gains faibles ou élevés dans la réponse de la flamme en fonction de la fréquence. Ces mécanismes sont retrouvés par simulation aux grandes échelles (LES). Enfin, une analyse d'instabilité est réalisée en combinant la fonction de transfert généralisée expérimentale et un modèle acoustique du brûleur afin de déterminer la fréquence et l'amplitude des perturbations de vitesse au cycle limite.
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Poinsot, Thierry. "Analyse des instabilités de combustion de foyers turbulents prémélangés." Paris 11, 1987. http://www.theses.fr/1987PA112065.
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Développement de techniques spécifiques d'acquisition (diagnostics optiques et acoustiques) et de traitement de données, appliquées à un foyer de laboratoire, dans le but d'analyser et d'expliquer les modes de combustion instables. Un modèle de flamme mince développé pour une combustion stabilisée dans un canal, effectue le calcul non linéaire complet des oscillations de l'écoulement et permet de prévoir l'apparition d'oscillations auto-entretenues, donc d'instabilités et de calculer leurs seuils de déclenchement ainsi que les cycles limites associés
Books on the topic "Instabilités de front de flamme"
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Mégret, Bruno. La flamme: Les voies de la renaissance. Paris: R. Laffont, 1990.
Find full textBook chapters on the topic "Instabilités de front de flamme"
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Sato, Mako, and Yasuhide Fukumoto. "Influence of an oblique magnetic field on planar flame front instability." In 2019-20 MATRIX Annals, 439–59. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-62497-2_26.
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Ortoleva, Peter J. "Reaction Front Morphology." In Geochemical Self-Organization, 111–35. Oxford University PressNew York, NY, 1994. http://dx.doi.org/10.1093/oso/9780195044768.003.0007.
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Abstract Reaction fronts of planar, spherical, or other high-symmetry forms may be unstable to perturbations changing their shape. In this chapter we investigate both the linear instability and the nonlinear restabilization of these fronts into scalloped or other lower-symmetry forms. Such phenomena have been found in flames, secondary oil recovery, in situ coal gassification, crystal or particle growth, and reactive porous medium-flow systems. A scalloped reaction front is indicated schematically in Fig. 7-1. In this chapter the instability of planar reaction fronts and their restabilization to new morphologies and states of temporal oscillation are discussed. Numerical results on carbonate-cemented sandstones are presented that demonstrate the surprising richness of nonlinear phenomena that even the simplest systems can sustain.
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SIV ASHINSKY, G. I. "Nonlinear analysis of hydrodynamic instability in laminar flames—I. Derivation of basic equations." In Dynamics of Curved Fronts, 459–88. Elsevier, 1988. http://dx.doi.org/10.1016/b978-0-08-092523-3.50048-4.
Full textConference papers on the topic "Instabilités de front de flamme"
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BYCHKOV, VITALIY. "FLAME FRONT INSTABILITIES AND DEVELOPMENT OF FRACTAL FLAMES." In Conference on Fractals 2002. WORLD SCIENTIFIC, 2002. http://dx.doi.org/10.1142/9789812777720_0021.
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Gopalakrishnan, Harish Subramanian, Andrea Gruber, and Jonas Moeck. "Computation of Intrinsic Instability and Sound Generation From Autoignition Fronts." In ASME Turbo Expo 2022: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2022. http://dx.doi.org/10.1115/gt2022-82480.
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Abstract Burning carbon-free fuels such as hydrogen in gas turbines promises power generation with minimal emissions of greenhouse gases. A two-stage sequential combustor architecture with a propagation-stabilized flame in the first stage and an autoignition-stabilized flame in the second stage allows for efficient combustion of hydrogen fuels. However, interactions between the autoignition-stabilized flame and the acoustic modes of the combustor may result in self-sustained thermoacoustic oscillations, which severely affect the stable operation of the combustor. In this paper, we study an ‘intrinsic’ thermoacoustic feedback mechanism in which acoustic waves generated by unsteady heat release rate oscillations of the autoignition front propagate upstream and induce flow perturbations in the incoming reactant mixture, which, in turn, act as a disturbance source for the ignition front. We first perform detailed reactive Navier-Stokes (DNS) and Euler computations of an autoignition front in a one-dimensional setting to demonstrate the occurrence of intrinsic instability. Self-excited ignition front oscillations are observed at a characteristic frequency and tend to become more unstable as the acoustic reflection from the boundaries is increased. The Euler computations yield identical unsteady ignition front behaviour as the DNS computations, suggesting that inviscid mechanisms control the instability. In the second part of this work we present a simplified framework based on the linearized Euler equations (LEE) to compute the sound field generated by an unsteady autoignition front. Unsteady autoignition fronts create sources of sound due to local fluctuations in gas properties, in addition to heat release oscillations, which must be accounted for. The LEE predictions of the fluctuating pressure field in the combustor agree well with the DNS data. The findings of the present work are essential for understanding and modeling thermoacoustic instabilities in reheat combustors with autoignition-stabilized flames.
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Oravecz, Lisa M., Indrek S. Wichman, and Sandra L. Olson. "Instability of Flame Spread in Microgravity." In ASME 1999 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1999. http://dx.doi.org/10.1115/imece1999-1118.
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Abstract Results from the first part of an experimental study of flame spread instability are presented. The instabilities were investigated in the NASA drop facilities because the particular instabilities being examined were most pronounced in microgravity, when the influences of buoyancy were minimized. The flame front over thin cellulosic samples broke apart into separate flamelets which interacted with one another and oscillated (frequency ∼ 1 Hz). Different heat-sink backings, which were used to promote flame instability and flamelet productions are examined and described. Preliminary experiments in the NASA 5 second drop tower (Zero-G) drop facility are discussed.
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Mukaiyama, Kenji, and Kazunori Kuwana. "Influence of Flame Front Instability on Flame Propagation Behavior." In ASME/JSME 2011 8th Thermal Engineering Joint Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/ajtec2011-44223.
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This paper discusses flame acceleration due to flame instability mechanisms. In particular, the diffusive-thermal instability and hydrodynamic instability mechanisms are considered. The Sivashinsky equation is used to compute two-dimensional flame propagation behaviors, and the influence of each instability mechanism is separately considered. The effect of flame size on flame speed (accelerated due to the instability mechanisms) is particularly investigated. It is found that the flame propagation velocity (Vf) is independent of flame size under the influence of diffusive-thermal instability, whereas Vf increases with flame size under the influence of hydrodynamic instability. The fractal nature of the flame under the influence of hydrodynamic instability is confirmed based on the dependence of Vf on flame size. Fractal dimension is then calculated as a function of volume expansion ratio, the parameter that controls the hydrodynamic instability mechanism. An FFT analysis is conducted to further understand the flame’s fractal structure.
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Zhu, Shengrong, and Sumanta Acharya. "Effects of Hydrogen Addition on Swirl-Stabilized Flame Properties." In ASME Turbo Expo 2010: Power for Land, Sea, and Air. ASMEDC, 2010. http://dx.doi.org/10.1115/gt2010-23686.
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The role of hydrogen addition to swirl-stabilized methane flames is studied experimentally. Of specific interest are flame properties including flame surface density and curvature. The measurements are based on Particle Image Velocimetry (PIV), Mie-scattering and CH-chemiluminescence imaging. Identification of the flame front and its geometric characterization provides an understanding of the flame properties. Compared to the non-reacting flow, the methane flame broadens the central recirculation zone. Hydrogen enriched flames reduce the central recirculation zone and scales down the characteristic length of the flow. With hydrogen addition, the distribution of the flame front curvature is broadened and flame surface density is increased. This indicates that hydrogen addition increases the reaction front thermo-diffusive instability, causing the flame front to be more wrinkled, and increasing the flame surface area leading to an increase in the burning velocity.
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Baghirzade, Mammadbaghir, Md Nayer Nasim, Behlol Nawaz, Jonathan Aguilar, Martia Shahsavan, Mohammadrasool Morovatiyan, and John Hunter Mack. "Analysis of Premixed Laminar Combustion of Methane With Noble Gases as a Working Fluid." In ASME 2021 Internal Combustion Engine Division Fall Technical Conference. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/icef2021-67516.
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Abstract Hydrodynamic and diffusional-thermal instabilities affect the flame dynamics, which result in non-planar flame fronts with self-accelerating cellularities and wrinkles. In premixed flames, the driving mechanism for perturbations is hydrodynamic instabilities, which are associated with thermal expansion. Under high-pressure conditions, such as in spark-ignition engines, the flame curvature and morphology might be influenced by the hydrodynamic instabilities. This study focuses on the replacement of nitrogen with a noble gas (argon and krypton) as the working fluid in the premixed combustion of methane to investigate its effect on flame stability and dynamics. The utilization of noble gases can also enhance the ideal thermal efficiency of internal combustion engines due to the higher specific heat ratio they possess and may also reduce the NOx emissions markedly because of the lack of nitrogen in the working fluid. The experiments are conducted for various equivalence ratios (φ = 0.8, 1.0, 1.2) in a constant volume combustion chamber (CVCC) at atmospheric and elevated initial pressures and atmospheric temperature. As an outcome of this study, to understand the influence of krypton on methane combustion, spherically propagating flames are analyzed in terms of the laminar flame burning velocity, cellular instability, unburned gas Markstein length, and flame morphology utilizing a Z-type Schlieren optical diagnostic technique and fractal analysis, which is a promising approach to analyze flame surfaces. The fractal dimension of the flame fronts is calculated by a box-counting algorithm. The results are compared against the previously examined case studies in which argon was used as the primary working fluid.
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Kusakai, Takafumi, and Satoshi Kadowaki. "Numerical Simulation on the Instability of Cylindrically Expanding Premixed Flames With Radiative Heat Loss at Low Lewis Numbers." In ASME/JSME 2011 8th Thermal Engineering Joint Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/ajtec2011-44181.
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The instability of cylindrically expanding premixed flames with radiative heat loss was studied by two-dimensional unsteady calculations of reactive gases, based on the diffusive-thermal model equation. When the Lewis number was unity, instability phenomena were not observed. When the Lewis number was sufficiently low, on the other hand, cellular-shaped fronts on adiabatic and non-adiabatic cylindrical flames were observed, which was due to diffusive-thermal instability. As radiative heat loss increased, the behavior of cellular fronts became more unstable. This indicated that the radiation promoted the unstable behavior of flame fronts at low Lewis numbers. When radiative heat loss was much large compared with the quenching condition of a planar flame, cylindrical flames were broken up and several small flames appeared. This was in qualitative agreement with the experimental results on the dynamic behavior of lean hydrogen-air premixed flames with radiative heat loss under the low gravity condition. Several small flames appeared on the grounds that large curvature of flame fronts was necessary to keep high temperature against radiative heat loss.
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Samarasinghe, Janith, Wyatt Culler, Bryan D. Quay, Domenic A. Santavicca, and Jacqueline O’Connor. "The Effect of Fuel Staging on the Structure and Instability Characteristics of Swirl-Stabilized Flames in a Lean Premixed Multi-Nozzle Can Combustor." In ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/gt2017-63688.
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Fuel staging, or fuel splitting, is a commonly used strategy for the suppression of combustion instabilities in gas turbine engines. In multi-nozzle combustor configurations, this is achieved by varying the fuel flow rate to the different nozzles. The effect of fuel staging on flame stabilization and heat release rate distribution (referred to as flame structure), and self-excited instability characteristics is investigated in a research can combustor employing five small-scale lean-premixed industrial nozzles. The nozzles are arranged in a “four-around-one” configuration and fuel staging is achieved by injecting additional fuel to the middle nozzle. An operating condition was identified where all five nozzles were fueled equally and the combustor was subject to a self-excited instability. At the operating condition considered, the self-excited instabilities are suppressed with fuel staging: this is true for cases where overall equivalence ratio is increased by staging (by only increasing the fuel flow rate to the middle nozzle) as well as cases where overall equivalence ratio is kept constant while staging (by simultaneously decreasing the fuel flow rate of the outer nozzles while increasing the fuel flow rate to the middle nozzle). Fuel staging causes variations in the distribution of time-averaged heat release rate in the regions where adjacent flames interact. The locations of highest heat release rate fluctuation are not altered with increased fuel staging but the fluctuation amplitude is reduced. A breakup in the monotonic phase behavior that is characteristic of convective disturbances is observed with increased fuel staging, resulting in a lower pressure fluctuation amplitude. In particular, the monotonic variation in phase in the middle flame and the region where adjacent flames interact is out-of-phase with that of the outer flames, resulting in a cancellation of the global heat release rate oscillations. The distribution of local Rayleigh integral within the combustor shows that during a self-excited instability, the regions of highest heat release rate fluctuation are in phase-with the pressure fluctuation. When staging fuel is introduced, these regions fluctuate out-of-phase with the pressure fluctuation, further illustrating that fuel staging suppresses instabilities by altering the phase relationship of convective disturbances that travel along the flame front.
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Faldella, Filippo, Sebastián Eisenring, Taesung Kim, Ulrich Doll, and Peter Jansohn. "Turbulent Flame Speed and Flame Characteristics of Lean Premixed H2-CH4 Flames at Moderate Pressure Levels." In ASME Turbo Expo 2023: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2023. http://dx.doi.org/10.1115/gt2023-102527.
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Abstract Carbon dioxide emissions in gas turbine power generation can be reduced by adding an increasing amount of hydrogen to the existing natural gas-fueled combustion systems. To enable safe operation, more insight on how H2 addition affects turbulent flame speed and other important flame characteristics is needed. In this work, the investigation of hydrogen addition effects on certain flame properties has been carried out in a high-pressure axial-dump combustor at gas turbine relevant conditions. OH planar laser induced fluorescence (PLIF) was applied to retrieve flame front contours and turbulent flame speed. The results show that as the concentration of hydrogen in the fuel mixture increases, turbulent flame speed and flame characteristics change drastically. Two main regimes can be identified: From 0 to 50% vol. hydrogen, the turbulent flame speed increases weakly in an almost linear fashion, while from 50% vol. to 100% vol. the trend sharply changes and the higher reactivity of hydrogen, combined with a lower Lewis number, cause thermal-diffusive instability and preferential diffusion effects to become increasingly strong, leading to very high burning rates. The presented results, help to understand and to define the relevant modifications that are necessary to successfully operate gas turbine combustor systems with high H2 content fuels.
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Peracchio, A. A., and W. M. Proscia. "Nonlinear Heat-Release/Acoustic Model for Thermoacoustic Instability in Lean Premixed Combustors." In ASME 1998 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1998. http://dx.doi.org/10.1115/98-gt-269.
Full textAbstract:
Lean premixed combustors, such as those used in industrial gas turbines to achieve low emissions, are often susceptible to thermoacoustic combustion instabilities, which manifest themselves as pressure and heat release oscillations in the combustor. These oscillations can result in increased noise and decreased durability due to vibration and flame motion. A physically based nonlinear parametric model has been developed that captures this instability. It describes the coupling of combustor acoustics with the rate of heat release. The model represents this coupling by accounting for the effect of acoustic pressure fluctuations on the varying fuel/air ratio being delivered to the flame, causing a fluctuating heat release due to both fuel air ratio variations and flame front oscillations. If the phasing of the fluctuating heat release and pressure are proper, an instability results that grows into a limit cycle. The nonlinear nature of the model predicts the onset of the instability and additionally captures the resulting limit cycle. Tests of a lean premixed nozzle run at engine scale and engine operating conditions in the UTRC Single Nozzle Rig, conducted under DARPA contract, exhibited instabilities. Parameters from the model were adjusted so that analytical results were consistent with relevant experimental data from this test. The parametric model captures the limit cycle behavior over a range of mean fuel air ratios, showing the instability amplitude (pressure and heat release) to increase and limit cycle frequency to decrease as mean fuel air ratio is reduced.