Dissertationen zum Thema „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.
Der volle Inhalt der QuelleThe 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
Radisson, Basile. „Dynamique non linéaire de fronts de flammes : expériences et modélisation“. Thesis, Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0124.
Der volle Inhalt der QuelleIn 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
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.
Der volle Inhalt der QuelleDenet, Bruno. „Simulations numériques d'instabilités de front de flamme“. Aix-Marseille 1, 1988. http://www.theses.fr/1988AIX11155.
Der volle Inhalt der QuelleTrouvé, Arnaud. „Instabilités hydrodynamiques et instabilités de combustion de flammes turbulentes prémélangées“. Châtenay-Malabry, Ecole centrale de Paris, 1989. http://www.theses.fr/1989ECAP0097.
Der volle Inhalt der QuelleBoury, Gaël. „Etudes théoriques et numériques de fronts de flammes plissées : dynamiques non-linéaires libres ou bruitées“. Poitiers, 2003. http://www.theses.fr/2003POIT2255.
Der volle Inhalt der QuelleUsually, 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
Clanet, Christophe. „Instabilités de propagation de flammes monophasiques et diphasiques dans une enceinte semi-ouverte“. Aix-Marseille 1, 1995. http://www.theses.fr/1995AIX11071.
Der volle Inhalt der QuelleRego, Rui. „Sur un modèle non linéaire d'interaction entre flamme et acoustique“. Poitiers, 2006. http://www.theses.fr/2006POIT2304.
Der volle Inhalt der QuellePremixed 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
Palies, Paul. „Dynamique et instabilités de combustion des flammes swirlées“. Phd thesis, Ecole Centrale Paris, 2010. http://tel.archives-ouvertes.fr/tel-00545421.
Der volle Inhalt der QuellePoinsot, Thierry. „Analyse des instabilités de combustion de foyers turbulents prémélangés“. Paris 11, 1987. http://www.theses.fr/1987PA112065.
Der volle Inhalt der QuelleAlmarcha, Christophe Bernard Alphonse. „Instabilités hydrodynamiques du front d'ablation en fusion par confinement inertiel“. Aix-Marseille 1, 2007. http://www.theses.fr/2007AIX11049.
Der volle Inhalt der QuelleAn Inertial Confinement Fusion (ICF), hydrodynamic instabilities grow during the acceleration stage in the imploding of a target under an intense radiation. These instabilities, quite similar to Rayleigh-Taylor instability, disturb the spherical configuration necessary for ignition of nuclear reactions in the late compression stages. Understanding them requires the study of coupled hydrodynamic and thermal instabilities on a wide range of length scales, which make direct numerical simulations difficult to perform. Considering intermediate regimes of acceleration in the asymptotic limit of a large power index for thermal conduction, the model usually used in ICF reduces to a discontinuity (the ablation front) between two potential flows. This allows the use of precise numerical boundary integral methods. Simulations can be performed to highly non linear stages and show the appearence of a finite time singularity consisting in an explosion of both the velocity gradients and curvature
Valiev, Damir. „The role of Landau-Darrieus instability in flame dynamics and deflagration-to-detonation transition“. Licentiate thesis, Stockholm : Materialvetenskap, Kungliga Tekniska högskolan, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4334.
Der volle Inhalt der QuelleDemare, David. „Stabilisation d'une flamme suspendue non-prémélangée, influence d'un champ acoustique“. Rouen, 2003. http://www.theses.fr/2003ROUES024.
Der volle Inhalt der QuelleThe effects of an acoustic perturbation on a non-premixed lifted flame are analysed with imagery and velocimetry techniques. First, a study without acoustics is performed with a free jet flame, naturally organized. In that case, the flame always stabilizes on lateral ejections of matter formed by counter-rotating steamwise structures due to secondary instabilities. Secondly, the responses of the flame to a large range of frequencies and amplitudes are reported in a chart. This latter one shows different zones : - In high frequency zones (kilohertz), when the forcing is applied around the resonance frequencies, the flame stability is improved because of a better jet organization; in other cases, the weakest modulations act on the development of instabilities, leading to a definive flame reattachment. - In middle frequency zones (hectohertz), it is possible to avoid the anchoring of the lifted flame and change the combustion regime, the flame is shorter, its yellow plume due to soots vanishes because of an increase of the turbulence leading to the the improvement of the mixing. - In low frequency zones (decahertz), depending on the amplitude value, perturbations lead to liftoff height fluctuations which provide, either a definitive reattachment, or successive anchoring and lifting. All these responses are observed for different diameters and exit velocities while keeping moderate Reynold numbers (3000-6000) and a naturally organized jet
Edarh-Bossou, Toyo Koffi. „Etude de la propagation d'un front de flamme dans un milieu strié“. Lyon 1, 1993. http://www.theses.fr/1993LYO10195.
Der volle Inhalt der QuellePavec, Marc. „Instabilités barocline et paramétrique des courants de bord, application au front d'Ouessant“. Brest, 2007. http://www.theses.fr/2007BRES2042.
Der volle Inhalt der QuelleCoastal currents experience many sources of instability, resulting in the formation of coherent structures such as eddies. These structures play a fundamental role in the oceanic circulation and in the transfer of properties in the ocean. Three configurations of idealized coastal currents are studied in this thesis-: a frontal one, a quasi-geostrophic one and a shallow-water one. The well known baroclinic instability is shown to exist for all these currents, and a new mechanism, the parametric instability, is described. It appears on flows which present a periodic variation of one of their components. The oscillating parameter is the current speed in the frontal configuration, the baroclinic transport or PV in the quasi-geostrophic one and the barotropic flow in the shallow-water one. Analytical calculations allow to compare growth rates of both baroclinic and parametric instability and to show the amplification of parametric instability in the vicinity of the marginal stability curve for baroclinic instability. Numerical simulations are used to show that the effects of parametric instability are similar to the effects of baroclinic instability on the quasi-geostrophic flow. The shallow-water modal presents a density front with caracteristic scales representative of the Ushant front. It is shown from MICOM simulations that baroclinic instability can explain the observed instabilities of the front for a large part. Parametric instability effects are identified, but their impact seems to be weak
Sengissen, Aloïs. „Simulation aux grandes échelles des instabilités de combustion : vers le couplage fluide / structure“. Phd thesis, Toulouse, INPT, 2006. http://oatao.univ-toulouse.fr/7428/1/sengissen1.pdf.
Der volle Inhalt der QuelleSuys, Olivier. „Étude de la propagation d'un front de flamme dans un milieu solide hétérogène“. Bordeaux 1, 1996. http://www.theses.fr/1996BOR10518.
Der volle Inhalt der QuelleBlouquin, Rodolphe. „Contribution à l'étude théorique des interactions entre combustion et rayonnement“. Poitiers, 1996. http://www.theses.fr/1996POIT2363.
Der volle Inhalt der QuelleAl, Sarraf Elias. „Instabilités de flammes de prémélange en cellule de Hele-Shaw“. Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0590/document.
Der volle Inhalt der QuellePremixed combustion has been the subject of extensive work, concerning both applications and fundamental aspects. Although in most practical applications combustion occurs in a turbulent environment, the study of laminar flames is important to understand the fundamental mechanisms of turbulent flame propagation. The objective of this work is to study the various instabilities acting on a laminar premixed flame for mixtures of propane-air and methane-air, enriched or not with nitrogen. it consists in measuring the linear growth rates of disturbances in a Hele-Shaw burner formed by two glass plates ($150\times50cm$) separated by a thin gap width (2D burner). Using spatially modulated plates with different wavelengths, the linear growth rate of perturbations can be measured even in the presence of the most unstable wavelength. The experimental values of the linear growth rate as a function of wavenumber are fitted by a linear dispersion relation to estimate the Markstein number and the cutoff wavenumber. For a constant equivalence ratio with increasing values of the dilution in oxygen, the cutoff wavenumber grows with the flame velocity and it is becoming more unstable. The cutoff wave number rises also when the equivalence ratio increases for propane-air mixture and decreases for methane-air mixture, in relation to the evolution of thermal diffusive effects. An enlargement in the thickness of the Hele-Shaw cell results in an increase of the growth rate for small wavenumbers thus in the Markstein number, and in a decline in the growth rate for the large wavenumbers, in relation with the effects of heat losses
Noh, Dong-Soon. „Contribution à l'étude expérimentale d'une flamme turbulente de prémélange hydrogène-air : caractéristique des champs de vitesse et de la structure spatiale du front“. Rouen, 1991. http://www.theses.fr/1991ROUES014.
Der volle Inhalt der QuelleRoussel, Olivier. „Développement d'un algorithme multirésolution adaptatif tridimensionnel pour la résolution des équations aux dérivées partielles paraboliques : application aux instabilités thermo-diffusives de flamme“. Aix-Marseille 2, 2003. http://www.theses.fr/2003AIX22006.
Der volle Inhalt der QuelleJiang, Chongjun. „Etude des alternances récurrentes dans les skarns et des instabilités du front de dissolution/précipitation“. Phd thesis, Ecole Nationale Supérieure des Mines de Paris, 1993. http://tel.archives-ouvertes.fr/tel-01052909.
Der volle Inhalt der QuelleMasse, Laurent. „Etude linéaire de l'instabilité du front d'ablation en fusion par confinement inertiel“. Aix-Marseille 1, 2001. http://www.theses.fr/2001AIX11052.
Der volle Inhalt der QuelleSensiau, Claude. „Simulations numériques des instabilités thermoacoustiques dans les chambres de combustion annulaires“. Montpellier 2, 2008. http://www.theses.fr/2008MON20155.
Der volle Inhalt der QuelleThermoacoustic instabilities are spontaneously excited by a feedback loop between an oscillatory combustion process and one of the natural acoustic modes of the combustor. This phenomenon causes loss of performance and severe damages to the engine. However, aeronautical engines or gaz turbines manufacturers often observe this kind of instabilities during the experiments. In this work we propose a methodology dedicated to the computation of thermoacoustic instabilities usable in an industrial context. The coupling between acoustics and combustion is accounted for thanks to a specific Helmholtz equation including a reacting flow term. Using a finite element approach leads to an algebraic non-linear eigenvalue problem with N dimensions (N the number of nodes in the mesh). A point fix algorithm mixed with subspace iterative methods (Arnoldi implemented in ARPACK or Jacobi-Davidson) permits to solve this problem efficiently. Because aeronautical combustors usually present an annular shape with 10 to 20 injectors located all over the circumference, a multi-referenced (n-tau) flame transfer function is proposed. This thermoacoustic model shows amplified or damped, standing or spinning azimuthal modes depending on the parameter tau. This methodology is integrated in the calculation chain QUIET (AVBP-N3S-NOZZLE-AVSP) and it is used to study thermoacoustic instabilities of the Turbomeca ARDIDEN engine. The results are shown to be in good accordance with large eddy simulations of the whole combustor
Laverdant, Alain. „Contribution à l'étude des instabilités de combustion des foyers aérobies“. Rouen, 1991. http://www.theses.fr/1991ROUE5021.
Der volle Inhalt der QuellePavé, David. „Contribution à l'étude de la structure des flammes turbulentes de prémélanges pauvres de méthane-air“. Phd thesis, Université d'Orléans, 2002. http://tel.archives-ouvertes.fr/tel-00010987.
Der volle Inhalt der QuelleNous décrivons macroscopiquement la flamme par imagerie Mie avec les iso-c, l'épaisseur turbulente, l'échelle de plissements et la densité de surface de flamme. Nous étudions la structure du front de flamme instantané, la statistique de la courbure du front, l'épaisseur du front de flamme par imagerie Rayleigh. Nous caractérisons les épaisseurs thermiques (zone de réaction et de préchauffage) et déterminons la corrélation entre l'épaisseur et la courbure du front de flamme.
Nous confrontons nos données aux modèles de combustion turbulente de prémélange (BML et ceux basés sur la dissipation scalaire). Nous étudions les distributions des longueurs d'entrecroisement, et le taux de combustion. Nous comparons nos résultats à ceux obtenus dans la littérature par d'autres techniques de mesure.
Noiray, Nicolas. „Analyse linéaire et non-linéaire des instabilités de combustion : application aux systèmes à injection multipoints et stratégies de contrôle“. Châtenay-Malabry, Ecole centrale de Paris, 2007. http://www.theses.fr/2007ECAP1049.
Der volle Inhalt der QuelleCombustion instabilities induced by resonant acoustic-flame coupling occur in manypractical systems and cause severe difficulties and in extreme cases provoke failure or catastrophic damage. In most cases, the combustion process and the flow field are coupled by the system acoustic modes yielding strong oscillations of the flow and release of heat within the system. The problem has been extensively investigated over a number of years and a considerable amount of information has been gathered on the basic driving and coupling mechanisms. The present thesis aims at answering some of pending questions by combining systematic experiments, with theoretical modeling and numerical simulation. Theoretical developments are devised to model the physical phenomena encountered in the experimental layout. Numerical simulations are also used to complement the experimental and analytical work. The important results of this work are : (1) The nonlinear framework relying on the flame describing function (FDF). This constitutes a substantial progress in the understanding of mechanisms yielding limit cycles and of other nonlinear processes such as hysteresis or instability triggering, which are commonly observed in combustion applications. (2) the original passive control strategy which was developped and uses a dynamical phase converter (DPC) to reduce the sensitivity of the flame collection to incident perturbations (patent has been filed on this basis)
Bariki, Chaimae. „Interaction entre une flamme de prémélange et une structure tourbillonnaire“. Thesis, Orléans, 2018. http://www.theses.fr/2018ORLE2067.
Der volle Inhalt der QuelleUnderstanding and predicting the different mechanisms at play in turbulent premixed flames is a tremendously difficult issue for sizing or optimizing many combustion systems. Turbulent reactive flows are characterized by a complex interaction between the fluid motion, the inherent heat generated by the flame and turbulence. This challenge being extremely difficult to meet, the study of the interactions between a flat flame and a toroidal vortex provide an ideal canonical framework to better understand the physical mechanisms at play. In this perspective, experimental studies were carried out using a stagnation burner fed by a premixed fuel and air (methane/air,propane/air, hydrogen/air). A panel of experimental techniques as well as numerical tools have been used to characterize thoroughly the flame/vortex interactions. By modifying the equivalence ratio, the mixture composition and the vortex intensity, the temporal evolution of the interaction enable the extraction of the flame surface, the flame front stretch and curvature as well as the displacement/consumption speeds. In addition, the internal flame structure is deeply investigated by decomposing the flame front into a preheat zone and a reaction zone
Megninta, Abdramane. „Approche expérimentale de la dynamique d'un front de flamme oblique modulé par une allée de Von Karman“. Aix-Marseille 1, 1988. http://www.theses.fr/1988AIX11147.
Der volle Inhalt der QuelleMegninta, Abdramane. „Approche expérimentale de la dynamique d'un front de flamme oblique modulé par une allée de Von Karman“. Grenoble 2 : ANRT, 1988. http://catalogue.bnf.fr/ark:/12148/cb376161249.
Der volle Inhalt der QuelleRoussel, Olivier. „Développement d'un algorithme multirésolution adaptatif tridimensionnel pour la résolution des équations aux dérivées partielles paraboliques. Application aux instabilités thermodiffusives de flamme“. Phd thesis, Université de la Méditerranée - Aix-Marseille II, 2003. http://tel.archives-ouvertes.fr/tel-00719904.
Der volle Inhalt der QuelleLetty, Camille. „Etude d'une flamme en V diphasique : Approches expérimentale et numérique“. Rouen, 2008. http://www.theses.fr/2008ROUES036.
Der volle Inhalt der QuelleThis work deals with V-shaped two-phase flames stabilised in a pseudo-laminar or moderated turbulent flow. Some gaseous fuel is also injected to help turbulent flames stabilisation. An experimental approach and a numerical approach (Direct Numerical Simulation) are conducted simultaneously. The same tools are used for post-processing of experimental and numerical data. The flow is experimentally charaterised in term of droplet size distribution (Malvern), turbulent properties (PIV), qualitative fuel repartition (PLIF on acetone) and droplet temperature distribution (rainbow refractometry). The gaseous flow is numerically defined by Navier-Stokes equations in an eulerian framework. Two-way coupling is use to determine interaction of gaseous and liquid phases. A lagrangian solver is used for the dispersed phase. Chemical kinetics is derived from complex chemistry results computed with Chemkin (San Diego mechanism for n-heptane with acetone oxydation reactions). Flame front is artificially thickened (Flame thickness factor and efficiency function). This enables reduction of the mesh size which is time saving. Mean geometrical and local properties of the flame front are determined: morphology, flame angle, progress variable, flame brush evolution, curvature and strain rate. The mean flame angle is used to ajust DNS parameters. The evolution of the droplets mean temperature is presented for different turbulent conditions and from experimental and numerical approaches. DNS fields are used to develop a calculation method of strain rate from experimental data following tensorial method
Rojas, René. „Sur des Gouttes, Cristaux Liquides et Front“. Phd thesis, Université de Nice Sophia-Antipolis, 2005. http://tel.archives-ouvertes.fr/tel-00129102.
Der volle Inhalt der QuelleLa seconde partie est consacrée à l'étude d'une goutte déposée adiabatiquement sur un solvant plus dense. La goutte tombe dans le solvant jusqu'à une hauteur minimale, ensuite la fragmentation a lieu et les gouttelettes secondaires remontent à la surface. On a developpé un modèle théorique qui inclut l'essentiel du phénomène et prédit les échelles correctes du temps de montée et de la hauteur minimale.
La troisième partie concerne l'étude linéaire du modèle de la valve à cristaux liquides avec rétro-action optique. Elle permet de comprendre un nouveau type de structures localisées qui apparaissent comme des pics isolés sur une structure spatiale de plus faible amplitude.
Chanut, Clément. „Etude expérimentale de la propagation du front de flamme et de la vitesse de combustion d'une explosion de poussières d'aluminium“. Thesis, IMT Mines Alès, 2018. http://www.theses.fr/2018EMAL0008/document.
Der volle Inhalt der QuelleExplosions are one of the most feared events in the industry. Risk of explosions with combustible dusts can occur in a large variety of industry of different fields, because of the large amount of combustible dusts: organic dusts (flour, carbon, sugar…) but also metallic dusts (aluminum, magnesium…). All of these combustible dusts, if they are fine enough, and if they are dispersed in the air, can cause explosions. Companies have to quantify this risk present in their plant. Concerning gas explosions, the current state of knowledge allows an understanding and a precise modelling of the phenomenon. However, the state of knowledge about dust explosions is more limited, especially because of the difficulty to study the explosions experimentally. Some models, based on gas explosions, exist for the case of dust explosion. These models seem coherent in the case of organic dust explosions but less adapted for metallic dust.This PhD work focus on the experimental study of flame propagation during an aluminum dust explosion. To model an eventual propagation of the flame during the explosion, an experimental approach is required. For this experimental study, specific prototypes have been elaborated, and then improved, during the different tests. This work is mainly separated in two parts.In a first part the dispersion of the dust is studied. Indeed, to study the explosion phenomenon, a system has been elaborated to disperse the dust. A first part of study allows checking that the dispersion is well homogeneous in terms of concentration. Then, the turbulence level inside the prototype after the end of the dispersion is studied. Indeed, this parameters influence a lot the flame propagation, increasing the consequences of the explosion.Then, the flame propagation is studied. The dust dispersion, previously studied, is ignited by an electric spark. The phenomenon is studied thanks to visualization of the flame propagation and by the evolution of the pressure inside the prototype. Two main optical techniques, one based on the light emitted by the flame, the other one linked to refractive index variations (due to temperature variations) are used. Thanks to these methods, the propagation velocity in the laboratory referential is studied. However, this velocity depends mainly on the prototype used for his determination. A method is used to determine the burning velocity (consumption rate of the reactants by the flame front). Some potential limits of this method are then exposed, and a new method of determination of this burning velocity is proposed
Vignat, Guillaume. „Injection and combustion dynamics in swirled spray flames and azimuthal coupling in annular combustors“. Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASC024.
Der volle Inhalt der QuelleThe deployment of low-emission technologies in aero-engines does not only require that new designs produce reduced amounts of pollutants, but also that their dynamical behavior (ignition, blow-off, and combustion instabilities) be compatible with the high safety standards prevailing in aeronautics. This research is focused on the latter aspect of combustor design. A transparent annular combustor equipped with 16 swirled spray injectors is used to represent at the laboratory scale the combustion chamber of a jet engine. This system is used in conjunction with a single sector rig to investigate dynamical issues.Theory, experimentation and large eddy simulation are combined to examine a range of items pertaining to the injector dynamics, flow structure, swirl number determination, spray characteristics, and coupling between injector flow and acoustic field. A database of injectors is introduced to investigate the impact of injection parameters on combustion dynamics. These injectors are examined under steady and unsteady conditions by combining laser diagnostics and high-fidelity simulations which allows the characterization of spray-specific behaviors of relevance to the dynamics of injection systems. One important result is that the presence of a liquid film formed on the wall of the injection unit gives rise to a multi-modal distribution of droplet velocities. A novel method is introduced to examine the space-time behavior of the flow and flame of a swirling injector submitted to axial modulations. A detailed investigation of the process by which convective perturbations couple with the acoustic field allows to examine the time lags that control combustion instability and sort out the respective roles of convection and droplet spray evaporation. High speed tomography relying on SnO2 particles provides major results on the Precessing Vortex Core structure and show its behavior under acoustic forcing. The impact of injector head loss on combustion instabilities is examined using several injection systems with similar levels of swirl. The head loss is shown to play a major role in the coupling between the flame and the upstream plenum. The previous results obtained in a single sector rig are used to guide experiments on the annular combustor. The focus is placed on high amplitude combustion oscillations coupled by a standing azimuthal mode inducing flame blow-off near the pressure nodal line. The deformation of the acoustic distribution is tracked using a novel expansion on azimuthal harmonics allowing the determination of the critical conditions leading to this phenomenon. New results are also presented about the transient dynamics of an injector during ignition and about lean blow out with a proof of concept extension of the LBO limit by nanosecond plasma discharges
Wangher, Athéna. „Réponse de flammes de prémélange à des oscillations de pression“. Phd thesis, Université de Provence - Aix-Marseille I, 2009. http://tel.archives-ouvertes.fr/tel-00453390.
Der volle Inhalt der QuelleLamraoui, Ammar. „Acoustique et dynamique de flamme dans un foyer turbulent prémélangé swirlé : application à l'étude du bruit de combustion dans les chambres de turbines à gaz“. Phd thesis, Ecole Centrale Paris, 2011. http://tel.archives-ouvertes.fr/tel-00678248.
Der volle Inhalt der QuelleKaprielian, Leslie. „Modélisation 0D pour la combustion dans les moteurs à allumage commandé : développements en proche paroi et dans le front de flamme“. Thesis, Paris, ENSAM, 2015. http://www.theses.fr/2015ENAM0012/document.
Der volle Inhalt der QuelleRecently, the interest for zero-dimensional models has increased. Indeed, these models provide easily the engines thermodynamic behavior and can be coupled with control tools. However, their accuracy must be improved to meet the current technological challenges. In the spark ignition engines, the premixed turbulent flame is modeled as a set of coherent flamelets. This approach requires special treatment near the walls, motivated by the modifications of the flame structure due to boundary layers. The present work proposes 0D modeling of combustion near the walls and in the reaction zone of the flame. To combustion model near the walls, the flame is divided into a free propagation contribution, and an interacting contribution with the walls. Each contribution is divided into a convective zone, wherein the entrainment of fresh gas is described, and a reaction zone, wherein the combustion reaction is modeled. Adding a reaction zone near the walls allows modeling a thermal gradient and a slower combustion reaction near the walls. To model the reaction zone, a flame discretization is made into several reaction zones. An engine operating range is simulated with our models, for quantifying the calibration parameters variability. To do this, models are calibrated on each operating point, by a method of minimization of the quadratic error on the heat released rate. Linear correlations can be found, depending on engines parameters. A good agreement between experimental data and simulation results is obtained with these parameters correlations
Ghani, Abdulla. „Simulation aux grandes échelles des instabilités de combustion transverses des flammes parfaitement prémélangées et swirlées diphasiques“. Thesis, Toulouse, INPT, 2015. http://www.theses.fr/2015INPT0068/document.
Der volle Inhalt der QuelleIn this work longitudinal and transverse combustion instabilities are studied in two types of configurations. While longitudinal modes have been observed in many previous studies at low frequencies, the present work also focusses on high-frequency transverse modes. First, a premixed flame stabilized on a V-fame holder is investigated where experimental results obtained by Volvo are used to validate the simulations. For different operating conditions, longitudinal and transverse modes are observed in Large Eddy Simulations (LES) and show good agreement with the experimental data in terms of pressure frequency and flow dynamics. In a second step, a semi-industrial case is examined within the European project KIAI. Experiments are conducted by ONERA and LES of this two-phase flow configuration (called Lotar) are carried out. Transverse combustion instabilities are analyzed and key elements which drive instabilities are identied. These observations are used to reformulate the classic Flame Transfer Function (FTF) in order to predict the stability of transverse modes by use of an Helmholtz solver. The results reproduce fairly well the stability map generated by LES
Boukhalfa, Abdelkrim. „Combustion a l'etude de la structure scalaire dans les flammes turbulentes premelangees du type bunsen“. Orléans, 1988. http://www.theses.fr/1988ORLE2043.
Der volle Inhalt der QuellePajot, Olivier. „Etude expérimentale de l'influence de l'aérodynamique sur le comportement et la structure du front de flamme dans les conditions d'un moteur à allumage commandé“. Orléans, 2000. http://www.theses.fr/2000ORLE2018.
Der volle Inhalt der QuelleEgly, Hugues. „Contribution à la modélisation et à la simulation des instabilités de type Rayleigh-Taylor ablatif pour la FCI“. Paris 6, 2007. http://www.theses.fr/2007PA066684.
Der volle Inhalt der QuelleThis thesis deals with the dynamics of accelerated ablative front spreading in Inertial Confinement Fusion experiments. ICF is designed for the implosion of a mdeuterium or tritium spherical target. The outer shell, the ablator, is irradiated providing a high level pressure inside the target. During this first stage, the ablation front propagating inward is perturbed by hydrodynamics instabilities, which can prevent the fusion reaction in the decelerated stage. We propose here a study on Rayleigh-Taylor instabilities during ablation process, in the two dimensional case. In order to obtain a numerical solution, we perform an asymptotic analysis in the limit of a high temperature ratio, between the remaining cold ablator and the hot ablated plasma. This study is divided in two steps. First, the thermo-diffusive part of the set of equations is approximated by a Hele-Shaw model, which is then perturbed by the hydrodynamics part. Using a vortex method, we have to solve the advection of a vortical sheet moving with the ablation front. We compute the numerical solution on an eulerian mesh coupled with a front tracking method. The thermal part is calculated by implementing the Fat Boundary Method, recently developped. The hydrodynamic part is obtained from a Finit Volume scheme
Fragner, Romain. „Caractérisation expérimentale des plissements à petite échelle dans une flamme turbulente prémélangée : effets de la pression“. Thesis, Orléans, 2014. http://www.theses.fr/2014ORLE2072/document.
Der volle Inhalt der QuelleThe present work is an experimental study on the interactions between flame and turbulence. The pressure effect on the flame front wrinkling is characterised using laser diagnostics and hot wire anemometry. To begin with, the turbulence generated by a multi-grid system is characterised. It is shown that the present system produces a higher turbulence rate by 40% than for an equivalent mesh single-grid system. Moreover, the small turbulence scales sizes are experimentally found smaller with the multi-grid system. From those results, the interactions between premixed flames and turbulence were studied. By using the laser tomography diagnostic, the flame front of several gases premixes was observed. By changing the mixing conditions, the effect of parameters such as the Lewis number, the turbulence conditions and the small scale was observed. The low impact of the thermodiffusives instabilities in our conditions was demonstrated. However, the important effect of the turbulence conditions on the flame front characteristics was observed. Moreover, the present results showed the major impact of the Taylor micro scale on the flame front wrinkling for these study experimental conditions
Ghilani, Mustapha. „Simulation numérique de flammes planes stationnaires avec chimie complexe“. Paris 11, 1987. http://www.theses.fr/1987PA112325.
Der volle Inhalt der QuelleDelorme, Barthélémy. „Etude expérimentale des conditions initiales de l'instabilité de Rayleigh-Taylor au front d'ablation en fusion par confinement inertiel“. Thesis, Bordeaux, 2015. http://www.theses.fr/2015BORD0490/document.
Der volle Inhalt der QuelleNumerous designs and experiments in the domain of Inertial Confinement Fusion (ICF) show that, in both direct and indirect drive approaches, one of the main limitations to reach the ignition is the Rayleigh-Taylor instability (RTI). It may lead to shell disruption and performance degradation of spherically imploding targets. Thus, the understanding and the control of the initial conditions of the RTI is of crucial importance for the ICF program. In this thesis, we present an experimental and theoretical study of the initial conditions of the ablative RTI in direct drive, by means of two experimental campaigns performed on the OMEGA laser facility (LLE, Rochester). The first campaign consisted in studying the laser-imprinted ablative Richtmyer-Meshkov instability (RMI) which starts at the beginning of the interaction and seeds the ablative RTI.We set up an experimental configuration that allowed to measure for the first time the temporal evolution of the laser-imprinted ablative RMI. The experimental results have been interpreted by a theoretical model and numerical simulations performed with the hydrodynamic code CHIC. We show that the best way to control the ablative RMI is to reduce the laser intensity inhomogeneities. This can be achieved with targets covered by a layer of a low density foam. Thus, in the second campaign, we studied for the first time the effect of underdense foams on the growth of the ablative RTI. A layer of low density foam was placed in front of a plastic foil, and the perturbation was imprinted by an intensity modulated laser beam. Experimental data are presented : backscattered laser energy, target dynamic obtained by side-on selfemission measurement, and face-on radiographs showing the effect of the foams on the target areal density modulations. These data were interpreted using the CHIC code and the laser-plasma interaction code PARAX. We show that the foams noticeably reduce the amplitude of the laser intensity inhomogeneities and the level of the subsequent imprinted ablation front modulations. In conclusion, this thesis allowed us to develop an experimental platform and a suite of numerical tools for future, more detailed studies of hydrodynamic instabilities for ICFapplications
Lombard, Virginie. „Modes de Kovásznay pour l'étude de la stabilité linéaire d'écoulements d'ablation autosemblables“. Paris 6, 2008. http://www.theses.fr/2008PA066694.
Der volle Inhalt der QuelleSchuller, Thierry. „Mécanismes de couplage dans les interactions acoustiques-combustion“. Phd thesis, Ecole Centrale Paris, 2003. http://tel.archives-ouvertes.fr/tel-00250137.
Der volle Inhalt der QuelleGonzalez, Flesca Manuel. „Contributions en simulation, expérimentation et modélisation destinées à l’analyse des instabilités de combustion hautes fréquences des moteurs fusées à ergols liquides“. Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLC088/document.
Der volle Inhalt der QuelleThis research concerns some of the issues raised by high frequency combustion instabilities in rocket engines. These instabilities are known to have detrimental effects leading, in some cases, to the destruction of the propulsion system. To avoid the appearance of such instabilities it is important to gain an understanding of the processes driving such dynamical phenomena. One has to consider the complex coupling between injection, combustion and the acoustic resonances of the system. The present work contributes to this objective by developing three items.The first deals with numerical simulations of non-reactive and reactive jets submitted to different modulation conditions to understand the interaction between jets, flames and their environment. Numerical simulations of non-reactive round jets as well as more complex flames formed by coaxial injectors operating under transcritical conditions were carried out using large eddy simulation (LES) adapted to real gas situations by making use of the AVBP-RG flow solver. Round jets were submitted to transverse velocity fluctuations. It has been found that for all amplitudes and frequencies of modulation, the modulated jet is deformed and oscillates. This behavior can be represented by a model. The coaxial flames were submitted to mass flow rate and pressure modulation. For these cases it has been found that the modulation induces variations of the global heat release rate. A mathematical relationship between the modulated parameters and the heat release rate has been proposed.The second item includes experimental investigations. For this purpose a New Pressurized Coupled Cavities (NPCC) laboratory test rig has been developed. The possible coupling between the plenum and the thrust chamber was studied. A model, linking pressure and velocity fluctuations between the plenum and the thrust chamber, has been developed. The laboratory test rig was also used to gather some knowledge on the levels of damping and the damping coefficients could be determined.The last item of this document deals with the development of a reduced order dynamical model which includes some of the driving and damping mechanisms of high frequency combustion instabilities. This dynamical description was implemented in a high frequency stability code (STAHF). This code was used to examine a 87 MW liquid rocket engine (BKD operated at DLR, Germany) exhibiting high frequency oscillations. After the adjustment of some control parameters, STAHF was able to retrieve some the features observed in experiments carried out at DLR
Balusamy, Saravanan. „Etude expérimentale de la propagation de flammes dans un mélange stratifié“. Phd thesis, INSA de Rouen, 2010. http://tel.archives-ouvertes.fr/tel-00557915.
Der volle Inhalt der QuelleLhuillier-Marchand, Alexis. „Propagation des feux de végétation : expérimentations à l’échelle du laboratoire et validation d’un propagateur“. Thesis, Université de Lorraine, 2016. http://www.theses.fr/2016LORR0131/document.
Der volle Inhalt der QuelleThis work is devoted to the experimental and numerical study of wildland fire spread at laboratory scale. A tracking fire front method using visible cameras was used in order to follow the fire front positions during the propagation and to evaluate some fire front properties. The data include the Rate Of Spread (ROS), the fire front width, the length of fire, the profile of flames and the Heat Release Rate. An experimental campaign of 105 fire spread tests with wood shaving as fuel was conducted on the PROMETHEI plateform (Plateforme de Recherche Opérationnelle en Métrologie Thermique dédiée aux Essais Incendies) of the laboratory LEMTA. This campaign was essentially focused on the effect of the fuel bed width and the fuel loading on the fire dynamics (particularly on the ROS and fire width). An open-source data base provides the positions of the front and backing fire as a function of time. A fire spread model based on the small world concept with a hexagonal cell network was developed. Two approaches were studied: the first one is based on a radiative transfer model for the definition of the cell states and the other one is based on an estimated distribution function. A particle swarm optimization (PSO) algorithm was used for the identification of the different parameters of the model using the experimental results. Then, the model was compared to other experiments included fuel breaks or narrowing/widening of the fuel bed width