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Статті в журналах з теми "Mécanismes d'instabilité"
Debrauwère, H., A. Nicolas, G. Vergnaud, J. Buard, J. Tessier, and D. Aubert. "Mécanisme d'instabilité des minisatellites." médecine/sciences 16, no. 3 (2000): 415. http://dx.doi.org/10.4267/10608/1662.
Повний текст джерелаДисертації з теми "Mécanismes d'instabilité"
Numes, Renato. "Intéractions fluide-structure sur les mécanismes d'instabilité tourbillonnaires en cavité confinée." Poitiers, 2007. http://www.theses.fr/2007POIT2338.
Повний текст джерелаAnalysis of segmented flow field in a confined chamber was carried out in order to estimate the role of the vortex shedding sources. Specific attention was given to the potential interaction between vortex shedding that arises from thermal inhibitor and vortex generation issued from the injecting walls. Experimental investigations were carried out with an adapted cold gas experimental set-up and analyses were specifically study the fluid/structure potential role on the two vortex source of instability. Two different fluid/structure analyses were considered. First, a forced flapping movement induced from an adapted mechanical system allows one to force the thermal inhibitor motion. A flexible obstacle was also analysed in order to shed light on the potential passive control of instability. For a forced coupling, it was found that the wall injection vortex shedding was dominant as source of instability while introducing a flexible obstacle provides a significant reduction of the instability. The amplitude of such reduction is found to be linked to the thickness of the obstacle and the considered Mach number of the flow field. It strongly depends also to the internal geometry i. E. That controls directly the interaction of the vortex sources
Pétrélis, Francois. "Effet Dynamo : Etudes des mécanismes d'instabilité et de saturation du champ magnétique." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2002. http://tel.archives-ouvertes.fr/tel-00003842.
Повний текст джерелаPétrélis, François. "Effet dynamo : étude des mécanismes d'instabilité et de saturation du champ magnétique." Paris 6, 2002. https://tel.archives-ouvertes.fr/tel-00003842.
Повний текст джерелаArratia, Cristobal. "Mécanismes d'instabilité non-modaux dans les écoulements cisaillés avec et sans stratification en densité." Phd thesis, Palaiseau, Ecole polytechnique, 2011. http://www.theses.fr/2011EPXX0084.
Повний текст джерелаArratia, Cristobal. "Mécanismes d'instabilité non-modaux dans les écoulements cisaillés avec et sans stratification en densité." Phd thesis, Ecole Polytechnique X, 2011. http://pastel.archives-ouvertes.fr/pastel-00672072.
Повний текст джерелаDominiak, Pascal. "Analyse expérimentale des mécanismes d'instabilité lors de l'ébullition d'un milieu poreux chauffé à température constante." Vandoeuvre-les-Nancy, INPL, 2000. http://www.theses.fr/2000INPL056N.
Повний текст джерелаThe aim of this work is to study some experimental and theoretical aspects of unsteady mechanisms of boiling in porous media. We are interested in the case of boiling in a porous layer of glass beads saturated with water. A new experimental device has been built up with the following boundaries conditions: at the bottom impervious and imposed temperature ; at the top permeable and imposed temperature. Various experiments are presented for different sizes of beads. For beads of diameter 40-70 and 100-160 microns, a stable state is obtained with the superposition of a vapor film, a two-phase zone at the boiling temperature and a liquid zone at the top. For beads of diameter 200-250 microns, a unsteady periodic state with a movement of large amplitude of the front between the two-phase region and the liquid zone is observed. Last, for beads of diameter 800-1200 microns, whereas turbulent natural convection is present in the upper liquid zone, a return to the front stability is observed. The influence of a gravitational instability, of the natural convection and of the front movement is investigated using linear stability analyses
Dioc, Nathalie. "Etude expérimentale des mécanismes d'instabilité dans un brûleur à injection étagée : application aux turbines à gaz." Châtenay-Malabry, Ecole centrale de Paris, 2005. http://www.theses.fr/2005ECAP0994.
Повний текст джерелаThis experimental study aims to analyse instability mechanisms in an injection-staged burner, as in gas turbines. Therefore, an academic burner has been designed to be representative of industrial configurations. The complete characterization of this burner has been performed with different diagnostics: laser induced fluorescence, particle imaging velocimetry, laser tomography, etc. Spectral analysis of the burner has revealed non-stationary regimes, necessary in the development of unstable modes. In parallel, pollutant emissions are minimized for high levels of pulsation, as mixing is locally improved. This antagonist behaviour is associated to the influence of staging on flame structure and more particularly on the position of flame stabilization. A study of non-reactive flow aerodynamics enables to identify a “vortex breakdown” stabilization, typical of high-swirl burners. Precisely, the swirl movement implies a structure of “Precessing Vortex Core”, with an important internal recirculation zone. The stagnation point of this PVC is located in the injection system. The rotation frequency of the structure has been estimated near frequencies observed for unstable regimes. But, the similarity between non-reactive and reactive flows needs to be demonstrated. A detailed study of flame structure points out the link between staging and global shape and position of the reaction zone. With knowledge acquired on academic burners concerning instability mechanism, an industrial configuration has been implemented. The establishment of transfer functions enables to analyse the response of the burner to external pulsations
Zikikout, Souad. "Mécanismes d'instabilité de combustion dans un foyer à flammes non prémélangées simulant l'injection dans un moteur fusée cryogénique." Paris 11, 1988. http://www.theses.fr/1988PA112208.
Повний текст джерелаMany combustion problems have to be adressed for the design of a cryogenic rocket engine. The most important questions are ignition, flame stabilisation, extinction, pressure oscillations at low and high frequencies. These different phenomena are studied in a model combustor simulating the injection and the combustion process of the Ariane 5 rocket engine. The design of the combustor is defined by dimensional analysis. The similarity criteria retained lead to a six non-premixed flames of air and propane or air and hydrogen. Ignition mechanisms are studied with high speed schlieren imaging. It is found that the flame is ignited at very low air mass flow rate and high equivalence ratio. C2, CH and OH radiation measurements provide information on the heat release in the reaction zone and allow a determination of the ignition time lag. These results can be used for comparisons with numerical models of non-premixed flames. Spectral analysis of both the acoustic and free radicals light emission signais detected for each operating conditions shows that combustion instabilities occur when the pressure fluctuations are coupled with the heat release. We identify two different instability modes : (1) an intense low frequency pressure oscillations at 230Hz with periodic combustion. Large velocity fluctuations are produced at the injection plane and lead to cyclic reaction initiation and quenching. The coupling between the heat release and the acoustics is shown to drive the fluctuations. A theoretical model is proposed to determine low frequency instability limits in such circumstances, (2) a low frequency instability at 360 Hz produced by the interaction between the different flames taking the form of intense collisions and leading to total extinction of one or several injectors. Mode selective excitation is used to drive high frequency transverse oscillations. A theoretical formulation of the acoustic forcing in the combustor without flow and free of chemical reaction provides results which are in satisfactory agreement with experimental data. With combustion and under selective excitation the flames exhibit striking features. A sinuous motion is set up. These observations suggest that the unsteady heat release can be expressed in terms of the velocity fluctuations at the inlet plane. An instability model with heat release is then developed and it relies on the combustion sensitivity to velocity fluctuations. The displacements produced by the transverse velocity at the dump increase the mixing and activate the heat release after a certain delay. It is found that the coupling between heat release and transverse velocity fluctuations requires the presence of two modes. This model gives a theoretical basis for the experimental study performed with excitation
Schneider, Alexandra Patrizia. "Aerodynamic and aeroelastic investigation of a composite fan for ultra-high-bypass-ratio aircraft engines." Electronic Thesis or Diss., Ecully, Ecole centrale de Lyon, 2024. http://www.theses.fr/2024ECDL0018.
Повний текст джерелаModern low-speed Ultra-High Bypass Ratio (UHBR) fans operate predominantly on the flat part of the compression characteristic, have shorter intake lengths, and employ flexible, lightweight, composite blades. These changes promote the evolution of different types of instabilities with multi-physical interactions such as convective non-synchronous vibration (NSV). To enable further technological ad-vancements, experimental benchmark data on representative geometries required. Within this con-text, the European project CATANA was initiated at Ecole Centrale de Lyon. The open-test-case fan stage ECL5 was designed, following industrial guidelines, and tested experimentally on the facility ECL-B3. This thesis presents the experimental results of the CATANA project. The experimental investiga-tion of the ECL5 reference configuration shows that all design goals have been reached. The machine is operational in a wide range and aerodynamic performance at design condition is exactly coincident with the numerical prediction. In contrast, instability mechanisms are more complex than predicted by the employed numerical methods. Through application of synchronized multi-physical instrumenta-tion, the involved complex fluid-structure interaction is resolved. The analysis of the influence of in-flow conditions and geometrical and structural system symmetry allows to identify the sensitivity of aerodynamic and structural characteristics and the behavior close to the stability limit. The investiga-tion of a second rotor configuration featuring structural mistuning highlights the importance of geo-metrical blade-to-blade variations. They cause an asymmetry of the aerodynamic field at the blade tip and suppress coherently propagating aerodynamic disturbances resulting in a delayed onset of NSV. The results presented in this thesis provide a comprehensive multi-physical characterization of the ECL5 fan stage and serve as a benchmark data set for the validation of numerical simula-tions
Méry, Yoann. "Mécanismes d'instabilités de combustion haute-fréquence et application aux moteurs-fusées." Thesis, Châtenay-Malabry, Ecole centrale de Paris, 2010. http://www.theses.fr/2010ECAP0012.
Повний текст джерелаThis thesis presents a study of high frequency instabilities in rocket engines. This issue, which has plagued many engine development programs, is approached by three complementary viewpoints: experimental, theoretical, and numerical. First, experiments are carried out to identify the main processes involved and bring forth mechanisms taking place when an engine becomes unstable. To achieve this stage, a new modulator (the VHAM), capable of creating acoustic waves representative of what occurs in an actual engine, is designed and characterized. The second part of this thesis concern theoretical analysis. Two models are developed following the main conclusions of the experimental campaign: heat release oscillations are due to the transverse flames’ motion, and the phenomenon is triggered when droplets become small enough to be convected by the acoustic field. Using these models as a baseline, a numerical code (STAHF) is presented. Its purpose is to account for mechanisms identified previously for little computational cost. This code is validated on particularly responding situations observed during experiments. It is then shown that it can be used to study real scale rocket engines. The third point of view adopted to address the problem is numerical simulation. Full compressible LES is chosen to study the interaction between acoustics and combustion. A new combustion model for non-premixed flames with infinitely fast chemistry is presented and validated on a well documented flame (H3). It is then used to study the interaction between a transverse acoustic wave and the H3 flame. A comparison between the Rayleigh source term computed from the simulation and the one predicted by the theoretical model FAME is conducted eventually