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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.
Pełny tekst źródłaEloy, Christophe. "Instabilité multipolaire de tourbillons". Aix-Marseille 2, 2000. http://www.theses.fr/2000AIX22048.
Pełny tekst źródłaPacitto, Grégory. "Instabilités hydrodynamiques à l'interface de ferrofluides en géométrie confinée". Paris 7, 2001. http://www.theses.fr/2001PA077107.
Pełny tekst źródłaRiedinger, Xavier. "Instabilité radiative d'un tourbillon dans un fluide stratifié". Aix-Marseille 1, 2009. http://www.theses.fr/2009AIX11053.
Pełny tekst źródłaVortices are widely present in geophysical flows at all scales. They are involved in the dynamics of flows as well as in their statistical properties. In order to identify precisely their role in the global properties of the flow it is important to know their individual dynamics as finely as possible. With this purpose, we study in this thesis through theoretical, numerical and experimental means, the stability properties of models of stratified vortices : The Lamb-Oseen vortex and a family of Taylor-Couette and Keplerian rotative °ows. We show, in particular, that these flows, stable in a homogeneous fluid, can become unstable in the presence of a stable stratification along their rotation axis. The three kinds of flows are subject to the same form of destabilisation, the radiative instability of which we describe the mechanism. For the Lamb-Oseen vortex, a comprehensive numerical study is performed by varying the Reynolds number and the Froude number which characterize the viscosity and the buoyancy of the fluid. For low Reynolds numbers, we show that the most unstable mode leads to an undulation of the vortex that we have obtained successfully in the experiments. For the Taylor-Couette flow generated by the rotation of a cylinder, the most unstable mode is also helical but it exhibits a more pronounced radiative structure. We also succeeded in obtaining this mode experimentally. The frequency and wavelength of the mode have been measured using shadowgraphy and the synthetic schlieren technique, and a very good agreement with the numerics has been demonstrated. Other numerical results are presented which show, in particular, that the radiative instability is only partially reduced by planetary rotation and that it could be present in Keplerian flows
Boulanger, Nicolas. "Dynamique d'un tourbillon en milieu stratifié : instabilité centrifuge et effets de l'inclinaison". Aix-Marseille 1, 2006. http://www.theses.fr/2006AIX11058.
Pełny tekst źródłaDauchy, Christophe. "Etude numérique d'une instabilité secondaire dans le sillage de cylindres finis". Aix-Marseille 2, 1995. http://www.theses.fr/1995AIX22200.
Pełny tekst źródłaBallesta, Pierre. "Instabilité de Faraday dans les fluides complexes". Phd thesis, Université Sciences et Technologies - Bordeaux I, 2006. http://tel.archives-ouvertes.fr/tel-00811893.
Pełny tekst źródłaLefort, Eric. "Caractérisation des bifurcations et de la dynamique d'une lentille thermique par analyse spectrale". Rouen, 1987. http://www.theses.fr/1987ROUES019.
Pełny tekst źródłaDelorme, 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.
Pełny tekst źródłaNumerous 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
Latrache, Noureddine. "Étude expérimentale des modes supérieurs des instabilités d'écoulements newtoniens ou viscoélastiques dans le système de Couette-Taylor". Le Havre, 2005. http://www.theses.fr/2005LEHA0054.
Pełny tekst źródłaThis work appears in the context of the transition to the turbulence in the flows sheared with of current curve lines. We are interested to study the transition to the turbulence in the Couette-Taylor flow for liquid confined between two coaxial cylinders in differential rotation. For a newtonien liquid (for example, water), and when the two cylinders are in counter-rotation, the non- axisymmetric and instationery critical modes named Taylor spirals (SPI) or interpenetrating spiral (IPS) appear at the threshold of the instability. We have shown that these Taylor's spirals have the anomalous dispersion property. This anomalous dispersion of spirals permits to give in the setting of the Ginzburg-Landau theory a good interpretation of the stability of the source separating two counterpropagating spirals. The transition to turbulence in viscoelastic Couette-Taylor has been studied with polyethyleneoxide (PEO) solutions when the outer cylinder is rest. For the solutions with concentrations c [500,700] ppm (moderate elasticity), and close to the threshold of the instability, the base circular of Couette flow bifurcates to left and right counterapropagating spirals weakly non-linear and non coupled (inertioelastic effects). For a weak increase of the control parameter , the right and left counterpropagating spirals present a strong non-linear coupling witch appears by the existence of the intense spatial and temporal harmonic modes. The coupled counterapropagating spirals are described by the phenomenological equations of Ginzburg-Landau with added new terms permitting to generate the spatial and temporal harmonics. The transition to the turbulence is done via the apparition the turbulent spots (spatiotemporal intermittency). For the large concentrations of PEO c [800,900] ppm (large elasticity), the primary instability mode is formed by the superposed left and right spirals that they bifurcate brutally to pattern formed by large domains containing spirals waves (elastic effects). For large values of the control parameter , the domains subdivided and become less large. The spirals disappear inside the domains. These domains multiply with the control parameter , and the flow transit to the turbulence regime (elastic turbulence)
Wodlei, Florian. "Self-pulsations of a dichloromethane drop on a surfactant solution". Thesis, Toulouse 3, 2017. http://www.theses.fr/2017TOU30188/document.
Pełny tekst źródłaFar-from-equilibrium systems exhibit a wide variety of spatial and temporal patterns known as dissipative structures. The interplay between physico-chemical processes and mass or heat transfer can give rise to spatio-temporal structures induced by convective flows. These flows may result from density or surface tension gradients. They are the expression of the conversion from chemical into mechanical energy. When surface tension is the driving force, the corresponding effects are known as Marangoni effects. They are at play in numerous applications as extraction processes, oil recovery, and chemical reactors at all scales and noticeably modify transfer rates. The complexity of real systems deserves the development of model systems, essentials to settle, on a fundamental level, the theory governing the related dynamics. A succession of dynamical regimes is observed during the dissolution of a dichloromethane drop deposited on aqueous solutions of a cationic surfactant (cetyltrimethylammonium bromide, CTAB). The remarkable range of shapes and motion patterns that emerges is related to the surfactant concentration, which is used as a control parameter. For low surfactant concentrations, we observe translational motion and pulsations of the drop. At intermediate concentrations the drop transforms and starts to rotate. At higher concentrations polygonal shapes are observed. Although chemically simple and of easy implementation, the system is relatively complex and involves several processes: evaporation, solubilization, surfactant mass transfer, interfacial adsorption and self-aggregation. Thermal and transport effects induced are at the origin of local variations of interfacial tension leading to the Marangoni flows. In this thesis, we focused on the behavior of the dichloromethane drop when the aqueous surfactant concentration (0.5 mM) leads to the pulsating regime. At this concentration, we have first analyzed the behavior of the drop during the induction period that precedes the instable regime. Drop shape analysis, correlated to Particle Image Velocimetry (PIV) measurements, showed that dissolution flows initially hinder adsorption of CTAB at the water/oil interface. The instability is only triggered when dissolution is reduced and water/oil adsorption becomes effective. The induction period appears as a slow transition from an initial negative spreading coefficient (a lens shape drop) towards a positive spreading coefficient that triggers film expansion and following pulsations. These pulsations are accompanied by the ejection of smaller droplets which are formed from a toroidal rim that is created during the expanding phase of the drop. The break-up of this toroidal rim, resembles to what is known as the Rayleigh-Plateau (RP) instability. Nevertheless, the observed characteristic wavelength is a factor of 2 too small in respect to the classical RP instability. We have found the origin of this discrepancy in the fact that modulations that appear on the rim before it transforms into droplets are settled by deformations arising at the surface of the expanding film. They appear as wrinkles that form in the film and may be related to thermal Marangoni effects known as Benard-Marangoni instability. These wrinkles play an important part in the highly organized dewetting structure described in the last chapter of the thesis. The addition of CTAB also in the organic (drop) phase leads to faster pulsations which, after a very high amplitude expanding stage and the ejection of a perfect crown of droplets, result during the film receding stage in the formation of a pattern which symmetry is reminiscent of a flower. A qualitative interpretation aimed at identifying the main processes at play and based on independent surface tension data gives a consistent explanation of the observed pulsations and related self-organized patterns
Fabre, David. "Instabilité et instationnarités dans les tourbillons : Application aux sillages d'avions". Paris 6, 2002. http://www.theses.fr/2002PA066520.
Pełny tekst źródłaThe trailing wake generated by an aircraft is composed of persistant vortices wich pose a danger to following aircrafts. This thesis is concerned with the instabilité and instationaritymechanisms characterising these vortices. Emphasis is laid on the properties of realistic trailingwakes and the possible contribution of these mechanisms to wake dissipation. The first part of the thesis is devoted the properties of trailing wakes, and is based on analyses of wind tunnel experiments. Several "realistic" vortex models are described. In the second part the linear mechanisms affecting an isolated vortex are studied using a spectral collocation method. The Kelvin waves (or inertial waves) are first cconsidered, and it is shown that in "realistic" vortices most of these waves become damped. The properties of the short-wave Widnall instabilities are then described for the same "realistic vortices. A family of viscous instabilities existing in high-Reynolds vortices in the presence of axial flow is then considered. In a third part the long-wave cooperative instabilities in systems of parallel vortices are studied using a vortex filament method. The case of two vortices is first considered ; counter-rotating pairs are affected by the long-wave Crow instability while corotating pairs are stable. The stability of an aircraft wake model composed of two pairs is then considered. An optimal perturbation analysis is used and allows to emphasize the interest of counter-rotating configuration and the necessity of a long wavelength forcing in order to achieve a rapid wake dissipation. In the fourth part the Crow and Widnall insatbilities are reconsidered in the framework of spatial theory, and the convective or absolute nature of these instabilities are evaluated
Astruc, Dominique. "Instabilité de Kelvin-Helmholtz en régime subsonique : développement spatial et conditions aux limites ouvertes". Toulouse, INPT, 1993. http://www.theses.fr/1993INPT131H.
Pełny tekst źródłaRigon, Gabriel. "Instabilités hydrodynamiques : Application à l'astrophysique de laboratoire et diagnostics X à haute résolution". Thesis, Institut polytechnique de Paris, 2020. http://www.theses.fr/2020IPPAX020.
Pełny tekst źródłaDuring the 20th century, the development of high power laser enabled scientist to reach a regime known as High Energy Density (HED), where matter is carried under extreme conditions. This allow the development of a new discipline: the laboratory astrophysics. This discipline aims to reproduce, in the laboratory, conditions similar to those observed in astrophysics, for instance in planet or star interiors, during cataclysmic phenomena.This thesis corresponds to an experimental and numerical study of hydrodynamic instabilities, which can be found in such situations. These instabilities affect the evolution of astrophysical objects and hinder their observation. Here, we will focus on the Rayleigh-Taylor (RTI) and the Richtmyer-Meshkov (RMI) instabilities. The first one does arise when a high density fluid is lying above a low density one. The second can be seen as a special case of the first, where the force responsible for the motion of the instability is linked to a shock wave. In astrophysics, both instabilities can be found in supernovae remnants, which are composed of the matter ejected during the death (explosion) of massive stars. They can also be found in inertial confinement fusion, and are responsible of the failure of ignition.In this thesis, we will show the results of experiments on those instabilities carried on LULI2000 (Palaiseau, France), GEKKO XII (Osaka, Japan), and SACLA (Japan) facilities. Thanks to these experiments, we observed directly and reconstructed the evolution of the RTI from its linear phase, early in time, up to its turbulent phase, late in time. We proceeded to a parametric study of the RTI, where we varied classical parameters: the wavelength modulation, the density ratio (Atwood number). Therefore, this constitutes a complete experimental study of the RTI with hitherto unseen results. Especially our observation of the turbulence with an unprecedented resolution in this regime (HED).To complete this experimental study, simulations were performed using FLASH, a magneto-hydrodynamic code developed by the FLASH centre (University of Chicago). These simulations allowed us to design our experiments and to analyse and understand our results.Concurrently, we developed a new high resolution X-ray radiography diagnostic. This diagnostic is based on a LiF crystal used as a detector. We proceed to the characterisation of this diagnostic on the SOLEIL synchrotron (spectral response, change in resolution...). This allowed us to use this diagnostic as our main detector on a SACLA experiment, which results on a sub-micron spatial resolution and to a temporal resolution of 10 fs
Sierra, Christophe. "Instabilité en fluidisation gaz-solide : dynamique des lits denses et influence des conditions aux limites". Aix-Marseille 1, 2002. http://www.theses.fr/2002AIX11064.
Pełny tekst źródłaLanglois, Vincent. "Instabilité d'un lit granulaire cisaillé par un écoulement fluide". Phd thesis, Université Rennes 1, 2005. http://tel.archives-ouvertes.fr/tel-00011456.
Pełny tekst źródłade l'instabilité d'un lit granulaire cisaillé par un écoulement
fluide continu.
Nous avons caractérisé expérimentalement la longueur d'onde initiale des
rides, ainsi que l'évolution de leur amplitude et de leur longueur d'onde
moyenne. Par ailleurs, nous nous sommes intéressés à la transition morphologique
des rides perpendiculaires à l'écoulement vers des motifs 3D plus complexes.
Nous avons également développé une analyse de stabilité linéaire
du problème, dans le cas d'un écoulement laminaire, qui permet de prédire
correctement la longueur d'onde à l'initiation. D'autre part, une analyse
faiblement non-linéaire rend compte de l'apparition de motifs 3D.
Enfin, nous avons abordé la dynamique non-linéaire des rides: des
simulations numériques en 2D, basées sur l'étude théorique précédente,
ont permis de retrouver qualitativement l'évolution aux temps longs observée
expérimentalement.
Pieri, Alexandre. "Turbulence barocline : effets couplés de rotation, stratification et cisaillement". Phd thesis, Ecole Centrale de Lyon, 2012. http://tel.archives-ouvertes.fr/tel-00781602.
Pełny tekst źródłaMammeri, Youcef. "SUR QUELQUES MODELES ASYMPTOTIQUES DANS LA THEORIE DES ONDES HYDRODYNAMIQUES". Phd thesis, Université des Sciences et Technologie de Lille - Lille I, 2008. http://tel.archives-ouvertes.fr/tel-00342347.
Pełny tekst źródłaNotre travail se divise alors en trois parties. Dans la première partie, on rappelle la modélisation des différentes équations. On montre plus particulièrement que les modèles BBM s'obtiennent à partir du principe fondamental de la dynamique via une analyse asymptotique. On compare alors les solutions des équations de KP, respectivement de BO, avec les solutions des équations de type BBM.
Dans la seconde partie, on s'intéresse à certaines propriétés qualitatives des équations généralisées de type BBM. Des résultats de prolongement en temps des bornes sur les normes de Sobolev, de décroissance en temps et de prolongement unique des solutions sont établis.
Enfin, on termine avec une étude numérique des solutions des équations KP généralisées en dimension 3 d'espace. Dans cette dernière partie, en collaboration avec F. Hamidouche et S. Mefire, on inspecte numériquement les phénomènes de dispersion, d'explosion en temps fini, de comportement solitonique et d'instabilité transversale.
Pavec, Marc. "Instabilités barocline et paramétrique des courants de bord, application au front d'Ouessant". Brest, 2007. http://www.theses.fr/2007BRES2042.
Pełny tekst źródłaCoastal 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
Tadmouri, Rawad. "Tensioactifs en système biphasique eau-huile : propriétés, transfert et instabilité de Marangoni". Toulouse 3, 2011. http://thesesups.ups-tlse.fr/1360/.
Pełny tekst źródłaHydrodynamics instability have been observed and studied during the mass transfer in two water/oil biphasic systems. The first is a non-reactive system involving the transfer of two series of ionic surfactants (tetraalkylammonium bromide (CnTAB) and tetraalkylammonium dodecylsulfate (TAADS)). In this case, the instability is periodic. The second system is a reactive system, the biphasic hydrolysis of myristoyl chloride (RCOCl). The transfer of myristoyl chloride to the aqueous phase is induced by the hydrolysis reaction leading to the formation of surface-active compounds. Studies in the geometry of the Hele-Shaw cell showed that this biphasic reaction gives rise to a well-defined regime of chemo-Marangoni convection cells. Our objective was initially to determine quantitatively the physicochemical properties of these systems. We have developed a methodology based on the modeling of interfacial tension measurements, to determine the partition and adsorption properties at the water/air and water /oil interface and aggregation. We have showed for the two series of surfactants the formation of oil in water microemulsions. We have also studied the kinetics of transfer and showed a particular dynamic accelerating due to the catalytic effect. For the non-reactive system, this acceleration, observed during the transfer of the organic phase to the aqueous phase, is due to the formation of oil-in-water microemulsions. For the reactive system, the shape of the kinetics is different from that observed for simple transfer of the surfactant. The sigmoid curve in this case is perfectly symmetrical. This observation certainly indicates a mechanism different from above. It also implies a change of solubilization of the aqueous phase but this time not by the formation of aggregates but by the formation of dimers
Igonin, Maksim. "Instabilités hydrodynamiques des liquides magnétiques miscibles et non miscibles dans une cellule de Hele-Shaw". Phd thesis, Université Paris-Diderot - Paris VII, 2004. http://tel.archives-ouvertes.fr/tel-00007716.
Pełny tekst źródłaAbou, Bérengère. "instabilité interfaciale d'une couche de ferrofluide sous champ magnétique normal; étude de la transition hexagones - carrés". Phd thesis, Université Pierre et Marie Curie - Paris VI, 1998. http://tel.archives-ouvertes.fr/tel-00002669.
Pełny tekst źródłaBergeon, Alain. "Instabilités de Marangoni-Bénard en présence d'effet Soret". Ecully, Ecole centrale de Lyon, 1995. http://www.theses.fr/1995ECDL0023.
Pełny tekst źródłaThe prediction and control of hydrodynamic instabilities are important for material processing from a melt, as these instabilities often perturb the quality of the material. The theoretical and numerical work presented in this thesis deal with the Marangoni-Bénard instability in binary mixtures with Soret effect. This type of instability is obtained when a fluid layer differentially heated presents a free surface subjected to surface tension depending on temperature and concentration. The natural fluctuations of temperature and concentration along the interface give surface tension gradients. These gradients generate surface forces which can lead, if viscous dissipation and diffusion are unable to damp the motion, to the formation of convective cells. The results concern the onset of this instability and the evolution of the convective structures which are created in two- and three- dimensional parallelepipedic cavities without gravity. First, the linear stability analysis of the conductive solution is presented. This analysis is performed analytically for laterally unbounded cavities and numerically for confined cavities. The nonlinear analysis giving the selection of flow structures beyond the thresholds is performed numerically with the use of a continuation method which has been developed specifically. The results are presented under the form of bifurcation diagrams which are maps of evolution of the physical and mathematical solutions of the system with regard to the variation of one of the characteristic parameters. These diagrams have given many informations on the dynamic of our system allowing for example to explain the disparition or the stabilisation of some of the solutions
Mailliet, Corentin. "Etude expérimentale et numérique du stade fortement non-linéaire de l'Instabilité de Rayleigh-Taylor au front d'ablation en attaque directe". Thesis, Bordeaux, 2018. http://www.theses.fr/2018BORD0288/document.
Pełny tekst źródłaExperimental and numerical study of the non-linear stage of the ablative Rayleigh-Taylor instability in direct drive
Derebail, Muralidhar Srikanth. "Instabilité de l'écoulement le long d'un cylindre semi-infini en rotation". Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEC033/document.
Pełny tekst źródłaThis work concerns the steady, incompressible flow around a semi-infinite, rotating cylinder and its linear-stability properties. The effect of cylinder curvature and rotation on the stability of this flow is investigated in a systematic manner. Prior to studying its stability, we first compute the basic flow. At large Reynolds numbers, a boundary layer develops along the cylinder. The governing equations are obtained using a boundary-layer approximation to the Navier–Stokes equations. These equations contain two non-dimensional control parameters: the Reynolds number (Re) and the rotation rate (S), and are numerically solved to obtain the velocity and pressure profiles for a wide range of control parameters. The initially thin boundary layer grows in thickness with axial distance, becoming comparable and eventually larger than the cylinder radius. Above a threshold rotation rate, a centrifugal effect leads to the presence of a wall jet for a certain range of streamwise distances. This range widens as the rotation rate increases. Furthermore, the wall jet strengthens as S increases. Asymptotic analyses of the flow at large streamwise distances and at large rotation rates are presented. A linear stability analysis of the above flow is carried out using a local-flow approximation. Upon normal-mode decomposition, the perturbation equations are transformed to an eigenvalue problem in complex frequency (ω). The problem depends on five non-dimensional parameters: Re, S, scaled streamwise direction (Z), streamwise wavenumber (α) and azimuthal wavenumber m. The stability equations are numerically solved to investigate the unstable regions in parameter space. It is found that small amounts of rotation have strong effects on flow stability. Strong destabilization by small rotation is associated with the presence of a nearly neutral mode of the non-rotating cylinder, which becomes unstable at small S. This is further quantified using smallS perturbation theory. In the absence of rotation, the flow is stable for all Re below 1060, and for Z above 0.81. However, in the presence of small rotation, the instability becomes unconstrained by a minimum Re or a threshold in Z. The critical curves in the (Z, Re) plane are computed for a wide range of S and the consequences for stability of the flow described. Finally, a large-Z asymptotic expansion of the critical Reynolds number is obtained
Hadj, Achour Miloud. "Fragmentation de métal liquide dans l'eau". Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0215/document.
Pełny tekst źródłaThe phenomenon of dispersion/fragmentation of corium remains one of the most complex and uncertain elements of nuclear accident modeling. In order to validate the sub-mesh models implemented in the MC3D software (developed by IRSN), an experiment without vapor explosion has been conceived. It consists of a low-melting liquid metal jet (Field metal) interacting with a stagnant water in a large tank. This thesis is divided into two parts ; the first one is related to the study of the so-called secondary fragmentation of an isolated drop of Field’s metal, for low Weber number. To this end, we designed an experimental device, GaLaD (drop-on-demand droplet generator). In this part, a literature review on liquid-liquid fragmentation is conducted with a quantitative comparison of the secondary fragmentation for a single drop in the liquid-liquid and the gas-liquid cases. The second part concerns the study of a jet of Field’s metal. For this purpose, GaLaD was modified, so as to be able to generate small jet of liquid metal in water. The obtained results allowed a better understanding of the physical phenomena involved in two-phase turbulent jet fragmentation. In the framework of this thesis, an additional experimental device designated by JaLaD is developed. Subsequently, this device will be dedicated to the study of metal jet in water and must allow us to reinterpret the data of classical experiments via new innovative measurement techniques
Vich, Gaétan. "Déstabilisation d'un jet liquide par un écoulement gazeux perpendiculaire". Rouen, 1997. http://www.theses.fr/1997ROUES087.
Pełny tekst źródłaBatson, William. "Faraday waves in small cylinders and the sidewall non-ideality". Thesis, Lille 1, 2013. http://www.theses.fr/2013LIL10022/document.
Pełny tekst źródłaThis work is an inquiry into the current understanding of experimental single-mode Faraday waves, from the perspective of linear stability theory. At low frequency, the characteristic wavelength is of the order of the cell dimensions, and theoretically the wavelengths associated with the modes available for excitation are discretized by the sidewall boundary condition. Mathematically, the condition which eases manipulation is a stress-free sidewall condition, which is unrealistic due to viscous boundary layers and capillary hysteresis. We report the experimental investigation of a low frequency system designed to approximate this condition, by careful choice of the fluid liquids and thereby increasing the relative importance of the interior damping. The design has permitted close connection between the experimental thresholds and the predictions, contrasting the traditional approach of phenomenologically measuring the mode dissipation and treatment as a single degree of freedom system. Non-ideal behavior of the sidewall persists, evident by the contact meniscus and the sidewall film which is formed during wave excitation. The presence of these non-idealities is translated to trends in the deviation between the observed and predicted thresholds, depending upon the mode structure and wave periodicity. The presence of harmonically excited waves from the meniscus seems to result in observation of amplitudes consistently lower than the predictions, indicating a mixed resonance between the parametric instability and the forced meniscus oscillations. Furthermore, it is seen this interaction can be adjusted by excitation with two commensurate parametric frequencies
Abcha, Nizar. "Caractérisations quantitative et qualitative des modes supérieurs des instabilités d'écoulements newtoniens ou viscoélastiques dans le système de Couette-Taylor". Le Havre, 2007. http://www.theses.fr/2007LEHA0011.
Pełny tekst źródłaThe thesis work was concerned with three experimental studies on the instability modes in the Couette-Taylor system, formed of the flow between two coaxial differentially rotating cylinders. In the first study, we have used two experimental techniques: visualization technique by Kalliroscope flakes and PIV technique. Comparing the space-time digrams from visualization and PIV data, we have shown that in the case of fixed outer cylinder, the reflected light intensity by Kalliroscope flakes is related to the radial velocity component. In the second study, we have determined the nonlinear properties of Taylor spirals observed in the flow when the cylinders are counter-rotating : dissymmetry between the inflow and outflow, anharmonicity and mirror symmetry breaking. Furthermore, we have used the velocity measurements to describe the asymptotic dynamics in the neighbourhood of the defects resulting from spiral collisions (amplitude profile, jumping phase,…). In the last study, we have characterized the propreties of primary and secondary instability modes observed in the viscoelastic flow of Polyethylene Oxyde (PEO) when the outer cylinder is fixed. We have found the radial propagation of the waves in agreement with theoretical studies of inertia-elastic modes
Caquas, Aurore. "Vidange tourbillonnaire : propriétés de l'écoulement et de l'entrainement gazeux". Electronic Thesis or Diss., Institut polytechnique de Paris, 2023. http://www.theses.fr/2023IPPAE014.
Pełny tekst źródłaOne day, our childlike gaze stopped on the vortex created by our bathtub. Seemingly simple, as it appears common to us, the flow is actually characterized by astonishing complexity. Swirling drainage is indeed the subject of numerous articles in the literature, particularly on the modeling of the velocity field and the characteristic profile of the interface. Yet, many questions remain unanswered. These studies are often conducted in steady-state conditions when the water level is kept constant by a water injection system. The unsteady case, where water simply flows due to gravity, is rarely explored. We propose to study and compare these two regimes. The questions addressed concern the influence of the vortex on Torricelli's law, the conditions for bubble formation at the tip of the interface deformation, and the draining velocity of an ideal rotating water bottle.These questions, which touch on our daily lives, have significant industrial implications: estimating the drainage time of a container or preventing the phenomenon of bubble entrainment. These bubbles are indeed the cause of safety issues in nuclear and hydraulic power plants, as well as in many other industrial systems.Our study initially focuses on the modification of the drainage flow by the presence of the vortex, and particularly on the development of a new model for the draining velocity of the container. For this purpose, a human-sized device has been designed on a rotating platform with an onboard measurement system. The obtained model relies on the classical Torricelli law, which can be generalized by taking into account the effect of interface deformation induced by the vortex. The flow structure is also strongly impacted by the presence of the vortex, and we propose to comparatively study the cases of steady and unsteady drainage.The shape of the interface is a complex problem to model, depending on surface tension effects. Under the influence of increasing and concentrated vorticity, this deformation elongates. The gaseous core thus formed can destabilize, oscillate, and generate air bubbles that will be entrained in the flow. This thesis proposes to experimentally study the conditions for the appearance of this instability.Then, our study focuses on the particular case of draining an ideal water bottle, i.e., a hermetically sealed cylindrical tank set in rotation. We have also studied the conditions for the appearance of an optimum, where drainage is achieved more quickly, and thus tried to better understand the very popular experiment of creating a whirlpool in a water bottle to drain it faster. Specifically, we describe the different flow regimes during this type of drainage, as well as the transitions between these regimes.Finally, numerical simulations based on solving the Navier-Stokes equations are carried out using TrioCFD codes, which use the Front-tracking method, and OpenFoam, which uses the Volume of Fluid method, and allow for the reproduction of certain swirling drainage experiments. However, the phenomenon of bubble detachment, due to its sharpness, remains a numerical challenge that we will address after a comparative study of the performance of the codes used on various reference test cases
Semin, Benoît. "Intercation d'une fibre et d'un écoulement en géométrie confinée". Palaiseau, Ecole polytechnique, 2010. http://pastel.archives-ouvertes.fr/docs/00/55/93/59/PDF/these_BSemin.pdf.
Pełny tekst źródłaThe motion of elongated objects in a fluid is encountered in many scientific fields, ranging from oil recovery and paper production to microorganism swimming. In the present thesis we study the behavior of a long cylindrical fiber in a confined flow (fracture, microfluidic channel). We first determine both experimentally and numerically the drag on this object as a function of its orientation and position in the aperture. A fiber parallel to the flow only slightly perturbs the flow, and the force on it can be estimated using 2D models. On the contrary, if it is perpendicular to the flow, the latter becomes 3D if blockage is partial. In this configuration, the lift is sufficient to keep the cylinder in the middle of the flow. For Reynolds numbers higher than 20, this position becomes unstable and the cylinder oscillates between the walls. The threshold of this instability is lower than that of Bénard-Von Kármán vortex shedding. The position of the cylinder satisfies a Van der Pol equation, which allows for a quantitative prediction of the Hopf bifurcation of the system. A hydrodynamic interpretation of the coefficients of this equation is given. We also develop and validate a new image processing method, which give the shape of the fiber with a sub-pixel precision. Moreover, the tangent vector angle and the curvature, of interest because it is related to the bending moment, are accurately measured
Naso, Aurore. "Intermittence en Turbulence pleinement développée et en Dynamique non linéaire". Phd thesis, Université de Nice Sophia-Antipolis, 2005. http://tel.archives-ouvertes.fr/tel-00011134.
Pełny tekst źródłaLa seconde partie est consacrée à l'étude de la transition au chaos spatio-temporel par intermittence dans un système hydrodynamique réel. Cette transition est d'abord étudiée quantitativement, puis un modèle d'intermittence spatio-temporelle est appliqué aux conditions aux limites de l'expérience. Comme le système réel, les solutions de ce modèle présentent pour certaines valeurs des paramètres dont il dépend un régime de bistabilité, près du seuil, entre l'intermittence spatio-temporelle et un régime où le désordre n'est présent que sur les bords.
Watteaux, Romain. "Détection des grandes structures turbulentes dans les couches de mélange de type Rayleigh-Taylor en vue de la validation de modèles statistiques turbulents bi-structure". Phd thesis, École normale supérieure de Cachan - ENS Cachan, 2011. http://tel.archives-ouvertes.fr/tel-00669707.
Pełny tekst źródłaNikiema, Oumarou. "Modélisation de la circulation côtière sur une marge continentale soumise à un apport fluvial important : application au cas du plateau nord brésilien sous influence de l'Amazone". Aix-Marseille 2, 2006. http://theses.univ-amu.fr.lama.univ-amu.fr/2006AIX22057.pdf.
Pełny tekst źródłaMarine circulation above the northern Brazilian continental shelf is subject to energetic forcing factors of various origins : high water buoyancy fluxes, a strong coastal current associated with a mesoscale current (North Brazil Current (NBC)), a forcing by semi diurnal tide and by Northeast or Southeast trade winds according to the season. Using a three-dimensional hydrodynamic numerical model (MOBEEHDYCS), and realistic bathymetry and coastline of the northern Brazilian shelf, we study the influence of some specific physical forcings on the morphology of the Amazon plume. We have shown that, contrary to other studies, the coastal current is the principal cause of the plume deviation northwestward. The numerical results are compared to field data and satellite images. Finally, the fate of the Amazonian suspended matter is investigated with the numerical model, and comparison between the modelled turbid plume and satellite image shows a good qualitative agreement
Castrillon, Escobar Sebastian. "Instabilité et dispersion de jets de corium liquides : analyse des processus physiques et modélisation dans le logiciel MC3D". Thesis, Université de Lorraine, 2016. http://www.theses.fr/2016LORR0102/document.
Pełny tekst źródłaIn the case of a severe accident in a nuclear power plant, the molten core may flow into water and interact with it. The consequences of this fuel-coolant interaction (FCI) for the follow-up of the accident may be numerous so the phenomenon needs to be described accurately, one of them called “steam explosion” can lead to the failure of the nuclear reactor containment. FCI is a complex multiphase interaction involving several physical phenomena. The premixing phase of the interaction consists in the fragmentation and dispersion of corium in the coolant pool. This phase is driven by the fragmentation process which modifies heat transfers (coolant boiling dynamics) and chemical reactions (corium oxidation and hydrogen generation). This thesis brings new elements about the corium jet and droplet breakup with the main goal of improve fragmentation models on the MC3D multiphase code, developed by the IRSN. Our study is based on a multi-scale fragmentation process where the jet fragmentation rate and final droplet dimensions are not coupled themselves. We suppose a fragmentation process resulting from a primary instability (mass transfer within jet and big droplets) depending on the large flow scales and a secondary instability depending on the small flow scales (leading to final droplet breakup). This model has been implemented in MC3D in combination with the MUSIG method recently added to MC3D. In this method, droplets are represented using several classes, each of them with their own droplet diameter, mass and energy fields. Despite new improvements on modeling corium fragmentation, there is still a lack on the comprehension and characterization on the liquid droplet fragmentation, particularly on liquid/liquid configurations. In this thesis, we study in detail droplet breakup using the computational fluid dynamics software GERRIS. As a result, we find a new droplet breakup classification in liquid/liquid configurations, we improve the droplet breakup dynamics comprehension and we analyze the droplet-vortex interaction to determine breakup regime transition
Biagi, Sofia. "A mesoscale investigation of the endothelial glycocalyx and its interaction with blood flow". Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAY083/document.
Pełny tekst źródłaPolymer brushes are dense matrices of grafted macromolecules. In addition to brushes finely designed in laboratory, various examples are offered by Nature, as the endothelial glycocalyx, decorating the lumen of mammalian blood vessels. The interaction of such network with the flowing plasma and cells is still partially unknown.The present thesis, by mean of Dissipative Particle Dynamics simulations, proposes a coarse-grained model for the self-consistent analysis of a dense polymer brush under parabolic flow. Our mesoscale investigation highlights the relevance of collective effects, driven by hydrodynamics, and proposes novel interpretations regarding the rich phenomenology of the brush-flow system.Preliminary results are also provided for the interplay between a mesoscopic deformable flowing object (prototype of a red blood cell) and the grafted polymers
Roy, Clément. "Dynamique et stabilité de tourbillons avec écoulement axial". Phd thesis, Université de Provence - Aix-Marseille I, 2008. http://tel.archives-ouvertes.fr/tel-00436894.
Pełny tekst źródłaTuerke, Florian. "Interaction entre deux cavités opposées dans un canal hydrodynamique". Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS078/document.
Pełny tekst źródłaThis work investigates the flow in a symmetric channel with a sudden expansion and contraction, creating two facing cavities, a so called double cavity. Double cavity flow at moderate Reynolds numbers is studied experimentally, numerically and analytically, as the inflow velocity and the distance between the cavities are varied. The focus is put on the interaction of the two shear layers and the intracavitary hydrodynamic feedback in the incompressible limit.Experimentally, standard 2D2C particle image velocimetry (PIV) measurements in a given spanwise plane provide information on the instantaneous and mean velocity flow fields. Laser Doppler velocimetry and time resolved 2D2C PIV measurements reveal the richness of the streamwise fluctuating velocity spectra. The flow is characterized based on times series, recorded in one of the cavity's shear layers, for a wide range of inflow velocities and cavity distances.Two dimensional and three dimensional direct numerical simulations, which give easy access to the entire flow field, are used to study the intracavitary hydrodynamic feedback mechanism. Vorticity fields, obtained from 2D numerical simulations, show the importance of the recirculating intracavitary back flow. Vorticity packages, injected by the oscillating and impinging shear layer at the downstream cavity edge, are advected upstream in the recirculation region, creating a ``carousel-like'' pattern. The interaction of this vortex carousel with the oscillating shear layer is found to be responsible for the self-sustained oscillations observed experimentally in single and double cavity flow. The quantification of three characteristic time scales of the rotation allows to identify in which regime the flow resides.Temporal and spatio-temporal inviscid linear stability analyses are applied to a one dimensional base flow of single and double cavity flows. To account for the finite extent of the system, the spatio-temporal linear stability analysis is conditioned by a so called Kulikowskii condition, which allows the reflection of hydrodynamic instability waves within the cavity domain. This feedback mechanism yields a set of discrete, non-harmonic frequencies, some of which compare well with experimental results
Mejni, Fatah. "Structures synchronisées dans les écoulements inhomogènes de convection mixte en milieux poreux". Thesis, Lille 1, 2008. http://www.theses.fr/2008LIL10071/document.
Pełny tekst źródłaMixed convection flow in porous media heated from below non uniformly and subjected to an horizontal pressure gradient is studied theorettcally and numericalIy. The prescribed temperature at the bottom boundary is assumed to vary slowly in space. The result is the establishment of a weak inhomogeneous basic state, the stabIllty of which is carried out using the WKBJ approximation. Depending on the choice of the imposed inhomogeneous temperature profile, two cases prove to be of interest: the base flow displays an absolute instability region either detached from the inlet or attached to it. Results from combined direct numerical simulations and limear stability approach have revealed that in the first case, the nonlinear solution is a steep nonlinear global mode, with a sharp stationary front located at a margimally absolutely unstable station. ln the second configuration, the scaling laws for the establishment of a nonlmear global mode quenched by the inlet are found to perfectly agree with the theory. It is also found that in both configurations, the global frequency of synchronized oscillations corresponds to the local absolute frequency determined by Iinear criterion, even far from the threshold of global instability. All these results agree remarkably with recent advances of nonlinear global modes theory, A good agreement is also found between the predictions of the theory and the measured global frequencies
Daimallah, Ahmed. "Étude des phénomènes d'instabilités en présence d'une suspension dans l'écoulement de Taylor-Dean". Electronic Thesis or Diss., Brest, 2013. http://www.theses.fr/2013BRES0018.
Pełny tekst źródłaThe analytical solution of the stability problem of a solid suspension (rigid spherical particles) in the system of cylindrical Taylor-Couette was conducted. We are based on the work of Ali and Lueptow (2002) to formulate the equations governing the stability of the flow in a linear theory. These equations are valid in the approximation of small gap configuration and aim to predict the primary instability. For this purpose, we used a variational method such as the Galerkin method to solve the eigenvalue problem leading to establish the stability diagram related to the wave number in the vicinity of the critical state of development of the first instability. First, we develop the calculations in the case of Taylor-Couette flow with reference to classic work of Ali and Lueptow (2002). Then, we carried out a systematic solution of the equations of motion and we search to determine the criterion of onset of instabilities in the presence of suspended particles and coupling parameters are simultaneously determined from liquid-solid interaction force. All work carried out and will remove the fundamental contradiction between theory and experiment. The experimental study has analyzed the effect of the concentration of suspended particles (disks) and radial aspect ratio ' on the occurrence of instabilities in the Taylor-Dean flow system. The experimental device used consists of a rotating inner cylinder and the outer cylinder is stationary. The rheological behavior of the fluid is viscoplastic obeying to Herschel Bulkley model. The onset of instability is examined using a visualization technique. For a given concentration in the range studied, the nature of the structure appearing in the flow system depends on ', while for a given value of ' in the range studied, the value of the critical Taylor number Tac depends on the particle concentration. We obtain that the critical Taylor number Tac corresponding to the onset of the first instability evolves nonlinearly versus '. In addition, we examined experimentally the effect of axial limitation (endwall effects) on the onset of instabilities in the Taylor-Dean flow system. The results show that the rotating endwalls do not affect the type of structures that appear in the Taylor-Dean flow system. However, they influence the threshold of appearance of instabilities which is characterized by high values of the critical Taylor number for rotating endwalls indicating a stabilizing effect of the rotating endwalls
Varela, López Fernando. "Instabilités hydrodynamiques dans les procédés d'enduisage". Paris 11, 2001. http://www.theses.fr/2001PA112346.
Pełny tekst źródłaIn this work the process of liquid roll coating application is studied, paying particular attention to the hydrodynamical instability occurring at the free surface of the transferred film. This process is widely used in coating industry, particularly in coated steel. This experimental work intends to a better understanding of the physical mechanisms that governs this kind of processes. Several experiments were conducted, not only to measure the onset and further development of the instability but also to fully characterize the rheological properties of the fluids. A correlation between experimental results and physical properties of fluids has been established, as well as an experimental verification of simple hydrodynamical models, which permits a qualitative understanding of the destabilizing mechanisms. The main result found in this work is related to the viscoelastic effects: the presence of normal stress differences generates a reduction in threshold onset, which has been studied both with respect to geometrical parameters and rheological properties. This allowed the determination of the relation between polymer concentration and threshold. Also, further development of instability has been studied, finding morphological differences with the Newtonian case. Results of base flow measurements showed that there exists some range where viscoelastic effects can be considered small enough, such that weak viscoelasticity hypothesis are fulfilled and the simple model developed in this work should apply. Thus it can be asserted that in the weak viscoelasticity limit elastic effects modifies the onset of instability via boundary conditions rather than base flow changes. This work has been conducted in the Grupo de Medics Porosos at Facultad de Ingenieria, Universidad de Buenos-Aires, and at FAST (Fluids, Automatique et Systems Thermiques), Orsay, France
Godey, Cyril. "Bifurcations locales et instabilités dans des modèles issus de l'optique et de la mécanique des fluides". Thesis, Bourgogne Franche-Comté, 2017. http://www.theses.fr/2017UBFCD008/document.
Pełny tekst źródłaIn this thesis we present several contributions to qualitative study of solutions of nonlinear partial differential equations in optics and fluid mechanics models. More precisely, we focus on the existence of solutions and their stability properties. In Chapter 1, we study the Lugiato-lefever equation, which is a variant of the nonlinear Schrödinger equation arising in sereval contexts in nonlinear optics. Using tools from bifurcation and normal forms theory, we perfom a systematic analysis of stationary solutions of this equation and prove the existence of periodic and localized solutions. In Chapter 2, we present a simple criterion for linear instability of nonlinear waves. We then apply this result to the Lugiato-Lefever equation, to the Kadomtsev-Petviashvili-I equation and the Davey-Stewartson equations. These last two equations are model equations arising in fluid mechanics. In Chapter 3, we prove a criterion for linear instability of periodic solutions with small amplitude, with respect to certain quasiperiodic perturbations. This result is then applied to the Lugiato-Lefever equation
Razafindrakoto, Mirijason Richard. "Modèle hydrodynamique de transistor MOSFET et méthodes numériques, pour l'émission et la détection d'onde électromagnétique THz". Thesis, Montpellier, 2017. http://www.theses.fr/2017MONTS035/document.
Pełny tekst źródłaDue to its interesting properties, the electromagnetic THz frequency range may lead to numerous technological applications, ranging from imaging to spectroscopy or even communications. However, technological constraints prevented the efficient emission and detection of such waves with conventional electronics, leading to the idea of the terahertz gap. In the last decades, multiple novel solutions to resolve this gap have been proposed. Amongst these, one may find the use of simple field effect transistors as the most promising one. Their production benefits from currently available CMOS technology thus drastically decreasing the fabrication cost of such a device while allowing it to be easily integrated within electronic circuits. The mechanism behind the emission and detection is the interaction between THz electromagnetic radiations and current oscillations, that is plasma waves, in the transistor's channel. This channel forms a cavity for plasma oscillations, hence, the device may act either resonantly or non-resonantly, depending on various parameters. This thesis deals with the numerical simulation of the transistor in different regimes using hydrodynamical models. These models account for multiple phenomena that have been considered in previous theoretical studies. Some theoretical results on both the emission and detection of THz radiation are presented. In the non-resonant case, we study how one can increase the linear regime of detection. In the resonant case, we show the existence of unexpected resonance frequencies, enlarging the detection spectrum of such detectors
Longobardi, Raffaele. "Instabilité hydrodynamique dans les systèmes d'écoulement complexes". Thesis, Toulouse 3, 2019. http://www.theses.fr/2019TOU30103.
Pełny tekst źródłaStability analysis is a very powerful tool in order to investigate the properties of a complex fluid system. For example, it turns out to be very useful for understanding the laminar&;turbulent transition scenario or to investigate the dynamic evolution of a fluid in very complex situations such as wakes, jets, recirculation bubbles etc. In this work, linear stability theory has been applied to very different situations. In the first part, we investigate the stability characteristics of a 2D T shaped micro mixer, a very common device in micro- and nano-fluidics, fitted with an anisotropic superhydrophobic texture on the walls of the outlet channel, using a global stability approach. A parametric analysis has been carried out by varying the surface properties, i.e. the equivalent slip length of the grooves and their orientation angle with respect to the direction of the main pressure gradient. We characterize both the primary and the secondary instability of such kind of flow. We show that in some conditions, the presence of the SHS generates an unsteady instability apt to improve the mixing in the channel. The second and third parts concern the linearized study of an incompressible laminar viscous jet passing through a circular aperture. In particular, in the second part we considered the flow passing through a hole of zero thickness. We compute the response of such kind of flow to harmonic perturbations. We characterize both the spatial amplification of perturbations and the impedance, defined as the ratio between the pressure jump and the flow rate across the hole, which is a key quantity to investigate the response of the jet to an acoustic forcing. Owing to the strong spatial amplification of the perturbation the computation requires a special treatment of the downstream boundary conditions, and quickly becomes impossible when the Reynolds number is increased. We introduce a method based on the analytical continuation in the complex plane of the axial coordinate, thus extending the range of Reynolds number investigated up to Re = 3000. The third part concerns the stability of a jet through a circular aperture in a thick plate. Experiments and simulations show that if the plate is thick enough, strong periodic oscillations can occur and lead to characteristic whistling tones, suggesting the existence of a feedback mechanism that supports self-sustained oscillations. We show that, contrary to previous expectations, the feedback mechanism is not related to acoustics and an instability can exist even in a purely incompressible description. We investigate the stability properties of such kind of flow using both the Nyquist criterion, based on the impedance analysis, and the classical global stability approach. Finally, we perform a structural-sensitivity analysis showing that the instability of such kind of flows is connected to the presence of a recirculation region in the hole. In the last part of the thesis we apply the stability analysis to the production of sound in a more traditional configuration, namely the birdcall, where the flow is constrained to pass through two successive holes in curved rigid plates. Although the production of sound in this classical whistle is a compressible phenomenon, an incompressible approach can provide some useful information at least in the region near the hole. We thus initially perform a purely incompressible stability analysis. We identify the critical conditions, the global frequencies, and discuss the structure of the resulting global eigenmodes. In order to reintroduce and evaluate compressible effects, which can be relevant in the cavity between the two holes, we model the cavity as a Helmholtz resonator and couple it to the incompressible simulation. Finally, a fully compressible stability analysis is performed in order to check the accuracy of these simplified approaches in term of critical conditions, global frequencies and structure of the modes
Ella, Eny Geremino. "Instabilités thermiques et thermodiffusives de fluides viscoélastiques saturant un milieu poreux". Thesis, Lille 1, 2011. http://www.theses.fr/2011LIL10156/document.
Pełny tekst źródłaIn this theoretical and numerical work, we study differents instabilities which can develop in a porous media saturated by viscoelastic fluid and heated from below. The mathematical formulation of the equations of this problem is based on phenomenological Darcy law generalized to a viscoelastic fluid verifying Boussinesq estimate. This problem admits a solution of conduction, and we find that two types of structures may appear when the conduction state loses his stability : stationary and oscillatory structures.The apparition thresholds of these thermo-convectives structures are studied and depend on the non-dimensionnalized parameters of the problem, Rayleigh number, relaxation and retardation time associated to the fluid elasticity. A linear and non linear stability is also realized. It is interesting to note that it can have a competition between stationary and oscillatory structures near a point named codimension 2 point. A linear analysis is also realized near this point and is compared to the numerical simulation results.Finally, by taking into account binary mixtures properties of the viscoelastic fluids, a theoretical study is realized and we show that there is a competition between two states : a state in which viscoelasticity is dominant and another state in which binaries properties are also dominants. This result can explain experimental observations
Tijani, Niass. "Instabilités d'interfaces dans un écoulement gaz-liquide à contre courant". Vandoeuvre-les-Nancy, INPL, 1996. http://www.theses.fr/1996INPL111N.
Pełny tekst źródłaRichard, Denis. "Instabilités hydrodynamiques dans les écoulements en rotation différentielle". Phd thesis, Université Paris-Diderot - Paris VII, 2001. http://tel.archives-ouvertes.fr/tel-00001393.
Pełny tekst źródłaKitenbergs, Guntars. "Instabilités hydrodynamiques de fluides magnétiques en écoulements microfluidiques". Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066311/document.
Pełny tekst źródłaMagnetic field induced instabilities of magnetic fluids in microfluidic environment are investigated experimentally. Electrically stabilized water-based magnetic nanocolloids are used and throughout characterized.Magnetic micro-convection, observed at a miscible magnetic fluid-water interface in a Hele-Shaw cell in homogeneous field, is studied quantitatively and compared with theoretical predictions and numerical simulations, micro-convective flows being characterized by particle image velocimetry. Besides the critical field determination, it is shown that an increase of the magnetic field H speeds up the finger growth, which scales as H2, while the size of the fingering pattern is not changed. An application towards mixing enhancement in microfluidics is considered.The micro-convection study reveals a much larger effective diffusion coefficient of the nanoparticles than expected from Stokes - Einstein relation and standard determinations. Investigations with the same setup and with continuous microfluidics show that the effective diffusion mostly arises from a flow induced by the density difference between the miscible fluids. Additionally, the diffusion coefficient seems to be influenced by the particle stabilizing agents.Drops of a concentrated magnetic phase in co-existence with a dilute one are formed by phase separation after salt addition to the magnetic fluid and/or the application of a magnetic field. Their under-field shape deformations allow investigating the time evolution of the concentrated phase. Experiments show that in a precessing field at magic angle, the drops behave as in a rotating field except the initial shape deformation before quick elongation
Zerhboub, Mohammed. "Instabilités hydrodynamiques lors d'écoulements polyphasiques en milieu poreux". Bordeaux 1, 1988. http://www.theses.fr/1988BOR10566.
Pełny tekst źródłaMagdelaine-Guillot, de Suduiraut Quentin. "Hydrodynamique des films liquides hétérogènes". Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS531.
Pełny tekst źródłaCoating processes allow functionalizing a surface to obtain new properties, as anti-glare or anti-scratch. Amongst the various methods, wet coating, the process of spreading then drying a liquid layer containing a material of interest, is particularly appealing because of its efficiency and low cost. One key hurdle, however, is the possible apparition of defects in the film during the drying process, notably, thickness variations over large areas. These imperfections degrade the aspect and the optical properties of the surface. In this Ph.D. thesis, we shed light on the apparition of these defects, by studying the flows triggered by the evaporation in liquid films of binary mixtures. Indeed, the evaporation of the solvent can induce variations of composition which generate in return gradients of tension at the film surface which destabilize it. The combination of model experiments, theoretical modeling and numerical simulations allowed us to reveal and describe quantitatively several regimes, which correspond to the factor limiting the instability: gravity, Laplace pressure, lateral homogenization by diffusion of the compounds or by their vertical stratification due to the evaporation. An independent study has been lead on the generation of bubble trains when air is slowly injected in a bath