Dissertations / Theses on the topic 'Mécanique des fluides – Stabilité'
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Paddick, Matthew. "Stabilité de couches limites et d'ondes solitaires en mécanique des fluides." Thesis, Rennes 1, 2014. http://www.theses.fr/2014REN1S049/document.
This thesis deals with a couple of stability problems in fluid mechanics. In the first two parts, we work on the inviscid limit problem for Navier-Stokes equations. We look to show whether or not a sequence of solutions to Navier-Stokes in a half-space with a Navier slip condition on the boundary converges towards a solution of the inviscid model, the Euler equation, when the viscosity parameters vanish. First, we consider the 2D incompressible model. We obtain convergence in L2 of weak solutions of Navier-Stokes towards a strong solution of Euler, as well as the instability in L∞ in a very short time of some initial data chosen as stationary solutions to the Euler equation. These results are not contradictory, and we construct initial data that allows both phenomena to occur simultaneously in the periodic setting. Second, we look at the 3D isentropic (constant temperature) compressible equations. We show that solutions exist in conormal Sobolev spaces for a time that does not depend on the viscosity when this is small, and we get strong convergence towards a solution of the Euler equation on this uniform time of existence by compactness arguments. In the third part of the thesis, we work on a solitary wave stability problem. To be precise, we consider an isentropic, compressible, inviscid fluid with internal capillarity, governed by the Euler-Korteweg equations, and we show the transverse nonlinear instability of solitons, that is that initially small 2D perturbations of a 1D travelling wave solution can end up far from it
Le, Meur Hervé. "Existence, unicité et stabilité d'écoulements de fluides viscoélastiques avec interfaces." Paris 11, 1994. http://www.theses.fr/1994PA112406.
De, Felice Valerio Francesco. "Il vortice a superficie libera in quanto instabilità." Toulouse 3, 2008. http://thesesups.ups-tlse.fr/253/.
The spontaneous genesis of free surface whirlpools represents a traditional hydrodynamic phenomenon of which the causes are not yet completely clarified. The scientists supposed for a long time that the rotation was due to the gradual concentration of the vorticity, coming from the upstream flow, which through a mechanism of convention was accumulated on the axis of the rising whirlpool. One second assumption supposes that the formation is due to an hydrodynamic instability; this possibility has been analyzed in an experimental work and some numerical simulations in the case of an axisymmetric flow. In this work it's shown that, in the presence of non uniform boundary conditions, as the Reynolds number is increased, an instability, which lead to a rotation in the flow, is observed. In the first part of the work is made a linear analysis of stability on the flow in an axisymmetric conditions. Is then considered a flow with non uniform inlet conditions in the azimuthal direction: the least stable eigenvalue (and the associated eigenfunction) of the system is calculated and it's also calculated the Reynolds number at which the flow becomes unstable. In the second part is described the experimental work made at the IMFT on the same geometry and flow. The experimental results agree with the numerical results to confirm the thesis which the swirls can be generated by a phenomenon d' instabilited
Martinand, Denis. "Détermination analytique des modes globaux tridimensionnels en écoulement de convection mixte du type Rayleigh-Bénard-Poiseuille." Lyon 1, 2003. http://tel.archives-ouvertes.fr/docs/00/04/56/12/PDF/tel-00003461.pdf.
Poncet, Sébastien. "Écoulements de type rotor-stator soumis à un flux axial : de Batchelor à Stewartson." Aix-Marseille 1, 2005. http://www.theses.fr/2005AIX11010.
This experimental and numerical study deals with the characterization of rotor-stator flows when an axial throughflow is superimposed according to the angles: turbulence and stability. New velocity measurements are compared to the predictions of a advanced Reynolds Stress Model essentially for turbulent flows with separated boundary layers. In a closed cavity or when a centripetal throughflow is superimposed, the flow structure is of Batchelor type: the boundary layer on the rotor and the one on the stator are separated by a central rotating core. The tangential velocity in the core is proportional to the local disk speed with the proportionality coefficient K. This coefficient can be determined thanks to a local flowrate coefficient according to a simple analytical law with two coefficients depending only on the prerotation level of the fluid. This law is independent on the interdisk space and on the geometry of the cavity. For strong centrifugal throughflows, the flow structure switches to Stewartson type with only one boundary layer on the rotating disk. The transition between these two flow structures can be characterized by a Rossby number based on the radial gap between the rotor and the shroud. This transition is continuous and does not depend on the interdisk space and on the geometry. Turbulence is concentrated in the two boundary layers and increases towards the periphery of the cavity. When a throughflow is superimposed, the relaminarized area close to the axis disappears and the turbulence intensity is maximum in the outlet and inlet areas. The influence of a throughflow on the stability of torsional Couette flows (joined boundary layers), mixed flows and Batchelor flows has been investigated from flow visualizations. The circle and spiral networks as well as the solitary waves and the turbulent spots observed in the case of a closed cavity subsist when a throughflow is superimposed but the appearance thresholds are moved. Some new instabilities appear also. A "crossflow'' instability, generic of these type of flows, has been observed. These are positive spirals located at the periphery of the cavity closed to the stator boundary layer. It is due to the inflexion points in the axial profiles of the mean velocity components
Brizzi, Laurent-Emmanuel. "Contribution à l'étude de l'instabilité générée par un jet cylindrique débouchant perpendiculairement à un écoulement transversal." Poitiers, 1994. http://www.theses.fr/1994POIT2334.
Albert, Fabrice. "Stabilité d'une interface entre deux fluides cisaillés : étude numérique et asymptotique." Toulouse, INPT, 1996. http://www.theses.fr/1996INPT126H.
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.
Mettot, Clément. "Stabilité linéaire, sensibilité et contrôle passif d'écoulements turbulents par différences finies." Phd thesis, Ecole Polytechnique X, 2013. http://pastel.archives-ouvertes.fr/pastel-00921908.
Loueslati, Karim. "Stabilité hydrodynamique et magnétohydrodynamique d'un jet capillaire tournant." Vandoeuvre-les-Nancy, INPL, 2000. http://docnum.univ-lorraine.fr/public/INPL_T_2000_LOUESLATI_K.pdf.
Pouliquen, Olivier. "Instabilites et solitons de phase a l'interface de deux fluides non miscibles." Palaiseau, Ecole polytechnique, 1993. http://www.theses.fr/1993EPXX0011.
Lafranche, Éric. "Influence du couplage des orientations et des contraintes internes sur la stabilité dimensionnelle des pièces injectées." Lille 1, 1996. https://pepite-depot.univ-lille.fr/LIBRE/Th_Num/1996/50376-1996-408.pdf.
Sartor, F. "Instationnarités dans les interactions choc/couche-limite en régime transsonique : étude expérimentale et analyse de stabilité." Phd thesis, Aix-Marseille Université, 2014. http://tel.archives-ouvertes.fr/tel-01018720.
Fourel, Loïc. "Stabilité et instabillité de la lithosphère continentale." Paris, Institut de physique du globe, 2009. http://www.theses.fr/2009GLOB0008.
Most of the studies concerning cratonic longevity tackle the problem from the stability point of view and not the instability. We analyze stability and instability conditions of continental lithosphere through numerical simulations and laboratory experiments. Continental lithosphere is made of differentiated mantle, more viscous and less dense than the primitive mantle. We treat cases in which viscosity is constant and where it depends on temperature. We characterize two different regimes. In the first one, the lithosphere remains stable over a convection which only implies the underlying mantle. In the second one, the lower part of lithosphere is unstable and the characteristics of convection only depend on its viscosity (not the viscosity of the underlying mantle). Scaling laws are derived from numerous simulations for both regimes. They allow us to estimate the temperature difference available for convection underneath the continents as well as the buoyancy number for continental lithosphere. Laboratory experiments define the behaviour of such instabilities in the case of continents of finite horizontal width. For every geometry tested, the convective pattern develops radially over a corona which width depends on the dimensionless numbers of the system. The aspect ratio, defined as height over width, of a continent affects its stability. The greater it is, the stabler is the continent
Kahouadji, Lyes. "Analyse de stabilité linéaire d'écoulements tournants en présence de surface libre." Paris 6, 2011. http://www.theses.fr/2011PA066325.
Stewart, Bronwyn. "Dynamique et stabilité de l'écoulement autour de corps non profilés roulants." Phd thesis, Université de Provence - Aix-Marseille I, 2008. http://tel.archives-ouvertes.fr/tel-00436896.
Agbessi, Yao. "Stabilité de l’écoulement de Taylor-Couette de fluides complexes." Thesis, Université de Lorraine, 2015. http://www.theses.fr/2015LORR0160/document.
When increasing the Reynolds number of a flow, it passes gradually from an ordered state, called laminar, to a chaotic state, called turbulent. During this transition, organized hydrodynamic structures appear which disorganize under successive destabilizations. These structures may cause problems for example in the relation to the homogenization of suspensions, because particles may be trapped in the structures, leading to under or over-concentrated zones. Furthermore, most of the fluids found in nature and in the industry are non-Newtonian. In order to better understand and control the apparition of hydrodynamic structures in such fluids, we focused during this PhD on the instability mechanisms governing the transition to turbulence of complex fluids in the simplified configuration of Taylor-Couette. In a theoretical and numerical approach, concepts of hydrodynamic instabilities were applied to the circular Couette flow for three rheological models: the power law, the Carreau and the Bingham models. Two radius ratios and different rotation velocities were considered for the cylinders. The destabilization of the circular Couette flow was studied to predict the apparition of structures such as Taylor vortex at long times. An analysis at short time was also performed to study the phenomena of transient growth. In an experimental approach, a Taylor-Couette device was designed. First, the torque on the inner cylinder was measured for a Newtonian fluid (glycerol) and successfully compared to previous results of the literature. Secondly, rheological measurements were conducted in order to select fluids showing rheological behaviors considered in the theoretical approach. Visualizations were then performed in order to detect the apparition of instabilities and the critical conditions were compared to the predicted by means of the linear stability analysis. Finally, PIV measurements provided velocity fields in the flow. These different studies evidenced a subcritical transition and chaotic flow due to the shear-thinning character of the fluids
Stewart, Bronwyn Elaine. "Dynamique et stabilité de l'écoulement autour de corps non profilés roulants." Aix-Marseille 1, 2008. http://theses.univ-amu.fr.lama.univ-amu.fr/2008AIX11057.pdf.
A numerical and experimental study of the flow around rolling and sliding bodies is presented. The body geometry is fixed as being either spherical or cylindrical and the Reynolds number of the flow is restricted to Re ≤ 500. This range is sufficient to capture the primary two- and three-dimensional transitions in the flow. The primary aim of this study is to understand the effects of body rotation and a nearby wall on the flow transitions when these effects are acting in tandem. In the case of the cylinder moving along the wall, both two- and three-dimensional flows are investigated and the results of a linear stability analysis are reported. The flow around a rolling and sliding sphere is investigated using both experiments and three-dimensional simulations. The parameter space under consideration is defined in terms of the Reynolds number, based on the body diameter, and the rotation rate of the body, α. For a body moving along a wall in a quiescent fluid, the rotation rate corresponds to the ratio of tangential velocity on the surface of the body to the translational velocity. Five discrete values of the rotation rate have been selected, α = 1, 0. 5, 0, −0. 5 and −1. These range from ‘normal’ rolling, where there is no slip between the body and the wall, to reversed rolling, where the body rotates in the opposite sense. This range is selected to correspond with the range of rotation rates observed in experiments of freely rolling bodies with and without lubrication effects. [. . . ]
Leweke, Thomas. "Etude expérimentale et modélisation du sillage d'un tore à bas nombre de Reynolds." Aix-Marseille 1, 1994. http://www.theses.fr/1994AIX11028.
Fosas, De Pando Miguel Ángel. "Tonal noise generation in flows around aerofoils : a global stability analysis." Palaiseau, Ecole polytechnique, 2012. https://theses.hal.science/tel-00816987.
The generation of discrete acoustic tones in the compressible flow around an aerofoil is addressed in this thesis by means of nonlinear numerical simulations and global stability analyses. To this end, a nonlinear simulation code featuring a novel technique for gaining access to the linearized direct and adjoint dynamics has been developed and applied to the flow around an aerofoil. The nonlinear simulations confirm the appearance of discrete tones in the acoustic spectrum, and for the chosen flow case, the global stability analyses of the mean-flow dynamics reveal that the linearized operator is stable. However, the flow response to incoming disturbances exhibits important transient growth effects that culminate into the onset of aeroacoustic feedback loops, involving instability process on the suction- and pressure-surface boundary-layers together with their cross interaction by acoustic radiation at the trailing edge. The features of the aeroacoustic feedback loops and the appearance of discrete tones are then related to the features of the least stable modes in the global spectrum: on the one hand, the spatial structure of the direct modes display the growth of hydrodynamic instabilities on the suction surface and the near wake; on the other hand, the associated adjoint modes display increased receptivity of the flow on the pressure surface. Finally, the analysis of the wavemaker region highlights, in agreement with previous experimental investigations, the sensitivity of the flow to the pressure-surface boundary layer
Griffith, Martin. "Stabilité et dynamique des écoulements en géométrie de sténose." Phd thesis, Université de Provence - Aix-Marseille I, 2007. http://tel.archives-ouvertes.fr/tel-00437443.
Métivier, Christel. "Instabilités thermoconvectives pour des fluides viscoplastiques." Thesis, Vandoeuvre-les-Nancy, INPL, 2006. http://www.theses.fr/2006INPL092N/document.
The stability of the Poiseuille Rayleigh-Bénard flow for yield stress fluids is performed via linear, weakly non linear and non linear approaches. These fluids are widely used in industrial processes and at a larger scale in geophysics. It is assumed that the rheological behaviour of the material is described by the Bingham model. This model assumes that the material moves as a rigid solid when the applied stress is less than the yield stress and as a viscous fluid when the yield stress is exceeded. The aim of this study is to understand the influence of the yield stress on the stability conditions. It arises from the modification of the thickness of the yielded regions, the viscosity stratification inside these regions and the modification of the viscous dissipation. A fundamental difficulty by comparison with the Newtonian case lies in the description of the behaviour of the interface separating the ``gel-like" and ``fluid-like" phases. First, a linear analysis using modal and energetic approaches is developped. Results clearly highlight the stabilizing effect of the yield stress. Then, a weakly non linear analysis is performed to identify the nature of the bifurcation. Original results are obtained and show a change in the nature of the bifurcation at Péclet number . This is a consequence of the strong viscosity stratification. Finally, a non linear analysis was done using Reynolds-Orr type equation. The behaviour of the critical conditions as function of the yield stress is determined
Vincent, Huber. "Contribution au calcul d'écoulements de fluides complexes." Phd thesis, Université Sciences et Technologies - Bordeaux I, 2012. http://tel.archives-ouvertes.fr/tel-00745794.
Benusiglio, Adrien. "Indiscrétions aux interfaces." Phd thesis, Ecole Polytechnique X, 2013. http://pastel.archives-ouvertes.fr/pastel-00860739.
Bouchet, Eric. "Étude du bruit d'interaction pale-sillage d'un rotor principal d'hélicoptère." Le Havre, 2002. http://www.theses.fr/2002LEHA0011.
Understanding the mecanisms responsible for the BWI noise of helicopter main rotor which occures during perpendicular blade-vortex interaction. An extensive analysis of the blade pressure is performed to get a deeper insight of the BWI mecanism. A stability analysis of modelization of the incident flow (two rectilinear and parallel filaments) is undertaken. The numerical and theoritical results are found to be in good agreement and consistent with the proposed instability hypothesis
Lopépé, Frédéric. "Influence de la présence d'une paire de vortex contrarotatifs sur la stabilité d'un jet rond." Vandoeuvre-les-Nancy, INPL, 2002. http://www.theses.fr/2002INPL024N.
Dastugue, Laurent. "Contributions à l'étude de la stabilité d'écoulements autosemblables d'onde thermique pour la fusion par confinement inertiel." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2013. http://tel.archives-ouvertes.fr/tel-00975215.
Gaillard, Antoine. "Flow and stability of a viscoelastic liquid curtain." Thesis, Sorbonne Paris Cité, 2018. http://www.theses.fr/2018USPCC011/document.
The flow and the stability of viscoelastic liquid curtains are investigated using solutions of flexible and semi-rigid polymer chains. These viscoelastic liquids are extruded from a slot at constant flow rate and fall in ambient air under gravity. We show that the curtain flow of polymer solutions is characterized by an initial balance between gravity and the elastic stresses arising from the stretching of polymer molecules, until inertia finally dominates and the classical free-fall behavior is recovered. We show that the flow is mostly influenced by the value of the extensional relaxation time of the solution measured by a filament thinning technique. New insights on the theoretical description of Newtonian curtains allow us to find the master curve of the viscoelastic curtain flow by analogy. Concerning the curtain stability, we show that the critical flow rate for curtain formation is not affected by the presence of polymers whereas the minimum flow rate below which the curtain rapidly breaks is reduced by polymer addition, thus revealing a greater resistance of the sheet to hole initiations. Furthermore, we observe the onset of a flow instability for the most shear-thinning solutions, where thick bands (where the liquid velocity is larger than average) are formed within the curtain. Visualizations of the flow inside the die reveal that this phenomenon is linked to a flow instability at the contraction plane upstream of the slot where the flow is unsteady and three-dimensional in nature
Fakri, Aboulfida. "Etude numérique de la stabilité spatiale des écoulements de type couche limite : Application à l'étude du bruit rayonné par un profil placé en écoulement sain." Lyon 1, 1985. http://www.theses.fr/1985ECDL0085.
Léon-Becerril, Elisabeth. "Analyse de stabilité et simulation numérique des colonnes à bulles." Toulouse, INSA, 2001. http://www.theses.fr/2001ISAT0010.
The objective of this thesis is the numerical simulation of hydrodynamics and mixing in bubble columns. Experimentally, two different flow behaviours for bubble columns can be observed. In the homogeneous flow, the gas bubbles move upward uniformly. If the gas flow rate increases, the system becomes heterogeneous. This flow is characterised by the presence of large structures. These structures have an unsteady behaviour, and it is possible that they enhance the mixing in bubble columns. In the first part, the existence of large structures in bubble columns is explained by a stability analysis. An uniform bubbly flow is perturbed and the analysis of stability determines the conditions at which this perturbation is amplified. This analysis is based on two main approaches presented in the literature. A particular objective of this research was the synthesis of such approaches, taking into account the importance of bubble deformation in stability. The proposed approach was validated with experimental data of gas velocity and kinematic velocity at several liquid flow rates. In addition this approach allows to analyse the stability and to determine the transition between flow regimes in bubble columns and in pipe flows. The second point is devoted to the numerical simulation of bubble columns in unsteady flows. Simulations were performed for a rectangular system without liquid flow and with a punctual gas flow rate (Sokolichin & Eigenberger, 1994). The importance of the added mass force which is modelled as a function of the gas fraction and bubble deformation is determined. Finally, a simplified CFD model of bubble column has been constructed with a rectangular surface and an uniformly distributed gas feed at the bottom. The aim of such simulations was to test different models for the drag and added mass forces. Simulated tracer tests were carried out and the results confirmed the importance of the large structures in terms of the concentration transport
Jajoo, Vibhor. "Instabilités de Faraday dans les fluides binaires." Thesis, Bordeaux, 2017. http://www.theses.fr/2017BORD0929/document.
While it is well known that the phenomenon of Faraday instability is a manifestation of vibrational acceleration, its behaviour when both the capillary and gravitational effects vanish, remains unexplored theoretically and experimentally. A detailed experimental and theoretical study is performed to understand the physics of this phenomenon in small rectangular geometry where the proximity of wall results in considerable sidewall stresses. A novel binary liquids system is utilized with low interfacial tension for a near flat interface. Thermal control of fluid system is utilized for achieving reduction in capillary force with study of miscible fluids where interfacial tension reduces to almost zero. In order to discriminate between gravity and capillarity effects, experiments were performed in parabolic flight campaigns. . For the theoretical approach a linear stability analysis is performed through Navier-Stokes equations in a Newtonian incompressible viscous fluid system. This is achieved through a Fourier Floquet method resulting into an eigenvalue problem. Equations are solved by including viscous damping effects for compensating sidewall stresses. Experimentally binary fluids provided a convenient option of changing the coefficient of interfacial tension by temperature control and going through immiscible to miscible system without change of liquid charge. Viscous damping rate is determined experimentally by measuring the linear damping rate. The correction in the theoretical calculations with the viscous damping rate helped in achieving a better understanding of the prediction of the experimental critical amplitude for sub-harmonic and harmonic modes
Margerit, Daniel. "Mouvement et dynamique des filaments et des anneaux tourbillons de faible épaisseur." Vandoeuvre-les-Nancy, INPL, 1997. http://docnum.univ-lorraine.fr/public/INPL_T_1997_MARGERIT_D.pdf.
Valette, Rudy. "Etude de la stabilité de l'écoulement de Poiseuille de fluides viscoélastiques. Application au procédé de coextrusion des polymères." Phd thesis, École Nationale Supérieure des Mines de Paris, 2001. http://tel.archives-ouvertes.fr/tel-00480359.
Teinturier, Samuel. "Dynamique et stabilité de tourbillons océaniques en interaction avec la cote ou la topographie." Palaiseau, Ecole polytechnique, 2008. https://pastel.archives-ouvertes.fr/tel-00430962.
Guénanff, Ronan. "Couplage instationnaire Navier-Stokes/Euler pour la génération et le rayonnement des sources de bruit aérodynamique." Rennes 1, 2004. https://tel.archives-ouvertes.fr/tel-00068113.
Charru, François. "Stabilite d'une interface entre deux fluides visqueux." Toulouse, INPT, 1991. http://www.theses.fr/1991INPT054H.
Duffaut, Yvan. "Calcul des modes d'oscillations d'un liquide dans un réservoir de satellite stabilisé par rotation." Paris 6, 1994. http://www.theses.fr/1994PA066813.
Guimbard, David. "L'instabilité elliptique en milieu stratifié tournant." Phd thesis, Toulon, 2008. https://theses.hal.science/tel-00436895/fr/.
A theoretical and experimental study of the stability of elliptical vortex in rotating stratified flows is completed in the present study. Firstly, we analyze the stability of a Lagrangian unsteady non-uniform vortices with a shorter wavelength WKB type formalism. It appears that the mechanism of destabilization of these eddies is the same as the one destabilizinga elliptical uniform vortex. This result shows that the elliptical instability is a universal 3D mechanism of destabilization 2D vortex. In a second time, is theoretically and experimentally studied the stability of elliptical eddies confined in a stratified fluid in rotation. The experimental device allowing the study consists of a rotating cylinder (filled with a stratified fluid in density following the vertical), elliptical distorted by two rolls fixed, all united by a panel also rotating. By varying the parameters of our experience (the frequency of Brunt-Väisälä Nb and the absolute vorticity Ta, the two quantities are non dimensional by the relative rate of rotation of fluid particles), we observed that the rotation and the stratification have antagonist contribution to the stability of elliptical vortices. Thus, if the stratification is sufficiently strong (Nb > 1), we observe that only anticyclones (such as |Ta| < 1) are unstable. Cyclones will remain still stable. Moreover, if the stratification is low (Nb < 1), areas of instability reversed. Finally, the wavelengths are in good agreement with theoretical predictions
Boniface, Paul. "Instabilité de Kelvin-Helmholtz et allée de Bénard-von Karman en géométrie rectangulaire confinée." Paris 7, 2014. http://www.theses.fr/2014PA077049.
The Kelvin-Helmholtz instability and its mechanism can be observed when a flow velocity field has an inflexion point, or at the interface between two flows with different velocities. This phenomenon has been widely investigated during the past century, but very few studies have explored it in a confined geometry, where the instability development is limited, or in a closed geometry, where it cannot be advected. We partially dragged the central surface of a rectangular tank filled with water, using a tape or a rope. Depending on the experiment parameters, the flow showed different patterns. At the slowest velocities, the free surfàce on the lateral sides of the tape is dragged in the tape direction and the fluid recirculation occurs mostly at the bottom of the tank. For faster velocities, this recirculation becomes mostly lateral, while the fluid under the belt is dragged. Then, the shear between these two flows leads to a Kelvin-Helmholtz¬like instability. Under some conditions, the vortices developing on each side of the belt can be coupled and a stable vortex street can appear. It has been shown that the only parameter that has an influence on the geometric properties of the street is the lateral confinement of the flow. We observe a confined Bénard-von Kârmân vortex street created without the classic use of a blunt body in a parallel flow. Rosenhead predicted that this street is stabilized by the confinement as that in this case there is a band of stability instead of the classical unique stability condition predicted by von Karman in a plane. Our experiment is one of the first experimental confirmations of the old theoretical prediction of Rosenhead
Flachard, Laurent. "Étude de contraintes et qualification de modèles aux tensions de Reynolds." Toulouse, ENSAE, 2000. http://www.theses.fr/2000ESAE0015.
Airiau, Christophe. "Stabilité linéaire et faiblement non linéaire d'une couche limite laminaire incompressible par un système d'équations parabolisé (PSE)." Toulouse, ENSAE, 1994. http://www.theses.fr/1994ESAE0023.
Nicoud, Edouard. "Quantification de la stabilité de la combustion dans les moteurs essence à injection directe par simulation aux grandes échelles." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLC062.
The automotive industry finds itselfat the center of current environmental concerns.Modern direct injection engines, operated underlean condition have the potential to reducepollutant emissions. As a drawback, they aresubject to large cyclic combustion variability(CCV), that can be explained only partially byexperimental measurements. Large-EddySimulation (LES) appears as an adapted tool tocomplement experiments, due to its naturalability to capture unsteady phenomena. Thepresent PhD thesis first aims at reproducing theCCV, and at contributing achieving a betterunderstanding of their occurrence.In this context, a special effort is put on thereproduction of near-wall phenomena, throughthe proposal of a new wall boundary conditionthat is validated on cases of differentcomplexity. Then the focus is put on the M256case, for which an extensive experimentaldatabase is available. The causes of CCV areexplored, and in particular, the impact of thevariability of the intake flow on the flame frontpropagation is clarified
Allery, Cyrille. "Contribution à l'identification des bifurcations et à l'étude des écoulements fluides par des systèmes dynamiques d'ordre faible (P. O. D. )." Poitiers, 2002. http://www.theses.fr/2002POIT2319.
In this report we have tested and developed various numerical methods. They allows the identification of stationary bifurcations in the fluid flows characterized by the attachment of a jet to a wall by Coanda effect, and the prediction of the dynamic of these flows. These methods, which are the Asymptotic Numerical Method (MAN), Large Eddy Simulations and a low order dynamical system (DS) obtained by proper orthogonal decomposition (POD), are applied to various geometries : sudden expansion, opened cavity, long diffuser. . . In order to increase the prediction of DS, some methods of stabilizations are tested and we suggest a method of correction which take account that the velocity field derived from the LES is not the physical field but the filtered field. In order to avoid the pressure term in the DS we propose to use a stress formulation with a penalization method
Kitsios, Vassili. "Recovery of fluid mechanical modes in unsteady separated flows." Poitiers, 2010. http://www.theses.fr/2010POIT2292.
Cette étude s’intéresse à la détermination de modes pouvant être utilisés en mécanique des fluides pour décrire les propriétés physiques d'écoulements instationnaires décollés. La configuration d'écoulement qui nous intéresse est un profil d'aile NACA 0015 transversalement homogène caractérisé par un décollement laminaire au bord d'attaque et une zone de recirculation turbulente. Comprendre en profondeur la dynamique instationnaire de l'écoulement et ses propriétés de stabilité peut aider à améliorer l'efficacité de futures stratégies de contrôle de décollement. Afin de mieux appréhender la physique, l'écoulement est d’abord simulé puis caractérisé pour plusieurs valeurs du nombre de Reynolds allant jusqu’au régime turbulent. On retrouve alors que les modes obtenus par décomposition orthogonale aux valeurs propres (Proper Orthogonal Decomposition) représentent de manière efficace les échelles instationnaires du mouvement. Par ailleurs, les modes de stabilité linéaire sont recherchés afin d'identifier comment une perturbation évolue dans un environnement instationnaire. La détermination des modes de Proper Orthogonal Decomposition pouvant nécessiter une grande quantité de données, cette étude présente un moyen de les évaluer par calcul parallèle. Pour permettre l'analyse de stabilité, il a fallu développer des programmes permettant de réaliser les calculs pour un écoulement stationnaire bidimensionnel en géométrie semi-complexe. Les corrections nécessaires pour effectuer l'analyse de stabilité dans des écoulements turbulents instationnaires ont aussi été identifiés en utilisant un modèle de viscosité tourbillonnaire non linéaire pour fermer les équations de stabilité en décomposition triple. La détermination de ces modes en mécanique des fluides doit aider le développement futur de modèles réduits nécessaires au contrôle d'écoulement instationnaire décollé
Dussillols, Laurent. "Calculs de stabilité et transition sur des configurations hypersoniques complexes." Toulouse, ENSAE, 1999. http://www.theses.fr/1999ESAE0001.
Fosas, De Pando Miguel Ángel. "Génération d'ondes acoustiques à fréquences discrètes autour d'un profil d'aile : analyse de stabilité globale." Phd thesis, Ecole Polytechnique X, 2012. http://tel.archives-ouvertes.fr/tel-00816987.
Bissen, Edouard. "Semi-analytical methodology for stability and bifurcation analysis in a low pressure boiling channel for GEN4 SFR safety R&D on two-phase flow limit cycles." Thesis, Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0417.
The objective of the study undertaken in this work is to better understand the highly non-linear behaviour of two-phase flows (liquid-vapour). The establishment of bifurcation diagrams for simple academic configurations (flows in a vertical cylindrical tube, heated at its wall) is therefore an important first step in the implementation of our numerical approach. To achieve this objective, we have developed a methodological approach, which we believe is quite original in this field, since it is based on a semi-analytical method of solving the simplified equations of the problem (one-dimensional drift model). The implemented continuation method is based on the numerical asymptotic method, which allows us to calculate with good numerical efficiency (good accuracy and low computation times) the stationary solutions of the base flow over the entire range of interest (liquid single phase, liquid-vapour two phase, steam single phase). When the branch of stationary solutions is calculated in this way, we then carry out a linear stability analysis, the only part in which any linearization step is introduced. The model is then used to conduct parametric studies to highlight the most influential parameters on flow stability, facilitating the physical understanding of the mechanisms at play
Guimbard, David. "L'instabilité elliptique en milieu stratifié tournant." Phd thesis, Université du Sud Toulon Var, 2008. http://tel.archives-ouvertes.fr/tel-00436895.
Arbie, Muhammad Rizqie. "Stability of self-propelled body wake." Thesis, Aix-Marseille, 2016. http://www.theses.fr/2016AIXM4754/document.
The caudal fin of swimming animals can be modelled as a thrust-producing flapping foil. When considered alone, such a foil produces on average a jet wake with a positive net momentum. It has been argued that the instability characteristics of these averaged wakes are linked to the propulsion efficiency of swimming animals. Here, we reconsider this question by taking into account both the thrust and the drag exerted on a self-propelled swimming body. To do so, we study the stability of a family of momentumless wakes, constructed as the Oseen approximation of a force doublet moving at constant velocity. By performing a local stability analysis, we first show that these wakes undergo a transition from absolute to convective instability. Then, using the time-stepper approach by integrating the linearised Navier-Stokes system, we investigate the global stability and reveal the influence of a non-parallel base flow as well as the role of the locally absolutely unstable upstream region in the wake. Finally, to complete the global scenario, we address the nonlinear evolution of the wake disturbance. These results are then discussed in the context of aquatic locomotion. According to the present stability results, the momentumless wake of aquatic animals is generally stable, whereas the corresponding thrust part is unstable. It is therefore essential to consider all forces exerted on a self-propelled animal when discussing its wake stability and its propulsion efficiency
Bonne, Nicolas. "Stabilité de l'intéraction onde de choc/ couche limite laminaire." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLX025/document.
The shock wave boundary layer (BL) interaction phenomenon is ubiquitous in aerodynamic. In general this interaction generates some low frequency oscillations which can be disastrous for the machines. The typical example is the buffet phenomenon on an airfoil in transonic conditions. Buffet is dangerous since its low frequency can excite the structural modes of the airfoil and break it. The phenomenology has been wildly studied when the incoming BL is turbulent. These studies have derived several credible scenarii and efficient methodologies to capture its dynamic, especially the stability analysis tools on an averaged turbulent flow (RANS). However laminar technologies, the use of laminar BL to reduce the fuel consumption of planes, represent a new scientific challenge on this problematic. In fact, the physic of the interaction is importantly impacted by the laminar nature of the BL especially because of its weak resilience to an adversed pressure gradient and of the transition to turbulence.The thesis deals with the methodologies for the stability analysis on a RANS base flow in the case of a laminar BL. The originality and the contribution of this work have been to take into account a transition criteria in the linearised dynamic on a RANS base flow. The model used (RANS and transition) have then been linearized in order to make a stability analysis which take into account all the aerodynamic varaibles. The validation of this methodology has been made by comparison to expermient and simulation (LES) on two configurations of application. The first one is a weak reflected shock wave on a flat plate. The second one is the strong shock around an airfoil in a transonic regime. In both cases the incoming BL is laminar.Stability and resolvent analysis have been made. These approches have been able to caratirized the ocillator/noise amplifier behavior of the flow and to enabled a physical analysis of the unsteadinesses observed in the experiments.The case of the reflected shock wave is caracterized by three frequencies. The stability analysis shows that they don't correspond to globally unstable modes but to a noise amplifier behavior of the flow. The resolvent analysis identifies the three frequencies. The analysis of the optimal response, coupled with a local stability analysis, enables to proposed physical scenarii of these dynamics.In the case of the strong shock on an airfoil in transonic regime, the flow is globally unstable. Two unstable modes have been identified. The first one, at low frequency, correspond to the buffet phenomenon also observed in the turbulent case. The second one appears at higher frequency and correspond to the oscillation of the separation bubble formed at the feet of the shock.More generally, this thesis suggests that some dynamics of these two interactions result from the same mecanism linked to the breathing motion of the laminar separation bubble