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Gnanga, Honoré. "Analyse numérique d'écoulements turbulents anisotropes à l'aide de modèles non-linéaires de turbulence". Thesis, Lille 1, 2008. http://www.theses.fr/2008LIL10057/document.
Pełny tekst źródłaThe aim of this work is to predict numerically the three - dimensional turbulent flows of a Newtonian and incompressible fluid using nonlinear stress - strain models. The Explicit Algebraic Stress Models (EASM), which can take into account the anisotropy of turbulence with less CPU time and computer memory than RSM or approach DNS and LES, are adopted as a turbulence model. Among these models, we choosed Shih et al. (1995) and Craft et a1.(1996) models. These models are studied using a priori and a posteriori investigations. The study is carried out in square duct. This configuration presents a secondary flow and a significant anisotropy between the Reynolds stress components. To predict the significant viscous effects due to the wall and the corner, the damping functions are implemented. The maps of the second and third invariants in the plan of Lumley exhibited show the various states of turbulence and a good anisotropy level obtained. The mean flow field and the turbulent statistics are compared with existing numerical and experimental data for square and rectangular duct flow. The model performance is shown to be satisfactory. ln particular, the mean secondary velocity vectors and stream wise vorticity are well predicted
Campana, Lorenzo. "Modélisation stochastique de particules non sphériques en turbulence". Thesis, Université Côte d'Azur, 2022. http://www.theses.fr/2022COAZ4019.
Pełny tekst źródłaThe motion of small non- spherical particles suspended in a turbulent flow is relevant for a large variety of natural and industrial applications such as aerosol dynamics in respiration, red blood cells motion, plankton dynamics, ice in clouds, combustion, to name a few. Anisotropic particles react on turbulent flows in complex ways, which depend on a wide range of parameters (shape, inertia, fluid shear). Inertia-free particles, with size smaller than the Kolmogorov length, follow the fluid motion with an orientation generally defined by the local turbulent velocity gradient. Therefore, this thesis is focused on the dynamics of these objects in turbulence exploiting stochastic Lagrangian methods. The development of a model that can be used as predictive tool in industrial computational fluid dynamics (CFD) is highly valuable for practical applications in engineering. Models that reach an acceptable compromise between simplicity and accuracy are needed for progressing in the field of medical, environmental and industrial processes. The formulation of a stochastic orientation model is studied in two-dimensional turbulent flow with homogeneous shear, where results are compared with direct numerical simulations (DNS). Finding analytical results, scrutinising the effect of the anisotropies when they are included in the model, and extending the notion of rotational dynamics in the stochastic framework, are subjects addressed in our work. Analytical results give a reasonable qualitative response, even if the diffusion model is not designed to reproduce the non-Gaussian features of the DNS experiments. The extension to the three-dimensional case showed that the implementation of efficient numerical schemes in 3D models is far from straightforward. The introduction of a numerical scheme with the capability to preserve the dynamics at reasonable computational costs has been devised and the convergence analysed. A scheme of splitting decomposition of the stochastic differential equations (SDE) has been developed to overcome the typical instability problems of the Euler–Maruyama method, obtaining a mean-square convergence of order 1/2 and a weakly convergence of order 1, as expected. Finally, model and numerical scheme have been implemented in an industrial CFD code (Code_Saturne) and used to study the orientational and rotational behaviour of anisotropic inertia-free particles in an applicative prototype of inhomogeneous turbulence, i.e. a turbulent channel flow. This real application has faced two issues of the modelling: the numerical implementation in an industrial code, and whether and to which extent the model is able to reproduce the DNS experiments. The stochastic Lagrangian model for the orientation in the CFD code reproduces with some limits the orientation and rotation statistics of the DNS. The results of this study allows to predict the orientation and rotation of aspherical particles, giving new insight into the prediction of large scale motions both, in two-dimensional space, of interest for geophysical flows, and in three-dimensional industrial applications
El, Amraoui Rachid. "Etude de modèles de turbulence pour application aux écoulements à masse volumique variable avec et sans combustion". Rouen, 1993. http://www.theses.fr/1993ROUES029.
Pełny tekst źródłaAupoix, Bertrand. "Application de modèles dans l'espace spectral à d'autres niveaux de fermeture en turbulence homogène". Lyon 1, 1987. http://www.theses.fr/1987LYO10044.
Pełny tekst źródłaBentaleb, Yacine. "Modélisation et simulation numérique de la turbulence par des approches statistiques bas-Reynolds et hybride Rans/Les". Pau, 2007. http://www.theses.fr/2007PAUU3028.
Pełny tekst źródłaThe work presented in this thesis concerns the turbulence modelling and numerical prediction of high Reynolds number flows by performing the integration of the governing equations up to the wall. The main objective is to reconsider existing turbulence models, using recent numerical tools, in order to obtain more accurate results on unstructured meshes, particularly in the near-wall region. In the perspective of hybridisation with a LES approach, we study first a linear low-Reynolds k-ε model. Then, we compare it with a cubic eddy-viscosity model, which allows accounting for anisotropy effect. The compressible Navier-Stokes solver uses an implicit unsteady mixed finite element/volume method. In two steady flow cases (turbulent channel and backward-facing step flows), we obtain satisfactory results with the linear model, whereas the nonlinear extension shows a substantial sensitivity to the eddy-viscosity parameter Cµ. In the unsteady flow (circular cylinder), the nonlinear model shows higher performances. Next, we propose a novel combination of RANS and LES approaches. The basic idea is to solve the averaged flow field by the RANS equations, and to correct it by adding the remaining resolved fluctuations with VMS (Variational Multi-Scale) approach of LES. The correction term is damped by a smooth blending function across the computational domain. The obtained model is applied to a three-dimensional flow past a circular cylinder with turbulent separation. We analyse the different flow regions and the flow topology. The statistics computed from numerical simulations are consistent with the experimental data and the hybrid approach of DES-type
Alam, Boulos. "Modélisation numérique de la turbulence et de la dispersion atmosphérique par faibles vents en milieu urbain". Electronic Thesis or Diss., université Paris-Saclay, 2023. https://www.biblio.univ-evry.fr/theses/2023/interne/2023UPAST179.pdf.
Pełny tekst źródłaThis thesis is situated in the context of atmospheric dispersion modeling, particularly in the presence of low winds. Atmospheric pollution sources, often located near the ground and influenced by complex obstacles, generate high concentrations of pollutants nearby, resulting in significant concentration fluctuations. Low winds, typically associated with stable atmospheric conditions, pose a specific challenge in modeling pollutant dispersion, requiring a thorough analysis of meteorological data and adaptation of prediction models. To address this complex challenge, the use of Computational Fluid Dynamics (CFD) is necessary, although further research is needed to validate its effectiveness in the near-field and in the presence of low winds. The Code_Saturne® software (EDF R&D) is selected due to its proven efficiency in simulating atmospheric pollutant dispersion. This thesis is divided into three distinct phases : the first phase focuses on the fundamentals of atmospheric dispersion, exploring the impact of various parameters such as the atmospheric boundary layer structure, atmospheric turbulence, and atmospheric stability. These elements play a crucial role in how pollutants disperse in the air. The second phase details the methodology used in Code_Saturne for conducting simulations, including the turbulence models employed and the criteria for evaluating these models. In addition to traditional isotropic models, this research investigates the use of anisotropic turbulence models to study dispersion in various contexts. The third phase of the thesis concentrates on the evaluation of different turbulence models and velocity-scalar correlations using observations conducted in urban environments under neutral and stable atmospheric conditions. Finally, the last phase of the research explores conditions of low and stable winds, typically characterized by wind speeds below 2 m/s and random wind variations. This phase examines the meandering patterns in pollutant dispersion and assesses the limitations of analytical and CFD models in predicting concentration in such conditions. To this end, a URANS model is developed and evaluated. Ultimately, a segmented Gaussian method is devised to compare the results with CFD predictions and field observations
Loyau, Hugues. "Etude numérique et modélisation algébrique des phénomènes d'anisotropie en turbulence statistique". Rouen, 1996. http://www.theses.fr/1996ROUES067.
Pełny tekst źródłaChang, Ze Zhou. "Etude de collisions interparticulaires en écoulement turbulent isotrope ou anisotrope par une approche lagrangienne à plusieurs trajectoires simultanées". Rouen, 1998. http://www.theses.fr/1998ROUES008.
Pełny tekst źródłaYahyaoui, Omar El. "Évaluation de modèles non-linéaires de turbulence à partir de simulations numériques directes des équations de Navier-Stokes". Lille 1, 2003. https://ori-nuxeo.univ-lille1.fr/nuxeo/site/esupversions/b805d85e-4438-419e-b3c7-3b4549924063.
Pełny tekst źródłaBelme, Anca. "Aérodynamique instationnaire et méthode adjointe". Nice, 2011. http://www.theses.fr/2011NICE4071.
Pełny tekst źródłaIn this thesis, we first focused on error estimates for unsteady problems. We have contributed to both a posteriori and a priori error estimators for unsteady inviscid problems and viscous unsteady problems. For the first one, we have been interested on linearized methods for reducing dissipation errors. Regarding the a priori errors, a new estimator is proposed with application to viscous compressible flows. These a priori estimators have been employed for goal-oriented anisotropic mesh adaptation problems, for both Euler and laminar Navier-Stokes flows, in a joint work with Gamma3 team we have developed a method to derive an optimal mesh to observe/improve a given output functional in an unsteady context. The weights of the interpolation error are adjoint states in this case. A new global fixed-point algorithm is proposed herein order to converge the couple mesh/solution. We have applied this algorithm for blast wave problems and acoustics, for both 2D and 3D cases
Oceni, Abdou Gafari. "Modélisation algébrique explicite à pondération elliptique pour les écoulements turbulents en présence de paroi". Phd thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aéronautique, 2009. http://tel.archives-ouvertes.fr/tel-00413841.
Pełny tekst źródłaLaage, de Meux Benoît de. "Modélisation des écoulements turbulents en rotation et en présence de transferts thermiques par approche hybride RANS/LES zonale". Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2012. https://theses.hal.science/docs/00/74/35/42/PDF/these_de_Laage.pdf.
Pełny tekst źródłaThe numerical simulation of turbulent flows in cooling system of hydrau- lic pumps sealing requires considering large computational domains and long integration times. The zonal hybrid RANS/LES modelling of turbulence could deal with such appli- cations, in order to reproduce the whole thermal and dynamical phenomena of the flow, with a computational cost compatible with industrial studies. This approach aims at pro- perly interfacing a Large Eddy Simulation (LES), which provides an accurate unsteady description of turbulence in some critical regions of the flow, with the statistical RANS approach, less demanding in computational resources, applied in the whole remaining fluid domain in order to take into account the imposed global variations of the flow (cool water injection in hot water, shaft and rotor rotation,. . . ). To this end, a detailed study of tur- bulence models appropriate for rotating flows is presented, following both the RANS and the LES approaches. Numerous turbulence models are compared in the rotating channel flow test case. The zonal coupling at boundary faces using the Synthetic Eddy Method (SEM) is studied and an innovative volumic coupling using a source term on overlapping RANS/LES area, the Anisotropic Linear Forcing, is proposed. For the first time, these two coupling methods are extended to heat transfer. The present zonal hybrid RANS/LES computations of static or rotating channel flows in isothermal or forced convection regimes, show the applicability of such modelling for industrial studies
Andrade, João Rodrigo. "Spectral analysis of the turbulent energy cascade and the development of a novel nonlinear subgrid-scale model for large eddy simulation". Thesis, Lille 1, 2019. http://www.theses.fr/2019LIL1I006/document.
Pełny tekst źródłaThe purpose of the present work is to analyze and to provide an enhancement of the knowledge about the subgrid-scale behavior and to propose novel nonlinear subgrid-scale models for large eddy simulations of turbulent fluid flows. In this way, the present thesis is subdivided into three main parts. The first topic is an analysis of the statistical uncertainties associated with direct numerical simulation data for turbulent channel flow, showing a novel physicallybased quantification of these errors. In this analysis, the mean velocity error is estimated by considering the Reynolds stress tensor, and using the balance of mean force equation. This analysis is performed in order to verify the quality of the statistical data coming from the direct numerical simulation applied in the present work. Secondly, seeking to understand the contained physics in the whole wavenumber spectrum of turbulent flows, an analysis of the spectral turbulent kinetic energy budget in fully developed turbulent plane channel flow is performed. The analysis is focused on the influence of the Reynolds number on the spectral cascade of energy and the corresponding energy cascade in physical space in the presence of inhomogeneity and anisotropy. Finally, a novel nonlinear subgrid-scale model for large eddy simulation based on a set of objective tensors is presented. In the proposed closure model, the modeled subgrid-scale stress tensor is a function of the resolved rate-of-strain tensor and the resolved non-persistence-of-straining tensor, where both are local and objective kinematic entities. The non-persistence-of-straining tensor represents the local ability of the fluid to avoid being persistently stretched. To check the consistency of the proposed model, a priori and a posteriori tests are performed by simulating different wall-bounded turbulent flows. Comparisons with the exact subgrid-scale stress tensor and experimental data revealed that the inclusion of nonlinear terms on the subgrid-scale model can significantly increase the accuracy of the results, showing the great potential of the proposed tensorial base
Bigot, Barbara. "Ondes et turbulence dans les écoulements MHD anisotropes : applications solaires". Paris 11, 2008. http://www.theses.fr/2008PA112072.
Pełny tekst źródłaI present a theoretical, phenomenological and numerical study dedicated to anisotropic astrophysical plasmas. The incompressible magnetohydrodynamic (MHD) fluid approximation, in presence of an ambient magnetic field B0, is used in the regime of turbulence. In order to characterize the transition between strong and weak (or wave) MHD turbulence, my numerical work is focused on the development of anisotropy, its spectral and spatial signatures, as well as its influence on the energetic transfers in freely decaying tri-dimensional MHD flows. This analysis is performed according to the intensity of the applied B0 field. The energetic decay decreasing as the B0 intensity is increasing, new temporal laws are derived for the shear- and pseudo-Alfvén wave energies in the asymptotic limit of wave turbulence (strong B0). These predictions are then tested against direct numerical simulation of the MHD equations and of the wave kinetic equations. Finally, I propose an analytical model of solar coronal heating by Alfvén wave turbulence for strongly anisotropic structures, such as coronal loops or open magnetic field lines. The solar coronal heating rates found are then compared with the observational predictions
Lamriben, Cyril. "Transferts anisotropes d'énergie en turbulence en rotation et excitation de modes d'inertie". Phd thesis, Université Paris Sud - Paris XI, 2012. http://tel.archives-ouvertes.fr/tel-00734192.
Pełny tekst źródłaHe, Jun. "Modélisation des écoulements gaz-solides en régime dilué : influence des collisions entre particules et de l'anisotropie de leur mouvement fluctuant". Compiègne, 1994. http://www.theses.fr/1994COMPD698.
Pełny tekst źródłaPinsonneault, Steve. "Enrichissement chimique du milieu intergalactique par des vents galactiques anisotropes". Thesis, Université Laval, 2012. http://www.theses.ulaval.ca/2012/28775/28775.pdf.
Pełny tekst źródłaGarino, Alain. "Modélisation d'écoulements turbulents anisotropes à l'aide de schémas multiéchelles aux tensions de Reynolds". Aix-Marseille 2, 1988. http://www.theses.fr/1988AIX22082.
Pełny tekst źródłaUgalde-Saldaña, Edgardo. "Modèles dynamiques pour la turbulence locale". Aix-Marseille 1, 1996. http://www.theses.fr/1996AIX11044.
Pełny tekst źródłaBois, Richard. "Adaptation de maillages anisotropes par un estimateur d'erreur hiérarchique". Thesis, Université Laval, 2012. http://www.theses.ulaval.ca/2012/29273/29273.pdf.
Pełny tekst źródłaIn this thesis, we present a new hierarchical error estimator that can be used in a mesh adaptation algorithm to obtain a more accurate approximation to the solution of a partial differential equation. This error estimator has many advantages that other existing error estimators do not have or lack of. For instance, it is, by construction, independant of the differential operator used to model a certain physical phenomena. It is also naturally generalisable to the case of approximations of arbitrary order, and this, without any specific treatment to the underlying theory. Finally, it is efficient, optimal in a sense that will be defined and permits the elements to stretch in a priviledged direction (anisotropy) in order to obtain high accuracy against regularly refined meshes. Many examples are given in the one, two and three dimensional cases. Analytical examples (the solution is known) is given to measure the effiency and precision of the new error estimator. Other examples of mesh adaptation for equations modeling different physical phenomena like the flow of a fluid around a cylinder, unsteady diffusion and contact between deformable elastic bodies are presented. These examples show that the new error estimator can be used for a wide variety of problems.
Ali, Hani. "Étude mathématique de quelques modèles de turbulence". Rennes 1, 2011. http://www.theses.fr/2011REN1S164.
Pełny tekst źródłaIn order to construct suitable weak solutions to the Navier-Stokes equations, we use an α regularization for these equations. The α models were introduced as sub-grid scale models based on the Navier-Stokes-α (LANS-α) model. In this work, we study some of these α regularizations like the Leray-α, the modified Leray-α and the simplified Bardina models. The first part of this work concerns a general Leray-α family with critical regularization under periodic boundary conditions. In this section, we give the optimal value of regularizations needed to ensure global existence and uniqueness for the solution. In addition, we consider the subcritical cases where we focus our study on the Hausdorff dimension of the time singular set. The results interpolate between the result of regularity for critical regularization and the bound for the time singular set dimension of the Navier-Stokes equations proved by Scheffer. In the second part, we consider the Leray-α model of turbulence with more physical boundary conditions the Navier Slip boundary condition. The third part of my work deals with the mathematical analysis of the Turbulent Kinetic Energy (TKE) model of turbulence with unbounded viscosity and nonlinear Navier boundary conditions. The renormalized method of Diperna Lions is used to show the existence of suitable weak solutions to this model
Bouha, Arezki. "Phénoménologie du mélange de scalaire passifs en écoulements isotropes et anisotropes axisymétriques. Interaction mouvement cohérent-turbulence". Rouen, 2016. http://www.theses.fr/2016ROUES058.
Pełny tekst źródłaAnnular jets (hereafter AJ) are widely used in industrial processes. They are known for their ability to mix inlet flow with the ambient on relatively short distances compared to standard jets. The attempt is to assess the turbulent mixing of a passive scalar in AJ flows. The flow is experimentally investigated through simultaneous Hot/Cold wires and PIV/PLIF measurements. It is well recognized that ’bluff-body’-type geometry leads to coherent structures (CS) in the AJ flows. The aim of this research is to understand and quantify the exact influence of Coherent Structures (CS) on small-scale turbulence (Random Scales, RS), in particular for the transfer of a passive scalar fluctuations and kinetic energy at each scale r. Scale-by-scale energy budget equation for the scalar variance is established analytically along the jet axis, based on the self-similarity of the structures functions. We assess the appropriate normalization parameters for the similarity of the scalar structures functions to be valid. Invoking the triple decomposition, the contribution of CS (based on the specific Strouhal of the CS) and RS are considered separately, for either the instantaneous signal, or the one-point energy, or the two-point energy. Their interaction is investigated using phase-and time-averaged scale-by-scale energy. It is shown that this interaction becomes more perceptible at low Reynolds numbers. It is most likely that that this departure is more enhanced for small scales of the scalar than those of the kinetic energy
Bennis, Anne-Claire. "Etude de quelques modèles de turbulence pour l'océanographie". Phd thesis, Université Rennes 1, 2008. http://tel.archives-ouvertes.fr/tel-00343712.
Pełny tekst źródłaBennis, Anne-Claire. "Étude de quelques modèles de turbulence pour l'océanographie". Rennes 1, 2008. https://tel.archives-ouvertes.fr/tel-00343712.
Pełny tekst źródłaThe ocean is fundamentaly turbulent and it is essential to modelize the oceanic turbulence in order to improve the understanding of its effects. In this work, turbulence models for the ocean are theoretically and numerically studied. In the first part, we present a brief state of art on URANS (Unsteady Reynolds Averaged Navier-Stokes) and LES (Large Eddy Simulation) turbulence models. In the second part, URANS models are studied. We present a new model whose the existence and uniqueness of the stationary solution we show. Moreover, we show that the new model can be used to study the turbulence induced by the wind stress when we have convective phenomenons which is not true for the Pacanowski-Philander and Gent models. In the third part, LES models are studied. We adapt the "Leray-deconvolution" model to the ocean/atmosphere boundary conditions. We introduce, for this, a continuous deconvolution equation whose its solution as convective velocity in "Leray-deconvolution" model we set. So, we consider a new LES model called deconvolution model. We notably show that the solution of the deconvolution model converges to a dissipative solution of the Navier-Stokes equations. We numerically validate the deconvolution model thanks to DNS (Direct Numerical Simulation) results for 2D cases with and without bathymetry
Charef, Hamid. "Modèles macroscopiques de conduction et d’élasticité linéarisée pour des milieux fortement hétérogènes et anisotropes". Thesis, Toulon, 2012. http://www.theses.fr/2012TOUL0014/document.
Pełny tekst źródłaIn this thesis we study some macroscopic models for drivers or elastic media highly heterogeneous and anisotropic obtained by homogenization. We consider the case of periodic homogenization. In particular the system of linearized elasticity modeling small deformations of a fiber material, we study the effect of material anisotropy on the macroscopic model and show that the combined effect of the boundary conditions and the anisotropy of the fiber system modeling movement at the macroscopic scale involves non-standard terms. We consider several scalings and two geometric situations: in the first radius of cylindrical fibers is of the same order of magnitude as the size of the middle period and in the second the radius is small compared to the period. The results obtained in both cases, independent of symmetry assumptions on the material used to find the results already known in the case of isotropic materials
Charef, Hamid. "Modèles macroscopiques de conduction et d’élasticité linéarisée pour des milieux fortement hétérogènes et anisotropes". Electronic Thesis or Diss., Toulon, 2012. http://www.theses.fr/2012TOUL0014.
Pełny tekst źródłaIn this thesis we study some macroscopic models for drivers or elastic media highly heterogeneous and anisotropic obtained by homogenization. We consider the case of periodic homogenization. In particular the system of linearized elasticity modeling small deformations of a fiber material, we study the effect of material anisotropy on the macroscopic model and show that the combined effect of the boundary conditions and the anisotropy of the fiber system modeling movement at the macroscopic scale involves non-standard terms. We consider several scalings and two geometric situations: in the first radius of cylindrical fibers is of the same order of magnitude as the size of the middle period and in the second the radius is small compared to the period. The results obtained in both cases, independent of symmetry assumptions on the material used to find the results already known in the case of isotropic materials
Kessar, Mouloud. "Simulation numérique directe de la turbulence hélicitaire maximale et modèles LES de la turbulence magnétohydrodynamique". Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAI042/document.
Pełny tekst źródłaHomogeneous and isotropic turbulence was first formalized by Kolmogorov (1941), through dimensional analysis. He managed to show that the spectral density of kinetic energy, $E(k)$, was following a $k^{-5/3}$ law. This behaviour is known as Kolmogorov's cascade. For many geophysical and astrophysical flow, kinetic helicity plays an important role. For instance, Parker (1955) showed that for conductive fluids such as Sun, kinetic helicity could contribute to amplify the magnetic field. Brissaud {it et al} (1973) tried to show that kinetic helicity could have an influence on the spectral density of kinetic energy. Through dimensional analysis they suggested the existence of a cascade for which the kinetic energy spectra would follow a $k^{-7/3}$ law. In the first part of this thesis we will confirm thanks to Direct Numerical Simulations (DNS) the existence of such an asymptotic limit in $k^{-7/3}$. We will also use helical decomposition to perform a deep analysis of the physics encountered within such flows. In several geophysical and astrophysical fluids, turbulence is very strong, and involves a large range of scales. Despite the strong development of computational resources the last few decades, it remains impossible to simulate this range of scales for realistic configurations. One solution is known as Large Eddy Simulations (LES). While a LES is performed, only the large scales of the flow are resolved, and the interactions between large and small scales are modeled. Several turbulence models have been developed for LES of turbulence. Nevertheless, the limitations of these models are not always well known for magnetohydrodynamic (MHD) turbulence, i.e for conductive fluids that can be encoutered in geophysics and astrophysics. In the second part of this thesis we will evaluate the functional performances (see Sagaut (2002)) of these models for several flow configurations involving turbulent dynamo action, i.e when a magnetic field is amplified though the action of a turbulent conductive fluid. In particular we will study the capabilities of LES models to reproduce energy exchanges between large and small scales. In order to do so, we will perform several DNS, for both non-helical flows (i.e leading to small scale dynamo) and helical flows (i.e leading to large scale dynamo). Thanks to a filtering operation we will compute the exact subgrid-scale transfers and compare them to the predictions given by several models. Finally we will achieve LES using subgrid-scale models and we will compare them to filtered DNS
Honnert, Rachel. "Quelle turbulence dans les modèles atmosphériques à l'échelle kilométrique ?" Thesis, Toulouse, INPT, 2012. http://www.theses.fr/2012INPT0119/document.
Pełny tekst źródłaThe turbulence is well-represented on grid coarser than 2 km. Indeed, in meso-scale models, the turbulence is entirely sub-grid. The turbulence is also well-represented at very high resolution (10 to 100 m) by LES models for which turbulence is mainly resolved. However we do not know which part of the turbulence should be resolved and which part of it should be parameterized when a model runs at kilometric scales, the so-called “Terra Incognita“ from Wyngaard (2004). Thanks to increasing computational resources, in a near future, limited area NWP models will reach grid spacings on the order of 1 km or even 500 m. The aim of this study is to develop a parameterization which will provide adequate turbulence to these new-generation, high-resolution models. At first, this study describes a new diagnostic based on LES, which clarifies which part of turbulence should be parameterized at kilometric scales. This reference called “partial similarity function“ is a precious tool to quantify the error made by atmospheric models when running at kilometric scales. These errors are quantified for a state-of-the-art meso-scale model (Méso-NH) with several turbulence mixing options : different mixing lengths, different dimensionalities, a K-gradient scheme or an EDMF approach (K-gradient with a mass-flux scheme). K-gradient turbulence schemes are unable to reproduce the counter-gradient zone. In the grey-zone, this characteristic has a disastrous effect. As the instability is too large, the boundary layer is mixed by the dynamic of the model and the resolved mixing is too strong. The counter-gradient zone can be reproduced by adding a mass-flux scheme to the K-gradient turbulence scheme (Pergaud et al. (2009)). However the mass-flux scheme in its original form only produces wholly subgrid thermals at a grid size for which boundary-layer thermals should be partly resolved. In this case, the subgrid mixing is too strong. So the question arises as what is a subgrid thermal in the “grey zone“, when the mesh contains one thermal at the most and a part of the thermal has to be resolved by the advection scheme of the model. A conditional sampling is defined in order to detect the subgrid part of the thermals. It allows to determine the characteristics of the subgrid thermals in the “grey zone“ and to find out which assumptions of the mass-flux schemes are not verified. In the light of this study, the mass-flux scheme equations are established by taking the thermal fraction and the resolved vertical velocity into account. Finally, the system of equations is closed. The new parameterization is valid in the grey zone
Fortin, Pierre Yves. "Modèle vectoriel d'ondes couplées pour les processus non linéaires d'interaction photonique dans les milieux anisotropes". Thesis, Université Laval, 2010. http://www.theses.ulaval.ca/2010/26920/26920.pdf.
Pełny tekst źródłaMalecki, Pierre. "Étude de modèles de turbulence pour les couches limites tridimensionnelles". Toulouse, ENSAE, 1994. http://www.theses.fr/1994ESAE0013.
Pełny tekst źródłaZille, Pascal. "Modèles multi-échelles pour l'analyse d'images : application à la turbulence". Thesis, Ecully, Ecole centrale de Lyon, 2014. http://www.theses.fr/2014ECDL0029/document.
Pełny tekst źródłaThis thesis is concerned with image analysis within a multi-scale framework. Specific attention is given to fluid images in the presence of turbulence. In a first part, we adress the problem of multi-scale motion estimation from image sequences. Starting from OFCE equation, we derive several image data terms allowing to take into account, while estimating the solution coarse scales, the contribution of the finer scales components usually neglected in classic approaches. The performances of the resulting estimators is demonstrated on both general and fluid images. The second step of this study is concerned with the problem of passive scalar images super- resolution : starting from low resolution input images, we aim at recovering some of the missing high frequencies. We proposed several methods inspired by the LES framework, as well as data assimilation techniques, in order to ensure the solution consistency over time. Such approaches are experimented and compared over various image sequences. Finally, we propose a multi-resolution estimation method simultaneously combining informations from different grid levels
Bian, Nicolas. "Turbulence convective et transport intermittent dans un plasma magnétisé". Aix-Marseille 1, 2002. http://www.theses.fr/2002AIX11012.
Pełny tekst źródłaShurgalina, Ekaterina. "Dynamique de champs de vagues irréguliers en zone côtière". Thesis, Ecole centrale de Marseille, 2015. http://www.theses.fr/2015ECDM0002/document.
Pełny tekst źródłaSurface and internal gravity waves have an important impact on the hydrological regime ofthe coastal zone. Intensive surface waves are particularly interesting to study because they canbe a serious threat to ships, oil platforms, port facilities and tourist areas on the coast; suchwaves hampered the implementation of human activities on the shelf. Nonlinear internal wavesaffect the underwater biosphere and cause sediment transport, they create washouts soil at thebase of platforms and pipelines, affect the propagation of acoustic signals. Freak waves have aparticularly strong impact, and they are studied in this thesis. Therefore, the study of freak waveformation in the coastal zone is relevant and practically significant.The main goal of the thesis is the study of particularities of abnormal wave formation incoastal zones under different assumptions on the water depth and wave field form. In particular,it is demonstrated that the mechanism of dispersion focusing of freak wave formation "works"for waves interacting with a vertical barrier. It is shown that just before the maximum waveformation a freak wave quickly changes its shape from a high ridge to a deep depression.Lifetime of freak wave increases with the growth of number of individual waves in anomalouswave packet, and lifetime of freak wave increases with water depth decreasing.It is demonstrated that pair interaction of unipolar solitons leads to decrease of the thirdand fourth moments of the wave field. It is shown that in the case of heteropolar solitoninteraction the fourth moment increases.The nonlinear dynamics of ensembles of random unipolar solitons in the framework of theKorteweg - de Vries equation and the modified Korteweg - de Vries equation is studied. It isshown that the coefficients of skewness and kurtosis of the soliton gas are reduced as a resultof soliton collision, the distribution function of wave amplitudes are defined. The behavior ofsoliton fields in the framework of these models is qualitatively similar. It is shown that in thesefields the amplitude of the big waves is decreased in average due to multi-soliton interactions.A new braking effect of soliton with a small amplitude and even changing of its direction inmulti-soliton gas as a result of nonlinear interaction with other solitons is found in the frameworkof the modified Korteweg-de Vries equation.It is shown that in heteropolar soliton gas abnormally big waves (freak waves) appear inthe frameworks of the modified Korteweg - de Vries equation. With increasing of soliton gasdensity the probability and intensity of freak waves in such systems increases
Levent, Emmanuel. "Modélisation de faisceaux ultrasonores en milieux anisotropes par décomposition en ondes planes". Compiègne, 1998. http://www.theses.fr/1998COMP1093.
Pełny tekst źródłaArif, Irwandy. "Modélisation des milieux anisotropes et fractures : application aux exploitations ardoisières". Vandoeuvre-les-Nancy, INPL, 1991. http://www.theses.fr/1991INPL126N.
Pełny tekst źródłaGruescu, Ion Cosmin. "Approche par changement d'échelle de l'endommagement des matériaux anisotropes : application aux composites à matrice fragile". Lille 1, 2004. https://pepite-depot.univ-lille.fr/LIBRE/Th_Num/2004/50376-2004-229-230.pdf.
Pełny tekst źródłaDans le cadre des techniques d'homogénéisation basées sur l'utilisation des tenseurs d'Eshelby, on propose ensuite une approche tridimensionnelle des milieux orthotropes contenant des fissures ouvertes modélisées par des cylindres infinis. Les résultats obtenus (tenseur d'Eshelby, tenseur de Hill) sont entièrement nouveaux, notamment dans le cas de fissures arbitrairement orientées par rapport aux axes d'orthotropie. Ils mettent clairement en évidence l'interaction entre l'orientation de la microfissuration et l'orthotropie initiale du matériau. Le dernier volet de l'étude est dédié à la modélisation tridimensionnelle de l'endommagement dans les composites à symétrie orthotrope de révolution, affaiblis par des fissures de forme circulaire ("penny-shaped cracks"). En raison de la difficulté particulière à aborder ce problème 3D dans le cadre des méthodes d'homogénéisation, on propose une approche mixte originale combinant les théorèmes de représentation et des résultats issus de la micromécanique. Les bonnes capacités prédictives du modèle macroscopique d'endommagement ainsi élaboré, de même que les comparaisons avec des données expérimentales, permettent de valider la démarche développée
Baerenzung, Julien. "Modélisation de la turbulence hydrodynamique et magnétohydrodynamique". Nice, 2008. http://www.theses.fr/2008NICE4086.
Pełny tekst źródłaThe work presented in this thesis is principally about the development and the numerical validation of Large Eddy Simulation models (LES) for the hydrodynamic and magnetohydrodynamic (MHD) turbulence. These models are based on the Eddy Damped Quasi Normal Markovian (EDQNM) approximation. In our LES for the Navier-Stokes equations three distinct modifications are implemented. Whereas in current approaches a Kolmogorov-like spectrum is assumed for the subgrid scale, in our method, this spectrum dynamically adapts it-self to the large-scale resolved spectrum. The intrinsic variations of the kinetic helicity spectrum in the non-local transfer are also taken into account through a quantity called “helical eddy diffusivity”. Finally, an original method of velocity field reconstruction allows to include the energetic contribution of the EDQNM emission terms on the resolved scales. In order to test the model, comparisons with Direct Numerical Simulations (DNS) of the Three-dimensional Navier-Stokes equations are performed on fluids driven by an ABC (Beltrami) flow which is a prototype of fully helical flows. The extension of the LES model to the MHD equations is then realized. New eddy damping times are derived and integrated into the model. They allow the simulation of flows at any kinetic and magnetic Reynolds number. The evaluation of this approach is done through the comparison with DNS of freely decaying turbulence for various initial conditions and magnetic Prandtl numbers. The LES MHD model was then applied on the magnetic field generation by dynamo effect. 3 In this parametric study, the influence of the kinetic helicity on the critical threshold of the dynamo instability is analysed through the simulation of three distinct flow presenting different levels of helicity
Kalmthout, Eric van. "Stabilisation et modélisation des flammes turbulentes non-prémélangées : étude théorique et simulation directe". Châtenay-Malabry, Ecole centrale de Paris, 1996. http://www.theses.fr/1996ECAP0528.
Pełny tekst źródłaSuard, Sylvain. "Propagation pulsatoire des flammes de brouillard". Laboratoire de modélisation et simulation numérique en mécanique et génie des procédés (Marseille), 2004. http://www.theses.fr/2004AIX22100.
Pełny tekst źródłaLarcher, Aurélien. "Schémas numériques pour les modèles de turbulence statistiques en un point". Phd thesis, Université de Provence - Aix-Marseille I, 2010. http://tel.archives-ouvertes.fr/tel-00553161.
Pełny tekst źródłaPerrot, Yohann. "Etude, mise au point et validation de modèles de turbulence compressible". Phd thesis, INSA de Rouen, 2006. http://tel.archives-ouvertes.fr/tel-00134262.
Pełny tekst źródłaDebaty, Pascal. "Performances des modèles de turbulence au second ordre appliqués à des configurations axisymétriques simulées par éléments finis". Ecully, Ecole centrale de Lyon, 1994. http://www.theses.fr/1994ECDL0057.
Pełny tekst źródłaUhlmann, Markus. "Etude de modèles de fermeture au second ordre et contribution à la résolution numérique des écoulements turbulents compressibles". Ecully, Ecole centrale de Lyon, 1997. http://www.theses.fr/1997ECDL0012.
Pełny tekst źródłaRisso, Frédéric. "Déformation et rupture d'une bulle dans une turbulence diffusive". Toulouse, INPT, 1994. http://www.theses.fr/1994INPT103H.
Pełny tekst źródłaBerlemont, Alain. "Modélisation eulérienne et lagrangienne de la dispersion particulaire en écoulement turbulent". Rouen, 1987. http://www.theses.fr/1987ROUES028.
Pełny tekst źródłaDelhaye, Benoït. "Etude des flammes de diffusion turbulentes : simulations directes et modélisation". Châtenay-Malabry, Ecole centrale de Paris, 1994. http://www.theses.fr/1994ECAP0396.
Pełny tekst źródłaLessinnes, Thomas. "Magnetohydrodynamic turbulence modelling: application to the dynamo effect". Doctoral thesis, Universite Libre de Bruxelles, 2010. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210042.
Pełny tekst źródłaIl est surprenant qu'alors que les mouvements fluides à l'intérieur de ces objets célestes sont turbulents, les champs magnétiques généré soient de grande échelle spatiale et stables sur de longues périodes de temps. De plus, ils peuvent présenter une dynamique temporelle régulière comme c'est le cas pour le champ magnétique solaire dont la polarité s'inverse tous les onze ans.
Décrire et prédire les mouvements d'un fluide turbulent reste l'un des problèmes les plus difficiles de la mécanique classique.
%La description aussi bien analytique que numérique d'un fluide hautement turbulent est d'une effroyable complexité, si pas tout simplement impraticable. Dans cette situation,
Il est donc utile de construire des modèles aussi proches que possible du système de départ mais de moindre complexité de sorte que des études théoriques et numériques deviennent envisageables.
Deux approches ont été considérées ici. D'une part, nous avons développé des modèles présentant un très petit nombre de degrés de liberté (de l'ordre de la dizaine). Une étude analytique est alors possible. Ces modèles ont une dépendance en les paramètres physiques - nombres de Reynolds cinétique et magnétique et injection d'hélicité - qualitativement similaire aux dynamos célestes et expérimentales.
D'autre part, les modèles en couches permettent de caractériser les transferts d'énergie entre les structures de différentes tailles présentes au sein du champ de vitesse. Nous avons développé un nouveau formalisme qui permet d'étudier aussi les échanges avec le champ magnétique.
De plus, nous proposons une étude de la MHD dans le cadre de la décomposition hélicoïdale des champs solénoïdaux - une idée similaire à la décomposition de la lumière en composantes polarisées et que nous sommes les premiers à appliquer à la MHD. Nous avons montré comment exploiter cette approche pour déduire systématiquement des modèles simplifiés de la MHD. En particulier, nos méthodes multiplient le nombre de situations descriptibles par les modèles en couche comme par exemple le problème anisotrope de la turbulence en rotation. Elles permettent aussi de construire des modèles à basse dimension en calquant les résultats de simulations numériques directes. Ces modèles peuvent alors être étudiés à moindre coûts.
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Magnetohydrodynamics (MHD) is both the science and the formalism that describe the motion of an electro-conducting fluid. Such motion may yield the dynamo effect consisting in the spontaneous generation of a large scale stationary magnetic field. This phenomenon is most likely the reason behind the existence of planetary, stellar and galactic magnetic fields.
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Doctorat en Sciences
info:eu-repo/semantics/nonPublished
Bel, Fdhila R'bei. "Analyse expérimentale et modélisation d'un écoulement vertical à bulles dans un élargissement brusque". Toulouse, INPT, 1991. http://www.theses.fr/1991INPT090H.
Pełny tekst źródłaGilson, Jean-Louis. "Structures singulières et intermittence dans les modèles en couches de la turbulence". Université Joseph Fourier (Grenoble), 1996. http://www.theses.fr/1996GRE10171.
Pełny tekst źródłaDaumont, Isabelle. "Ordre et désordre dans les modèles en couches de la turbulence hydrodynamique". Université Joseph Fourier (Grenoble), 1999. http://www.theses.fr/1999GRE10228.
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