1,721,122 research outputs found
Progress in Hybrid RANS-LES Modelling
No full textThis book reports on the latest developments in computational fluid dynamics and turbulence modeling, with a special emphasis on hybrid RANS-LES methods and their industrial applications. It gathers the proceedings of the Sixth Symposium on Hybrid RANS-LES Methods, held on September 26-28 in Strasbourg, France. The different chapters covers a wealth of topics such as flow control, aero-acoustics, aero-elasticity and CFD-based multidisciplinary optimization. Further topics include wall-modelled Large Eddy Simulation (WMLES), embedded LES, Lattice-Bolzman methods, turbulence-resolving applications and comparisons between LES, hybrid RANS-LES and URANS methods. The book addresses academic researchers, graduate students, industrial engineers, as well as industrial R&D managers and consultants dealing with turbulence modelling, simulation and measurement, and with multidisciplinary applications of computational fluid dynamics
Modelling Laminar Separation Bubbles at Low Reynolds Number
Full text linkLaminar separation bubbles is one of the main critical aspects of flows at low Reynolds number in the range 104 − 105. The flow separates in the laminar regime and the turbulence developing inside the re-circulation region enhances the momentum transport and the flow can re-attach. Models based on the Reynolds Averaged Navier Stokes equations suffer of two main issues. The determination of the transition onset and the level of the pressure recovery downstream the reattachment of the flow. This paper reports on the activities performed in the framework of a project set-up by a GARTEUR action group. Common test-cases have been performed by several institutions. The low Reynolds number flow around the SD 7003, EPPLER 387, and NACA 0015 airfoils are analyzed. The results are compared to experimental data and large eddy simulations available in literature. The comparison of different methods and models has allowed to individuate advice for the numerical simulation of the laminar separation bubbles
Progress in Hybrid RANS-LES Modelling
No full textThis book gathers the proceedings of the Seventh Symposium on Hybrid RANS-LES Methods, which was held on September 17-19 in Berlin, Germany. The different chapters, written by leading experts, reports on the most recent developments in flow physics modelling, and gives a special emphasis to industrially relevant applications of hybrid RANS-LES methods and other turbulence-resolving modelling approaches. . The book addresses academic researchers, graduate students, industrial engineers, as well as industrial R&D managers and consultants dealing with turbulence modelling, simulation and measurement, and with multidisciplinary applications of computational fluid dynamics (CFD), such as flow control, aero-acoustics, aero-elasticity and CFD-based multidisciplinary optimization. It discusses in particular advanced hybrid RANS-LES methods. Further topics include wall-modelled Large Eddy Simulation (WMLES) methods, embedded LES, Lattice-Bolzman methods and turbulence-resolving applications and a comparison of the LES methods with both hybrid RANS-LES and URANS methods. Overall, the book provides readers with a snapshot on the state-of-the-art in CFD and turbulence modelling, with a special focus to hybrid RANS-LES methods and their industrial applications
NSIBM : a parallel Navier-Stokes solver with automatic mesh refinement based on immersed boundary method
No full textCette thèse, intitulée NSIBM : un solveur parallèle de Navier-Stokes avec raffinement automatique basé sur la méthode des frontières immergées, a été effectuée au sein du laboratoire iCube, département de mécanique, à Strasbourg, dans le quartier de l'Orangerie, sous la direction du professeur Yannick Hoarau. L'essentiel du travail effectué consiste en le développement d'un programme capable de résoudre numériquement l'équation de Navier-Stokes qui régit des fluides en mouvement. Une attention particulière a été portée à la production de maillages conformes aux géométries proposées et à leur génération. Les moyens mis en œuvre ici pour gérer l'éternel problème de la finesse du maillage opposée au trop grand nombre de cellules sont multiples : le raffinement, la parallélisation et les frontières immergées. Dans un premier temps, j'ai conçu un générateur de maillage en deux et trois dimensions en y intégrant la possibilité de diviser des cellules, et cela de manière automatique, par des critères géométriques, numériques ou physiques. Il permet également de supprimer des cellules, de manière à ne pas mailler le vide ou les parties solides de la géométrie.Dans un deuxième temps, j'ai rendu ce code parallèle en lui donnant la capacité d'utiliser plusieurs processeurs, afin de calculer plus vite et donc d'utiliser davantage de mailles. Cette étape fait appel à deux technologies : Metis, qui partage équitablement les mailles sur le nombre choisi de processeurs et OpenMPI, qui est l'interface de communication entre ces processeurs. Enfin, la méthode des frontières immergées a été introduite au code pour gérer les bords non verticaux ou horizontaux dans un maillage cartésien, c'est-à-dire formé de rectangles ou de pavés droits. Elle consiste à donner un caractère hybride à une cellule traversée par une frontière par l'introduction d'un terme numérique de forçage simulant la présence de la paroi.Ce travail de développement a ensuite été mis à l'épreuve et validé dans une série de cas tests en deux comme en trois dimensions. Des exemples de maillages complexes générés facilement sont donnés.This thesis, entitled NSIBM: a parallel Navier-Stokes solver with automatic mesh refinement based on immersed boundary method, has been conducted within the iCube laboratory dedicated to mechanics and located in Strasbourg. It has been supervised by Professor Yannick Hoarau. This work mainly deals with coding a program able to solve the Navier-Stokes equations that governs moving fluids, in a numerical way. Particular attention was paid to the production of meshes that suit given geometries and their generation.The means used here to handle the eternal problem of the fineness of the mesh opposed to too many cells are several~:refinement, parallelization and the immersed boundary method.Initially, I designed a two and three-dimensional mesh generator that includes the possibility of dividing cells,in an automatic way, by geometrical, numerical or physical criteria. It also allows to remove cells, where there is no point keeping it. Secondly, I parallelized the program by giving him the ability to use multiple processors to calculate faster and therefore use bigger meshes.This step uses two available libraries~: \textit{Metis}, which gives a optimal mesh partition, and \textit{openMPI}, which deals with communication between nodes. Finally, the immersed boundary method has been implemented to handle non-vertical or non-horizontal edges in a cartesian grid. Its principle is to confer a hybrid status to a cell which is crossed by an edge by adding a numerical force term simulating the presence of the boundary. This development work was then tested and validated in a serie of test cases in two and three dimensions. Examples of complex meshes easily generated are given
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Mesh refinement adapted to the Chimera method
No full textL’essentiel du travail effectué consiste en l’intégration au sein du solveur NSMB d’une méthode de raffinement de maillage à partir d’ajout de blocs chimère. Dans un premier temps j’ai du adapter de la structure de données du code existant afin d’ajouter la modularité nécessaire à l’intégration de la méthode. Dans un second temps j’ai implanté la création de blocs de maillages chimères raffinés au cours de l’exécution du calcul. Le raffinement est modulable en fonction de paramètres d’entrées utilisateur. L’ajout de nouveaux blocs de maillages chimère peut être réalisé de manière séquentielle ou parallèle grâce à la parallélisation openMPI. Les maillages raffinés peuvent permettre d’affiner une partie de l’écoulement ou s’adapter à une géométrie plus complexe. Ce travail de développement a ensuite été éprouvé et validé sur différentes configurations planes.The main part of this work consists in the integration into the solver NSMB of a mesh refinement method based on the addition of chimera blocks. First, i had to adapt the data structure of the existing code in order to add the necessary modularity to integrate the method. In a second step i implemented the creation of refined chimera mesh blocks during the execution of the calculation. The refinement can be adjusted according to user input parameters. The addition of new chimera mesh blocks can be done sequentially or in parallel thanks to the parallelization openMPI. Refined mesh sizes can be used to refine part of the flow or to adapt to more complex geometry. This development work was then tested and validated on different flat configurations
Numerical and experimental studies of burried geothermal rainwater tanks for passive cooling of buildings
No full textFace au changement climatique, caractérisé notamment par des périodes caniculaires plus longues et intenses, mais aussi par une disponibilité irrégulière de la ressource en eau, il est nécessaire d’apporter des solutions sobres en consommations énergétiques pour renforcer la résilience des bâtiments. Les cuves de récupération d’eaux de pluie enterrées sont des systèmes de plus en plus exploités qui permettent la gestion et le stockage de l’eau. En y immergeant un échangeur de chaleur, il est possible de profiter de l’effet géothermique de l’eau et du sol environnant pour rafraîchir les bâtiments de façon passive. Ce travail de recherche vise à étudier les performances et la faisabilité de ces systèmes hybrides. Un modèle numérique a été développé et validé grâce aux données recueillies par l’instrumentation de prototypes à l’échelle 1 pendant près de trois ans. L’exploitation du modèle a mis en évidence les facteurs influents du système. Des règles de prédimensionnement pour évaluer la quantité d’énergie potentiellement récupérable ont ensuite été établies. Le modèle du système a ensuite été intégré dans un outil de simulation énergétique du bâtiment pour évaluer les gains en termes de confort des occupants.In the face of climate change, characterized by longer and more intense heatwaves, as well as irregular availability of water resources, it is essential to provide energy-efficient solutions to strengthen the resilience of buildings. Underground rainwater tanks are increasingly being exploited as systems for managing and storing water. By immersing a heat exchanger in the tank, it is possible to harness the geothermal effect of the water and surrounding soil to passively cool buildings. This research aims to study the performance and feasibility of these hybrid systems. A numerical model was developed and validated using data collected from the monitoring of full-scale prototypes over a period of nearly three years. The model was used to highlight the key factors influencing the system. The model was used to identify the factors influencing the system. Presizing rules were then established to assess the amount of energy that could potentially be recovered. The system model was then integrated into a building energy simulation tool to assess the gains in terms of occupant comfort
Modélisation des écoulements diphasiques pour la simulation des accidents de perte de réfrigérant dans les réacteurs nucléaires
No full textCette thèse étudie la dynamique des écoulements gaz-liquide, en se concentrant spécifiquement sur les accidents de perte de réfrigérant dans les réacteurs à eau pressurisée. Ces accidents représentent des défis de sécurité majeurs, car ils entraînent une perte rapide de réfrigérant, pouvant potentiellement causer des accidents graves du réacteur. L’étude met en avant le rôle crucial des états métastables, qui surviennent lorsque l’eau, généralement maintenue à haute pression pour rester sous forme liquide, subit une dépressurisation rapide.Pour aborder ces phénomènes complexes, cette recherche implémente et valide différents modèles d’écoulement diphasique dans un solveur numérique personnalisé. Deux modèles spécifiques sont examinés : un modèle à six équations intégrant un équilibre de vitesse relâché et un modèle à quatre équations basé sur des hypothèses d’équilibre cinétique, mécanique et thermique. De plus, le modèle à six équations avec une méthode de relaxation à taux arbitraire est étudié pour mettre en évidence le transfert de masse non instantané, qui est crucial pour prédire avec précision l’état métastable lors des transitions de phase. Les modèles sont validés à l’aide d’une gamme de cas tests, comprenant à la fois des cas standard trouvés dans la littérature et des cas spécifiques liés aux accidents de perte de réfrigérant.This thesis investigates the dynamics of gas-liquid flows, focusing specifically on Loss of Coolant Accidents (LOCAs) in Pressurized Water Reactors (PWRs). LOCAs present significant safety challenges, as they lead to rapid coolant loss, potentially causing severe reactor accidents. The study emphasizes the critical role of metastable states, which occur when water, typically maintained at high pressure to remain in liquid form, experiences rapid depressurization.To address these complex phenomena, this research implements and validates different two-phase flow models within a custom-built numerical solver. Two specific models are examined: a six-equation model incorporating a relaxed velocity equilibrium and a four-equation model based on kinetic, mechanical, and thermal equilibrium assumptions. Additionally, the six-equation model with an arbitrary-rate relaxation methodis investigated to emphasize the non-instantaneous mass transfer, which is critical for accurately predicting the metastable state during phase transitions. The models are validated using a range of test cases, including both standard cases found in the literature and specific test cases related to loss-of-coolant accidents
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
- …
