Tesi sul tema "URANS model"

The use of Large Eddy Simulation (LES) for modelling air flows in buildings is a growing area of Computational Fluid Dynamics (CFD). Compared to traditional CFD techniques, LES provides a more detailed approach to modelling turbulence in air. This offers the potential for more accurate modelling of low energy natural ventilation which is notoriously difficult to model using traditional CFD. Currently, very little is known about the performance of LES for modelling natural ventilation, and its computational intensity makes its practical use on desk top computers prohibitive. The objective of this work was to apply LES to a variety of natural ventilation strategies and to compile guidelines for practitioners on its performance, including the trade-off between accuracy and cost.

Cette thèse se situe dans le contexte de la modélisation de la dispersion atmosphérique, en particulier en présence de vents faibles. Les sources de pollution atmosphérique, souvent situées près du sol et influencées par des obstacles complexes, engendrent des concentrations élevées de polluants à proximité, ce qui se traduit par des fluctuations significatives de ces concentrations. Les vents faibles, généralement associés à des conditions atmosphériques stables, posent un défi particulier en matière de modélisation de la dispersion des polluants, nécessitant une analyse approfondie des donnéesmétéorologiques et une adaptation des modèles de prédiction. Afin de relever ce défi complexe, l'utilisation de la Dynamique des Fluides Numérique (CFD) est incontournable, même si des recherches supplémentaires sont nécessaires pour valider son efficacité dans le champ proche des sources et en présence de vents faibles. Le logiciel Code_Saturne® (EDF R&D) est sélectionné en raison de sonefficacité avérée dans la simulation de la dispersion de polluants atmosphériques. Cette thèse se décompose en trois phases distinctes : la première phase se concentre sur les fondements de la dispersion atmosphérique, en explorant l'impact de différents paramètres tels que la structure de la couche limite atmosphérique, la turbulence atmosphérique et la stabilité de l'atmosphère. Ces éléments jouent un rôle crucial dans la manière dont les polluants se dispersent dans l'air. La deuxièmephase détaille la méthodologie utilisée dans Code_Saturne pour effectuer les simulations, notamment les modèles de turbulence utilisés et les critères d'évaluation de ces modèles. En plus des modèles isotropes classiques, cette recherche se penche sur l'utilisation de modèles de turbulence anisotropes pour étudier la dispersion dans divers contextes. La troisième phase de la thèse se concentre sur l'évaluation de différents modèles de turbulence et de corrélations vitesse-scalaire à l'aide d'observations effectuées en milieu urbain dans des conditions atmosphériques neutres et stables.Enfin, la dernière phase de la recherche explore les conditions de vent faible et stable, caractérisées généralement par des vitesses de vent inférieures à 2 m/s et des variations aléatoires du vent. Cette phase examine les méandres dans la dispersion des polluants et évalue les limites des modèles analytiques et CFD pour prédire la concentration dans de telles condi- tions. À cet effet, un modèle URANS est développé et évalué. Enfin, une méthode gaussienne segmentée est élaborée pour comparer les résultats aux prédictions CFD et aux observations sur le terrain
This 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

La simulation numérique des écoulements turbulents cavitants revêt de nombreuses difficultés tant dans la modélisation des phénomènes physiques que dans le développement de méthodes numériques robustes. En effet de tels écoulements sont caractérisés par un changement de phase associé à des gradients de la masse volumique, des variations du nombre de Mach causées par une chute de la vitesse du son, des zones de turbulence diphasique et la présence d'instationnarités.Les travaux de la présente thèse s'inscrivent dans la continuité des études expérimentales et numériques menées au sein du Laboratoire des Ecoulements Géophysiques et Industriels (LEGI),qui visent à améliorer la compréhension et la modélisation d'écoulements cavitants. Les simulations s'appuient sur un code compressible associé à une technique de pré-contionnement bas-Mach qui permet de traiter les zones incompressibles. Les écoulements diphasiques sont reproduits à l'aide d'un modèle de mélange homogène 1-fluide avec discrétisation implicite en pas de temps dual. Enfin la résolution adopte l'approche moyennée RANS qui couple le système des équations de conservation avec des modèles de turbulence du premier ordre basés sur la notion de viscosité turbulente.Dans les zones diphasiques, le calcul des variables thermodynamiques nécessite l'introduction d'équations d'état. La pression au sein du mélange est ainsi reliée aux grandeurs conservatives soit à partir d'une équation d'état de mélange des gaz raides, soit par une relation sinusoïdale incorporant la fraction volumique de vapeur (le taux de vide). La valeur ajoutée de ces travaux de thèse repose sur l'introduction d'une équation de transport pour le calcul du taux de vide. Celle-ci incorpore un terme source dont le transfert de masse entre les phases est fermé grâce à une hypothèse de proportionnalité à la divergence du champ de vitesse. Outre l'amélioration des phénomènes de convection, de dilatation et de collapse, cette équation supplémentaire permet de relaxer l'équilibre thermodynamique local et d'introduire un état métastable pour la phase vapeur.Les simulations 2D et 3D sont réalisées sur des géométries de type Venturi caractérisées par le développement de poches de cavitation partielle instables. L'objectif consiste à reproduire les instationnarités inhérentes à chaque profil telles que la formation d'un jet rentrant liquide à proximité de la paroi ou la production de nuages de vapeur convectés par l'écoulement principal.Les résultats numériques mettent en avant une variation de la fréquence des instationnarités en fonction du calcul de la vitesse du son en zone de mélange. D'autre part, la prise en compte de déséquilibre de la phase vapeur amplifie les phénomènes de propagation d'ondes de pression générées par le collapse des structures cavitantes et participe à la déstabilisation de la poche. Enfin, l'influence de l'équation de transport de taux de vide est analysée en confrontant les résultats des simulations à ceux obtenus ultérieurement à partir d'un modèle à seulement trois équations de conservation
The computation of turbulent cavitating flows involves many difficulties both in modeling the physical phenomena and in the development of robust numerical methods. Indeed such flows are characterized by phase transitions and large density gradients, Mach number variation due to speed of sound decrease, two-phase turbulent areas and unsteadiness.This thesis follows experimental and numerical studies led at the Laboratoire des Ecoulements Géophysiques et Industriels which aim to improve the understanding and modeling of cavitating flows. Simulations are based on a compressible code coupled with a pre-conditionning technique which handles low-Mach number areas. The two-phase flows are reproduced using a one-fluid homogeneous model and temporal discretisation is performed using an implicit dual-time stepping method . The resolution is based on the RANS approach that couples conservation equations with firts-order closure models to compute eddy viscosity.In two-phase flows areas, the computation of thermodynamic quantities requires to close the system with equations of state (EOS). Thus, two formulations are investigated to determine the pressure in the mixture. The stiffened gas EOS is written with conservative quantities while a sinusoidal law deduces the pressure from the volume fraction of vapor (the void fraction). The present study improves the homogeneous equilibrium models by including a transport equation for the void ratio. The mass transfer between phases is assumed to be proportional to the divergence of the velocity. In addition to a better modeling of convection, expansion and collapse phenomenon, this added transport equation allows to relax the local thermodynamic equilibrium and to introduce a mestastable state to the vapor phase.2D and 3D simulations are performed on Venturi type geometries characterized by the development of unstable partial cavitation pockets. The goal is to reproduce unsteadiness linked to each profile such as the formation of a re-entrant jet or the quasi-periodic vapor clouds shedding. Numerical results highlight frequency variations of unsteadiness depending on the speed of sound computation. Moreover, the simulation conducted with a relaxed vapor density increase the pressure wave propagation magnitude generated by the collapse of cavitating structures. It contributes to the destabilization of the pocket. Finally, the role of the void ratio equation is analyzed by comparing the simulation results to those obtained subsequently from a model involving only three conservation equations

Cette thèse s’inscrit dans le contexte de la simulation d’efforts et d’écoulement dynamiques autour d’un profil en mouvement complexe dans un écoulement uniforme : la combinaison d’une rotation autour d’un axe distant et d’un tangage classique autour du quart de corde. Elle vise à mettre en place des méthodes de simulation simples de dimensionnement et de prédiction de performance d’une turbine Darrieus à contrôle actif de pas ; elle vise également à proposer une méthode de calcul permettant la simulation de l’écoulement et l’optimisation de ce type de turbine dont les pales ont leur calage qui varie cycliquement. Elle trouve son application dans l’étude et le développement des énergies marines renouvelables, et plus particulièrement des machine d’extraction d’énergie cinétique de courants de marée ou fluvial à axe transverse. L’objectif est de construire des outils de simulation permettant une étude approfondie des possibilités des systèmes à axe transverse avec variation cyclique active de pas. Pour répondre à cela deux stratégies de modélisation ont été suivies. D’une part l’adaptation du pas variable à une méthode énergétique couplée à différents modèles de prédiction des efforts instationnaires sur un profil; et d’autre part une simulation URANS avec maillage tournant/déformant pour prendre en compte cette variation de pas. La variation d’angle de calage a permis d’obtenir me augmentation de performance maximal de 52%. L’essai des différents modèles fluides disponibles a mis en évidence l’efficacité du modèle turbulent. Le modèle de transition, pourtant prometteur et semblant plus adapté aux cas d’application considérés, s’est révélé peu performant, mais aucune investigation supplémentaire n’a été effectuée. La comparaison avec l’expérience dans le cas turbulent avec modèle de turbulence kw - SST s’est révélée encourageante, notamment pour les rapports de vitesse périphériques opérationnels, autour de ʎ = 5. Pour les ʎ plus faibles les résultats sont en moyenne similaires mais le modèle peine à reproduire les variations aux fréquences naturelles du décrochage, dues aux lâchers tourbillonnaires. La continuité de cette étude réside d’une part dans l’étude d’autres lois de calage, et d’autre part dans l’application à un système concret pour pouvoir aboutir à des systèmes transverses plus efficace
This work describes the numerical simulation of an acti4e variable pitch Darrieus turbine with two methods, one of which is derived from momentum theory and ONERA-EDLIN unsteady model, and the other is 0Ff). Though almost no Darrieus turbine produced electrical power from wind since early 90s, a renewed interest arose from the development of water turbines because most drawbacks which prevented this system from becoming a major wind turbine system do not exist in water. For this reason many publications tackling various issues in water crossflow turbines were written in the past few years. Dynamic and static stall characteristics of an airfoil have a very strong influence on the turbine performance. Considering how the vortex method could not predict it accurately, and the complexity of a CFD simulation in an optimisation process, the ONERA-EDLIN model is a very interesting compromise. On top of that, it has the ability to model any special kinematics and not just only pitch; it can predict installed dynamic behavior based on a potential formulation; and it can calculate dynamic stall for the moments, which is interesting in the case of variable pitch. An URANS method was then used, using the solver ANSYS-CFX. The spatial and temporal discretization have been studied to be used in future simulations. Blades’ motion was obtained through mesh deformation for pitch modification, and the main rotation was implemented through global rotation of a circular mesh domain, with general grid interface model at its boundaries. The following turbulence models were used laminar, kw - SST. And Langtry Menter transition model. Five experimental cases were used to assess models’ performance. Comparison was best for kw - SST. The two others predicted early stalls, especially the laminar model. Further simulations, for other conditions and pitch function are needed and are currently being carried out. Agreement with experimental data was found to be fairly good, event though discrepancies exist in some specific cases. Agreement level could not be related to a particular operational condition. Variable pitch was implemented for a tip speed ratio of 5, aiming at performance improvement primarily. Sinusoidal functions of different orders were tested. One of them obtained a performance increase of 52%. For this regime optimal pitch variation seems to require a very slight recirculation and an incidence decrease on upwind section, and an incidence increase on downwind section. The flow deceleration through turbine was found to be a primary factor in function performance evaluation. Finally torque required to set blades into motion around their quarter chord was compared with power coefficient. Its influence was found to be close to 0, or even positive

Ce manuscrit présente une étude numérique des instabilités aérodynamiques dans le compresseur centrifuge Turbocel, actuellement en essais au LMFA. L’étude vise à mieux comprendre les mécanismes des instabilités tournantes et de la restabilisation à bas débit observées dans le compresseur à régime partiel. L’étude est restreinte au rouet seul sans prendre en compte les autres composants de l’étage (Roue Directrice d’Entrée et diffuseur radial), au moyen de simulations RANS et URANS d'un seul canal (conditions de périodicité aux frontières latérales), à une iso-vitesse à régime partiel. Le code utilisé est le code elsA.Les simulations RANS sont capables de reproduire la forte augmentation du taux de pression du rouet observée à bas débit en essais. D’après les simulations ce comportement résulte d’une forte augmentation du travail transmis par les pales au fluide, coïncidant avec le développement d’un écoulement de retour en tête dans l’inducteur du rouet. Celui-ci s’initie entre le bord d’attaque des pales principales et celui des pales intercalaires, peu avant le pic de la caractéristique de taux de pression du rouet. Il commence par l’inversion du fluide issu du décollement au bord d’attaque des pales principales, après sa remontée jusqu’au carter et son transport par le jeu. La zone de recirculation s’étend lorsque le débit diminue, à la fois vers le moyeu et au-delà des plans d’entrée et de sortie du rouet. Les simulations URANS permettent ensuite de caractériser l’écoulement instationnaire dans le rouet. Bien que restreintes à un unique canal, elles captent l’apparition de structures tournantes dans l’inducteur du rouet, dans la zone à pente positive de la caractéristique de taux de pression issue des calculs RANS. Dans les deux zones à pente négative en revanche les champs restent stationnaires, identiques à la solution RANS. Les structures observées diffèrent du décollement tournant dans son acceptation classique car leur propagation n'est pas due à un effet de répartition du débit d’un canal à l’autre (puisqu’il n’y a qu’un seul canal), mais à la propagation d’une structure tourbillonnaire lâchée par un décollement au bord d’attaque et convectée par l’écoulement de jeu autour de la circonférence. La comparaison avec les résultats expérimentaux montre que ces structures reflètent correctement les cellules observées en essais. Les simulations mono-canal sont en outre validées par une comparaison à une simulation 360° sur un point de fonctionnement pour lequel l’instabilité est pleinement développée. En l’absence de perturbation extérieure et sans les autres composants de l’étage, le résultat du calcul 360° reste identique au calcul mono-canal sur le temps de calcul simulé, avec autant de structures tournantes que d’aubes. Dans les calculs la présence de ces structures tournantes coïncide avec des oscillations de débit importantes dans tout le domaine. Ces oscillations sont attribuées au fait que le nombre de cellules est égal au nombre d’aubes du rouet, de manière similaire à une interaction rotor-stator entre un rotor et un stator de même nombre d’aubes. D'autre part les performances moyennes sont supérieures aux performances obtenues en RANS. Pour tenter de comprendre pourquoi, des résultats illustratifs avec le modèle analytique de pompage et de décollement tournant de Moore-Greitzer sont présentés pour un cas axial. Ce modèle prédit des performances moyennes supérieures à la caractéristique dite sous-jacente du compresseur, ce qui fournit une piste d'explication. Enfin, le modèle de Moore-Greitzer ne capte pas les oscillations de débit observées dans les calculs. Cela suggère qu'il serait intéressant d'intégrer dans le modèle un mécanisme d'interaction rotor-stator entre les cellules de décollement tournant et les aubes
This work presents a numerical investigation of the aerodynamic instabilities occurring in the centrifugal compressor Turbocel, which is currently tested at the LMFA laboratory. The study aims at better understanding the mechanisms of these instabilities, as well as the mechanisms of the restabilization which is observed in the compressor at low mass flow rates and partial regime. The computational domain is restricted to the isolated impeller without the other components of the stage (Inlet Guide Vane and radial diffuser). RANS and URANS simulations are carried out on a single channel of the impeller, with the elsA solver. RANS simulations are able to capture the strong increase in impeller pressure ratio, which is observed in the tests at low flow rate. The simulations show that this increase results from a strong rise in the work transferred to the flow by the blades. This coincides with the initiation of a reversed flow zone in the impeller inducer, in the zone between the main blades and the splitter blades leading edges. The first flow particles to reverse are those coming from a stall zone on the main blade leading edge, after they have gone up to the shroud and have been transported by the tip clearance flow. This recirculation zone extends towards both the hub and the inlet when the mass flow decreases. Secondly, URANS simulations are used to characterize the unsteady flow in the impeller. Albeit restricted to a single channel, these simulations capture the existence of rotating structures in the impeller inducer, at mass flow rates which correspond to the positively-sloped part of the pressure ratio performance curve obtained from RANS results. On the other hand, in the two negatively-sloped parts of the characteristic, the field remains steady and equal to the corresponding RANS solution. The simulated rotating structures differ from classical rotating stall because their propagation is due to a convection effect by the tip flow around the circumference, rather than a mass flow repartition between the different channels. The numerical results are then validated against experimental results, and against a full-annulus simulation as well. Without external perturbation, the results of the full-annulus and isolated channel simulations remain identical during the simulated time. In the computations the presence of such rotating instabilities coincides with mass flow rate oscillations in the whole computational domain. The latter are attributed to a mechanism of rotor-stator interaction between the blades and the stall cells, due to the fact that the number of blades and the number of stall cells are equal. Moreover, when these stall cells are observed in the simulations, the average performance of the impeller is higher than the RANS performance. Illustrative results with the analytical model of Moore-Greitzer for surge and rotating stall are presented in an axial configuration. They also result in a performance which stands above the steady, underlying characteristic of the compressor. Finally, the Moore-Greitzer model proves to be unable to capture the mass flow rate oscillations which are observed in the simulations. As an outlook, this suggests to integrate the rotor-stator interaction between the rotating stall cells and the blades in the analytical model, in order to improve the fast prediction of aerodynamic instabilities in the future

La récupération, grâce aux hydroliennes, de l’énergie cinétique de courants marins et fluviaux constitue une source d’énergie renouvelable considérable et prédictible. La simulation fine, par une description statistique instationnaire de type URANS, de l’écoulement autour d’une hydrolienne isolée à axe vertical, bi-rotor et munie d’un carénage (hydrolienne de type HARVEST) donne accès à une estimation précise de la puissance produite. Cependant, le coût élevé de cette approche URANS la rend inadaptée à la simulation d’un parc de machines. Une analyse de la littérature conduit à retenir un modèle basse-fidélité de type Blade Element Momentum (BEM) pour décrire à moindre coût l’effet du rotor de la turbine sur l’écoulement, dans le contexte d’une description 2D (coupe horizontale). La performance de l’hydrolienne est alors prédite par un calcul RANS incluant des termes sources distribués dans un anneau rotor virtuel et conservant le maillage des parties fixes (carénage). Ces termes sources sont construits grâce à une procédure originale exploitant les conditions locales de l’écoulement en amont des cellules du rotor virtuel et le débit de l’écoulement traversant l’hydrolienne. Les coefficients hydrodynamiques utilisés pour le calcul des termes sources BEM-RANS sont construits une fois pour toutes en exploitant une série de simulations URANS préliminaires ; ils intègrent les effets du carénage et le fonctionnement de chaque rotor à une vitesse de rotation optimale (maximisant la puissance produite) grâce au système de régulation de l’hydrolienne. Le modèle BEM-RANS développé est validé par comparaison avec des simulations URANS de référence : il fournit une estimation fiable de la puissance produite (erreur de quelques % par rapport à l’approche URANS) pour un coût réduit de plusieurs ordres de grandeur. Ce modèle est appliqué à l'analyse de la puissance produite par une rangée d’hydroliennes HARVEST dans un canal pour différents facteurs de blocage et d’espacement latéral ainsi qu’à une ferme marine composée de trois hydroliennes
The capture, thanks to hydrokinetic turbines, of the kinetic energy generated by sea and river currents provides a significant and predictable source of renewable energy. The detailed simulation, using an unsteady statistical description of URANS type, of the flow around an isolated water turbine of HARVEST type (cross flow vertical axis ducted water turbine) provides an accurate estimate of the power output. However, the cost of the URANS approach is much too expensive to be applied to a farm of several turbines. A review of the literature leads to select a low-fidelity model of Blade Element Momentum (BEM) type to describe at a reduced cost the rotor effect on the flow, in a 2D context (horizontal cross-section). The turbine performance is then predicted using a steady RANS simulation including source terms distributed within a virtual rotor ring and preserving the mesh of the turbine fixed parts (duct). These source terms are derived using an original procedure which exploits both the local flow conditions upstream of the virtual rotor cells and the flow rate through the turbine. The hydrodynamic coefficients used to compute the BEM-RANS source terms are built once for all from a series of preliminary URANS simulations; they include the effects of the duct on the flow and the rotor operating at optimal rotational speed (maximizing the power output) thanks to the turbine regulation system. The BEM-RANS model is validated against reference URANS simulations: it provides a reliable prediction for the power output (within a few % of the URANS results) at a computational cost which is lowered by several orders of magnitude. This model is applied to the analysis of the power produced by a row of Vertical Axis Water Turbines in a channel for various values of the blockage ratio and lateral spacing as well as to a 3-machine sea farm

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Many monthly, others weekly play in lottery games ignoring the randomness of the results, believing in luck or strategies that are sold to them in books about games. This monograph aims to show some concepts of probability and statistics unexplored in high school and also day to day situations that contain mathematical concepts of probability more accessible to this level of education showing some mathematical theories applied in practice games. Concepts will be discussed here: some probability distributions, their hope and variance, as well as lottery games and their probability calculations. Probability distributions will be calculated and listed in situations created from models of urns with two colors of balls, always having green as the color whose extraction will be considered successful and the red, whose extraction will be considered a failure. Now extractions with replacement balls will be made and sometimes extractions will be done without replacing them. Also, there is the case where new balls are added to both colors or one color.
Muitos jogam mensalmente, outros semanalmente, em jogos de loterias desconhecendo a aleatoriedade dos seus resultados, acreditando na sorte ou em estratégias que lhes são vendidas em livros sobre jogos. A presente monogra a tem como objetivo mostrar alguns conceitos da Probabilidade e Estatística não explorados no Ensino Médio e também situações do dia a dia que contenham conceitos matemáticos sobre Probabilidade mais acessíveis a este nível de ensino, mostrando um pouco de teorias matemáticas aplicadas na prática de jogos. Serão conceitos aqui discutidos: algumas distribuições de probabilidade, sua esperan ça e variância, além de jogos de loterias e seus cálculos de probabilidade. As distribuições de probabilidade serão enunciadas e calculadas em situações criadas a partir de modelos de urnas com duas cores de bolas, tendo sempre o verde como a cor cuja extração será considerada sucesso e, o vermelho, cuja extração será considerada insucesso. Ora serão feitas extrações com reposições das bolas e ora serão feitas extrações sem a reposição das mesmas. Também, há o caso em que serão adicionadas novas bolas de ambas as cores ou uma cor apenas.

Vegetation is commonly modelled as emergent arrays of rigid, circular cylinders. However, the drag coefficient (CD) of real stems or trunks is closer to that of cylinders with a square cross-section. In this thesis, vegetation has been idealised as square cylinders in laboratory experiments with a turbulence intensity of the order of 10% which is similar to that of typical river flows. These cylinders may also represent other obstacles such as architectural structures. This research has determined CD of an isolated cylinder and cylinder pairs as a function of position as well as the average drag coefficient (CDv) of larger arrays. A strain gauge was used to measure CD whilst CDv was computed with a momentum balance which was validated by strain gauge measurements for a regularly spaced array. The velocity and turbulence intensity surrounding a pair of cylinders arranged one behind the other with respect to mean flow (in tandem) were also measured with an Acoustic Doppler Velocimeter. The isolated cylinder CD was found to be 2.11 in close agreement with other researchers. Under fixed flow conditions CD for a cylinder in a pair was found to be as low as -0.40 and as high as 3.46 depending on their relative positioning. For arrays, CDv was influenced more by the distribution of cylinders than the flow conditions over the range of conditions tested. Mean values of CDv for each array were found to be between 1.52 and 3.06. This new insight therefore suggests that CDv for vegetation in bulk may actually be much higher than the typical value of 1 which is often assumed to apply in practice. If little other information is available, a crude estimate of CDv = 2 would be reasonable for many practical applications. The validity of a 2D realizable k-epsilon turbulence model for predicting the flow around square cylinders was evaluated. The model was successful in predicting CD for an isolated cylinder. In this regard the model performed as well as Large Eddy Simulations by other authors with a significant increase in computational efficiency. However, the numerical model underestimates CD of downstream cylinders in tandem pairs and overestimates velocities in their wake. This suggests it may be necessary to expand the model to three-dimensions when attempting to simulate the flow around two or more bluff obstacles with sharp edges.

This Thesis focuses on the aero-structural simulation and optimization of Darrieus Vertical Axis Wind Turbines. Aerodynamic simulation tools based on different techniques are developed, improved with respect to state-of-art tools, and validated against experimental data. The main considered approaches are based on the Blade Element Momentum, Vortex, two- and three-dimensional Unsteady Reynolds-Averaged Navier-Stokes (URANS) Computational Fluid Dynamics (CFD) models. The models are developed keeping in mind the final coupling with an optimization algorithm, therefore with particular emphasis on the computational effort and simulation robustness. A structural simulation tool based on the Euler-Bernoulli beam theory is also developed and validated against experimental data to perform an efficient aero-structural simulation. The validated models are coupled with an optimization algorithm under certain constraints to create an iterative loop able to produce improved designs. Different applications are considered based on the most relevant research topics and real case scenarios. The particular case of a floating Troposkien Vertical Axis Wind Turbine is analysed by improving the baseline aerodynamic design for the 5 MW rotor developed in the FP7 DeepWind project and evaluating the aerodynamic performance under rotor tilted conditions for the 1 kW demonstrator. The airfoil shape for the blade of a 500 kW H-rotor is also subjected to an optimization analysis with the aim to increase the aerodynamic production, obtaining a new geometry different from literature design. Finally, the aerodynamic and structural simulation tools are coupled to perform a complete aero-structural optimization of blade shape and chord distribution for a 500 kW Troposkien rotor. Both aerodynamic production and rotor stress are targeted in the routine and new blade shapes are found and discussed. The Thesis results, beside the increased performance with respect to the baseline case, prove that iterative loops, obtained by coupling a fast simulation tool and an optimization algorithm, can be adopted in the design and test phase of Darrieus Vertical Axis Wind Turbines, by providing the designer an advanced insight on the aerodynamic and structural phenomena experienced by these complex machines.
Questa Tesi ha come oggetto la simulazione e l'ottimizzazione aero-strutturale di Turbine Eoliche ad Asse Verticale Darrieus. Strumenti per la simulazione aerodinamica basati su differenti tecniche sono sviluppati, migliorati rispetto allo stato dell'arte, e validati rispetto a dati sperimentali. I principali approcci considerati sono basati sui modelli Blade-Element Momentum, Vortex e Unsteady Reynolds-Averaged Navier-Stokes (URANS) Computational Fluid Dynamics (CFD) bi- e tri-dimensionali. I modelli sono sviluppati tenendo a mente l'accoppiamento con un algoritmo di ottimizzazione, quindi con particolare enfasi sullo sforzo computazionale e sulla robustezza della simulazione. Uno strumento di simulazione strutturale basato sulla teoria della trave di Eulero-Bernoulli è, in aggiunta, sviluppato e validato rispetto a dati sperimentali per effettuare una efficiente simulazione aero-strutturale. I modelli validati sono accoppiati con un algoritmo di ottimizzazione per la creazione di un ciclo per l'ottenimento di configurazioni migliorate. Differenti applicazioni sono considerate, basate sui temi di ricerca più rilevati e scenari reali. Il caso particolare di una Turbina Eolica ad Asse Verticale Troposkiana è stato considerato al fine di migliorare la configurazione aerodinamica di base di un rotore da 5 MW sviluppato nell'ambito del progetto FP7 DeepWind e di valutare le prestazioni aerodinamiche del dimostratore da 1 kW con rotore inclinato. La forma del profilo per la pala di un rotore ad H da 500 kW è oggetto anch'essa di un'attività di ottimizzazione finalizzata all'aumento della produzione aerodinamica, ottenendo una nuova geometria completamente differente da quelle disponibili in letterature. Infine, gli strumenti di simulazione aerodinamica e strutturale sono accoppiati per condurre una completa ottimizzazione aero-strutturale della forma della pala e della distribuzione di corda per un rotore Troposkiano da 500 kW. Sia la produzione aerodinamica che lo stato tensionale sono considerati come obiettivi e nuove forme palari sono individuate e discusse. I risultati della Tesi, oltre all'incremento di prestazioni rispetto alle geometrie di base, provano che i cicli iterativi, ottenuti tramite l'accoppiamento di un veloce strumento di simulazione e un algoritmo di ottimizzazione, possono essere adottati nella progettazione e test di Turbine Eoliche ad Asse Verticale Darrieus, fornendo al progettista un avanzato strumento di analisi dei fenomeni aerodinamici e strutturali agenti in queste complesse macchine.

Desde os primórdios da agricultura e pecuária, o homem seleciona indivíduos com características desejáveis para reprodução e aumento da proporção de novos indivíduos com tais qualidades. Com o conhecimento da estrutura de DNA e o advento da engenharia genética, a identificação e caracterização de espécies e indivíduos conta com novas tecnologias para auxiliar no desenvolvimento de novas variedades de plantas e animais para diversos fins. Tais tecnologias envolvem procedimentos bioquímicos e físicos cada vez mais apurados que produzem medidas cada vez mais precisas, um exemplo disso são as técnicas que empregam a espectometria de massa para comparar polimorfismos de base única (SNPs). Nas plantas é comum a ocorrência de poliploidia, que consiste na presença de mais de dois cromossomos num mesmo grupo de homologia. A determinação do nível de ploidia é fundamental para a correta genotipagem e por consequência maior eficiência no estudo e aprimoramento genético de plantas. Neste trabalho caracterizamos o fenômeno da poliploidia com modelos probabilísticos de urnas e bolas, propondo um método eficiente e adequado de simulação, assim como uma técnica simples para inferir níveis de ploidia e classificar amostras bialélicas aproveitando características geométricas do problema. Análises de dados simulados e reais provenientes de um experimento de cana-de-açúcar foram realizadas com diferentes medidas de separação entre agrupamentos e diferentes condições experimentais. Para os dados reais, métodos gráficos descritivos evidenciam a corretude e coerência do método proposto, que pode ser generalizado para a genotipagem de locos multialélicos poliplóides. Encerramos o trabalho comparando nossos resultados com a abordagem SuperMASSA [Serang2012] que trouxe excelentes resultados ao problema. Todo código desenvolvido em linguagem R está disponibilizado com o texto.
Since the beginnings of agriculture and livestock, the man selects individuals with desirable characteristics to breed and increase the proportion of new individuals with such qualities. With knowledge of the DNA structure and the advent of genetic engineering, the identification and characterization of individual species can make use of new technologies to help develop new varieties of plants and animals for many purposes. These technologies involve complex biochemical and physical procedures that produce even more accurated measures, like techniques that employ mass spectrometry to compare single nucleotide polymorphisms (SNPs). In plants it is common the occurrence of polyploidy, which is the presence of more than two chromosomes in the same group of homology. The determination of polyploidy level is essential for correct SNPs genotype calling and therefore greater efficiency in the study and genetic improvement of plants. In this work we characterize the phenomenon of poliploidy with probabilistic urns and balls models, proposing an efficient and appropriate method of simulation, as well as a simple technique to infer ploydy levels and classify biallelic samples accurately taking advantage of geometrical characteristics of the problem. Analysis of simulated and real data from an experiment of sugarcane were conducted with different measures of separation between groups and different experimental conditions. For the actual data, descriptive graphical methods show the correctness and consistency of the proposed method, which can be generalized to multi-allelic loci genotyping polyploid. We end our work comparing our results with the SuperMASSA [Serang2012] approach that brought excellent results to the problem. All code developed in language R were provided with the text.

In the present thesis turbulent natural convection of air within different challenging test cases are investigated numerically by means of an unstructured finite volume code, Code_Saturne. First, flow within both two-dimensional vertical and inclined differentially heated rectangular cavities at 60° and 15° to the horizontal for an aspect ratio of H/L=28.6 and Rayleigh number of 0.86×10e6 is computed using several high and low-Re models. Here the effectiveness of the RANS models in Code_Saturne is assessed through comparisons with a range of available experimental data. After some tests of thermal field inside vertical cavity, the “two-velocity-scale wall function” is chosen to be used with high-Re models. In both vertical and inclined cases the overall flow pattern appears similar, with a single circulation cell, and a boundary layer at the wall. The levels of turbulence energy are generally slightly lower in the inclined case. Most models give a reasonable prediction of measured Nusselt number, with the two low-Re approaches generally being closer to the data than the schemes employing wall functions. For the 15° inclined cavity, a multi cellular motion is shown by the high-Re models. Nevertheless, all the model predictions disagree with experimental data due to the presence in real flow of 3-D unsteady structures as found in Benard convection problems. These cannot, definitely, be reproduced using a 2-D geometry. Both highly resolved LES and unsteady RANS computations are then conducted, for turbulent natural convection of air inside 15° unstably and stably stratified cavities. In accordance with recent experimental data, the LES computations for both enclosures returned three-dimensional time-averaged flow fields. In the case of the unstably stratified enclosure, the flow is highly unsteady with coherent turbulent structures in the core of the enclosure. Results of LES computations show close agreement with the measured data. Subsequent comparisons of different URANS schemes with the present LES are used in order to explore to what extent these models are able to reproduce the large-scale unsteady flow structures. All URANS schemes have been found to be able to reproduce the 3-D unsteady flow features present in the 15° unstable cavity. However, the low-Re model tested as well as requiring a high resolution near-wall grid, also needed a finer grid in the core region than the high-Re models, thus making it computationally very expensive. Flow within the 15° stable cavity also shows some 3-D features, although it is significantly less unsteady, and the URANS models tested here have been less successful in reproducing this flow pattern. Finally, natural convection of CO2 inside a horizontal annular penetration enclosure, which can be found in AGR's, has been performed using a highly resolved LES and a set of RANS models. The Rayleigh number is 1.5×10e9. RANS models agree with the present LES on the fact that the flow is unsteady and there are large-scale oscillations present which decrease in amplitude as one moves from the open towards the closed end of the annular enclosure. Overall heat transfer and thermal quantitative and dynamic results show that RANS schemes are in close agreement with the current LES data except some discrepancies shown by the high-Re model which can be returned to the limitation of the simple wall function used to predict such complex flow.

This doctoral thesis offers a quantitative and qualitative analysis of the changes in the urban shape and landscape of the Girona Counties between 1979 and 2006. The theoretical part of the research lies within the framework of the dispersed city phenomenon, and is based on the hypothesis of convergence towards a global urban model. The empirical part demonstrates this proposition with a study of 522 zone development plans in the Girona Counties. The results point to the consolidation of the dispersed city phenomenon, as shown by the sudden increase in built-up space, the spread of urban development throughout the territory, and the emergence of a new, increasingly generic landscape comprising three major morphological types: urban extensions, low density residential estates and industrial zones. This reveals shortcomings of planning for urban growth, weakening of the city as a public project, and a certain degradation of the Mediterranean city model.
La present Tesi doctoral conté una anàlisi quantitativa i qualitativa dels canvis en la forma i el paisatge urbans a les Comarques Gironines entre 1979 i 2006. La part teòrica situa la recerca en el marc del fenomen de la ciutat dispersa i parteix de la hipòtesi de la convergència cap a un model urbà global. La part empírica demostra aquest pressupost a través de l’estudi dels 522 plans parcials d’urbanisme aprovats durant aquest període. Els resultats permeten validar la consolidació del fenomen de la ciutat dispersa en tant que explosió de l’espai urbanitzat, difusió de la urbanització sobre el territori i aparició d’un nou paisatge cada cop més genèric, format per tres grans tipologies morfològiques: eixamples, urbanitzacions i polígons d’activitat econòmica. Tot plegat posa de manifest les carències que ha tingut el planejament per ordenar el creixement urbà, el debilitament de la ciutat com a projecte públic i una degradació del model de ciutat mediterrània.

In this work the predictive capability of a number of Reynolds stress transport(RST) models was first tested in a range of non-equilibrium homogeneous flows, comparisons being drawn with existing direct numerical simulation (DNS) results and physical measurements. The cases considered include both shear and normally strained flows, in some cases with a constant applied strain rate, and in others where this varied with time. Models were generally found to perform well in homogeneous shear at low shear rates, but their performance increasingly deteriorated at higher shear rates. This was attributed mainly to weaknesses in the pressure-strain rate models, leading to over-prediction of the shear stress component of the stress anisotropy tensor at high shear rates. Performance in irrotational homogeneous strains was generally good, and was more consistent over a much wider range of strain rates. In the experimental plane strain and axisymmetric contraction cases, with time-varying strain rates, there was evidence of an accelerated dissipation rate generation. Significant improvement was achieved through the use of an alternative dissipation rate generation term, Pε , in these cases, suggesting a possible route for future modelling investigation. Subsequently, the models were also tested in the inhomogeneous case of pulsating channel flow over a wide range of frequencies, the reference for these cases being the LES of Scotti and Piomelli (2001). A particularly challenging feature in this problem set was the partial laminarisation and re-transition that occurred cyclically at low and, to a lesser extent, intermediate frequencies. None of the models tested were able to reproduce correctly all of the observed flow features, and none returned consistently superior results in all the cases examined. Finally, models were tested in the case of a plane jet interacting with a rectangular dead-end enclosure. Two geometric configurations are examined, corresponding a steady regime, and an intrinsically unsteady regime in which periodic flow oscillations are experimentally observed (Mataoui et al., 2003). In the steady case generally similar flow patterns were returned by the models tested, with some differences arising in the degree of downward deflection of the impinging jet, which in turn affected the level of turbulence energy developing in the lower part of the cavity. In the unsteady case, only two of the models tested, a two-equation k-ε model and an advanced RST model, correctly returned purely periodic solutions. The other two RST models, based on linear pressure-strain rate terms, returned unsteady flow patterns that exhibited complex oscillations with significant cycle-to-cycle variations. Unfortunately, the limited availability of reliable experimental data did not allow a detailed quantitative examination of model performance.

Understanding distortion transfer and generation through fan and compressor blade rows is able to assist in blade design and performance prediction. Using full annulus unsteady RANS simulations, the effects of distortion as it passes through the rotor of a transonic fan at five radial locations (10%, 30%, 50%, 70%, and 90% span) are analyzed. The inlet distortion profile is a 90-degree sector with a 15% total pressure deficit. Fourier distortion descriptors are used in this study to quantitatively describe distortion transfer and generation. Results are presented and compared for three operating points (near-stall, design, and choke). These results are used to explain the relationship between inlet total pressure distortion, pressure-induced swirl, total pressure distortion transfer, total temperature distortion generation, and circumferential rotor work variation. It is shown that very large changes in pressure-induced swirl and distortion transfer and generation occur between near-stall and design, but only small changes are seen between design and choke. The greatest changes are shown to be near the tip. Local power variations are shown to correlate with total pressure distortion transfer and total temperature distortion generation.It can be difficult to predict the transfer of distortion through a fan or compressor because traditional experimental and computational methods are very expensive and time consuming. The Harmonic Balance approach is a promising alternative which uses Fourier techniques to represent fluid flow solutions and which can provide unsteady solutions much more quickly than traditional unsteady solvers. Relatively little work has been done to assess how much Fourier information is necessary to calculate a sufficiently accurate solution with the Harmonic Balance Solver. A study is performed to analyze the effects of varying the amount of modal content that is used in Harmonic Balance simulations. Inlet distortion profiles with varying magnitudes are used in order to analyze trends and provide insight into the distortion flow physics for various inlet conditions. The geometry is a single stage axial compressor that consists of an inlet guide vane followed by the NASA Stage 37 rotor. It is shown that simulations with greater magnitudes of distortion require more modal content in order to achieve sufficiently accurate results. Harmonic Balance simulations are shown to have significantly lower computational costs than simulations with a conventional unsteady solver.

In many countries over the world (including Sweden), metal toxicity in freshwater resources causes a severe drinking water quality problem and poses a threat to the environment and human health. Among the different toxic metals in the water resources of Sweden, arsenic and uranium are the biggest threats to health. These elements, over long time consumption, may even lead to cancer and/or neurological disorder. Most of the wells are installed in crystalline and sedimentary bedrock and the received water comes from water bearing fractures in the bedrock. The handling of such water is an issue and there is a need to reduce the arsenic and uranium exposure by improving processes and technologies. It is a very serious problem demanding a safe, sustainable and eco-friendly arsenic and uranium removal technology prior to drinking water supply. Different treatment systems are available, but many of them are not suitable due to their high cost, operation complexity and waste management issues. Through this study, chitosan biopolymer the second largest abundant polysaccharide on earth after cellulose, was verified as a potential adsorbent for arsenic(V) and uranium(VI) removal from water solution. Adsorbent characterizations were also conducted by XRD, FTIR, SEM, UV-visible spectrum and TGA/DTA investigations. Bench-scale batch experiments were conducted using chitosan biopolymer (DDA-85%) as an adsorbent to determine the arsenic(V) and uranium(VI) removal efficiency, by allowing four important effective parameters e.g. chitosan dosages, pH, contact time and contaminant concentration. The adsorption data at optimum conditions were fitted with Langmuir, Freundlich and Dubinin-Radushkhevic (D-R) isotherm and Lagergren pseudo-first-order and pseudo-second-order kinetic model to investigate the adsorption process. The characterization of materials assured the presence of effective amino, hydroxyl, and carboxyl groups of chitosan. Another advanntage is that the materials are bio-degradable. The results show that the arsenic(V) and uranium(VI) removal efficiency was 100% and 97.45% after 300 minutes with optimum pH of 6.0 and 7.0 respectively. The optimum adsorbent dosages and initial concentration were 60 and 80g/L and 100 and 250 µg/L respectively. The adsorption process was suitably described by Freundlich isotherm (R2 = 0.9933) and Langmuir isotherm (R2 = 0.9858) correspondingly for arsenic(V) uranium(VI) compared to other isotherms. This is an important indicator of homogeneous monolayer adsorption of metals. For both of arsenic(V) and uranium(VI), pseudo-second-order explained the adsorption kinetics better than pseudo-first-order and the second-order kinetic regression coefficient (R2) were 0.9959 and 0.9672 correspondingly. Connecting to the above mentioned results, it can be summed up that the chitosan biopolymer (DDA 85%) can be used as an inexpensive, sustainable and environment-friendly treatment option for arsenic(V) and uranium(VI) contaminated drinking water.
I många länder världen runt (även i Sverige) orsakar metallers toxicitet besvärliga vattenkvalitetsproblem och utgör ett hot mot människors hälsa. Bland de toxiska metaller som finns i svenska vatten utgör arsenik och uran i dricksvatten allvarliga hälsorisker vid långvarig exposition då de kan orsaka cancer och neurologiska problem. Flertalet brunnar är installerade i kristallint berg och sedimentära bergarter och vattnet kommer vanligen från sprickor i berggrunden. Hanteringen av sådant vatten kan kräva reduktion av expositionen för arsenik- och uraninnehåll genom förbättrade processer och teknologier. Detta är ett angeläget problem som kräver en säker, pålitlig och ekovänlig teknologi att tillämpas innan vattnet distribueras. En rad olika behandlingssystem är tillgängliga men många av dem är inte lämpliga beroende på deras höga kostnad, den komplicerade tillämpningen och problem med hanteringen av restprodukter. I denna studie has biopolymeren chitosan, den näst vanligaste polymeren efter cellulosa, konstaterats vara en möjlig adsorbent för att avlägsna arsenik(V) och uran(VI) från vatten. Karakterisering av adsorbenten har också genomförts genom XRD, FTIR, SEM, UV och strålning i synligt ljus samt TGA/DTA undersökningar. Batch-tester i bänkskala har genomförts med användning av chitosan (DDA-85%) som adsorbent för att bestämma dess förmåga att avlägsna arsenik(V) och uran(VI)genom att variera fyra parametrar, nämligen kontakttid, pH, dos av chitosan och halt av föroreningen. Adsorptionsdata vid optimala förhållanden bestämdes genom tillämpning av Langmuir, Freundlich och Dubinin-Radushkhevic (D-R) isotermerna. Vidare tillämpades Lagergrens pseudo-first-order och pseudo-second-order kinetiska modell för att undersöka adsorptionsprocessen. Karakteriseringen av materialet visade förefintligheten av effektiva amino- (N-H), hydroxyl- (O-H) samt karboxylgrupper (C=O) i chitosan-polysackariden och att det är lätt nedbrytbart. Preliminära resultat visar att reduktionen av arsenik(V) och uran(VI) var 100 respektive 97,45 % efter 300 minuters kontakttid med optimalt pH på 6,0 respektive 7,0. De optimala doserna av adsorbent och den initiala koncentrationen var 60 och 80 g/L och 100 och 250 µg/L. Adsorptions process beskrevs bäst av Freundlich-isotermen för arsenik(V) (R2 = 0.9933) och med Langmuir-isotermen för uran(VI) (R2 = 0,9858) jämfört med andra isotermer vilket var en viktig indikation på en homogen monolager-adsorption. För både arsenik(V) och uran(VI) beskrev pseudo-second order adsorptionen bättre än pseudo-first-order. Second-order kinetiska regressionskoefficienten (R2) var 0.9959 och 0.9872 respektive. De ovanstående resultaten visar sammanfattningsvis att chitosan (DDA-85%) kan användas som en billig, pålitlig och miljövänlig behandlingsmetod av vatten för arsenik(V) och uran(VI).

QC 20150526

ChitoClean

The groundwater bacterium Pseudomonas fluorescens (CCUG 32456) isolated at a depth of 70 m in the Äspö Hard Rock Laboratory secretes a pyoverdin-mixture with four main components (two pyoverdins and two ferribactins). The dominant influence of the pyoverdins of this mixture could be demonstrated by an absorption spectroscopy study. The comparison of the stability constants of U(VI), Cm(III), and Np(V) species with ligands simulating the functional groups of the pyoverdins results in the following order of complex strength: pyoverdins (PYO) > trihydroxamate (DFO) > catecholates (NAP, 6­HQ) > simple hydroxamates (SHA, BHA). The pyoverdin chromophore functionality shows a large affinity to bind actinides. As a result, pyoverdins are also able to complex and to mobilize elements other than Fe(III) at a considerably high efficiency. It is known that EDTA may form the strongest actinide complexes among the various organic components in nuclear wastes. The stability constants of 1:1 species formed between Cm(III) and U(VI) and pyoverdins are by a factor of 1.05 and 1.3, respectively, larger compared to the corresponding EDTA stability constants. The Np(V)-PYO stability constant is even by a factor of 1.83 greater than the EDTA stability constant. The identified Np(V)-PYO species belong to the strongest Np(V) species with organic material reported so far. All identified species influence the actinide speciation within the biologically relevant pH range. The metal binding properties of microbes are mainly determined by functional groups of their cell wall (LPS: Gram-negative bacteria and PG: Gram-positive bacteria). On the basis of the determined stability constants raw estimates are possible, if actinides prefer to interact with the microbial cell wall components or with the secreted pyoverdin bioligands. By taking pH 5 as an example, U(VI)-PYO interactions are slightly stronger than those observed with LPS and PG. For Cm(III) we found a much stronger affinity to aqueous pyoverdin species than to functional groups of the cell wall compartments. A similar behavior was observed for Np(V). This shows the importance of indirect interaction processes between actinides and bioligands secreted by resident microbes.

La soufflante de la nouvelle génération de moteurs Snecma est caractérisée par des pales de rotor aux bords de fuite épais, ainsi que par un OGV hétérogène intégrant les bras supports.L’objectif de cette thèse est de caractériser l’influence de ces innovations technologiques sur la génération des sources et le rayonnement sonore dans la manche secondaire liés à l’interaction du sillage du rotor avec l’OGV. Ce mécanisme est principalement responsable des émissions tonales et à large bande qui sont traitées indépendamment. D’une part, une simulation URANS de l’étage rotor-stator fournit les sources déterministes sur le stator hétérogène ainsi que le champ sonore dans la manche traversée par les bras supports. L’extension de modèles acoustiques permet d’accéder au spectre de raies obtenu soit en propageant les sources par un modèle fondé sur le principe de l’analogie acoustique, soit directement à partir du champ sonore issu de la CFD. Il est alors montré que l’hétérogénéité du stator induit l’émergence de la raie du fondamental, et que les bras supports engendrent une onde stationnaire dans la manche secondaire.D’autre part, la simulation d’un canal complet du rotor avec une approche ZDES permet d’accéder aux perturbations turbulentes du sillage. Ces dernières alimentent un code acoustique fondé sur la théorie d’Amiet permettant de prévoir le bruit à large bande rayonné en conduit. Bien que plus coûteuse, la ZDES permet de s’affranchir des hypothèses restrictives et du calibrage délicat des modèles de turbulence homogène isotrope en fournissant des données directement exploitables, conduisant ainsi à des estimations plus précises.L’ensemble des simulations numériques et des prévisions acoustiques est validé grâce aux mesures issues d’une campagne d’essais au banc RACE
Modern turbofans are characterized by rotor blades with large chords, as well as heterogeneous OGV with mechanical struts integrated.The aim of this thesis is to characterize the impact of these technological innovations on sources generation and sound radiation in the bypass duct due to the interaction of the rotor wakes with the OGV. This mechanism is mainly responsible in tonal and broadband noise emissions which are dealt separately.On one hand, a URANS computation of the rotor-stator row provides the periodic sources on the heterogeneous stator as well as the sound field in the bypass duct crossed by the struts. The expansion of sound models allows to access to the tonal spectra obtained either by propagating sources thanks to a model based on the acoustic analogy principle, or by the sound field directly issued from the CFD. Then, it is shown that the stator heterogeneity induces the appearance of the fundamental tone, and that the struts lead to standing waves in the bypass duct.On the other hand, the simulation of a complete rotor channel with a ZDES approach provides the turbulent wakes. These erturbations feed an acoustic code based on the Amiet theory to predict the broadband noise radiated in the bypass duct. Despite the cost, ZDES stays clear of restrictive assumptions and sensitive calibration of isotropic homogeneous turbulence models by providing data directly workable, leading to more accurate predictions. Each of numerical simulations and acoustic predictions is validated thanks to the measurements performed in the RACE test rig

A detailed reactor core modeling of the LOVIISA-2 PWR and FORSMARK-3BWR was performed in the Serpent 2 Continuous Energy Monte-Carlocode.Both models of the reactors were completed but the approximations ofthe atomic densities of nuclides present in the core differedsignificantly.In the LOVIISA-2 PWR, the predicted atomic density for the nuclidesapproximated by Chebyshev Rational Approximation method (CRAM)coincided with the corrected atomic density simulated by the Serpent2 program. In the case of FORSMARK-3 BWR, the atomic density fromCRAM poorly approximated the data returned by the simulation inSerpent 2. Due to boiling of the moderator in the core of FORSMARK-3,the model seemed to encounter problems of fission density, whichyielded unusable results.The results based on the models of the reactor cores are significantto the FANCSEE Nuclear fuel cycle simulator, which will be used as adataset for the nuclear fuel cycle burnup in the reactors.
FANCSEE

This thesis aims at analysing the predictive capabilities of statistical URANS and hybrid RANS-LES methods to model complex flows at high Reynolds numbers and carrying out a physical analysis of the near-region turbulence and coherent structures. This study handles configurations included in the European research programmes ATAAC (Advanced Turbulent Simulation for Aerodynamics Application Challenges) and TFAST (Transition Location Effect on Shock Wave Boundary Layer Interaction). First, the detached flow in a configuration of a tandem of cylinders, positionned behind one another, is investigated at Reynolds number 166000. A static case, corresponding to the layout of the support of a landing gear, is initially considered. The fluid-structure interaction is then studied in a dynamic case where the downstream cylinder, situated in the wake of the upstream one, is given one degree of freedom in translation in the crosswise direction. A parametric study of the structural parameters is carried out to identify the various regimes of interaction. Secondly, the physics of the transonic buffet is studied by means of time-frequency analysis and proper orthogonal decomposition (POD), in the Mach number range 0.70–0.75. The interactions between the main shock wave, the alternately detached boundary layer and the vortices developing in the wake are analysed. A stochastic forcing, based on reinjection of synthetic turbulence in the transport equations of kinetic energy and dissipation rate by using POD reconstruction, has been introduced in the so-called organised-eddy simulation (OES) approach. This method introduces an upscale turbulence modelling, acting as an eddy-blocking mechanism able to capture thin shear-layer and turbulent/non-turbulent interfaces around the body. This method highly improves the aerodynamic forces prediction and opens new ensemble-averaged approaches able to model the coherent and random processes at high Reynolds number. Finally, the shock-wave/boundary-layer interaction (SWBLI) is investigated in the case of an oblique shock wave at Mach number 1.7 in order to contribute to the so-called "laminar wing design" studies at European level. The performance of statistical URANS and hybrid RANS-LES models is analysed with comparison, with experimental results, of integral boundary-layer values (displacement and momentum thicknesses) and wall quantities (friction coefficient). The influence of a transitional boundary layer on the SWBLI is featured.

The groundwater bacterium Pseudomonas fluorescens (CCUG 32456) isolated at a depth of 70 m in the Äspö Hard Rock Laboratory secretes a pyoverdin-mixture with four main components (two pyoverdins and two ferribactins). The dominant influence of the pyoverdins of this mixture could be demonstrated by an absorption spectroscopy study. The comparison of the stability constants of U(VI), Cm(III), and Np(V) species with ligands simulating the functional groups of the pyoverdins results in the following order of complex strength: pyoverdins (PYO) > trihydroxamate (DFO) > catecholates (NAP, 6­HQ) > simple hydroxamates (SHA, BHA). The pyoverdin chromophore functionality shows a large affinity to bind actinides. As a result, pyoverdins are also able to complex and to mobilize elements other than Fe(III) at a considerably high efficiency. It is known that EDTA may form the strongest actinide complexes among the various organic components in nuclear wastes. The stability constants of 1:1 species formed between Cm(III) and U(VI) and pyoverdins are by a factor of 1.05 and 1.3, respectively, larger compared to the corresponding EDTA stability constants. The Np(V)-PYO stability constant is even by a factor of 1.83 greater than the EDTA stability constant. The identified Np(V)-PYO species belong to the strongest Np(V) species with organic material reported so far. All identified species influence the actinide speciation within the biologically relevant pH range. The metal binding properties of microbes are mainly determined by functional groups of their cell wall (LPS: Gram-negative bacteria and PG: Gram-positive bacteria). On the basis of the determined stability constants raw estimates are possible, if actinides prefer to interact with the microbial cell wall components or with the secreted pyoverdin bioligands. By taking pH 5 as an example, U(VI)-PYO interactions are slightly stronger than those observed with LPS and PG. For Cm(III) we found a much stronger affinity to aqueous pyoverdin species than to functional groups of the cell wall compartments. A similar behavior was observed for Np(V). This shows the importance of indirect interaction processes between actinides and bioligands secreted by resident microbes.

Large-eddy simulation (LES) and unsteady Reynolds-averaged Navier-Stokes (URANS) calculations have been performed to investigate the effects of different mathematical models for scalar variance and its dissipation rate as applied to both a non-reacting bluff-body turbulent flow and an extension to a reacting case. In the conserved scalar formalism, the mean value of a thermo-chemical variable is obtained through the PDF-weighted integration of the local description over the conserved scalar, the mixture fraction. The scalar variance, one of the key parameters for the determination of a presumed β-function PDF, is obtained by solving its own transport equation with the unclosed scalar dissipation rate modelled using either an algebraic expression or a transport equation. The proposed approach is first applied to URANS and then extended to LES. Velocity, length and time scales associated with the URANS modelling are determined using the standard two-equation k-ε transport model. In contrast, all three scales required by the LES modelling are based on the Smagorinsky subgrid scale (SGS) algebraic model. The present study proposes a new algebraic and a new transport LES model for the scalar dissipation rate required by the transport equation for scalar variance, with a time scale consistent with the Smagorinsky SGS model.

Tesis (Lic. en Física)--Universidad Nacional de Córdoba, Facultad de Matemática, Astronomía, Física y Computación, 2020.
En este trabajo estudiamos una combinación de los clásicos modelos de urnas de Ehrenfest y del votante. En nuestro modelo, a cada paso temporal se efectúa el modelo de Ehrenfest con probabilidad α, o el del votante con probabilidad (1 − α). Este modelo puede ser visto como una caminata aleatoria unidimensional en una red finita. Analizamos los estados de equilibrio del sistema y determinamos una transición de fase para α = 1/N . Asimismo, definiendo el tamaño de avalancha como la cantidad de pasos necesarios para volver al estado de equilibrio por primera vez, estudiamos la distribuciones de tamaños de avalanchas y de retornos, para determinar si el comportamiento del sistema presenta, además, criticalidad auto- organizada. Desde el punto de vista de la sociofı́sica, este modelo representa un modelo de opinión, donde el cambio de opinión puede darse por interacción, (modelo del votante), o sin interacción, (modelo de Ehrenfest). Para valores de α relativamente chicos (∼ 1/N ), el sistema evoluciona a una sociedad polarizada.
In this work we present a combination of two classical urn models: Ehrenfest and voter . At every time step of our model either an Ehrenfest step is performed with probability \alpha or a voter step is performed with probability (1 − α). This model can be seen as an unidimensional random walk in a finite lattice. We analyzed the equilibrium states of the system and found a phase transition at α = 1/N. Furthermore, by defining the size of an avalanche as the amount of steps needed for the system to return to the equilibrium state for the first time, we studied the distribution of avalanches sizes and returns, in order to determine also if the system has Self-Organized Criticality. From the point of view of social physics this model represents an opinion model, where an agent can change its opinion by interacting with other agents (voter model) or without any interaction at all (Ehrenfest model). For relatively small α values (∼ 1 / N), the system evolves into a polarized society.
Fil: Perachia, Florencia. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía, Física y Computación; Argentina.

In dieser Arbeit wurden mittels winkelaufgelöster Photoemission verschiedene Verbindungen mit stark korrelierten Elektronen untersucht. Es wurde gezeigt, dass diese Technik einen direkten Zugang zu den niederenergetischen Wechselwirkungen bietet und dadurch wichtige Informationen über die Vielteilchenphysik dieser Systeme liefert. Die direkte Beobachtung der scharfen Quasiteilchenstrukturen in der Nähe der Fermikante ermöglichte insbesondere die genaue Betrachtung der folgenden Punkte: 1. Quantenphasenübergang: analog zu [27] wurde gezeigt, dass die hochaufgelöste PES Zugriff auf die lokale Energieskala TK bietet. Außerdem konnte im Rahmen eines störungstheoretischen Modells allgemein gezeigt werden, wie sich kleine RKKY-Störungen auf TK auswirken. Aus der experimentellen Entwicklung von TK(x) in CeCu6-xAux lassen sich mit Hilfe dieses Modells Rückschlüsse auf den Quantenphasenübergang bei T = 0 ziehen. 2. Kondogitter: mit Hilfe einer geordneten CePt5/Pt(111)-Oberflächenlegierung wurde demonstriert, dass mit ARPES Kondogittereffekte beobachtet werden können. Dazu zählen die Beobachtung von Hybridisierungsbandlücken und der starken Renormierung der Bandmassen in der Nähe von EF. Diese Effekte lassen sich, mit Hilfe unterschiedlicher Anregungsenergien und Messungen an einer isostrukturellen LaPt5-Schicht, eindeutig dem Resultat einer d f -Mischung der elektronischen Zustände zuweisen. Anhand von temperaturabhängigenMessungen konnte erstmals der Übergang von lokalisierten zu kohärenten Quasiteilchen in einem Kondosystem mittels ARPES beobachtet werden. 3. Phasenübergänge: bei FeSi und URu2Si2 wurde jeweils gezeigt, dass die ARPES sensitiv für kleinste Änderungen der elektronischen Struktur in unmittelbarer Umgebung der Fermienergie ist. Es konnten charakteristische Energien und Temperaturen, sowie am Phasenübergang beteiligte Bänder und deren effektive Massen m* quantifiziert werden. Insbesondere wurde gezeigt, dass Heavy-Fermion-Bänder mit m* = 40 me eine wichtige Rolle beim Hidden-order-Phasenübergang in URu2Si2 spielen. 4. Oberflächeneffekte: für alle Proben, außer CeCu6-xAux, musste festgestellt werden, dass Oberflächenzustände beträchtliche Anteile am Spektrum besitzen können. Daher ist bei jedem Material größte Vorsicht bei der Präparation der Oberfläche und der Interpretation der Spektren angebracht. Als eine geeignete Methode um Oberflächen und Volumenanteile auseinander zu halten, stellten sich anregungsenergieabhängige Messungen heraus. 5. theoretische Modelle: trotz der Bezeichnung “stark korrelierte Systeme”, unterscheiden sich die untersuchten Verbindungen bezüglich ihrer theoretischen Beschreibung: die Physik der Cersysteme (CeCu6, CePt5/Pt(111)) ist bei T > TK durch lokale Störstellen bestimmt und lassen sich somit im Rahmen des SIAM beschreiben. Bei tieferen Temperaturen T < TK treten jedoch Anzeichen von beginnender Kohärenz auf und geben somit den Übergang zum PAM wieder. Schwere, dispergierenden Bänder in URu2Si2 und FeSi zeigen, dass beide Systeme nur mit Hilfe eines geordneten Gitters beschreibbar sind. Insbesondere stellt sich für FeSi heraus, dass eine Erklärung im Kondoisolator-Bild falsch ist und ein Hubbard-Modell-Ansatz angebrachter scheint
In this thesis angle-resolved photoemission investigations on diverse strongly- correlated systems were presented. It was shown that this technique gives a direct access to the low-energy excitations of a solid and therefore provides important information about its many-body physics. In particular the spectroscopic investigation of the sharp quasi-particle features near the Fermi edge gave information about the following points: 1. quantum phase transition: as already investigated in [27], it was shown that high resolution PES gives a direct access to the local energy scale TK. In the framework of a pertubative model, it was presented how small RKKY corrections influence the Kondo temperature. From the experimental evolution of TK(x) in CeCu6-xAux conclusions could be drawn about the quantum phase transition at T = 0. 2. Kondo lattice: an ordered CePt5/Pt(111) surface alloy was prepared and investigated by ARPES. The sharp spectra show the characteristics of a Kondo lattice: hybridization gaps and a strong renormalization of the band mass in the vicinity of the Fermi edge. With the aid of different excitation energies and measurements on an isostructural LaPt5 surface alloy it was shown, that these effects are due to a d f -mixing. For the first time, the transition from the single-impurity to the heavy-fermion regime could be observed by ARPES. 3. phase transitions: for FeSi and URu2Si2 the sensitivity of ARPES to small changes in the Fermi surface was shown in the temperature dependent spectra. The measurements reveal characteristic energies and temperatures of the phase transitions. Furthermore the bands which are involved in the phase transition and their effective masses m* could be quantified. In the case of URu2Si2 it was shown that a heavy-fermion band with m* = 40 me is affected by the hidden-order phase transition. 4. surface effects: besides CeCu6-xAux all samples showed significant surface contribution to the spectra. Excitation energy dependent measurements were found to be a good tool to distinguish between bulk and surface contributions. 5. theoretical models: despite the shared expression “strongly correlated systems” the compounds differ in their theoretical description: it was found that the physics of cerium systems (CeCu6, CePt5/Pt(111)) at T > TK can be described in the framework of the SIAM. However, at lower temperatures (T < TK) the signatures of coherence appear in the spectra. These can only be described by the PAM. Heavy dispersing bands have been observed for URu2Si2 and FeSi. Thus these systems must be described by a Hamiltonian with lattice properties, too. Especially the transition metal compound FeSi was shown to be no Kondo insulator. A description in the framework of a multi-band Hubbard Hamiltonian seems to be more appropriate for this compound