La Société le Nickel ’SLN’ est l’un des plus grands exploitants de nickel en Nouvelle Calédonie. Le Stockage des déchets de l’exploitation minière sur le site d’exploitation se fait sous forme de tas manufacturés appelés versants. Pour assurer la stabilité de ces versants, il est nécessaire d’assurer un stockage hors d’eau de ces stériles miniers. Pour se faire, une mise en place des ouvrages en enrochement enterrés se fait au fur et à mesure de l’avancement des travaux d’installation des versants. Le rôle de ces ouvrages enterrés est de maintenir l’écoulement d’eau à travers le milieu poreux. Le premier objectif de la thèse est donc de mieux comprendre les interactions hydrodynamiques dans les milieux très perméables dans le cas d’écoulements pleinement turbulents. La première partie de ce travail concerne une étude expérimentale menée à l’Institut National Agronomique de Tunisie (INAT) mais aussi à l’Institut de mécanique de fluide de Toulouse (IMFT) dont le but est d’étudier à la fois l’évolution de la ligne d’eau dans les milieux macroporeux et la variation de la perméabilité de ces derniers en fonction du nombre de Reynolds. Des simulations avec des modèles de perte de charge les plus utilisés dans la littérature ont été effectuées, pour tester leur capacité à reproduire la ligne d’eau dans les conditions de nos expériences. Les deux relations de Forchheimer (1901) et d’Ergun (1952) donnent des résultats proches de nos expériences avec des valeurs de coefficients adaptés pour notre cas, alors que la relation de Barree et Conway (2004) ne semble pas reproduire les résultats attendus. L’eau qui circule dans les ouvrages enterrés est une eau chargée d’où l’intérêt d’étudier le transport sédimentaire dans ces milieux macroporeux. Pour se faire, une étude expérimentale a été réalisée sur le transport et le dépôt des particules dans des milieux synthétiques constitués de particules de diamètre moyen de 15 cm / The 'SLN' Company is one of the largest nickel operators in New Caledonia. The mining wastestorage at the operation site is as a slope. To ensure the stability of these slopes, it is necessary toensure an out of water storage of the waste rock. To do that, an underground rockfillimplementation is installed. The purpose of these buried structures is to maintain the flow of waterthrough its pores. The first objective of the thesis is to better understand the hydrodynamicinteractions in highly permeable porous media and in case of fully turbulent flows. The first part ofthis work relates to an experimental study carried out at the National Agronomic Institute of Tunisia(INAT) and the Institute of Fluid Mechanics of Toulouse (IMFT) whose aim is to study the waterprofile evolution in macro porous media and the permeability variation as a function of theReynolds number. Simulations with the most widely used pressure drop relationships in theliterature were performed to check their ability to reproduce our experimental water profile. Thetwo relations of Forchheimer (1901) and Ergun (1952) give the most satisfactory results withadapted coefficients values for our case, whereas the Barree and Conway (2004) formula doesn’tseems to give expected results. Given that the circulating water in these buried structures is acharged water, we studied the sedimentary transport in macro porous media. To do this, anexperimental study was carried out on the transport and deposition of particles in the studiedporous media which mean diameter is d=15 cm.

Lorsqu’un corps flexible non-profilé est immergé dans un écoulement, les forces instationnaires associées au phénomène de détachement tourbillonnaire peuvent provoquer une réponse vibratoire de la structure. Ces vibrations induites par vortex (VIV) se produisent via un mécanisme de synchronisation entre l’instationnarité du sillage et le déplacement du corps, aussi appelé mécanisme de lock-in. Les VIV ont un effet néfaste sur beaucoup de systèmes industriels, mais elles peuvent également être utilisées comme convertisseur d’énergie mécanique pour l’extraction d’énergie. Dans ce travail, les VIV d’un cylindre circulaire rigide, monté sur un support flexible, sont étudiées dans différentes configurations sur la base de simulations numériques directes. (i) Les mécanismes d’interaction sont d’abord examinés au début du régime turbulent, où les VIV ont rarement été étudiées numériquement. Le nombre de Reynolds, basé sur le diamètre du cylindre et la vitesse incidente, est fixé à 3900. Une analyse conjointe des réponses structurelles et des forces fluides est réalisée sur un intervalle de vitesses réduites (inverse de la fréquence naturelle du corps), dans le cas où le cylindre est libre d’osciller dans les directions longitudinale et transverse, c.a.d les directions parallèle et perpendiculaire à l’écoulement incident. (ii) Le comportement du système lorsque le corps est libre d’osciller dans une direction seulement est également exploré, révélant les interactions possibles entre les déplacements longitudinal et transverse dans le cas à deux degrés de liberté (2-ddl) ; l’analyse montre par exemple comment des oscillations longitudinales de grandes amplitudes peuvent être induites par un déplacement transverse du corps. (iii) Le sillage tri-dimensionnel se développant en aval du cylindre est analysé dans le cas 2-ddl et dans le cas du corps fixe. Les structures d’écoulement dans la direction axiale (parallèle à l’axe du cylindre) sont analysées quantitativement à partir des amplitudes et longueurs d’onde des fluctuations de vorticité dans cette direction ; l’altération de ces structures lorsque le corps oscille diffère dans les couches cisaillées et plus en aval dans le sillage. (iv) La dernière configuration étudiée concerne un cylindre immergé dans un écoulement linéairement cisaillé dans la direction transverse. L’impact de la brisure de symétrie, induite par le cisaillement, sur le comportement du système fluide-structure, est exploré. Différents régimes d’interaction sont mis en évidence dans l’espace paramétrique défini par le taux de cisaillement et la vitesse réduite. Certains d’entre eux sont associés à une profonde reconfiguration du sillage et à une altération majeure des forces fluides. / When a flexible body with bluff cross-section is immersed in a flow, the unsteady fluid forces accompanying the vortex-shedding phenomenon may lead to structural vibrations. These vortexinduced vibrations (VIV) occur through a mechanism of synchronization between flow unsteadiness and body displacement, referred to as lock-in. VIV are detrimental to many industrial systems, but may also be used as mechanical energy converter in the context of flow energy harvesting. In the present work, the VIV of a rigid circular cylinder mounted on a elastic support are investigated in various configurations on the basis of direct numerical simulations. Four aspects are studied. (i) The interaction mechanisms are first examined in the early turbulent regime, where VIV have been rarely studied numerically. The Reynolds number, based on the cylinder diameter and oncoming flow velocity, is set to 3900. A combined analysis of the structural responses and fluid forcing in the case where the cylinder is free to oscillate in the in-line and cross-flow directions, i.e. the directions parallel and perpendicular to the oncoming flow, is performed over a range of the reduced velocity (inverse of the oscillator natural frequency). (ii) The system behavior when the body is free to oscillate in a single direction only is also explored, shedding some light on the possible interactions between in-line and cross-flow motions in the two-degree-of-freedom (2-dof) case; the analysis shows for instance how large-amplitude in-line oscillations may be induced by cross-flow motion. (iii) The three-dimensional wake developing downstream of the oscillating body is analyzed in the 2-dof case as well as in the fixed body case. The spanwise flow patterns, which are analyzed quantitatively in terms of wavelength and amplitude of vorticity fluctuations, are differently altered in the shear-layer and wake regions, when the body oscillates. (iv) The last physical configuration involves a cylinder immersed in a flow linearly sheared in the cross-flow direction. The impact of the symmetry breaking induced by the shear, on the flow-structure system behavior, is explored. Different interaction regimes are uncovered in the shear rate - reduced velocity domain. Some of them are associated with a profound reconfiguration of the wake and a major alteration of the fluid forces.

Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / One of the parameters involved in the design of pressurized hydraulic systems is the pressure drop of the pipes. This verification can be performed through the Darcy-Weisbach formulation, which considers a coefficient of loss of charge (f) that can be measured by the implicit Colebrook-White equation. However, for this determination it is necessary to use numerical methods. Numerous explicit approaches have been proposed to estimate the "f", with different precisions and complexity. Considering the above, the objective of this work is to analyze the explicit approximations of the pressure loss coefficient for pressurized conduits in relation to the Colebrook-White formulation, through the relative performance and error index, determining the most accurate ones so that they can replace the standard Implied for the turbulent flow regime. It was analyzed 29 explicit equations in the literature, determining the coefficient of loss of charge through Reynolds number values in the range of 4x10³ ≤ Re ≤ 108 and relative roughness of 10-6 ≤ Ɛ / D ≤ 5x10-2, obtaining 160 points for each equation, totaling 4800 points. Statistical analysis was performed by the performance index (Id) and the relative error (ER) of the explicit equations in relation to Colebrook-White. The equations of Chen (1979), Shacham (1980), Sonnad Goudar (2006), Buzzelli (2008), Vantankhah and Kouchakzadeh (2008), Fang et al. (2011) and Offor and Alabi (2016a) apply for the entire range of 4x10³ ≤ Re ≤ 108 and 10-6 ≤ Ɛ / D ≤ 5x10-2, and presented high “Id” and high precision, the latter being highlighted by extreme precision, which is indicated to replace the use of the Colebrook-White standard approximation. / Um dos parâmetros envolvido no dimensionamento de sistemas hidráulicos pressurizados é a perda de carga das tubulações. Essa verificação pode ser realizada através da formulação de Darcy-Weisbach, que considera um coeficiente de perda de carga (f) que pode ser mensurado pela equação implícita de Colebrook-White. Porém, para essa determinação é necessário utilizar métodos numéricos. Numerosas aproximações explícitas têm sido propostas para estimar o “f”, com diferentes precisões e complexidade. Diante do exposto, o objetivo desse trabalho é analisar as aproximações explícitas do coeficiente de perda de carga para condutos pressurizados em relação a formulação de Colebrook-White, através do índice de desempenho e erro relativo, determinando as mais precisas para que possam substituir a padrão implícita, para o regime de fluxo turbulento. Foi analisado 29 equações explícitas presentes na literatura, determinando o coeficiente de perda de carga através de valores do número de Reynolds na faixa de 4x10³ ≤ Re ≤ 108 e rugosidade relativa de 10-6 ≤ Ɛ/D ≤ 5x10-2, obtendo 160 pontos para cada equação, totalizando 4800 pontos. A análise estatística foi realizada pelo índide de desempenho (Id) e pelo erro relativo (ER) das equações explícitas em relação à Colebrook-White. As equações de Chen (1979), Shacham (1980), Sonnad Goudar (2006), Buzzelli (2008), Vantankhah e Kouchakzadeh (2008), Fang et al. (2011) e Offor e Alabi (2016a) se aplicam para todo intervalo de 4x10³ ≤ Re ≤ 108 e 10-6 ≤ Ɛ/D ≤ 5x10-2, e apresentaram elevado Id e elevada precisão, destacando-se a última por extrema precisão, sendo esta a indicada para substituir o uso da aproximação padrão de Colebrook-White.

Thesis submitted in fulfilment of the requirements for the degree Doctor of Technology: Mechanical Engineering in the Faculty of Engineering at the Cape Peninsula University of Technology 2014 / Open channels, flumes or launders are used in the mining industry to transport slurries during processing and to disposal sites. Water plays a major part in the makeup of these slurries, its usage and availability is critical in countries where there are strict water usage management programs. The optimisation of flume design involves the maximisation of solids transport efficiency whilst, at the same time reduces water usage. The design of open channels is complex as it is dependent on both the slurry rheology and the channel shape. Very little has been reported in the literature for predicting non-Newtonian laminar flow in open channels of arbitrary cross-section. The only method available was that proposed by Kozicki and Tiu (1967, 1986). The shape factors they used were those evaluated from analytical solutions for flow of Newtonian fluids in open channels of the same cross-section. However, they carried out no experimental work to validate their model. Few experimental studies have been made on the effect of shape on non-Newtonian flow in open channels. Naik (1983) tested kaolin in water suspensions in a rectangular channel. Coussot (1994) provided some data for the flow of a Herschel-Bulkley fluid in rectangular and trapezoidal channels. Fitton (2007; 2008) obtained data for flow of three different non-Newtonian fluids (carboxymethylcellulose, carbopol and thickened tailings) in a semi-circular channel. A large experimental database for non-Newtonian flow in rectangular open channels was published by Haldenwang (2003) at the Flow Process Research Centre, Cape Peninsula University of Technology. Guang et al. (2011) performed Direct Numerical Simulations of turbulent flow of a yield- pseudoplastic fluid in a semi-circular channel. They compared their simulations with actual field measurements and found them to over-predict the flow velocity by approximately 40%. The source for this discrepancy was difficult to ascertain. A comprehensive database was compiled during this research of the flow of three non–Newtonian fluids in rectangular, trapezoidal, semi-circular and triangular channels. The flow of carboxymethylcellulose solutions and aqueous kaolin and bentonite suspensions was investigated in a 10 meter long flume at angles ranging from 1° to 5° from the horizontal plane. The effect of channel shape on the friction factor-Reynolds number relationship for laminar and turbulent open channel flow of these three fluids was investigated. New models for the prediction of laminar and turbulent flow of non-Newtonian fluids in open channels of different cross-sectional shapes are proposed. The new laminar and turbulent velocity models are compared with three previously-published velocity models for laminar flow and five previously-published velocity models for turbulent flow using average velocity as comparison criteria. For each channel shape, the laminar flow data can be described by a general relationship, f = K/Re where f is the Fanning friction factor and Re is the appropriate Haldenwang et al. (2002) Reynolds number. The K values were found to be 14.6 for triangular channels with a vertex angle of 90°, 16.2 for semi-circular channels, 16.4 for rectangular channels and 17.6 for trapezoidal channels with 60 degree sides. These K values were found to be in line with those reported by Straub et al. (1958) and Chow (1969) for open channel laminar flow of Newtonian fluids as opposed to the assumption made by Haldenwang et al. (2002; 2004) of using a constant value of 16 based on the pipe flow paradigm for all channel shapes. This new laminar model gave a closer fit to the laminar flow data than those from the three previously-published models. However, the presence of the yield stress still presents a problem, which makes the flow prediction in laminar flow for such fluids not very accurate. The investigation on non-Newtonian turbulent flow of the three fluids in the four different shaped open channels revealed that the data was described by the modified Blasius equation f = a Re b where a and b are constant values determined for each channel shape and Re is the Haldenwang et al. (2002) Reynolds number. Values of a and b for a rectangular channel were found to be 0.12 and -0.330, for a semi- circular channel 0.048 and -0.205, for a trapezoidal channel with 60° sides, 0.085 and -0.266 and for a triangular channel with vertex angle of 90°, 0.042 and -0.202. New laminar and turbulent velocity models were derived from using the new laminar f = K/Re and turbulent f = a Re b, friction factor-Reynolds number relationship. The laminar velocity model did not always give the best result, but the majority of the time it did, compared to the three previously published models. The new turbulent velocity model yielded the best results when compared to the five previously published models using average velocity as comparison criteria. The composite power law modelling procedure of Garcia et al. (2003) used for pipe flow predictions was extended to the present work on non-Newtonian flow in open channels of various cross-sections. The results show that the modelling technique used by Garcia et al. (2003) for pipe flow can be used to adequately predict flow in an open channel of a given cross-sectional shape provided that an appropriate Reynolds number is used to take into account the non-Newtonian behaviour of the test fluid. It was found that the results using the Haldenwang et al. (2002) Reynolds number yielded better results than those based on the adapted Metzner-Reed Reynolds number. The correlations and models developed and experimentally validated during this research can be used to further improve the design of rectangular, semi-circular, trapezoidal and triangular open channels to transport non-Newtonian fluids.

Orientador: Katia Lucchesi Cavalca Dedini / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-24T00:13:00Z (GMT). No. of bitstreams: 1 Galera_Larissa_M.pdf: 7841610 bytes, checksum: b4caff2b3c8de6cf54d4ef086fd47585 (MD5) Previous issue date: 2013 / Resumo: A análise dinâmica de rotores visa prever o comportamento e identificar desvios caracterizados por meio das respostas dinâmicas do conjunto, fornecendo indicadores de mau funcionamento ou diagnóstico de falhas, e minimizando os riscos de paradas imprevistas no sistema. O estudo dinâmico de máquinas rotativas deve ser realizado considerando a interação entre os componentes envolvidos na sua construção, como por exemplo, rotores, eixos, mancais, selos de fluxo e estruturas de suporte. Os selos de fluxo causam forças de reação que podem ser representadas por coeficientes dinâmicos. Este componente é o principal responsável por diferenças entre um modelo usando apenas eixo-mancal e a vibração real do sistema, como por exemplo, em bombas centrífugas. Dentro deste contexto, este trabalho tem por objetivo a determinação dos coeficientes dinâmicos de três tipos de selos planos, sendo eles: cilíndrico, cônico e escalonado, os quais serão integrados ao modelo global de sistemas rotativos, de modo a tornar a análise do conjunto girante mais completa. A análise dos selos de fluxo será realizada utilizando o método de volumes finitos para determinar a distribuição de velocidade circunferencial e de pressão ao longo do selo, que caracterizam as forças de reação. Estas, por sua vez, podem ser representadas em coeficientes de rigidez, amortecimento e inércia. Além disso, será verificada a influência de diversos parâmetros geométricos e operacionais nestes coeficientes. A inserção dos coeficientes dinâmicos dos selos planos e a análise do conjunto girante, a partir do pacote computacional Rotortest®, permitirá verificar a influência desses tipos de selos no sistema rotativo, analisando como este elemento modifica as características do conjunto e como acopla o eixo à fundação / Abstract: The dynamic analysis of rotors aims to predict its behavior and identify deviations characterized by the dynamic response of the set, providing malfunction indications or failure diagnosis, and minimizing the risk of having unexpected halts on the system. The dynamic study of rotating machines must be conducted by taking in account the interactions between the components involved in its construction, such as rotors, shafts, bearings, fluid seals, and support structures. The fluid seals cause reaction-forces, which can be represented for dynamic coefficients. This component is mainly responsible for the differences between a model using only a rotor-bearing and the actual vibration of the set, for example in centrifugal pumps. In this context, this work aims the determination of the dynamic coefficients of three types of plain seals, namely: straight, tapered, and stepped seals, which will be integrated with the global model of rotating systems, in order to make the analysis of the rotating set more complete. The fluid seals analysis will be accomplished through the finite volume method in order to determine the circumferential velocity and pressure distribution along the seal, which characterizes the reaction forces. Those can be, in turn, represented by stiffness, damping, and inertia coefficients. Besides, it will be verified the influence of several geometric and operational parameters on these coefficients. The insertion of the dynamic coefficients of plain seals and the analysis of the rotating set in the computational package Rotortest®, will verify the influence of these seals on the rotating system, analyzing how this element modify the set's characteristics and the coupling of the shaft to the foundation / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestra em Engenharia Mecânica

L'étude de l'écoulement turbulent au sein des passes à fentes verticales est nécessaire afin d'améliorer ces dispositifs de franchissement contenant des barrières physiques aux mouvements migratoires des poissons. En effet, les études menées sur les passes existantes ont montré leurs limites pour permettre le franchissement des petites espèces de poissons avec des faibles capacités de nage. L'objectif de notre étude est d'adapter l'écoulement turbulent dans la passe aux capacités de nage des poissons. Des mesures de vitesse bidimensionnelle par Vélocimétrie par Imagerie de Particules (PIV) et les mesures de vitesse tridimensionnelle par Vélocimétrie Acoustique par effet Doppler (ADV) ont montré que les grandeurs cinématiques de l'écoulement au sein des passes existantes sont très importantes et donc affectent les capacités de nages des petites espèces de poissons. Une des stratégies pour répondre à ce problème est d'introduire des obstacles de forme cylindrique au sein des bassins de la passe à poissons. L'insertion de ces cylindres a pour objectif de réduire les quantités cinématiques de l'écoulement turbulent au sein de la passe afin d'adapter cet ouvrage au passage des petites espèces de poissons. Cette stratégie nécessite une méthode d'optimisation afin de trouver l'emplacement idéal des cylindres à partir de simulations numériques de l'écoulement (logiciel Star-CD). / The turbulent flow study in vertical slot fishway is necessary to improve this crossing device containing physical barriers to fish migration. Effectively, studies of existing fishways have shown their limits to ensure the crossing of small fish species with weak swimming abilities. The objective of our study is to adapt the turbulent flow to the fish species swimming abilities. The two-dimensional velocity measurements by Particle Image Velocimetry (PIV) and three-dimensional velocity measurements by Doppler Velocimetry Acoustics (ADV) have shown that the flow kinematic quantities within the existing fishways are very important next to the small fish species capacities. One of strategies to answer at this problem is to introduce obstacles with cylindrical shape in the fishways pools. The adjunction of cylinders is intended to reduce the kinematics quantities of the turbulent flow within the fishways in order to adapt this hydraulic structure to the passage of small fish species. This strategy requires an optimization method to find the ideal location of the cylinders from numerical simulations of the flow (Star-CD code).

Cette thèse s'inscrit dans le cadre d'un projet international (MARS) dont le but est d'améliorer l'efficacité du transport aérien par contrôle d'écoulement. Dans ce contexte, les travaux expérimentaux présentés ici sont focalisés sur l'utilisation d'un actionneur plasma à Décharge à Barrière Diélectrique (DBD) pour contrôler l'écoulement turbulent en aval d'une marche descendante (BFS) à Reh = 30000. Deux types de décharges sont étudiés : une ac-DBD qui produit une force électrohydrodynamqiue et une ns-DBD qui produit une onde de pression. Plusieurs positions de l'actionneur sont étudiés, de façon à optimiser les effets de la décharge sur l'écoulement. A l'aide d'un système PIV stéréoscopique, une étude étendue est destinée à l'évaluation des paramètres électriques du signal. Parmi tous les résultats obtenus, la zone de recirculation est réduite de 20%. De plus, d'autres quantités moyennes telles que les composantes de Reynolds, l'énergie cinétique et l'épaisseur de la couche cisaillée ont été aussi analysées. La dernière partie de la thèse comprend une analyse dynamique des modifications produites par l'actionneur. Pour cela, les structures dominantes sont examinées par leur signature fréquentielle et par une décomposition orthogonal aux valeurs propres (POD). Tous les résultats conduisent à la définition d'un cas d'action optimal pour lequel il est obtenu une réduction maximal de la longueur de rattachement. Le lâcher tourbillonnaire est renforcé par un mécanisme de type "lock-on". / This thesis is part of an international project (MARS) to improve air transport efficiency by active flow control strategy. In this context, the presented experimental works are focused on a surface Dielectric Barrier Discharge (DBD) as a solution to control the turbulent flow separation downstream a backward-facing step (BFS) at Reh = 30000. Two different plasma discharges are investigated: an ac-DBD resulting in a electrohydrodynamic force and a ns- DBD producing a pressure wave. Thanks to the versatility of plasma discharges and in order to optimize its effects on the flow, different locations of the DBD actuator have been investigated. Furthermore, an extended parametric study regarding the input variables of the discharge has been carried out by stereoscopic PIV. Among the obtained results, the mean reattachment length has been reduced up to 20%. In addition, other averaged quantities such as Reynolds stress components, the kinetic energy and the vorticity thickness of the separated shear layer have been analyzed to provide more extended information about the effects of the DBD actuator. The last part includes a dynamical analysis of the modifications produced by an optimal actuation. For that aim, the dominant structures are investigated by their signature in the frequency domain and by proper orthogonal decomposition (POD). All the results lead to the definition of an optimal actuation for which the mean reattachment position is reduced and the vortex shedding street can be reinforced by a lock-on control mechanism.

A l’heure actuelle, seuls des facteurs locaux, stationnels, sont considérés pour le calcul des risques liés au vent alors que le vent qui aborde un peuplement forestier est affecté par les surfaces sur lesquelles il vient de passer ; les lisières en particulier jouent un rôle important sur l’écoulement atmosphérique, en contribuant à générer de la turbulence. Dans un paysage fragmenté, constitué d’une mosaïque de surfaces de différentes hauteurs et rugosités, la multiplicité des lisières est ainsi susceptible d’avoir des effets cumulatifs perceptibles à l’échelle régionale, qui pourraient contribuer de manière significative à la fragilité des massifs face à des tempêtes. Certains niveaux de fragmentation semblent susceptibles de conduire à un accroissement des risques en cas de vent violent. Bien que la région de lisière a été étudiée de manière approfondie dans le passé en raison de leur importance pour la détermination des vitesses de vent, des niveaux de turbulence et des échanges entre l’atmosphère et la canopée, il n’y a aucune étude de l’impact de lisières multiples ou de la fragmentation des forêts sur les caractéristiques de la couche limite à l’échelle du paysage. Quelques rares études laissent penser que la fragmentation du paysage pourrait moduler de manière significative la structure turbulente de la couche limite atmosphérique mais ces études concernent des réseaux de brisevents plutôt qu’un ensemble de parcelles forestières. On cherche par conséquent à caractériser les champs de vent et de turbulence pour ces différentes configurations. Pour ce faire, une expérimentation en soufflerie à été réalisée, visant à caractériser l’écoulement sur des maquettes de paysage présentant cinq degrés de fragmentation (L = ~ 5, ~ 10, ~15, ~20, ~30h, où L est la distance entre deux patchs de forêts régulièrement espacés et h est la hauteur de la canopée). Un cas homogène a également été simulé et sert ici de référence. Pour le modèle de canopée choisi, ces expérimentations montrent que l’énergie cinétique turbulente présente dans la basse atmosphère ne passe pas par un maximum pour une valeur de l’espacement intermédiaire comme il était supposé à l’origine. Le cas homogène est la configuration la plus rugueuse. Pour de grands espacements l’influence d’une parcelle ne se fait guère sentir sur la suivante et lorsqu’ils sont faibles l’écoulement ne "ressent" guère les clairières et présente des caractéristiques semblables au cas homogène. Nous avons également évalué un modèle atmosphérique de type "simulation des grandes échelles" à l’aide des données présentées précédemment. Le modèle est capable de reproduire les grandes caractéristiques de la turbulence telles que les vitesses de vent horizontales et verticales, l’énergie cinétique turbulente, les contraintes de Reynolds et les coefficients d’asymétrie horizontale et verticale en tous points du domaine. Cela nous a permis de confirmer la validité des calculs numériques et de simuler l’écoulement sur une plus large gamme de paysages fragmentés. Les résultats démontrent l’importance de l’indice foliaire pour le calcul de la rugosité effective sur une succession de patchs de forêt. / At present only the characteristics of a forest stand and its immediate environment are taken into account in calculating forest wind risk. However, it is known that the wind is strongly affected by the surfaces over which it has previously flowed. Forest edges in particular play an important role in determining the characteristics of the atmospheric flow by generating increased turbulence, triggering the formation of coherent tree scale structures. In a fragmented landscape, consisting of surfaces of different heights and roughness, the multiplicity of edges may have cumulative effects at the regional scale leading to increased forest damage during storms. Flow changes in the atmospheric boundary-layer across surface roughness changes have received extensive study in the past because of their importance in determining velocities, turbulence levels and exchange between the atmosphere and biosphere or ground. There have also been a number of studies across single forest edges both in the field, wind-tunnels and computer models. However, there have been no studies of flow across multiple forest edges or the impact of forest fragmentation on the characteristics of the boundary-layer. The only studies on multiple surface changes have been wind-tunnel examination of the flow though and across multiple wind-breaks. In this thesis we show results from a series of wind tunnel experiments on a range of levels of forest fragmentation. Five gap spacings (L = ~ 5, ~ 10, ~15, ~20, ~30h, where L is the length of the gap and h is the canopy height) were investigated using 3D laser doppler velocimetry in order to assess the effects of fragmented landscapes on mean and turbulent wind characteristics. The fragmentation was two-dimensional with the transition between forest and gaps only being along the wind direction and the forest and gaps were continuous perpendicular to the wind direction. The wind speeds and turbulence characteristics are compared against measurements from a single forest edge in the wind tunnel, which acts as a reference. No enhancement of turbulence formation at a particular level of fragmentation was observed but there was a consistent pattern of wind speed and turbulence back from the first edge of each simulation with the horizontal velocity at tree top increasing and the turbulent kinetic energy decreasing as gap size increased. We also compare mean wind speeds (U and W) and turbulence characteristics (variance in u, v, and w; skewness in U, V, and W; Reynold’s stress, and TKE) at all points in the experimental measurement domain of the wind tunnel with Large Eddy Simulation (LES) results, which allows us to confirm the validity of the LES calculations and to conduct a wider range of experiments than was possible in the wind-tunnel. The results demonstrate the importance of the frontal area index or roughness density of elements (in this case trees) in determining the nature of the flow and the effective roughness of the overall surface. They also show that as the gaps between forest blocks increases the flow transitions (at a gap size between 10 to 15 tree heights) from flow comparable to that over a continuous forest to flow across a set of isolated forest blocks.

Les gaines rectangulaires utilisées dans les réseaux de transport de gaz, notamment dans l'industrie de l'aluminium, sont soumises à des excitations provenant du flux s'écoulant à l'intérieur. Ce travail de thèse vise à comprendre quels sont les phénomènes impliqués dans la vibration des gaines rectangulaires de transport de gaz. Dans un premier temps nous présentons un modèle semi-analytique de gaine rectangulaire homogène basé sur le couplage de 4 plaques. Cette modélisation nous permet ainsi de définir les caractéristiques modales de la gaine. Ce modèle a été validé expérimentalement et numériquement par un code élément-finis. Dans un second temps, nous appliquons diverses excitations aérodynamiques et aéroacoustiques à notre gaine afin de déterminer quelles sont les contributions prépondérantes. Les comparaisons entre les résultats numériques et expérimentaux dans le cas d'un écoulement en gaine droite montrent que les contributions aéroacoustiques sont prépondérantes. Les mêmes tendances ressortent lors d'essais dans des configurations en coude, sauf à proximité de celui-ci où les sources aérodynamiques sont également importantes. Pour finir, nous appliquons ces recherches à une gaine rectangulaire utilisées dans l'industrie de l'aluminium. Nous constatons que le modèle que nous avons développé permet d'obtenir des tendances sur la réponse vibratoire de la gaine et met de nouveau en avant l'importance des contributions de type aéroacoustiques. Des pistes de réduction des niveaux vibratoires sont explorées et notamment celles de l'impact des paramètres géométriques de la structure. / Rectangular duct used for gas transport ductwork, especially in the aluminium industry, are excited by the internal flow. This thesis seeks to understand what are the phenomena involved in the vibration of the gaz transport ductwork. Firstly, we present a semi-analytical model of a homogeneous rectangular duct based on the coupling of 4 plates. This modeling allow us to define the duct modal characteristics and is validated by using both experimental and numerical (FEM) ways. Secondly, we applied aeroacoustic and aerodynamic excitations to our duct in order to determine which are the main contributions. Comparisons between numerical and experimental results, in the case of a straight duct highlight that aeroacoustic sources are predominant. The same trends are found with a bend configuration with few changes close to the band where aerodynamic sources seems to be predominant also. Finally, we apply our model to a large rectangular duct used in the aluminium industry. We note that the model gives good trends and highlights again the importance of the aeroacoustic contributions. Some reflexions about how to reduce the vibration levels by changing geometrical parameters are given at the end.

Orientadores: José Roberto Nunhez, Nicolas Spogis / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-22T07:47:05Z (GMT). No. of bitstreams: 1 Vergel_JoseLuisGomez_M.pdf: 8156840 bytes, checksum: f0b5d7b4b0875d4716285f8ec3ce5fa2 (MD5) Previous issue date: 2013 / Resumo: O uso de malhas não estruturadas recentemente tem recebido uma considerável atenção para discretização do domínio computacional em simulações CFD (Vakili & Esfahany, 2009; Cabrales, et al., 2011). A malha não estruturada (comumente tetraédricas) permite uma adequada adaptação em geometrias irregulares e uma geração automática na maioria dos softwares comerciais em CFD. Na literatura constantemente tem sido sugerido que as malhas hexaédricas são preferidas as tetraédricas, porém esta última pode ser usada, desde que alguns cuidados sejam tomados para proporcionar uma boa representação do fenômeno físico do problema. Alguns trabalhos recentemente publicados mostram que as malhas tetraédricas quando utilizadas com cuidado, podem obter resultados satisfatórios (Spogis & Nunhez, 2009). A maioria dos trabalhos desenvolvidos com uso da simulação CFD para processos de mistura utilizam malha hexaédrica, enquanto os resultados obtidos com malhas tetraédricas não possuem a mesma aprovação (Joaquim Junior et al., 2007), parte deste trabalho esta focado em mostrar que elas podem fornecer bons resultados em simulações de processos de mistura. Outro objetivo desse trabalho é mostrar o efeito do refinamento em malhas tetraédricas. Investigou-se a influência dos elementos prismáticos perto da parede sobre parâmetros globais, tais como o número de potência e número de bombeamento. Foi também realizada uma análise inicial da sensibilidade de alguns modelos de turbulência e esquemas de discretização sobre o campo de fluxo produzido. Além disso, simulações com diferentes refinamentos de malha foram feitas usando a abordagem de múltiplos sistemas de referência (MFR); enquanto em outros casos foi proporcionada uma abordagem de malhas deslizantes (SG) no impelidor. Os esquemas de discretização foram limitados aos esquemas Upwind, High resolution e blend fator, uma vez que esquemas diferentes não funcionam adequadamente com elementos tetraédricos. O software comercial de CFD CFX 14.0 foi utilizado para simular os resultados. Um impelidor de pás inclinadas (PBT 45°, com bombeamento para baixo) foi simulado em regime turbulento. Os resultados obtidos pelas simulações CFD para o número de potência e bombeamento, e perfil da componente axial da velocidade são discutidos e comparados com dados experimentais (Machado et al. et al., 2011). A velocidade foi medida usando a técnica PIV (Particle Image Velocimetry). Uma significativa influencia foi observada em alguns parâmetros na determinação de importantes variáveis nos processos de mistura. De forma geral, a predição do perfil da velocidade é influenciada, de alguma forma, pela resolução da malha, pelo modelo de turbulência e pelo esquema de discretização / Abstract: The use of non-structured meshes has received recently considerable attention for discretization of the computational domain in CFD simulations (Vakili & Esfahany, 2009; Cabrales et al., 2011). The non-structured meshes (the most common are tetrahedral) allow adequate adaptation of irregular geometries and easy use of automated algorithms for mesh generation in most commercial CFD software. It has been consistently suggested in the literature that hexahedral meshes are preferred over tetrahedral. However, they can be used, provided that some care is taken to provide a good representation of the physical phenomena of the problem. Recently published works have been proving that if they are used with care, satisfactory results are obtained (Spogis & Nunhez, 2009). Most of works developed with the use of CFD simulation for mixing processes use hexahedral and to date tetrahedral do not have the same acceptance of hexahedral (Joaquim Junior et al., 2007) and part of this work is aimed at showing that they can provide good results when simulating mixing processes. Another objective of this work is to show the effect of mesh refinement in tetrahedral meshes. It is investigated the influence of the prismatic elements near wall on global parameters such as the Power and Flow numbers. An initial analysis of the sensitivity of some turbulence models (Standard k-? model, the shear stress transport (SST) and BSL-Reynolds stress model) and the discretization scheme on the flow field produced were also carried out in this work. In addition, simulations with different mesh resolutions were made using the multiple reference frame (MFR) approach; whereas other cases a sliding mesh modeling was provided for the impeller. The discretization schemes were limited to upwind, high resolution and blend factor, since other schemes do not work well with tetrahedral. The commercial CFD software CFX 14.0 was used to simulate the results. A pitched blade turbine (PBT 45°, down-pumping), was simulated in turbulent flow. The results obtained for the Power and Flow numbers, the axial velocity profile component of the model in CFD are discussed and compared with experimental data (Machado et al. et al., 2011). The velocity was measured using the PIV technique (Particle Image Velocimetry). A significant influence of some parameters is observed on the determination of some important variable mixing. In general, the predictions of the velocity profile are influenced in some way by the resolution of the mesh, turbulence model and the discretization scheme / Mestrado / Desenvolvimento de Processos Químicos / Mestre em Engenharia Química