Comprendre, prédire et finalement retarder la transition vers la turbulence dans les écoulements sont d'importants problèmes posés aux scientifiques depuis les travaux pionniers d'Osborne Reynolds en 1883. Ces questions ont été principalement adressées à l'aide de la théorie des instabilités hydrodynamiques. A cause des ressources informatiques limitées, les analyses de stabilité linéaire reposent essentiellement sur d'importantes hypothèses simplificatrices telles que celle d'un écoulement parallèle. Dans ce cadre, connu sous le nom de stabilité locale, seule la stabilité d'écoulement ayant un fort intérêt académique mais relativement peu d'applications pratiques a pu être étudiée. Néanmoins, au cours de la décennie passée, l'hypothèse d'écoulement parallèle a été relaxée au profit de celle d'un écoulement bidimensionnel conduisant alors à ce que l'on appelle la stabilité globale. Ce nouveau cadre permet alors d'étudier les mécanismes d'instabilité et de transition ayant lieu au sein d'écoulements plus réalistes. Plus particulièrement, la stabilité d'écoulements fortement non-parallèles pouvant présenter des décollements massifs, une caractéristique fréquente dans les écoulements d'intérêt industriel, peut maintenant être étudiée. De plus, avec l'accroissement constant des moyens de calcul et le développement de nouveaux algorithmes de recherche de valeurs propres itératifs, il est aujourd'hui possible d'étudier la stabilité d'écoulements pleinement tridimensionnels pour lesquels aucune hypothèse simplificatrice n'est alors nécessaire. Dans la continuité des travaux présentés par Bagheri et al. en 2008, le but de la présente thèse est de développer les outils nécessaires à l'analyse de la stabilité d'écoulements 3D. Trois écoulements ont été choisis afin d'illustrer les nouvelles capacités de compréhension apportées par l'analyse de la stabilité globale appliquée à des écoulements tridimensionnels réels : i) l'écoulement au sein d'une cavité entraînée 3D, ii) l'écoulement se développant dans un tuyau sténosé, et enfin iii) l'écoulement de couche limite se développant au passage d'une rugosité cylindrique montée sur une plaque plane. Chacun de ces écoulements a différentes applications pratiques allant d'un intérêt purement académique à une application biomédicale et aérodynamique. Ce choix d'écoulements nous permet également d'illustrer les différents aspects des outils développés au cours de cette thèse ainsi que les limitations qui leur sont inhérentes. / Understanding, predicting and eventually delaying transition to turbulence in fluid flows have been challenging issues for scientists ever since the pioneering work of Osborne Reynolds in 1883. These problems have mostly been addressed using the hydrodynamic linear stability theory. Yet, due to limited computational resources, linear stability analyses have essentially relied until recently on strong simplification hypotheses such as the “parallel flow” assumption. In this framework, known as “local stability theory”, only the stability of flows with strong academic interest but limited practical applications can be investigated. However, over the course of the past decade, simplification hypotheses have been relaxed from the “parallel flow” assumption to a two-dimensionality assumption of the flow resulting in what is now known as the “global stability theory”. This new framework allows one to investigate the instability and transition mechanisms taking place in more realistic flows. More particularly, the stability of strongly non-parallel flows exhibiting separation, a common feature of numerous flows of practical interest, can now be studied. Moreover, with the continuous increase of computational power available and the development of new iterative eigenvalue algorithms, investigating the global stability of fully three-dimensional flows, for which no simplification hypothesis is necessary, is now feasible. Following the work presented in 2008 by Bagheri et al., the aim of the present thesis is thus to develop the tools mandatory to investigate the stability of 3D flows. Three flow configurations have been chosen to illustrate the new investigation capabilities brought by global stability theory when it is applied to realistic three-dimensional flows: i) the flow within a cuboid lid-driven cavity, ii) the flow within an asymmetric stenotic pipe and iii) the boundary layer flow developing over a cylindrical roughness element mounted on a flat plate. Each of these flows have different practical applications ranging from purely academic interests to biomedical and aerodynamical applications. They also allow us to put in the limelight different aspects and possible limitations of the various tools developed during this PhD thesis.

In this dissertation, we are concerned with the numerical simulation for flows of electrically conducting fluids exposed to an external magnetic field (also known as magnetohydrodynamics or in short MHD). The aim of the present dissertation is twofold. First, the in-house CFD hydrodynamic solver SFELES is extended to MHD problems. Second, MHD turbulence is studied in the simple configuration of a MHD pipe flow within an external transverse magnetic field. Chapter 2 of this dissertation aims at reminding the physical equations that govern incompressible MHD problems. Two equivalent formulations are put forward in the particular case of quasi-static MHD. Chapter 3 is devoted to the detailed development of the hybrid spectral - stabilized finite element methods for quasi-static MHD problems. The extension of SFELES is made for both Cartesian and axisymmetric systems of coordinates. The short chapter 4 follows to provide the performances of SFELES executed by several processes in a parallel environment. The addition of a parallel direct solver is studied in regards with the memory and time requirements. The extension of SFELES is then validated in chapter 5 with test cases of increasing complexity. For this purpose, laminar flows with an existing analytical-asymptotic solution are considered. The subject of chapter 6 is the MHD turbulent pipe flow within an external transverse and uniform magnetic field. The results are partially compared with the corresponding hydrodynamic flow and with a few data available in the literature. / Le thème de cette thèse de doctorat est la simulation numérique d'écoulements de fluides conducteurs d'électricité qui sont exposés à un champ magnétique extérieur (également connu sous le nom de magnétohydrodynamique ou encore MHD). L'objectif de ce travail est double. Premièrement, le code CFD maison SFELES est étendu aux problèmes MHD. Deuxièmement, la turbulence MHD est étudiée dans la configuration de l'écoulement en conduite cylindrique à l'intérieur d'un champ magnétique transverse. Le chapitre 2 de cette thèse a pour but de rappeler les équations qui gouvernent les problèmes de MHD incompressible. Deux formulations équivalente sont mises en évidence dans le cas particulier de la MHD quasi-statique. Le chapitre 3 est dévoué au développement détaillé des méthodes spectrale - éléments finis pour la MHD quasi-statique. L'extension de SFELES est réalisée dans les systèmes de coordonnées cartésiennes et axisymétriques. Le court chapitre 4 suit pour fournir les performances de SFELES exécuté sur plusieurs processeurs dans un environnement parallèle. L'ajout d'un solveur parallèle direct est étudié en ce qui concerne les demandes en temps et mémoire. L'extension de SFELES est alors validée dans le chapitre 5 avec des cas d'étude de complexité croissante. Dans ce but, des écoulements laminaires avec solution théorique-asymptotique sont envisagés. Le sujet du chapitre 6 est l'écoulement MHD turbulent en conduite cylindrique à l'intérieur d'un champ magnétique transverse et uniforme. Les résultats sont partiellement comparés avec l'écoulement hydrodynamique correspondant et avec des données disponibles dans la littérature. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Ce travail est une contribution expérimentale à l’étude rhéologique et en écoulement de fluides complexes (à seuil et thixotropes) transitant dans un circuit hydraulique. Il s’agit notamment de suspensions de bentonite ainsi que des complexes bentonite/polymère. L’étude porte sur l’évolution des pertes de charge et des champs de vitesse et se situe en régime laminaire, transitoire et turbulent. L’étude a été réalisée en utilisant un vélocimètre ultrasonore Doppler pulsé développé au laboratoire. Dans la première partie expérimentale de la thèse, des mesures rhéologiques et en écoulement ont été effectuées sur des suspensions de bentonite pures (sans additifs) à différentes concentrations. A partir des essais sur boucle hydraulique, une étude détaillée est présentée sur l’évolution des coefficients de frottement et des profils de vitesse pour les différents régimes d’écoulement. Dans une seconde partie, une suspension de bentonite pure et des mélanges bentonite/CMC à différentes concentrations massiques ont été étudiées en termes de comportement rhéologique et hydrodynamique en écoulement en conduite. En ce qui concerne les mesures effectuées en boucle hydraulique, il a été montré que le polymère a des propriétés viscosifiantes en régime laminaire. Par contre, en régime turbulent, le polymère agit comme un réducteur de frottement. La dernière partie de la thèse a été consacrée à l’étude de l’influence de la température sur le comportement rhéologique des solutions de polymère et des mélanges argile/polymère. Les mesures rhéologiques à différents paliers de températures ainsi que les balayages en température ont mis en évidence le caractère thermodépendant des dispersions. / This experimental work is a contribution to the study of rheological and pipe flow proprieties of complex fluids (yield stress and thixotropic). Bentonite suspensions and mixtures containing bentonite and carboxymethyl cellulose were investigated. The axial velocity distribution was determined using ultrasonic pulsed Doppler velocimetry technique. In the first experimental part of the thesis, rheological and pipe flow measurements were performed for pure bentonite suspensions at different concentrations. A detailed study is presented on the evolution of the friction factors and velocity profiles for different flow regimes. In a second part, suspension of bentonite and mixtures of bentonite / CMC at different mass concentrations of polymer were studied in terms of their rheological and hydrodynamic flow behavior. It was shown that the polymer has viscosifying properties in laminar regime. However, in the turbulent regime, the polymer acts as a friction reducer. The last part of the thesis was devoted to the study of the effect of temperature on the rheological behavior of polymer solutions and mixtures of clay / polymer. The rheological measurements at different temperatures showed a thermodependent character of the different fluids.

This work is focused on computational modelling of mixing fluids in pipeline with static mixers. Main objective is to analyze several selected static mixers in a particular industrial application, namely dosing of the aluminium sulphate solution in the clarification process for potable water treatment. The analysis focuses on the degree of mixedness and pressure loss of individual mixers. Further, the aim of this work is to process the search of available types of static mixers. The benefit of this work is at least an effort to motivate the reader to deeper understanding of the mixing fluids, especially by static mixers.

Experimente mit neuartigen Messverfahren lieferten Daten über die Struktur von transienten Flüssig-keits-Gas-Strömungen für die Entwicklung und Validierung von mikroskopischen, d.h. geometrieunabhängigen Konstitutivbeziehungen zur Beschreibung des Impulsaustauschs zwischen Flüssig-phase und Gasblasen sowie zur Quantifizierung der Häufigkeit von Blasenkoaleszenz und -zerfall. Hierzu wurde eine vertikale Testsektion der Zweiphasentestschleife MTLoop in Rossendorf genutzt, wobei erstmals Gittersensoren mit einer Auflösung von 2-3 mm bei einer Messfrequenz von bis zu 10 kHz angewandt wurden. Dabei wurde die Evolution von Gasgehalts-, Geschwindigkeits- und Bla-sengrößenverteilungen entlang des Strömungsweges und bei schnellen Übergangsprozessen aufge-nommen und so die für die Modellbildung erforderlichen Daten bereitgestellt. Für den Test der Mo-dellbeziehungen wurde ein vereinfachtes Verfahren zur Lösung der Strömungsgleichungen entlang des Strömungswegs erstellt. Es basiert auf der Betrachtung einer größeren Anzahl von Blasengrö-ßenklassen. Die erhaltenen numerische Lösungen haben erstmals gezeigt, dass der bei Erhöhung der Gasvolumenstromdichte stattfindende Übergang von einer Blasenströmung mit Randmaximum zu einem Profil mit Zentrumsmaximum und anschließend zu einer Pfropfenströmung ausgehend von einem einheitlichen Satz physikalisch begründeter und geometrieunabhängiger Konstitutivgleichun-gen modelliert werden kann. Die Modellbeziehungen haben sich in einem abgegrenzten Gebiet der Volumenstromdichten als generalisierungsfähig erwiesen und sind für den Einbau in CFD-Modelle geeignet. Weiterhin wurden Arbeiten zur Kondensation durchgeführt, die direkten Bezug zu den Kon-densationsmodellen haben, die in Thermohydraulik-Codes enthalten sind. Die Untersuchung liefert darüber hinaus experimentelle Daten für die Modellvalidierung hinsichtlich des Verhaltens und des Einflusses nichtkondensierbarer Gase. Hierfür wurden spezielle Sonden für die Bestimmung der Konzentration und für die Lokalisierung von Pfropfen nichtkondensierbarer Gase entwickelt und bei transienten Kondensationsversuchen in einem leicht geneigten Wärmeübertragerrohr eingesetzt.

This work presents the development of a novel and non-invasive method that measures fluid flow rate and temperature in pipes. While current non-invasive flow meters are able to measure pipe flow rate, they cannot simultaneously measure the internal temperature of the fluid flow, which limits their widespread application. Moreover, devices that are able to determine flow temperature are primarily intrusive and require constant maintenance, which can shut down operation, resulting in downtime and economic loss. Consequently, non-invasive flow rate and temperature measurement systems are becoming increasingly attractive for a variety of operations, including for use in leak detection, energy metering, energy optimization, and oil and gas production, to name a few. In this work, a new solution method and parameter estimation scheme are developed and deployed to non-invasively determine fluid flow rate and temperature in a pipe. This new method is utilized in conjunction with a sensor-based apparatus--"namely, the Combined Heat Flux and Temperature Sensor (CHFT+), which employs simultaneous heat flux and temperature measurements for non-invasive thermal interrogation (NITI). In this work, the CHFT+ sensor embodiment is referred to as the British Thermal Unit (BTU) Meter. The fluid's flow rate and temperature are determined by estimating the fluid's convection heat transfer coefficient and the sensor-pipe thermal contact resistance. The new solution method and parameter estimation scheme were validated using both simulated and experimental data. The experimental data was validated for accuracy using a commercially available FR1118P10 Inline Flowmeter by Sotera Systems (Fort Wayne, IN) and a ThermaGate sensor by ThermaSENSE Corp. (Roanoke, VA). This study's experimental results displayed excellent agreement with values estimated from the aforementioned methods. Once tested in conjunction with the non-invasive BTU Meter, the proposed solution and parameter estimation scheme displayed an excellent level of validity and reliability in the results. Given the proposed BTU Meter's non-invasive design and experimental results, the developed solution and parameter estimation scheme shows promise for use in a variety of different residential, commercial, and industrial applications. / MS

A vibração induzida por escoamento é parte intrínseca do transporte de fluidos. Por exemplo, na indústria de petróleo e gás esse fenômeno pode ser encontrado em tubulações, tanto no setor upstream, quando downstream. Essas vibrações são produto das forças geradas pelo escoamento e, portanto, carregam informações sobre sua fenomenologia. No caso de escoamento bifásico em tubo, resultados experimentais indicam forte influência da velocidade da mistura, fração de vazio e padrão de escoamento no comportamento dinâmico da estrutura. Contudo, pouco foi feito na tentativa de obter informações do escoamento a partir da reposta estrutural. Assim, o objetivo do presente estudo é desenvolver métodos para a previsão dos parâmetros do escoamento baseados na resposta de um tubo submetido a escoamento bifásico. Foi conduzido um trabalho experimental da vibração induzida por diversos padrões gás-líquido numa tubulação horizontal (PVC Ø3/4\'\') duplamente engastada, com água e ar como fluidos de trabalho. A partir de uma abordagem analítica, corroborada com resultados experimentais para escoamento monofásico e bifásico, estabelece-se a existência de uma relação, de natureza quadrática, entre a velocidade de atrito e o desvio padrão da aceleração. Dado que a velocidade de atrito é função do fator de atrito bifásico, um método para a sua previsão é desenvolvido. Ele prevê de maneira precisa os dados coletados; todos eles com erro percentual menor do que 30%. O método foi comparado também com dados experimentais e modelos da literatura, mostrando boa concordância. Além disso, apresenta-se uma relação entre a frequência pico da resposta e a fração de vazio homogênea. No fim, são apresentados: (i) um método de identificação de escoamento pistonado, baseado na superposição dos mecanismos de vibração por turbulência e intermitente, com desempenho mínimo de 81.8%; (ii) um método experimental para determinação da velocidade da mistura (J) e fração de vazio homogênea (β). Os melhores resultados são obtidos para os padrões disperso e pistonado, prevendo adequadamente os parâmetros J e β com erro percentual absoluto médio de 24.1% e 20.65%, respectivamente. / Flow-induced vibration is intrinsic to piping problems. For example, in the oil and gas industry the FIV phenomenon can be found in pipe flow both in upstream and downstream applications. The structural vibration response contains information about the flow phenomenology. In the case of two-phase pipe flow, experimental results show a strong influence of mixture velocity, void fraction and flow pattern on pipe structural dynamics. However, efforts to obtain information of the flow from pipe response have been scanty. The goal of this study is to develop two-phase flow parameters predictive methods based on the structural pipe response. An experimental study of flow-induced vibration was carried out for several flow patterns in a clamp-clamp straight pipe (PVC Ø3/4\'\'), with air and water as working fluids. From an analytical approach, a quadratic relationship between shear velocity and standard deviation of acceleration is proposed and validated against the experimental data of single and two-phase flow. Since the shear velocity depends on the friction factor, a method to predict two-phase friction factor is presented. The method predicts accurately our experimental data with a mean absolute error up to 30%. Good agreement was also found when it was compared with some models and experimental data from the literature. Furthermore, an expression to correlate peak frequency and homogeneous void fraction as a function of added mass is offered. Finally, we present: (i) a slug flow identification technique based on the superposition of the turbulence and intermittent flow-induced vibration mechanisms, with performance of 81.8% and (ii) an experimental methodology to estimate mixture velocity (J) and homogeneous void fraction (β). The latter method shows better agreement for dispersed and slug flow-patterns, predicting J and β with a mean absolute error of 24.1% e 20.65%, respectively.

In this study, which is numerical in nature, direct numerical simulation (DNS) of the pipe flow is performed. For the DNS a solenoidal spectral method is employed, this involves the expansion of the velocity using divergence free functions which also satisfy the prescribed boundary conditions, and a subsequent projection of the N-S equations onto the corresponding dual space. The solenoidal functions are formulated in Legendre polynomial space, which results in more favorable forms for the inner product integrals arising from the Petrov-Galerkin scheme employed. The developed numerical scheme is also used to investigate the effects of spanwise oscillations and phase randomization on turbulence statistics, and drag, in turbulent incompressible pipe flow for low to moderate Reynolds numbers (i.e. $mathrm{Re} sim 5000$) ).

No description available.

A vibração induzida por escoamento é parte intrínseca do transporte de fluidos. Por exemplo, na indústria de petróleo e gás esse fenômeno pode ser encontrado em tubulações, tanto no setor upstream, quando downstream. Essas vibrações são produto das forças geradas pelo escoamento e, portanto, carregam informações sobre sua fenomenologia. No caso de escoamento bifásico em tubo, resultados experimentais indicam forte influência da velocidade da mistura, fração de vazio e padrão de escoamento no comportamento dinâmico da estrutura. Contudo, pouco foi feito na tentativa de obter informações do escoamento a partir da reposta estrutural. Assim, o objetivo do presente estudo é desenvolver métodos para a previsão dos parâmetros do escoamento baseados na resposta de um tubo submetido a escoamento bifásico. Foi conduzido um trabalho experimental da vibração induzida por diversos padrões gás-líquido numa tubulação horizontal (PVC Ø3/4\'\') duplamente engastada, com água e ar como fluidos de trabalho. A partir de uma abordagem analítica, corroborada com resultados experimentais para escoamento monofásico e bifásico, estabelece-se a existência de uma relação, de natureza quadrática, entre a velocidade de atrito e o desvio padrão da aceleração. Dado que a velocidade de atrito é função do fator de atrito bifásico, um método para a sua previsão é desenvolvido. Ele prevê de maneira precisa os dados coletados; todos eles com erro percentual menor do que 30%. O método foi comparado também com dados experimentais e modelos da literatura, mostrando boa concordância. Além disso, apresenta-se uma relação entre a frequência pico da resposta e a fração de vazio homogênea. No fim, são apresentados: (i) um método de identificação de escoamento pistonado, baseado na superposição dos mecanismos de vibração por turbulência e intermitente, com desempenho mínimo de 81.8%; (ii) um método experimental para determinação da velocidade da mistura (J) e fração de vazio homogênea (β). Os melhores resultados são obtidos para os padrões disperso e pistonado, prevendo adequadamente os parâmetros J e β com erro percentual absoluto médio de 24.1% e 20.65%, respectivamente. / Flow-induced vibration is intrinsic to piping problems. For example, in the oil and gas industry the FIV phenomenon can be found in pipe flow both in upstream and downstream applications. The structural vibration response contains information about the flow phenomenology. In the case of two-phase pipe flow, experimental results show a strong influence of mixture velocity, void fraction and flow pattern on pipe structural dynamics. However, efforts to obtain information of the flow from pipe response have been scanty. The goal of this study is to develop two-phase flow parameters predictive methods based on the structural pipe response. An experimental study of flow-induced vibration was carried out for several flow patterns in a clamp-clamp straight pipe (PVC Ø3/4\'\'), with air and water as working fluids. From an analytical approach, a quadratic relationship between shear velocity and standard deviation of acceleration is proposed and validated against the experimental data of single and two-phase flow. Since the shear velocity depends on the friction factor, a method to predict two-phase friction factor is presented. The method predicts accurately our experimental data with a mean absolute error up to 30%. Good agreement was also found when it was compared with some models and experimental data from the literature. Furthermore, an expression to correlate peak frequency and homogeneous void fraction as a function of added mass is offered. Finally, we present: (i) a slug flow identification technique based on the superposition of the turbulence and intermittent flow-induced vibration mechanisms, with performance of 81.8% and (ii) an experimental methodology to estimate mixture velocity (J) and homogeneous void fraction (β). The latter method shows better agreement for dispersed and slug flow-patterns, predicting J and β with a mean absolute error of 24.1% e 20.65%, respectively.