La thèse concerne la modélisation de deux écoulements issus de problèmes géophysiques. Un premier problème a trait à la présence de tourbillons longitudinaux apparaissant dans les cours d'eau. L'origine de ces structures reste indéterminée. On aborde ce problème par une simulation numérique d'un écoulement turbulent cisaillé dans un canal ouvert utilisant un code pseudo-spectral. On tente de voir si un cisaillement de surface même faible est capable ou non de comprendre ces observations. Le second problème est lié à la resuspension des sédiments sur les bords d'une mer ou d'un lac par des ondes internes. Ces ondes existent à cause de la stratification en densité de la colonne d'eau. Lorsque elles s'approchent de la côte, elles se déstructurent générant un cisaillement sur le fond capable de resuspendre du sédiment. On a envisagé à nouveau cette étude par le biais de la simulation numérique directe. On examine comment l'onde interne se brise sur les bords en fonction de (a) la nature de la stratification, (b) la forme de la topographie du fond et (c) l'amplitude des ondes. On calcule dans chaque cas le cisaillement sur le fond. On en déduit le flux et le transport de sédiment dans toute la colonne d'eau. / This thesis studies the modeling of two problems that take their origin from a geophysical context. A first problem is related to the presence of longitudinal vortices which have been measured in rivers. The origin of these structures remains unknown. We address this problem by numerical simulations of a sheared turbulent flows in an open channel using a pseudo-spectral code. We try to determine if the presence of an imposed shear at the surface coupled with a pressure gradient is capable or not to explain these observations. The second study focuses on the sediment resuspension on shores of seas or lakes by the action of internal waves. These waves exist because of density stratification of the water column. When waves approach the shore, their patterns evolve generating a shear on the bottom capable to resuspend sediment. By direct numerical simulations, we analyse how internal waves breaking changes according to (a) stratification, (b) bottom topography and (c) wave amplitude. We compute for each case the shear exerted on the bottom, the sediment flux and transport throughout the water column.

L'étude des bruits aéronautique et hydroacoustique fait l'objet d'une forte demande industrielle en matière de recherche. En effet, dans le domaine des transports, l'écoulement du fluide sur la structure s'avère être une source de nuisance sonore non négligeable. La compréhension de ce type d'excitation est donc nécessaire pour minimiser leur impact. L'objectif de cette étude est d'identifier la pression pariétale turbulente excitant une structure à partir d'une méthode inverse vibratoire RI (Résolution Inverse) et de ses variantes RIFF (Résolution Inverse Filtrée Fenêtrée) et RIC (Résolution Inverse Corrigée). Dans un premier temps, les méthodes sont appliquées au domaine aéronautique. L'influence de la vitesse de l'écoulement sur la partie acoustique de l'excitation et la difficulté rencontrée pour identifier la totalité de la pression responsable de la vibration de la structure sont mises en avant.Dans un second temps, une application des méthodes au domaine naval est proposée. La capacité des méthodes à isoler la composante acoustique de l'excitation est mise en avant à travers des simulations. L'influence du couplage fluide-structure est étudiée et une méthode permettant de le prendre en compte est présentée. La potentialité de la méthode RIC est confirmée à travers une campagne de mesure réalisée à la DGA Techniques Hydrodynamiques. / The study of aeroacoustic and hydroacoustic noises is an important industrial research field. For example, in the transport industry, flows induced by a fluid over a structure, create a source of internal noise which cannot be neglected. To minimize its impact, it is necessary to have a good knowledge of this kind of excitation.The aim of this study is to identify the turbulent wall pressure which excites the structure, for the aeronautic and naval domains, by using an inverse vibration method, such as FAT (Force Analysis Technique) and its variations FWFAT (Filtered Windowed Force Analysis Technique) and CFAT (Corrected Force Analysis Technique).First, the methods are applied to the aeronautic domain. The influence of the flow velocity on the acoustic field and the difficulty to identify the pressure responsible for the structure vibration are pointed out.Second, an application to the naval domain is shown. The method ability to isolate the acoustic part of the excitation is introduced by using simulations. The significance of the fluid-structure coupling is studied and a method which allows taking it into account is proposed. The potentiality of CFAT method is confirmed with an experimental validation at DGA Techniques Hydrodynamiques.

Orientador: Milton Mori / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-27T18:43:17Z (GMT). No. of bitstreams: 1 SilvaJunior_JoaoLameuda_D.pdf: 4304757 bytes, checksum: 87ed8cbf9a1722317132a9054fbfd782 (MD5) Previous issue date: 2015 / Resumo: Nesta pesquisa investigou-se numericamente as características fluidodinâmicas de colunas de bolhas em leito de lama operando sob diferentes regimes de escoamento e concentrações de sólido particulado empregando a técnica CFD. A síntese de metanol em duas etapas (carbonilação e hidrogenação catalítica) também foi estudada numericamente em um reator em leito de lama. Na análise fluidodinâmica, o papel das interações entre as diferentes fases, a turbulência induzida pelas bolhas e o balanço populacional destas foram estudados. As predições das simulações foram validadas com dados experimentais obtidos da literatura. Na análise fluidodinâmica e cinética, os fenômenos de transferência de massa e de calor entre fases e as taxas das reações químicas foram avaliadas e os resultados foram comparados a dados experimentais de composição da fase líquida e de conversão do gás de síntese obtidos da literatura. As interações disperso-contínuo (arrastes gás-líquido e sólido-líquido) mostraram ser fundamentais na modelagem correta de sistemas trifásicos. As interações entre as fases dispersas (arraste gás-sólido e interação sólido-sólido) apresentaram influências significativas sob certas condições operacionais. O modelo de balanço populacional não-homogêneo promoveu bons resultados para a condição operacional estudada. A turbulência induzida pelas bolhas também demonstrou ser essencial na modelagem correta do escoamento de sistemas gás-líquido-sólido. Os modelos fluidodinâmicos com expressões cinéticas do tipo Langmuir-Hinshelwood para a síntese de metanol representaram bem o sistema reativo estudado. Em síntese, os modelos CFD propostos e simulados foram capazes de predizer o comportamento do escoamento de colunas de bolhas em leito de lama nas condições estudadas / Abstract: In the present work, numerical simulations using CFD were performed to study the fluid dynamic characteristics of a slurry bubble column operating under different flow regimes and particulate solid concentrations. The two-step methanol synthesis (carbonylation and catalytic hydrogenolysis) was also numerically investigated in a slurry bubble column reactor. In the fluid dynamic analysis, the role of phase interactions, bubble induced turbulence and population balance for bubbles were evaluated. The simulations were validated with experimental data from literature. In the fluid dynamic with chemical reactions analysis, mass and heat transfer between phases and reaction rates were evaluated and the results were compared with experimental data of liquid compositions and syngas conversion. Dispersed-continuous interactions (gas-liquid and solid-liquid drag forces) showed to be fundamental to model correctly three-phase systems. Dispersed-dispersed interactions (gas-solid drag force and solid-solid interactions) exhibited expressive influences under certain operating conditions. The inhomogeneous population balance model promoted good results for the operating conditions studied. Bubble induced turbulence is also an essential feature in the modelling of gas-liquid-solid systems. The fluid dynamic model with Langmuir-Hinshelwood-type rate expressions for the methanol synthesis represented well the reaction system studied. The proposed CFD models were capable to predict flow behaviour of slurry systems in the investigated operating conditions / Doutorado / Engenharia Química / Doutor em Engenharia Química

Grades da tomada dágua de usinas hidroelétricas são equipamentos de grande importância porque são responsáveis pela proteção das turbinas hidráulicas contra impacto de corpos flutuantes. Tais estruturas estão submetidas à ação de cargas dinâmicas oriundas do escoamento da água através das barras. O objetivo do presente trabalho é analisar grades submetidas à ação de fluxo de água. Ou seja, analisar as respostas da estrutura e o comportamento do escoamento da água utilizando os cálculos de dinâmica de estruturas acopladas às técnicas de dinâmica de fluidos computacional (CFD). Para a elaboração destas análises, foi utilizado o software comercial CFX versão 14. Tais análises foram elaboradas mediante o processo de interação fluido-estrutura. Primeiramente, um modelo estrutural simplificado das barras verticais das grades é elaborado a partir de dados de projetos conhecidos. A partir deste modelo define-se um volume de controle que representa o escoamento do fluido. Devido ao número de Reynolds calculado, utiliza-se o modelo de turbulência para obtenção dos resultados tais como tensões e deslocamentos nas barras verticais, e perfil de velocidades do escoamento. Considerando o modelo proposto, foram elaboradas análises com sete diferentes valores de velocidade de modo a comparar os dados calculados numericamente através do método de elementos finitos com valores obtidos experimentalmente. A partir do modelo verificado, é apresentada uma análise de uma grade inclinada submetida a um fluxo paralelo. / Trashracks are very important equipment because they are responsible for protecting turbines of hydroelectric plants against floating bodies. These structures are subjected to the action of dynamic loads due to the water flow through the vertical and horizontal bars. The objective of this study was to analyze trashracks submitted by action of water flow. In other words, to analyze the responses of the structure and the behavior of water flow using dynamic of structures calculations coupled with computational fluid dynamics techniques (CFD) for a turbulent regime, through the use of commercial software CFX version 14. This analysis is elaborated by the process of fluid structure interaction. First of all, a simplified structural model of vertical bars is defined from other similar projects. For this model is defined a volume of control that represents fluid flow. Due to the Reynolds number calculated, it is utilized a turbulence model in order to obtain the results. These results are: stresses and displacements of vertical bars; and profile of velocities of flow. The results are analyzed and discussed. After that, considering the simplified model, analyzes with seven different values of speed are executed in order to compare the results between the data calculated numerically by finite elements method, and the values obtained experimentally. Considering the model verified, an analysis, of an inclined trashrack subjected to a parallel flow, is presented.

This master’s thesis deals with the simulation of flow through the normalized orifice plate. There is described flow measurement with flowmeters, which reduces the cross-section of the pipe and causes the pressure difference before and after the flowmeter. Following is a description methods of modeling of turbulent flow and a description of software for the simulation of flow from the company Ansys. The theoretical part is followed a practical part, which is focused on determining the permanent pressure loss caused by the orifice plate and the verification of straight pipeline lengths between orifice and obstacle.

A caractérisation de l’écoulement, du transfert de chaleur et de masse lors du déplacement de gouttelettes de diamètre inferieur au millimètre dans un milieu extérieur font l’objet de notre étude. La première partie présente l’état de l’art des connaissances théoriques et expérimentales des comportements aérodynamiques ainsi que les mécanismes de transfert thermiques et massiques intervenant entre une phase dispersée et une phase continue. La deuxième partie est consacrée à l’étude du phénomène d’évaporation d’une gouttelette mono-dispersée en chute libre dans l’air. Pour cela, nous avons réalisé un dispositif expérimental. Les mesures, nous permettent de prédire l’évaporation de la gouttelette en fonction des caractéristiques physico-chimiques et de l’hygrométrie du milieu extérieur. Pour la modélisation du transfert de chaleur et de masse nous avons utilisé un modèle simple qui tient en compte du couplage entre le mouvement et les phénomènes de transferts, validé dans une précédente étude au sein du laboratoire. Un bon accord est observé. La troisième partie traite de la simulation numérique de l’interaction entre les particules sphériques dans un régime laminaire. Tout d’abord, nous avons proposé et validé un modèle simple qui ne tient pas en compte des phénomènes d’interaction. Les résultats obtenus sont en concordance avec la littérature. Par la suite, nous avons étudié l’interaction entre trois particules identiques et co-alignées. Ce modèle tient compte de la nature de la particule, du nombre du Reynolds et de la distance de séparation. Nous avons validé ce travail par une comparaison avec une étude précédente que nous avons généralisé. La dernière partie est cernée sur l’étude de la dispersion des gouttelettes dans un écoulement turbulent homogène et isotrope. Pour cela, nous avons proposé un modèle Lagrangien de suivi des trajectoires. La production de la turbulence est assurée par une condition de turbulence de grille. Nous avons considéré que les caractéristiques moyennes de l’écoulement fluide sont connues. La sélection des fluctuations de vitesse turbulente est assurée par une méthode probabiliste gaussienne que nous avons développée. La fluctuation est conservée durant un certain temps lié à turbulence, elle est renouvelée au cours du calcul. Ce renouvellement est donné par le temps caractéristique de turbulence. / The characterization of flow, mass and heat transfer during moving droplets of diameter inferior to the millimetre makes the object of our study. In the first part, we present the theoretical and experimental knowledge. In the second part, we studied the evaporation of a free falling droplet in the air. In the third part, we make a simulation of the interaction between the spherical particles in laminar flow. This model takes into account the nature of the particle, the Reynolds number and the separation distance. In the last part, we study the dispersion of droplets in a homogeneous and isotropic turbulent flow.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21723号 / 工博第4540号 / 新制||工||1708(附属図書館) / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 中川 一, 准教授 竹林 洋史, 准教授 川池 健司 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

An experimental investigation was performed to ascertain the nature of turbulence in a narrow apex angle isosceles triangular duct. The study involved the design and construction of a low noise, low turbulence wind tunnel that had an isosceles triangular test section with an apex angle of 11.5[degrees]. Experiments involved the measurement of velocity fluctuations using hot wire anemometry and wall pressure fluctuations using a condenser microphone. Measurement of the velocity fluctuations reconfirms the coexistence of laminar and turbulent regions at a given cross section for a range of Reynolds numbers. The laminar region is concentrated closer to the apex while the turbulent region is found closer to the base. The point of transition is a function of the Reynolds number and moves closer to the apex as the flow rate is increased. Moreover, it was found in this investigation that traditional scaling of the turbulent statistical quantities do not hold good in this geometry. Although velocity fluctuations showed distinctive flow regimes, no such distinction could be seen in the dynamic wall pressure data. The nature of the dynamic wall pressure was uniform throughout the entire cross section suggesting that wall pressure fluctuations, unlike the velocity fluctuations, are able to travel from the base to the apex, without being damped. This implies that the relationship between the velocity and the pressure fluctuations applicable in the other systems does not hold well in a narrow apex angle isosceles triangular duct. Further, the typical scaling relationships applied to wall pressure spectra of other geometries doesn't apply in this scenario and the ratio of the RMS pressure fluctuation to the mean shear is much higher compared to a flat plate or pipe flow situation.

Understanding the physics of mixing for two fluids is a complicated problem and has always been an interesting phenomenon to study. Surface discharge is the oldest, least expensive and simplest way of discharging industrial or domestic wastewater into rivers and estuaries. Because of the lower degree of dilution in surface discharges, critical conditions are more likely to occur. Having a better understanding of the mixing phenomenon in these cases will help to predict the environmental effects more accurately. In this study, surface discharges of jets into waterbodies with or without crossflows were investigated numerically and experimentally. Three-dimensional (3-D) Computational Fluid Dynamics (CFD) models were developed for studying the surface discharge of jets into water bodies using different turbulence models. Reynolds stress turbulence models and spatially filtered Large Eddy Simulation (LES) were used in the numerical models. The effects of inclusion of free surface water in the CFD models on the performance of the numerical model results were investigated. Numerical model results were compared with the experimental data in the literature as well as the experimental works performed in this study. Experimental works for buoyant and non-buoyant surface discharge of jets into crossflow and stagnant water were conducted in this study. A new setup was designed and built in the Civil Engineering Hydraulics Laboratory at the University of Ottawa to perform the desired experiments. Stereoscopic Particle Image Velocimetry (Stereo-PIV) was used to measure the instantaneous spatial and temporal 3-D velocity distribution on several planes of measurement downstream of the jet with the frequency of 40 Hz. Averaged 3-D velocity distribution was extracted on different planes of measurement to show the transformation of the velocity vectors from a “jet-like” to a “plume-like” flow regime. Averaged 3-D velocity distribution and streamlines illustrated the flow transformation of the surface jets. Experimental results detected the formation and evolution of vortices in the surface jet’s flow structure over the measurement zone. Additional turbulent flow characteristics such as the turbulent kinetic energy (k), turbulent kinetic energy dissipation rate (ϵ), and turbulent eddy viscosity (υt) were calculated using the measured time history of the 3-D velocity field.

No description available.