Made available in DSpace on 2014-10-09T12:38:39Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:05:15Z (GMT). No. of bitstreams: 1 06042.pdf: 9369626 bytes, checksum: 37950a2f878d6535f671de4a025da71c (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

O procedimento de dimensionamento de uma linha lateral de microirrigação necessita avaliar com precisão as perdas de carga distribuídas na tubulação e as perdas de carga localizadas nas inserções dos emissores com os tubos. Estas perdas localizadas podem ser significativas quando comparadas com as perdas de carga totais, devido ao grande número de emissores instalados ao longo da linha lateral. Este trabalho reporta os resultados de um experimento sobre perda de carga distribuída, fator de atrito e perda de carga localizada em conexões de emissores &#34;on-line&#34; em tubos de polietileno de pequeno diâmetro. Foram utilizados cinco tubos com diâmetros internos de 10,0 mm, 13,0 mm, 16,3 mm, 17,4 mm e 19,7 mm. O experimento foi conduzido para números de Reynolds no intervalo de 5000 a 68000, obtidos pela variação da vazão nos tubos, a uma temperatura média da água de 20 &#177; 2 &#176;C. Os resultados foram analisados e concluiu-se que o fator de atrito f da equação de Darcy-Weisbach pode ser estimado com c = 0,300 e m = 0,25. A equação de Blasius com c = 0,316 e m = 0,25 mostrou-se conservadora na estimativa do fator de atrito, porém esse fato não constitui limitação para sua utilização em projetos de microirrigação. As análises mostraram que as duas equações proporcionam estimativas de f com pequeno desvio médio (5,1%). Para um dado conjunto tubo-conexão o coeficiente de carga cinética (KL) foi praticamente independente do número de Reynolds, para R>20000, sugerindo que cada conjunto tubo-conexão pode ser caracterizado por um valor médio de KL. Para desenvolver um procedimento de estimativa de KL, a geometria da conexão entre o emissor e o tubo foi caracterizada por um índice de obstrução IO, que depende da razão (r) entre a área da seção transversal do tubo, onde o conector está localizado, e a área da seção transversal do tubo fora do conector. Uma função potência foi ajustada aos pares experimentais (IO, KL). A seleção do modelo é consistente com o fenômeno físico uma vez que KL = 0 para r = 1 (nenhuma obstrução dentro do tubo). Para 5000<R68000 a relação foi KL = 1,23 (IO)0,51 com R2 = 0,9556 e erro padrão do ajuste igual a 0,04245. As diferenças entre os valores de KL estimados e observados são normalmente distribuídas. / Microirrigation lateral design procedure needs to accuratel evaluation of both the pipe head losses and the local losses that are due to the protrusion of emitter barbs into the flow. These local losses, in fact (in relation to the high number of emitters located along the line) can become significant compared to the overall energy loss. On this paper, the results of an experimental study on the pipe head losses, friction factor and head local losses for small-diameters polyethylene pipes are reported. The experiment was carried out using a range of Reynolds number between 5000 to 68000, obtained by varying discharge at 20 &#177; 2 &#176;C water temperature, with a internal diameter pipes of 10,0 mm, 13,0 mm, 16,3 mm, 17,4 mm and 19,7 mm. According to the results analysis and experimental conditions the friction factor (f) of the Darcy-Weisbach equation can be estimated with c = 0,300 and m = 0,25. The Blasius equation (c = 0,316 and m = 0,25) gives a conservative estimative of f, although this fact is non restrictive for microirrigationsystem design. The analysis shows that both the Blasius and the adjusted equation parameters allow accurate friction factor estimate, characterized by low mean error (5,1%). For a given pipeconnection system, the fraction KL of kinetic head was practically independent of the Reynolds number, for R>20000, which suggested that each system can be characterized by the mean value of KL. To derive an estimating procedure of KL, the geometry of the connection between the emitter and the pipe was characterized by the obstruction index IO, which is dependent on the ratio (r) between the pipe cross-section area corresponding to the section in which the emitter is located, and the pipe cross-section area. A power relationship was then fitted to the experimental IO, KL data pairs. The selection form of thr relationship is consistent with the physical phenomenon since it estimates KL = 0 for r = 1 (no obstruction into the pipe). For 5000<R<68000 the relationship was KL = 1,23 (IO)0,51 with R2 = 0,9556 and standard fit error equal to 0,04245. The differences between KL observed values and the calculated ones are normally distributed.

Estudos do escoamento em vertedouros em degraus foram realizados experimentalmente por diversos autores, mas a utilização de ferramentas de computação numérica para a simulação destes casos ainda é muito escassa. Neste trabalho realizou-se um estudo da simulação numérica do escoamento sobre vertedores em degraus, utilizando-se um programa de fluidodinâmica computacional (CFD). As configurações geométricas e hidráulicas de alguns autores da literatura foram reproduzidas através das simulações em CFD. Com as simulações testaram-se as equações propostas experimentalmente ou compararam-se diretamente os resultados experimentais com os numéricos. As características dos escoamentos nos vertedouros em degraus que foram analisadas e comparadas são as seguintes: perda ou dissipação de energia, distribuição da velocidade, distribuição da concentração de ar, perfis de pressão do degrau, um estudo da resistência de atrito e um estudo da cavitação. Foram obtidas boas comparações entre os resultados experimentais e numéricos, desta forma, todas estas análises serviram, tanto para validar a utilização das ferramentas de fluidodinâmica computacional, como para caracterizar os escoamentos para uma possível proposta de melhora no desempenho desta estrutura hidráulica. Conhecendo-se o problema da cavitação, buscou-se uma solução para minimizar a ocorrência deste fenômeno no escoamento em vertedouro em degraus. Assim, foi realizado um estudo do escoamento em um aerador de fundo. Neste estudo do aerador de fundo foram caracterizados numericamente os perfis de concentração de ar, os perfis de pressão sob o salto do aerador, os perfis de velocidade e ainda foi realizado um estudo da vazão de ar que alimenta a aeração sob o jato do aerador. Após este estudo do aerador de fundo, uma nova de configuração geométrica foi proposta para o vertedouro em degrau, com a construção de um aerador de fundo no início do escoamento de forma a minimizar o risco de cavitação ou ainda aumentar as vazões máximas de serviço. / Several experimental studies about stepped spillways flow were carried out by several authors, no ever the use of numeric computation tools is still very scarce. This work study numeric simulation in stepped spillways flow was carried out using a computation fluid dynamic (CFD) software. Several hydraulics conditions from the literature were reproduced through simulations by CFD tools. Those simulation results were compared with experimental results. The characteristics of the flow in stepped spillways were analyzed and compared focusing the following aspects: energy dissipation, velocity distribution, air concentration distribution, pressure profiles in the steps, friction resistance and cavitation. The numerical simulation results had a good approximation to the experimental results. All these analyses could be used to validate the use of the computational fluid dynamic tools, to characterize the flow for a possible improvement proposal of this hydraulic structure. The cavitation problem is the great challenge in thigh velocity flows. One solution to reduce the cavitation in the stepped spillways is the construction of a bottom aerator. A numerical study of a bottom aerator was carried out, focusing out of air concentrations, pressures under jet and velocity profiles. It was studied the discharge of air under the jet. As final result, this work proposes a new geometric configuration for stepped spillways with a bottom aerator. This bottom aerator was suggested to be set in the beginning of the spillway chute in order to reduce cavitation risk or to increase the maximum discharge in spillway.

Bubbly turbulent flows occur in a variety of industrial, naval and geophysical problems. In these flows, the bubbles in the flow interact with turbulence and/or vortical structures present in the continuous phase, resulting in bubble motion and deformation, and at the same time modifying the turbulence and/or vortical structures. Despite the fact that this has been a subject of interest for some time, mechanisms of bubble break-up due to turbulence and turbulence modulation due to bubbles are not well understood. To help understand this two-way coupled problem, we study in this thesis, the interaction of single and multiple bubbles with vortical structures; the thesis being broadly divided in to three parts. In the first part, we study the interaction of a single bubble with a single vortical structure, namely a vortex ring, formed in the continuous phase (water). This may be thought of as a simplified case of the interaction of bubbles with vortical structures in any turbulent flow. We then increase the complexity and study the interaction of a single bubble with naturally occurring vortical structures present in a fully developed turbulent channel flow, and then finally to the case of a large number of bubbles injected in to a fully developed turbulent channel. The bubble motions and deformations in all three cases are directly imaged using high speed visualizations, while the flow field information is obtained using time-resolved Particle-Image Velocimetry (PIV) in the first two cases, and from pressure drop measurements within the channel in the latter case. The interaction of a single vortex ring with a bubble has been studied for a large range of vortex ring strengths, represented in terms of a Weber number (We). We find that in all cases, the bubble is first captured by the low pressure within the core of the ring, then stretched azimuthally within the core, and gradually broken up in to a number of smaller bubbles. Along with these bubble deformations, the vorticity within the core of the ring is also modified significantly due to bubble capture. In particular, at low We, we find that the core of the ring fragments as a result of the interaction resulting in a large reduction in the enstrophy of the ring and its convection speed. In the second part of the thesis, interaction of a single bubble with naturally occurring vortical structures present in a fully developed turbulent channel is studied. In this case, single bubbles of different sizes are injected either from bottom or top wall into a channel at Reynolds number of about 60,000. We study the trajectories of the single bubble, and also investigate the effect that such bubbles have on the naturally occurring vortical structures present in these flows. The injected bubble is found to have three broadly different types of bubble paths when injected from the bottom wall, which are sliding along the wall, bouncing motions and vertical escape from the vicinity of the wall. Even at the same bubble diameter Db and channel flow Re, we find that different realizations show considerable variations, with all three bubble paths being possible. PIV measurements of a bubble captured by a naturally occurring vortical structure in the flow, shows a more rapid decrease in enstrophy compared to naturally occurring structures in the absence of bubbles, as seen in the interaction of a bubble with a vortex ring. We also find that the bubble can interact with multiple vortical structures, depending on their strength and spatial distribution in the flow, resulting in a complex bouncing bubble motion. In the third part of the study, a large number of bubbles are injected in to the channel through porous plates fixed at the top and bottom channel walls. The main parameters here are the channel Re, bubble void fraction (α) and the orientation of injection. In this case, in addition to bubble visualizations, the pressure drop through the channel is measured at different vertical locations. These measurements show large vertical variations in the measured pressure drop due to the presence of bubbles. The overall drag reduction in these cases is obtained from an integral of the pressure drop variation along the vertical direction. The visualizations show a number of bubble dynamics regimes depending on the parameters, with possibilities of both increased and decreased drag compared to the reference no bubble case. From simultaneous measurements, we relate the variations in drag reduction to the different bubble dynamics regimes. We find that at the same void fraction (α), the drag reduction obtained can be very different due to changes in bubble dynamics regimes caused by changes in other parameters. Top wall injection is observed to give good drag reductions over a wide range of flow Re and α, but is seen to saturate beyond a threshold α. In contrast, the bottom wall injection case shows that drag reduction continuously increases with αat high Re. The present study shows a maximum of about 60% increase and a similar 60% reduction in wall drag over the entire range of conditions investigated.

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.