O estudo do comportamento de um perfil de uma seção aerolástica típica, com Reynolds na faixa de microaeronaves, constitui o principal foco deste trabalho, tomando como objetivo a estimativa de parâmetros do fenômeno de flutter. A pesquisa analisa o escoamento de um fluido sobre um corpo (cilindro e perfil de aerofólio) em estado estacionário e oscilante, em escoamento de velocidade constante, e, especificamente, o fenômeno de flutter. As equações de Navier-Stokes, com termo de força, são resolvidas pelo método da fronteira virtual para modelagem da interface escoamento/estrutura, representada pela geometria de um corpo de geometria complexa. Na discretização das equações governantes foi utilizado o método de diferenças finitas, sobre malhas deslocadas, com avanço temporal das velocidades do escoamento por meio de um esquema de Runge-Kutta de ordem 4. Os códigos computacionais, para as simulações das diretrizes e a lógica de cálculo, foram criados no contexto deste trabalho. A verificação foi feita através do método da solução manufaturada por meio de um problema fictício, que tem uma solução analítica conhecida, e que preenche as condições de contorno implementadas no código. O modelo da fronteira virtual é testado para os casos de escoamento sobre cilindro de base quadrada, cilindro de base circular e perfil de aerofólio tipo NACA0012, com malhas regular e não regular, e para condições estacionária e sob oscilação forçada. Foi estudado o comportamento de formação de vórtices, provocados por escoamento uniforme sobre o perfil de aerofólio, através dos coeficientes de arrasto, sustentação e pressão com visualização por meio da vorticidade e linhas de corrente, para vários ângulos de ataque e oscilação forçada com elevação e rotação em torno de um pivô posicionado no centro geométrico do perfil (50% da corda). Finalmente, é apresentada uma determinação numérica das características aeroelásticas para o perfil de aerofólio NACA0012, em escoamento de número de Reynolds ultra baixo (Re = 1.000), e parâmetros de flutter para um caso de baixa frequência de oscilação. / The behavior study of a profile of a typical aerolastic section, with Reynolds in range of micro aerial vehicle, is the main focus of this work, taking as objective the estimation of parameters of flutter phenomenon. The research analyzes of the flow of a incompressible fluid on a body (cylinder and airfoil profile) at steady state and oscillating with constant speed and, specifically, the flutter phenomenon. The Navier-Stokes equations, with force term, are solved by virtual boundary method for modeling interface flow/structure, represented by the geometry of a body of complex geometry. In discretization of the governing equations, the method of finite differences on staggered grid, with temporal advancement of discharge velocity through a Runge-Kutta of order 4. The computer codes, for simulations guidelines and logic calculation, were created in the context of this work. The verification was done by method ofmanufactured solution through a fictional problem, which has a known analytical solution, and satisfies the boundary conditions implemented in code. The model of the virtual boundary is tested for cases of flow over a square cylinder, circular cylinder and profile of a NACA0012 airfoil type, with regular and non-regular meshes, over stationary and forced oscillation conditions. We studied the behavior of vortex formation, caused by uniform flow over the airfoil profile, by the drag, lift and pressure coefficients with view through the vorticity and streamlines for various attack angles and forced oscillation with plunge and pich around a pivot witch was positioned at the geometric airfoil profile (half chord). Finally, it is presented a numerical determination of aeroelastic characteristics for the NACA0012 airfoil profile, flow under ultra low Reynolds number, and flutter parameters for a case of low oscillation frequency.

O escoamento em torno de corpos tem sido objeto de estudo de muitos pesquisadores e é muito explorado experimental e computacionalmente, devido a sua grande aplicabilidade na engenharia. No entanto, simular computacionalmente este tipo de escoamento requer uma atenção especial ao escolher o tipo malha a ser utilizado. Em muitos casos faz-se necessário o uso de uma malha que se adapte ao contorno do obstáculo, o que pode ocasionar um aumento no esforço computacional. Um maneira de contornar este problema é a utilização do Método das Fronteiras Imersas, que possibilita o uso de malha cartesiana na simulação computacional do escoamento em torno de obstáculos. Isso é possível através da adição de um termo forçante nas equações que modelam o escoamento, e assim as forças que agem sobre o contorno do corpo são transferidas diretamente para a malha. O objetivo deste trabalho de mestrado foi implementar o método das Fronteiras Imersas e simular o escoamento em torno de um cilindro circular em repouso, movimentando-se na mesma direção do escoamento, na direção perpendicular ao escoamento, ou rotacionando em torno do próprio eixo. As simulações computacionais possibilitaram a captura do fenômeno de Atrelagem Síncrona, caracterizado pela sincronia entre a frequência de desprendimento natural de vórtices e a frequência de oscilação do mesmo. O Método das Fronteiras Imersas mostrou um ótimo desempenho quando comparado a resultados experimentais e numéricos encontrados na literatura / The flow around bodies have been studied by many researchers. Both experimental and computational approaches have been extensively explored in researches on flow around bodies and have been applied in many engeneering problems. However, to choose an appropriate type of mesh to perform computational simulations of this type of problem requires special attention. In many cases, it is necessary to use a mesh that is able to conform to the boundary if a given obstacle. The need to perform this adaptation may increase the computational effort. The Immersed Boundary Method enables the use of cartesian meshes to perform computational simulations of flows around obstacles. The idea of this method is to add a forcing term in the equations that model the flow. Thus, the forces applied on the body boundaries are directly transfered to the mesh. The aim of this work was to perform a computational implementation of the Immersed Boundary Method to simulate the flow over a oscilating circular cylinder. This oscilation may be inline with the flow, cross-flow, or rotating. The computational simulations enabled the capture of the lock-in phenomena, which consists of the syncronization between the vortex shedding frequency and the cylinder oscilation frequency. The results obtained from the computational simulations using the Immersed Boundary Method were in good agreement with the numerical and experimental results found in the literature

Orientador: Marco Lucio Bittencourt / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-05T06:50:24Z (GMT). No. of bitstreams: 1 Gerardin_RodrigoCeccatto_M.pdf: 1433853 bytes, checksum: d1832bbbe32aa8b2f8edb3756793f3f5 (MD5) Previous issue date: 2005 / Resumo: Atualmente, devido as exigências comerciais e técnicas, os motores de combustão interna operam com pressões de combustão cada vez mais altas. Ao mesmo tempo, deve-se otimizar a operação de todo sistema e a forma dos componentes levando-se em conta a melhor performance e redução de peso. Para um melhor entendimento do comportamento dinâmico de um motor de multi cilindros, é necessário verificar a cinemática e a dinâmica para apenas um cilindro como feito neste trabalho. O foco principal deste trabalho é desenvolver um modelo matemático para determinar as distribuições de pressão e as forças atuantes nos mancais hidrodinâmicos para um cilindro de um motor de combustão interna. Um modelo dinâmico do sistema de pistão-biela-manivela é apresentado e permite calcular as forças dinâmicas e folgas no mancal principal, olhais maior e menor da biela derivados da pressão de combustão. O modelo matemático do mancal hidrodinâmico radial é oriundo da equação de Reynolds e resolvido utilizando o Método de Elementos Finitos. O sistema dinâmico não-linear é resolvido utilizando o método iterativo de Newton-Raphson para cada passo de integração no tempo / Abstract: Due to the current commercial and technical requirements, the internal combustion engines must operate under higher pressures. It is also necessary to optimize the system operation and the shape of the components aiming at increasing the performance and weight reducing. For a better understanding of the dynamical behavior of a multi-cylinder engine, it is necessary to verify the kinematics and dynamics for just one cylinder, as considered in this work. The main focus of this work is the development of a mathematical model to determine the pressure distributions and the hydrodynamic bearing forces for one cylinder internal combustion engine. The dynamical model of the piston-conrod-crank system is presented and allows the calculation of the dynamic forces and clearances obtained from the combustion pressure for the main, big-end and small-end bearings. The mathematical model of the hydrodynamic bearing comes from the Reynolds equation and is solved by the Finite Element Method. The non-linear dynamic system is solved by the iterative Newton-Rhapson method for each time integration step / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestre em Engenharia Mecânica

Long-span bridges are flexible and therefore are sensitive to wind induced effects. One way to improve the stability of long span bridges against flutter is to use cross-sections that involve twin side-by-side decks. However, this can amplify responses due to vortex induced oscillations. Wind tunnel testing is a well-established practice to evaluate the stability of bridges against wind loads. In order to study the response of the prototype in laboratory, dynamic similarity requirements should be satisfied. One of the parameters that is normally violated in wind tunnel testing is Reynolds number. In this dissertation, the effects of Reynolds number on the aerodynamics of a double deck bridge were evaluated by measuring fluctuating forces on a motionless sectional model of a bridge at different wind speeds representing different Reynolds regimes. Also, the efficacy of vortex mitigation devices was evaluated at different Reynolds number regimes. One other parameter that is frequently ignored in wind tunnel studies is the correct simulation of turbulence characteristics. Due to the difficulties in simulating flow with large turbulence length scale on a sectional model, wind tunnel tests are often performed in smooth flow as a conservative approach. The validity of simplifying assumptions in calculation of buffeting loads, as the direct impact of turbulence, needs to be verified for twin deck bridges. The effects of turbulence characteristics were investigated by testing sectional models of a twin deck bridge under two different turbulent flow conditions. Not only the flow properties play an important role on the aerodynamic response of the bridge, but also the geometry of the cross section shape is expected to have significant effects. In this dissertation, the effects of deck details, such as width of the gap between the twin decks, and traffic barriers on the aerodynamic characteristics of a twin deck bridge were investigated, particularly on the vortex shedding forces with the aim of clarifying how these shape details can alter the wind induced responses. Finally, a summary of the issues that are involved in designing a dynamic test rig for high Reynolds number tests is given, using the studied cross section as an example.

This study focuses on the investigation of flow behavior at low Reynolds numbers by the experimental and numerical performance testing of micro-channel heat exchangers. An experimental study of the heat transfers and pressure drop of compact heat exchangers with louvered fins and flat tubes was conducted within a low air-side Reynolds number range of 20 < ReLp < 225. Using an existing low-speed wind tunnel, 26 sample heat exchangers of corrugated louver fin type, were tested. New correlations for Colburn j and Fanning friction f factor have been developed in terms of non-dimensional parameters. Within the investigated parameter ranges, it seems that both the j and f factors are better represented by two correlations in two flow regimes (one for ReLp = 20 – 80 and one for ReLp = 80 – 200) than a single regime correlation in the power-law format. The results support the conclusion that airflow and heat transfer at very low Reynolds numbers behaves differently from that at higher Reynolds numbers. The effect of the geometrical parameters on the heat exchanger performance was investigated. The numerical investigation was conducted for further understanding of the flow behavior at the range of experimentally tested Reynolds number. Ten different heat exchanger geometries with varied geometrical parameters obtained for the experimental studies were considered for the numerical investigation. The variations in the louver angle were the basis of the selection. The heat transfer and pressure drop performance was numerically investigated and the effect of the geometrical parameters was evaluated. Numerical results were compared against the experimental results. From the comparison, it is found that the current numerical viscous laminar models do not reflect experimentally observed transitional two regime flow behavior from fin directed to the louver directed at very low Reynolds number ranging from 20 to 200. The flow distribution through the fin and the louver region was quantified in terms of flow efficiency. The flow regime change was observed at very low Reynolds number similar to the experimental observations. However, the effect of two regime flow change does not reflect on the thermal hydraulic performance of numerical models. New correlations for the flow efficiency � have developed in terms of non-dimensional parameters.

No description available.

The main purpose of this thesis was to propose and test a new approach that captures the features of single and multiple bubbles dynamics using the Shan and Chen-type lattice Boltzmann method (LBM). Two dimensional bubbles motions were simulated considering the buoyancy effect for which the topology of the bubble is characterized by the Eötvös (Eo), and Morton (M) numbers. A qualitative and quantitative validation were performed using the Level set method. Bubble shape deformation was captured and analysis based on terminal Reynolds number and degree of circularity show very good agreement with the experimental results and with available simulation results. In sum, this study presents crucial preliminary information to further analyze multiphase fluid flows in various contexts.

Cette thèse porte sur le problème du ballottement d'un liquide dans un réservoir, rencontré dans le transport et le stockage du GNL par des structures flottantes. La prédiction des chargements réels, dus au ballotement sur les parois du réservoir, est souvent basée sur des études expérimentales à petite échelle. La modélisation expérimentale à petite échelle respecte la similitude de Froude et le rapport de densité entre le gaz et le liquide. Cependant, d’autres similitudes sont biaisées comme la similitude par rapport au nombre de Weber et la similitude par rapport au nombre de Reynolds. De plus, les pressions enregistrées montrent une grande variabilité quand le même essai est répété. Dans une première partie, différentes sources physiques responsables de cette variabilité sont discutées, à savoir les instabilités de surface libre, la retombée des gouttes et des jets liquides sur la surface libre, et la production et l'entraînement des bulles dans le liquide. En fait, ces phénomènes sont à l'origine des perturbations de l'écoulement, de la variabilité de la géométrie de la vague et de cette façon des pressions engendrées par cette dernière sur la paroi. D'autres mécanismes de dissipation d’énergie sont identifiés. Ils sont liés aux frottements aux parois et aux déferlements de vagues. Nous montrons que cette dissipation induit un effet mémoire à courte durée pour l’écoulement, permettant de reproduire pour chaque impact la distribution statistique des pics de pression avec une courte durée des excitations. Ces sources de variabilité et ces mécanismes de dissipation dépendent de la tension de surface et de la viscosité du liquide. Ainsi nous étudions dans une deuxième partie, les effets de ces paramètres physiques. Nous montrons que la forme locale de la vague dépend de la tension de surface. Par contre, les effets sur la forme globale de la vague sont négligeables. Plus la tension de surface diminue, plus les pics pression sont faibles. Ce qui est dû aux différents phénomènes liés au développement des ligaments, la fragmentation en gouttes et la génération de la mousse sur la crête de la vague, et à l’entraînement des bulles dans le liquide. Quant à la viscosité du liquide, elle affecte à la fois la forme globale et la forme locale de la vague, là encore les pressions sont modifiées. Cette étude paramétrique permet, dans une troisième partie, d'étudier et comprendre les effets du nombre de Weber et du nombre de Reynolds, en comparant les résultats pour deux échelles différentes 1:40 et 1:20, quand les mêmes fluides sont considérés. De plus, en se basant sur différents cas de comparaison avec la similitude de Reynolds et/ou la similitude de Weber, nous montrons que la double similitude est indispensable pour obtenir une forme de vague avant l'impact indépendante de l'échelle. Cependant, la distribution statistique des pics de pression dépend aussi d’autres nombres adimensionnels à savoir le nombre de Mach du liquide et le nombre de Mach du gaz. / This work focuses on sloshing problem, encountered in the transport and storage of LNG by floating structures. The prediction of real sloshing loads is often based on small-scale experimental studies, respecting the Froude similarity and the density ratio between the gas and the liquid. However, other similarities are biased such as the Weber similarity and the Reynolds similarity. In addition, the recorded pressures show great variability when the same test is repeated. In a first part, different physical sources responsible for this variability are discussed, which are the free surface instabilities, the falling droplets and liquid jets impinging on the free surface, and the liquid entrainment by bubbles. In fact, these phenomena are at the origin of the flow disturbances, the variability of the wave shape, and hence its pressures on the wall. Other dissipation mechanisms are identified. They are related to wall frictions and breaking waves. Thanks to this energy dissipation, we show that the flow is characterized by a short-term memory, making it possible to reproduce for each impact its statistical distribution of pressure peaks with a short duration of excitations. These sources of variability and dissipation mechanisms depend on the surface tension and the viscosity of the liquid. Thus, we study, in a second part, these physical parameters. We show that the local wave shape depends on the surface tension. However, its effects on the global wave shape are negligible. Besides, when the surface tension is reduced, the statistical pressures are reduced. This is due to various phenomena related to the development of liquid ligaments, their fragmentation into drops and the generation of foam at the wave crest, and the liquid entrainment by bubbles. As for the viscosity of the liquid, it affects both the local and global shape wave shapes, again the pressures are changed. Based on this parametric study, The effects of Weber number and Reynolds number are studied by comparing the results for two different scales 1:40 and 1:20, when the same fluids are used. Moreover, considering different cases of comparison with Reynolds number similarity and / or Weber number similarity, the results show that both similarities are essential to obtain a scaleindependent wave shape. However, the statistical distribution of pressure peaks also depends on other dimensionless numbers, namely the Mach number of the liquid and the Mach number of the gas.

The goal of submitted thesis is to perform a computer simulation of bubble creation in T-channel. In the first section of the paper, the theoretical applications of microfluidic bubble, micromachines and droplet formation are described. In the second part of the text, author uses cross flowing method for simulation od bubble creation. Furthermore, several settings in computer simulation software Fluent are mentioned. In addition, the influence of velocity at the T-channel inlet on surface tension and on bubble length is presented.

Byla provedena měření turbulentní Rayleighovy-Bénardovy konvekce v kryogenním heliu v rozsahu Rayleighových čísel 1e8