No / The results of computational fluid dynamics simulation for convective heat transfer of turbulent flow in a cooled convergent-divergent nozzle are reported. The importance of the heat transfer coefficient is to find the most suitable metals for the nozzle wall as well as its application for producing nano-particles. ansys-icem and ansys-cfx 13.0 are used to mesh and simulate fluid flow in the nozzle, respectively. Effects of grid resolution and different turbulence models on the heat transfer coefficient are investigated. Three turbulence models of k-omega, k-epsilon and shear stress transport are applied to calculate the heat transfer coefficient. Stagnation absolute pressure and temperature are 10.3 bara and 840 K, respectively, the same as those in the experimental work. The heat transfer coefficients obtained from simulation are compared with the available experimental data in literature to find out the best suitable mesh grid and the turbulence model. Under the selected operating conditions, k-epsilon and k-omega models have shown the best agreement with the experimental data with the average error of 6.5% and 10%, respectively, while shear stress transport under predicts the values with 16% error.

Research has shown that mixing in cross-junctions in water distribution systems is far from perfect, and that the entering fluids bifurcate from each other rather than mix. The purpose of this thesis is to study the behaviour of two fluids entering a cross-junction in a water distribution system. In this context, experimental tests and numerical simulations are performed in order to produce and test the mixing at cross-junctions. This study focuses on cross-junctions with equal pipe diameters, with flows that can vary from laminar to turbulent. The fluids are pure water and tracer. Different tracer materials with various flow configurations were tested experimentally and numerically. Firstly, an experimental study of mixing in cross-junctions was performed at the TZW: DVGW-Technologiezentrum Wasser (German Water Center) in Dresden. This experimental study pro-vides an overview of the parameters that can affect the mixing in cross-junctions, and is used to validate the numerical simulations. Different numerical approaches for modelling the mixing in cross-junctions are presented. The simulations use an existing commercial CFD code, ANSYS CFX 19.1, and are also extensively validated using experimental and numerical results from other researchers. In ANSYS CFX there are several models that can be used to simulate the mixing of two fluids. In this study both fluids are considered to be isothermal incompressible and without phase change. Two mixing models are tested: the additional variable model and the multi-component model. The three-dimensional models use RANS turbulence models and LES simulations. The parameters of the numerical setup were investigated carefully in order to study their effect on the results. Furthermore, the effect of changing the turbulent Schmidt number in the RANS simulations was extensively studied, and the results are compared with the experimental results. The accuracy of using Large eddy simulation to simulate mixing in cross junction is also tested, taking into consideration the required mesh resolution and the turbulence in the initial bound-ary conditions. This work presents an applicable numerical approach to simulate the fluid behaviours in cross-junctions. Using this approach, the effect of different parameters is tested, such as: Reynolds number, pipe diameter, mixing time, diffusivity and density difference. The results produced using the numerical approach revealed that one of the main parameters that affect the mixing is the density difference. It has a great effect on the outgoing concentration in cross-junctions, and the mixing behaviour changes when the tracer material and the flow regime are changed. The used approach will help to investigate the effect of various flow parameters on the mixing in cross-junctions. Based on the data set of this study, an empirical conceptual model for mixing in cross-junction is also presented using multiple regression, and there is potential for this model to be further developed in combination with experimental and numerical studies.:Abstract Kurzfassung Nomenclature List of Figures List of Tables 1 Introduction and Literature Review 1.1 Introduction 1.2 Literature Review 1.2.1 Transport in water distribution system 1.2.2 Mixing in pipe junctions 1.3 Research problems 1.4 Research methodology and objectives 2 Theoretical Background 2.1 Basic equations and terms in pipe hydraulic 2.1.1 Conservation of mass (the equation of continuity) 2.1.2 Conservation of momentum (the Navier-Stokes equations) 2.1.3 Contaminant transport (transport equation) 2.1.4 Reynolds number 2.1.5 Flow development in pipes 2.1.6 Velocity distribution in pipe flows 2.1.7 Definition of concentration and mass fraction 2.1.8 Viscosity 2.2 Turbulence and modeling 2.2.1 Spatial discretization methods 2.2.2 Turbulence models 2.2.3 Direct numerical simulation (DNS) 2.2.4 Reynolds averaged Navier-Stokes Equations (RANS) 2.2.5 Large eddy simulation 2.3 Modeling of mixing in ANSYS CFX 2.3.1 Additional variable 2.3.2 Multi-component flow model 2.3.3 Two-phase flow model 2.4 Mixing in cross-junctions (available models) 2.4.1 Complete mixing model 2.4.2 Bulk advective mixing model (BAM) 2.4.3 BAM-Wrap mixing model 2.4.4 Shao mixing model 3 Experimental Study 3.1 Introduction 3.2 Description of the model network 3.3 Results and discussion 3.3.1 Turbulent flow experiments 3.3.2 Laminar flow experiments 3.3.3 The interpolation of the experimental results 3.4 Conclusion 4 3D Numerical Study using ANSYS CFX 4.1 Introduction to ANSYS CFX 4.1.1 Model setup in ANSYS CFX 4.1.2 Modeling of mixing in cross-junctions 4.2 Additional variable model 4.2.1 Application of Reynolds averaged Navier-Stokes simulation 4.2.2 Sensitivity analysis of URANS simulations 4.2.3 Application of the large eddy simulation 4.2.4 Summary 4.3 Multi-component flow model 4.3.1 Setup of the multi-component simulation model 4.3.2 Results and discussion 4.4 Summary 5 Mixing Model for Cross junction 5.1 Introduction 5.2 Parameter sensitivity Analysis 5.2.1 The influence of changing the Reynolds number 5.2.2 The influence of changing the pipe diameter 5.2.3 The influence of the inflow and outflow ratios 5.2.4 The influence of changing the tracer properties 5.2.5 The influence of the pipe roughness 5.3 Conceptual model for mixing in cross junction 6 Summary 7 Outlook References APPENDIX A APPENDIX B / Frühere Forschungsergebnisse haben gezeigt, dass das Vermischen von gelösten Substanzen in Rohrkreuzen in Wasserversorgungssystemen alles andere als perfekt ist und wenn zwei Flüssigleiten in einem Rohrkreuz eintreten, trennen sie sich eher voneinander anstatt sich zu vermischen. Das Ziel dieser Forschungsarbeit ist es, das Verhalten von zwei Flüssigkeiten in einem Rohrkreuz zu untersuchen. In diesem Zusammenhang werden experimentelle Unter-suchungen und numerische Strömungssimulationen durchgeführt, um das Vermischen an Kreuzungspunkten in Wasserversorgungssystemen zu untersuchen. Diese Arbeit konzentriert sich auf Rohrkreuzen mit gleichen Rohrdurchmessern in Strömungen, die von laminar bis turbulent variieren können. Verschiedene Eigenschaften der Flüssigkeiten mit verschiedenen Strömungskonfigurationen wurden experimentell und numerisch getestet. Zunächst wurden im TZW (DVGW-Technologiezentrum Wasser) die experimentellen Untersuchungen zum Mi-schen in Rohrkreuzungen durchgeführt. Die durchgeführten experimentellen Untersuchungen bieten einen Überblick über die Parameter, die das Mischverhältnis in Kreuzungspunkten be-einflussen können, und werden zur Validierung der numerischen Simulationen verwendet. Verschiedene numerische Ansätze zur Modellierung des Vermischens in Rohrkreuzen werden vorgestellt. Die 3D-numerische Strömungssimulationen verwenden einen vorhandenen kommerziellen CFD-Code, ANSYS CFX 19.1, und werden auch anhand experimenteller und numerischer Ergebnisse anderer Forscher umfassend validiert. In ANSYS CFX gibt es mehre-re Modelle, mit denen das Vermischen von Flüssigkeiten simuliert werden kann. In dieser Arbeit werden beide Flüssigkeiten als isotherm, inkompressibel und ohne Phasenwechsel betrachtet. Es werden zwei Mischmodelle getestet: das Additional Variable Model und das Multi-component Model. Die 3D -Strömungsmodelle verwenden RANS-Turbulenzmodelle und LES-Simulationen. Die Parameter des numerischen Aufbaus wurden sorgfältig untersucht, um ihre Auswirkung auf die Ergebnisse zu untersuchen. Darüber hinaus wurde der Einfluss der Änderung der turbulenten Schmidt-Zahl in den RANS-Simulationen ausführlich untersucht und die Ergebnisse mit den experimentellen Ergebnissen verglichen. Die Genauigkeit der Ver-wendung einer Large-Eddy-Simulation zur Simulation des Vermischens in Rohrkreuz wird ebenfalls getestet, wobei die erforderliche Netzauflösung und die Turbulenzen in den An-fangs- und Randbedingungen berücksichtigt werden. Diese Arbeit präsentiert einen anwend-baren numerischen Ansatz zur Simulation des Fließverhaltens in Rohrkreuzen. Mit diesem Ansatz wird die Wirkung verschiedener Parameter getestet, z. B.: Reynolds-Zahl, Rohrdurch-messer, Vermischungszeit, Diffusivität und Dichteunterschied. Die mit den numerischen Mo-dellen erzielten Ergebnisse zeigten, dass einer der Hauptparameter, die das Vermischen in Rohrkreuzen beeinflussen, der Dichteunterschied ist, welcher einen großen Einfluss auf die ausgehende Konzentration in Kreuzungen hat. Der verwendete numerische Ansatz wird dazu beitragen, die Auswirkung verschiedener Strömungsparameter auf das Vermischen in Rohr-kreuzen zu untersuchen. Basierend auf dem Datensatz dieser Studie wird auch ein empiri-sches konzeptionelles Modell für das Vermischen in Rohrkreuz unter Verwendung multipler Regression vorgestellt. Dieses Modell kann in Kombination mit experimentellen und numeri-schen Studien weiterentwickelt werden.:Abstract Kurzfassung Nomenclature List of Figures List of Tables 1 Introduction and Literature Review 1.1 Introduction 1.2 Literature Review 1.2.1 Transport in water distribution system 1.2.2 Mixing in pipe junctions 1.3 Research problems 1.4 Research methodology and objectives 2 Theoretical Background 2.1 Basic equations and terms in pipe hydraulic 2.1.1 Conservation of mass (the equation of continuity) 2.1.2 Conservation of momentum (the Navier-Stokes equations) 2.1.3 Contaminant transport (transport equation) 2.1.4 Reynolds number 2.1.5 Flow development in pipes 2.1.6 Velocity distribution in pipe flows 2.1.7 Definition of concentration and mass fraction 2.1.8 Viscosity 2.2 Turbulence and modeling 2.2.1 Spatial discretization methods 2.2.2 Turbulence models 2.2.3 Direct numerical simulation (DNS) 2.2.4 Reynolds averaged Navier-Stokes Equations (RANS) 2.2.5 Large eddy simulation 2.3 Modeling of mixing in ANSYS CFX 2.3.1 Additional variable 2.3.2 Multi-component flow model 2.3.3 Two-phase flow model 2.4 Mixing in cross-junctions (available models) 2.4.1 Complete mixing model 2.4.2 Bulk advective mixing model (BAM) 2.4.3 BAM-Wrap mixing model 2.4.4 Shao mixing model 3 Experimental Study 3.1 Introduction 3.2 Description of the model network 3.3 Results and discussion 3.3.1 Turbulent flow experiments 3.3.2 Laminar flow experiments 3.3.3 The interpolation of the experimental results 3.4 Conclusion 4 3D Numerical Study using ANSYS CFX 4.1 Introduction to ANSYS CFX 4.1.1 Model setup in ANSYS CFX 4.1.2 Modeling of mixing in cross-junctions 4.2 Additional variable model 4.2.1 Application of Reynolds averaged Navier-Stokes simulation 4.2.2 Sensitivity analysis of URANS simulations 4.2.3 Application of the large eddy simulation 4.2.4 Summary 4.3 Multi-component flow model 4.3.1 Setup of the multi-component simulation model 4.3.2 Results and discussion 4.4 Summary 5 Mixing Model for Cross junction 5.1 Introduction 5.2 Parameter sensitivity Analysis 5.2.1 The influence of changing the Reynolds number 5.2.2 The influence of changing the pipe diameter 5.2.3 The influence of the inflow and outflow ratios 5.2.4 The influence of changing the tracer properties 5.2.5 The influence of the pipe roughness 5.3 Conceptual model for mixing in cross junction 6 Summary 7 Outlook References APPENDIX A APPENDIX B

Submitted by William Justo Figueiro (williamjf) on 2015-06-16T23:47:58Z No. of bitstreams: 1 27.pdf: 3460975 bytes, checksum: 6fb4884eb12bbee8490b27b6414b47c0 (MD5) / Made available in DSpace on 2015-06-16T23:47:58Z (GMT). No. of bitstreams: 1 27.pdf: 3460975 bytes, checksum: 6fb4884eb12bbee8490b27b6414b47c0 (MD5) Previous issue date: 2013-08 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / FINEP - Financiadora de Estudos e Projetos / Furnas Centrais Elétricas / Comportas segmento invertidas são frequentemente utilizadas no controle do enchimento e esgotamento de eclusas de navegação de alta queda. Durante o período de abertura, altas velocidades e flutuações de pressão ocorrem a jusante destas comportas, o que aumenta o potencial para a ocorrência de cavitação no escoamento. Neste trabalho buscou-se analisar por meio de simulação numérica as características do escoamento a jusante de uma comporta segmento invertida. O modelo matemático é bifásico, tridimensional e composto pelas equações da conservação da massa, quantidade de movimento, fração volumétrica e equações do modelo de turbulência. O modelo computacional foi desenvolvido com o software comercial ANSYS-CFX, com malha computacional do tipo hexaédrica. Perfis de pressões no teto e na base do conduto a jusante da comporta foram utilizados para validação do modelo numérico com resultados experimentais, provenientes de estudos realizados pelo IPH-UFRGS (Instituto de Pesquisas Hidráulicas da Universidade Federal do Rio Grande do Sul). A comparação entre os resultados mostrou que o modelo numérico reproduz com boa precisão as principais características do escoamento médio observado no modelo experimental. Os coeficientes hidráulicos calculados para os resultados numéricos também mostraram boa concordância com os resultados do modelo experimental e com os disponíveis na literatura. A análise do campo de pressões mostrou que as pressões mínimas encontram-se sob a borda da comporta. Além disso, verificou-se por meio do campo de tensões cisalhantes na base do conduto e por meio de vetores de velocidade um padrão de escoamento tridimensional no jato a jusante da comporta, caracterizado pela presença de regiões de rotação próximo da base e das paredes. / Reversed Tainter gates are often used to control the filling and emptying of high lift navigation locks. During the opening period, high velocities and pressure fluctuations occur downstream the gates, which increases the potential for the occurrence of cavitation in the flow. In this work we seek to analyze by means of numerical simulation the characteristics of the flow downstream of a reversed Tainter gate. The computational model was validated by comparing the profiles of pressure of the roof and at the base of the conduit downstream of the gate with the average pressure profiles obtained in an experimental model from studies conducted by IPH-UFRGS. A comparison of the results showed that the model reproduced with good accuracy the main flow characteristics observed in experimental medium. The hydraulic coefficient calculated for the numerical results also showed good agreement with experimental results and those available in the literature. The analysis of the pressure field showed that the minimum pressures are under the edge of the gate. Furthermore, it was found by means of the shear stress at the base of the conduit and through velocity vector a threedimensional pattern in the jet flow downstream of the gate, characterized by the presence of vortex near the base and walls.

The premise of the work presented here is to use a common analytical tool, Computational Fluid dynamics (CFD), along with a difference turbulence models. Eddy viscosity models as well as state-of-the-art Large Eddy Simulation (LES) were used to study the flow past bluff bodies. A suitable CFD code (CFX5.6b) was selected and implemented. Simulation of turbulent transport for the gas through the gaps of the randomly distributed spherical fuel elements (pebbles) was performed. Although there are a number of numerical studies () on flows around spherical bodies, none of them use the necessary turbulence models that are required to simulate flow where strong separation exists. With the development of high performance computers built for applications that require high CPU time and memory; numerical simulation becomes one of the more effective approaches for such investigations and LES type of turbulence models can be used more effectively. Since there are objects that are touching each other in the present study, a special approach was applied at the stage of building computational domain. This is supposed to be a considerable improvement for CFD applications. Zero thickness was achieved between the pebbles in which fission reaction takes place. Since there is a strong pressure gradient as a result of high Reynolds Number on the computational domain, which strongly affects the boundary layer behavior, heat transfer in both laminar and turbulent flows varies noticeably. Therefore, noncircular curved flows as in the pebble-bed situatio n, in detailed local sense, is interesting to be investigated. Since a compromise is needed between accuracy of results and time/cost of effort in acquiring the results numerically, selection of turbulence model should be done carefully. Resolving all the scales of a turbulent flow is too costly, while employing highly empirical turbulence models to complex problems could give inaccurate simulation results. The Large Eddy Simulation (LES) method would achieve the requirements to obtain a reasonable result. In LES, the large scales in the flow are solved and the small scales are modeled. Eddy viscosity and Reynolds stress models were also be used to investigate the applicability of these models for this kind of flow past bluff bodies at high Re numbers.

Approved for public release; distribution is unlimited. / Ever-increasing demands for accuracy and range in modern warfare have expedited the optimization of projectile design. The crux of projectile design lies in the understanding of its aerodynamic properties early in the design phase. This research first investigated the aerodynamic properties of a standard M549, 155mm projectile. The transonic speed region was the focus of the research as significant aerodynamic variation occurs within this particular region. Aerodynamic data from wind tunnel and range testing was benchmarked against modern aerodynamic prediction programs like ANSYS CFX and Aero-Prediction 09 (AP09). Next, a comparison was made between two types of angle of attack generation methods in ANSYS CFX. The research then focused on controlled tilting of the projectile’s nose to investigate the resulting aerodynamic effects. ANSYS CFX was found to provide better agreement with the experimental data than AP09.

Submitted by Emanuel Varela Cardoso (emanuel.varela@ufcg.edu.br) on 2018-06-12T20:27:50Z No. of bitstreams: 1 JOSÉ VIEIRA DA SILVA – TESE (PPGEP) 2016.pdf: 3956370 bytes, checksum: bb7bbea5e31bda7d9464ab4275ea11d2 (MD5) / Made available in DSpace on 2018-06-12T20:27:50Z (GMT). No. of bitstreams: 1 JOSÉ VIEIRA DA SILVA – TESE (PPGEP) 2016.pdf: 3956370 bytes, checksum: bb7bbea5e31bda7d9464ab4275ea11d2 (MD5) Previous issue date: 2016-02-24 / CNPq / Este trabalho teve como objetivo estudar numericamente e experimentalmente a transferência de calor e massa durante a secagem de grãos de arroz em casca da cultivar BRSMG-CONAI. Um modelo matemático tridimensional transiente foi apresentado para predizer a transferência de massa e calor e simular a distribuição do teor de umidade e temperatura no interior do sólido, considerando a simetria do sólido, propriedades termofísicas e volume constantes. Foram realizados experimentos de secagem com grão de arroz em casca nas temperaturas de secagem de 40, 50, 60 e 70ºC doados pelo IPA (Instituto Agronômico de Pernambuco), localizado no município de Goiana-PE. O grão foi considerado como um elipsóide de revolução. Os resultados de teor de umidade obtido via CFD foram comparados com dados experimentais de secagem. Verificou-se que para baixas temperaturas a velocidade de secagem é menor, diminuindo os riscos de defeitos no produto e que, para temperaturas elevadas surgem altos gradientes de temperatura e umidade no interior do grão que geram tensões termo-hídricas, ocasionando grandes fissuras e trincas, principalmente no início do processo. Foram feitas comparações entre os dados teóricos e experimentais do teor de umidade médio e um bom ajuste foi obtido, que resultou na estimativa do coeficiente de difusão de massa em diversas condições de secagem. / This work aims to study numerically and experimentally heat and mass transfer during drying of rice grains (BRSMG-CONAI cultivar). A transient three-dimensional mathematical model to predict mass and heat transfer and simulate the moisture content and temperature distributions inside the solid considering solid symmetry, and constants thermophysical properties and volume is presented. Were performed drying experiments with rough rice grain in the drying temperatures 40, 50, 60 and 70°C supported by IPA (Agronomic Institute of Pernambuco), placed in Goiana-PE, Brazil. The grain was considered as an ellipsoid of revolution. Results of moisture content obtained via CFD were compared to experimental. It was found that at low temperatures the drying rate is lower, decreasing of risks in defects on the product and that for higher temperatures we have higher temperature and moisture content gradients inside the grain which generate thermal-hydric stresses, causing cracks and fissures mainly in the early stages of the process. Were made comparisons between theoretical and experimental data of average moisture content and a good fit was obtained, which resulted in the estimation of the mass diffusion coefficient in several drying conditions.

Submitted by Kilvya Braga (kilvyabraga@hotmail.com) on 2018-04-17T14:46:07Z No. of bitstreams: 1 ANTÔNIO JOSÉ FERREIRA GADELHA - TESE (PPGEQ) 2016.pdf: 6375453 bytes, checksum: 865ce4649601ce36b03d6876719da6d9 (MD5) / Made available in DSpace on 2018-04-17T14:46:07Z (GMT). No. of bitstreams: 1 ANTÔNIO JOSÉ FERREIRA GADELHA - TESE (PPGEQ) 2016.pdf: 6375453 bytes, checksum: 865ce4649601ce36b03d6876719da6d9 (MD5) Previous issue date: 2016-02 / Capes / A crescente demanda mundial por energia tem levado pesquisadores a buscar o aprimoramento de tecnologias com o objetivo de maximizar a geração de energia nas suas diferentes formas. Entre os diferentes métodos de produção encontra-se a energia produzida através de usinas termelétricas, que corresponde a mais 60% da energia produzida no mundo. Entre os principais problemas causados pela produção de energia em termelétricas está a emissão de poluentes gasosos para a atmosfera. O efluente gasoso emitido através da chaminé de uma termelétrica consiste basicamente de dióxido de carbono (CO2), dióxido de enxofre (SO2), óxidos nitrogenados (NOx), entre outros, que provocam problemas ambientais e de saúde. Neste sentido, o presente trabalho teve como objetivo avaliar a fluidodinâmica da dispersão de poluentes emitidos a partir da chaminé de uma termelétrica através de simulações numéricas utilizando CFD (Ansys CFX 15.0). Como modelo de turbulência utilizou-se o k   padrão. Com base nas simulações do planejamento experimental verificou-se que a variável mais significativa no processo foi a taxa de emissão do poluente seguida pela velocidade do vento. A partir dos resultados obtidos verificou-se que a altura da fonte de emissão apresenta uma influência determinante sobre a dispersão; que a variação lateral da intensidade da velocidade do vento e a variação da frequência com que o vento muda de direção são fatores decisivos na dispersão de espécies gasosas na atmosfera; e que a dispersão ocorre com maior intensidade sob condições atmosféricas instáveis, sob um ângulo de 30° e uma frequência de mudança de direção de 5 minutos. / The growing worldwide demand for energy has led researchers to pursue enhancement technologies in order to maximize the generation of electricity in its different forms. Among the different methods of production is the energy produced by thermal power plants, which accounts for over 60% of the energy produced in the world. It is an energy generated from the combustion of fuels such as coal, diesel oil, natural gas, etc. Among the main problems caused by power generation in thermal power plants is the emission of gaseous pollutants into the air. The off-gas emitted from the flue of a fuel consists mainly of carbon dioxide (CO2), sulfur dioxide (SO2), nitrogen oxides (NOx), among others, causing environmental and health problems. In this sense, this study aims to evaluate the fluid dispersion of pollutants emitted from the chimney of a thermal power plant through numerical simulations using CFD (ANSYS CFX 15.0). As turbulence model was used k   standard. Based on the experimental design simulations it was found that the most significant variable in the process was the pollutant emission rate followed by wind speed. From the results obtained it was found that the height of the emission source has a decisive influence on the dispersion; that the lateral variation of wind speed intensity and variation of the frequency with which the wind changes direction are decisive factors in the dispersion of gaseous species in the atmosphere; and that dispersion occurs more intensively under instable atmospheric conditions, at an angle of 30 ° and a frequency change of direction of 5 minutes.

Every computational fluid dynamics engineer deals with a never ending story – limitedcomputer resources. In computational fluid dynamics there is practically never enoughcomputer power. Limited computer resources lead to long calculation times which result inhigh costs and one of the main reasons is that large quantity of elements are needed in acomputational mesh in order to obtain accurate and reliable results.Although there exist established meshing approaches for the Siemens 4th generation DLEburner, mesh dependency has not been fully evaluated yet. The main goal of this work istherefore to better optimize accuracy versus cell count for this particular burner intended forsimulation of air/gas mixing where eddy-viscosity based turbulence models are employed.Ansys Fluent solver was used for all simulations in this work. For time effectivisationpurposes a 30° sector model of the burner was created and validated for the meshconvergence study. No steady state solutions were found for this case therefore timedependent simulations with time statistics sampling were employed. The mesh convergencestudy has shown that a coarse computational mesh in air casing of the burner does not affectflow conditions downstream where air/gas mixing process is taking place and that a majorpart of the combustion chamber is highly mesh independent. A large reduction of cell count inthose two parts is therefore allowed. On the other hand the RPL (Rich Pilot Lean) and thepilot burner turned out to be highly mesh density dependent. The RPL and the Pilot burnerneed to have significantly more refined mesh as it has been used so far with the establishedmeshing approaches. The mesh optimization has finally shown that at least as accurate resultsof air/gas mixing results may be obtained with 3x smaller cell count. Furthermore it has beenshown that significantly more accurate results may be obtained with 60% smaller cell count aswith the established meshing approaches.A short mesh study of the Siemens 3rd generation DLE burner in ignition stage of operationwas also performed in this work. This brief study has shown that the established meshingapproach for air/gas mixing purposes is sufficient for use with Ansys Fluent solver whilecertain differences were discovered when comparing the results obtained with Ansys Fluentagainst those obtained with Ansys CFX solver. Differences between Fluent and CFX solverwere briefly discussed in this work as identical simulation set up in both solvers producedslightly different results. Furthermore the obtained results suggest that Fluent solver is lessmesh dependent as CFX solver for this particular case.

Material properties are very important to model correctly when calculating solutions for multiphase flows with non-Newtonian fluids. The models can make the solution converge or diverge depending on how it is chosen. This paper mainly focuses of the applicability of solid pressure and viscosity models in Ansys CFX. The main goal is to create a list of criterions that material properties must fullfill to ensure that the solution converges. Furthermore a test environment in MATLAB was made that verifies if the models satisfies the list of criterions. It was found that as long as the material properties has continous derivatives without removable singularities and are non imaginary on their domain they are applicable in Ansys CFX. It was also found that if there was a discontinuity in their domain the discontinuity could be moved outside of the domain using an assymetric model for the volume fraction.

Modelos matemáticos são representações ou interpretações simplificadas da realidade ou uma representação de um fragmento de um sistema. As simulações destes fenômenos auxiliam na tomada de decisão da parte interessada, ou seja, aqueles que trabalham em uma área. A modelagem de um sistema de processos anaeróbios, como o tratamento de um efluente em reatores UASB (Upflow Anaerobic Sludge Blanket), auxilia os gestores destes sistemas na operação e no controle de estabilidade. O modelo ADM1 (Anaerobic Digestion Model Nº 1), criado pela IWA em 2002, simula o comportamento da digestão anaeróbia. Entretanto, este modelo não considera a hidrodinâmica do sistema como fator relevante no desempenho do processo. O estudo do comportamento do escoamento de efluente no interior de um reator é possível através de ensaios de hidrodinâmica. Estes são conduzidos, majoritariamente, por meio de experimentos laboratoriais que se utilizam de traçadores que, por sua vez, podem resultar em custos elevados. A Dinâmica de Fluidos Computacional (DFC) é uma área na mecânica dos fluidos que utiliza análises numéricas e algoritmos para solucionar e analisar problemas relacionados com escoamento de fluidos. Os softwares de DFC que resolvem estes algoritmos podem ser utilizados na simulação dos ensaios de hidrodinâmica. Foi utilizado nesta tese o pacote de DFC Ansys®, em que o software CFXTM foi o escolhido para realizar as simulações de escoamento. Um dos objetivos desta tese foi a validação desta simulação por meio de ensaios de laboratório e ensaios virtuais em um reator UASB em escala de bancada (1,5 L). Resultou-se, dessa comparação, em dados estatisticamente similares (teste U de Mann-Whitney), proporcionando validação do método. Após esta validação, simulou-se o mesmo tipo de ensaio para um reator UASB em formato de \"Y\" (escala piloto; 119,3 L). Foram simuladas três condições operacionais, em que se variou a vazão de alimentação, sendo esta função da carga orgânica volumétrica aplicada ao lodo (COV). As COV foram 7,5, 12,5 e 17,5 kgDQO m-3d-1. Obteve-se N-CSTR (número de reatores de mistura completa em série) igual a 11, 10 e 10 unidades para cada condição, respectivamente. A ferramenta de Dinâmica de Sistemas utiliza-se de uma abordagem de entendimento de modelos complexos e, por meio de ciclos de retroalimentação (feedback) e estoques e fluxos (stocks and flows), demonstra que modelos aparentemente simples podem ser muito complexos. Existem vários softwares de Dinâmica de Sistemas e neles podem ser implementados os mais variados modelos. Utilizando o software Vensim PLE®, modelou-se a digestão anaeróbia do ácido acético por meio de equações baseadas no modelo de cinética enzimática de Monod e no modelo de digestão anaeróbia ADM1. Considerou-se as taxas de consumo de substrato e crescimento de biomassa bacteriana, a inibição causada pelo pH e a quantidade de alcalinizante necessária para atingir o pH desejado deste meio. De forma complementar, integrou-se um modelo de cálculo de alcalinidade do meio e, desta forma, foi possível determinar as concentrações de cada espécie que confere alcalinidade ao meio, considerando o equilíbrio do carbonato. Denominou-se esta modelação (DFC e dinâmica de sistemas) de Modelo Hidro-bioquímico do processamento anaeróbio. Os resultados obtidos por Del Nery et al. (2016) corroboraram com os obtidos nesta tese. / Mathematical models are representations and simplified interpretations of reality or a representation of a system fragment. The modeling of anaerobic processes, such as wastewater treatment in UASB (Upflow Anaerobic Sludge Blanket) reactors, helps managers in the operation of these systems and stability control. The Anaerobic Digestion Model No. 1 (ADM1), created by IWA in 2002, simulates the behavior of anaerobic digestion. However, this model does not consider the system hydrodynamics as a relevant factor in the performance of the process. The effluent flow behavior studies on the reactor inside is possible by hydrodynamic tests. These are conducted through laboratory experiments that uses tracers and this can result in high costs in the conduct of the tests. The Computational Fluid Dynamics (CFD) is an area in fluid mechanics that uses numerical analysis and algorithms to solve and analyze problems related to fluid flow. CFD software can be used to simulate the hydrodynamics assays. It was used in this thesis Ansys® workbench, wherein the CFXTM software was chosen to perform CFD flow simulations. One objective of this thesis was to validate the CFD simulation through laboratory and virtual testing in a UASB bench scale (1.5 liters). In this comparison, it resulted in similar data statistically (Mann-Whitney U test). After validation of the hydrodynamic test, was simulated the same type of assay for an UASB reactor \"Y\" shaped (pilot scale; = 82.27 liters working volume). The test result was N-CSTR (number of complete mixing reactors in series) equal to 4 units, considering a 103.9 liters per day of feed flow (hydraulic retention time of 19 hours). The system dynamics tool makes use of understanding approach of complex models and, through feedback loops and stocks and flows, shows that seemingly simple models can be very complex. There are several system dynamics software and most varied models can be implemented. Using Vensim PLE® software, it was developed an acetate anaerobic digestion model (in this case acetic acid) via equations based on the Monod and ADM1 model. It was considered for the hydro-biochemical modeling, substrate consumption and growth of bacterial biomass rates, the pH inhibition and the amount of alkalizing necessary to achieve the desired pH of the medium. Complementarily, integrated into a calculation alkalinity model of the medium and thus it was possible to determine the concentrations of each species imparts environment alkalinity, considering the carbonate balance.