O presente trabalho realiza um estudo do desempenho aerodinâmico da turbina eólica de duas pás e 10 m de diâmetro da UAE Phase VI, testada pelo NREL no túnel de vento NASA Ames, através do uso de dinâmica dos fluidos computacional (CFD). Para tanto são apresentados conceitos fundamentais para análise da performance do aerogerador, a metodologia aplicada para a análise numérica e os resultados obtidos. O modelo geométrico da turbina foi inserido em ambiente computacional num domínio com as mesmas dimensões da seção de testes do túnel de vento. A esse domínio foi empregada uma malha de elementos tetraédricos. A modelagem numérica e as simulações foram efetuadas através do código comercial ANSYS FLUENT 13.0 e utilizaram as equações médias de Reynolds e modelos de turbulência k  SST e Spalart-Allmaras. A turbina simulada possui ângulo de giro (yaw) e de cone de 0°. Os casos simulados foram de turbina com ângulos de passo das pás de 0° e 3°, para velocidades de ar na entrada do domínio de 5 m/s, 7 m/s e 9 m/s. As simulações foram feitas em regime transiente utilizando o método de malha móvel. Dados provenientes da simulação numérica são comparados aos dados experimentais de empuxo, torque e potência, divulgados pelo laboratório. Os modelos de turbulência testados apresentaram boa concordância com os resultados experimentais de empuxo. O torque e a potência foram bem previstos para velocidades de entrada do domínio baixas, mas foram subdimensionados para velocidades mais altas. A separação da camada limite foi prevista por ambos os modelos. Na comparação com resultados obtidos com outros autores para o mesmo caso, o início de descolamento da camada limite se deu antes do previsto. A metodologia adotada nas simulações numéricas realizadas mostrou-se adequada e representativa nas análises desse estudo. / This study makes a CFD analysis of the aerodynamic performance of the NREL UAE Phase VI two-bladed wind turbine, which have been tested in the NASA Ames wind tunnel. Fundamental concepts on the evaluation of turbine performance, the applied methodology for the numerical analysis and the results are presented. A numerical model has been inserted in a computational environment that has the same dimensions as the real wind tunnel section, and a tetrahedral mesh has been created to fill this domain. Numerical modeling and the simulations have been performed using the ANSYS FLUENT 13.0 commercial code, making use of the RANS equations and the k  SST and Spalart-Allmaras turbulence models. The simulated turbine has 0 degrees of cone and yaw angle. Simulations were performed in unsteady state using the moving mesh technique. Results are compared to experimental data regarding to thrust, torque and power. The k  SST and Spalart-Allmaras turbulence models have shown good agreement with experimental values of thrust. Torque and power have been adequately predicted to lower free flow velocities, but have been underpredicted to higher velocities. Separation of the boundary layer has been adequately predicted by both models, but the beginning of the separation occurred earlier than expected in comparison with results of other authors to the same case. The methodology used in the numerical simulations proved to be adequate and representative in this study.

Os processos oxidativos avançados são promissores para a degradação de compostos orgânicos resistentes aos tratamentos convencionais, como o fenol. A fluidodinâmica computacional (CFD) tornou-se uma poderosa ferramenta para analisar processos fotoquímicos por resolver os balanços acoplados de quantidade de movimento, de massa e de radiação. O objetivo deste trabalho é investigar o processo UV/H2O2 num reator fotoquímico anular usando CFD e um modelo cinético mais realista. O modelo em CFD foi criado de forma progressiva. Inicialmente, foram determinados os campos de velocidade para três vazões (30, 60 e 100 L/h). Considerou-se dois diâmetros de lâmpada para reproduzir a configuração experimental do sistema. A discretização foi feita com malhas tetraédricas variando entre 390 000 e 1 200 000 elementos. Quatro modelos de turbulência RANS foram analisados: k-e, k-w, o shear stress transport (SST) e o modelo de tensões de Reynolds (RSM). O campo de velocidades foi validado comparando a DTR com seu levantamento experimental. A próxima etapa foi incluir o mecanismo de degradação de fenol proposto por Edalatmanesh, Dhib e Mehrvar (2008) no modelo em CFD. Trata-se de um modelo cinético baseado em equações dinâmicas para todas as espécies. O campo de radiação foi calculado pelo modelo radial e pela solução da equação de transporte de radiação através do método discrete transfer. As simulações reproduziram dados experimentais abrangendo uma larga gama de concentrações iniciais de fenol, razões molares H2O2/fenol e três potências de emissão das lâmpadas. O campo de velocidades obtido era dependente da vazão: o fluido pode manter movimento helicoidal sobre toda a extensão do reator ou se desenvolver como um escoamento pistonado. O modelo k-e não reproduziu bem o escoamento por não ser adequado para escoamentos rotativos. Os outros modelos geraram curvas de DTR com bom ajuste aos dados experimentais, especialmente o modelo k-w. O desvio médio entre as simulações de degradação de fenol e os dados experimentais é inferior a 8%. Verificou-se que, devido ao escoamento rotativo, os reagentes ficavam concentrados próximos à parede externa e migravam para a região da lâmpada ao longo do reator. A elevada intensidade de radiação na superfície da lâmpada criou uma camada ao seu redor na qual a fotólise do H2O2 ocorreu com grande taxa. Os radicais OH gerados nessa camada eram transportados para a região das paredes por convecção. Isso fez com que a maior parte do fenol fosse atacada na segunda metade do reator e gerou acúmulo do radical próximo à lâmpada na seção de saída do reator, já que o poluente já fora oxidado nessa área. O método discrete transfer previu intensidades de radiação maiores que o modelo radial, e, consequentemente, maior concentração de radicais OH. Os resultados satisfatórios indicam que CFD foi uma ferramenta adequada para analisar este escoamento reativo. / Advanced oxidation processes are a promising technology for degradation of organic compounds resistant to conventional treatments such as phenol. Computational fluid dynamics (CFD) has recently emerged as a powerful tool that allows a deeper understanding of photochemical processes in reactor engineering by solving the coupled momentum, mass and radiation balances. This work aimed to investigate the UV/H2O2 process in an annular photoreactor using CFD and a more realistic kinetic model. A progressive approach was used to develop the CFD reactor model. First, the velocity fields were determined for three volumetric flow rates (30, 60 and 100 L/h). Two lamp diameters were considered to reflect the experimental configuration of the system. Tetrahedral meshes varying form 390,000 to 1,200,000 elements were analyzed to achieve grid independence. For accounting turbulence effects, four RANS models were tested: k-e, k-w, the Shear Stress Transport (SST) and the Reynolds Stress models (RSM). The velocity field was validated through comparison to RTD experimental data. Next step was introducing the mechanism of phenol degradation proposed by Edalatmanesh, Dhib and Mehrvar (2008) into the CFD model. This kinetic model is based on dynamic equations for all species. The fluence rate field was calculated by the radial model and by solving the radiation transport equation with the discrete transfer method. Simulations reproduced experimental data spanning a wide range of initial phenol concentrations, H2O2/phenol molar ratios and three values for lamp power. It was found that the velocity field depends on the volumetric flow rate: either it maintains a swirling motion through the whole reactor or might develop like a plug flow. The k-e model did not represent the RTD data accurately, and the velocity field therefore, since it is not appropriate for swirling flows. The other turbulence models showed good match of RTD, especially the k-w model. Simulations of phenol degradation deviated less than 8% from experimental data. It was possible verified that, due to the swirling inlet effects, reactants got concentrated close to the outer wall and migrated on the lamp direction along the reactor path. High radiation intensities close to the lamp surface created a layer around it where photolysis of H2O2 took place with higher rates. OH radicals were generated in that layer and transported towards the outer wall by convection. This caused most of phenol to be consumed in the second half of the reactor and accumulation of the radical near the lamp and the reactor outlet, since the pollutant in this area was already oxidized. The discrete transfer method predicted higher incident radiation intensity than the radial model, and higher concentrations of OH radicals as a consequence. Satisfactory results indicated that CFD was an appropriate tool for analyzing this reactive flow.

O presente trabalho realiza um estudo do desempenho aerodinâmico da turbina eólica de duas pás e 10 m de diâmetro da UAE Phase VI, testada pelo NREL no túnel de vento NASA Ames, através do uso de dinâmica dos fluidos computacional (CFD). Para tanto são apresentados conceitos fundamentais para análise da performance do aerogerador, a metodologia aplicada para a análise numérica e os resultados obtidos. O modelo geométrico da turbina foi inserido em ambiente computacional num domínio com as mesmas dimensões da seção de testes do túnel de vento. A esse domínio foi empregada uma malha de elementos tetraédricos. A modelagem numérica e as simulações foram efetuadas através do código comercial ANSYS FLUENT 13.0 e utilizaram as equações médias de Reynolds e modelos de turbulência k  SST e Spalart-Allmaras. A turbina simulada possui ângulo de giro (yaw) e de cone de 0°. Os casos simulados foram de turbina com ângulos de passo das pás de 0° e 3°, para velocidades de ar na entrada do domínio de 5 m/s, 7 m/s e 9 m/s. As simulações foram feitas em regime transiente utilizando o método de malha móvel. Dados provenientes da simulação numérica são comparados aos dados experimentais de empuxo, torque e potência, divulgados pelo laboratório. Os modelos de turbulência testados apresentaram boa concordância com os resultados experimentais de empuxo. O torque e a potência foram bem previstos para velocidades de entrada do domínio baixas, mas foram subdimensionados para velocidades mais altas. A separação da camada limite foi prevista por ambos os modelos. Na comparação com resultados obtidos com outros autores para o mesmo caso, o início de descolamento da camada limite se deu antes do previsto. A metodologia adotada nas simulações numéricas realizadas mostrou-se adequada e representativa nas análises desse estudo. / This study makes a CFD analysis of the aerodynamic performance of the NREL UAE Phase VI two-bladed wind turbine, which have been tested in the NASA Ames wind tunnel. Fundamental concepts on the evaluation of turbine performance, the applied methodology for the numerical analysis and the results are presented. A numerical model has been inserted in a computational environment that has the same dimensions as the real wind tunnel section, and a tetrahedral mesh has been created to fill this domain. Numerical modeling and the simulations have been performed using the ANSYS FLUENT 13.0 commercial code, making use of the RANS equations and the k  SST and Spalart-Allmaras turbulence models. The simulated turbine has 0 degrees of cone and yaw angle. Simulations were performed in unsteady state using the moving mesh technique. Results are compared to experimental data regarding to thrust, torque and power. The k  SST and Spalart-Allmaras turbulence models have shown good agreement with experimental values of thrust. Torque and power have been adequately predicted to lower free flow velocities, but have been underpredicted to higher velocities. Separation of the boundary layer has been adequately predicted by both models, but the beginning of the separation occurred earlier than expected in comparison with results of other authors to the same case. The methodology used in the numerical simulations proved to be adequate and representative in this study.

No description available.

No description available.

The ability to quantify leakage flow and windage heating for labyrinth seals with honeycomb lands is critical in understanding gas turbine engine system performance and predicting its component lifes. Variety of labyrinth seal configurations (number of teeth, stepped or straight, honeycomb cell size) are in use in gas turbines, and for each configuration, there are many additional geometric factors that can impact a seal’s leakage and windage characteristics. To achieve high performance in modern gas turbine engines, the labyrinth seals operate at low clearances and high rotational speed which are generally deployed with honeycomb lands on the stator. During the transient operation of aircraft engines, the stator and rotor mechanical and thermal growths differ from one another and can often result in the rotor’s incursion into the stator honeycomb structure. The incursions create rub-grooves in the honeycomb lands that can subsequently enlarge as the engine undergoes various manoeuvres. However, the effects of different honeycomb cell size, rotation and presence of rub-groove have not been thoroughly investigated in previously published work. The objective of the present research is to numerically investigate the influence of the above three factors on seal leakage and windage heating. The present work focuses the development of a numerical methodology aimed at studying above effects. Specifically, a three-dimensional CFD model is developed utilizing commercial finite volume-based software incorporating the RNG k-ε turbulence model. Detail validation of the numerical model is performed by comparing the leakage and windage heating measurements of several rig tests. The turbulent Schmidt number is found to be an important parameter governing the leakage prediction. It depends on honeycomb cell size and clearance for honeycomb seals, and Reynolds number in the presence smooth lands. The present numerical model with the modified RNG k- turbulence model predicts seal leakage and windage heating within 3-10% with available experimental data. Using the validated numerical model, a broad parametric study is conducted by varying honeycomb cell size, radial clearance, pressure ratio and rotational speed for a four-tooth straight-through labyrinth seal with and without rub-grooves. They further indicate that presence of rub-grooves increases seal leakage and reduce windage heating, specifically at smaller clearance and for larger honeycomb cell size. Rotation significantly reduces leakage with smooth stator land and smaller honeycomb cells whereas the effect is minimal for larger (3.2mm) honeycomb cells. However, at very high rotational speed seal flow reduces in all seal configurations due to high temperature rise and Rayleigh line effects. At no rub condition and lower clearance, the larger honeycomb cells leak more flow due to high bypass flow through the honeycomb cells. This results into lower pocket swirl and higher windage. When the seal clearance increases the larger honeycomb cells offers more drag to the seal flow, therefore they leak less. At higher clearances the flow travels like a strong wall jet and isolates the pocket air from honeycomb cells. Hence, at open clearances labyrinth seals with any honeycomb cell size essentially produce the same pocket swirl and windage heating.

Tato diplomová práce je zaměřena na porovnání různých turbulentních a chemických modelů na příkladu volné metanové trysky ústící do vzduchu. Nejprve je uveden teoretický úvod k modelům, následován CFD (Ansys Fluent) simulacemi plamene pomocí vybraných modelů. Jako součást práce je provedeno a vyhodnoceno experimentální měření. V závěru jsou experimentální výsledky porovnány s nasimulovanými daty.

No description available.

Computational Fluid Dynamics is a powerful and widely used tool for developing projectsthat concern flow motion, in very different fields. Industrial CFD solvers are continuouslydeveloped with the aim of improving accuracy and reducing the computational cost of thesimulations. Turbulent wall-flow cases are particular demanding as the presence of a solidsurfaceinterface generates steep gradients in the proximity of the wall. Resolving suchgradients can be crucial to obtain a consistent solution but also very expensive in terms ofgrid refinement, and hence computational time. Wall functions are widely used and offersignificant computational savings when it comes to near-wall flow resolution. Previous wallfunction implemented in the M-Edge solver suffered by poor performances in complex flowscharacterized by strong pressure-gradient phenomena, such as separation. A new formulationhas been developed and validated for k − omega and Spalart-Allmaras turbulence models. Testsimulations started from simple and near-ideal cases (2D zero pressure gradient flat plate)and advanced to always more complex flow cases and geometries (full 3D general fighter).Every case has been run coupling the wall-function boundary condition with three differentturbulence models: the Menter SST, the Menter BSL with an EARSM and the Spalart-Allmaras one-equation model. Overall results showed the upgraded performance of new wallfunction in flow resolution together with more agile grid requirements, faster and deeperconvergence of the residuals and a general reduction in computational time. / Berör strömmande fluider inom mycket olika områden. Industriella CFD-lösare utvecklaskontinuerligt i syfte att förbättra noggrannheten och minska beräkningskostnaderna försimuleringarna. Turbulent strömning nära väggar är särskilt krävande eftersom närvaron avett fast ytgränssnitt genererar stora gradienter i närheten av väggen. Att lösa upp sådanagradienter kan vara avgörande för att få en konsistent lösning men också mycket beräkningskrävandepå grund av nödvändig nätförfining.Väggfunktioner används ofta och ger betydandereduktioner i beräkningstid när det gäller att lösa upp strömningen nära vägg. En tidigareväggfunktion implementerad i M-Edge-lösaren led av dåliga prestanda i komplexa flödenmed starka tryckgradienter, såsom separation. En ny formulering har utvecklats och valideratsför k − omega och Spalart-Allmaras turbulensmodeller. Den har testats för enkla generiska fall(2D-plan platta utan tryckgradient) och för mer avancerade och komplexa strömningsfall ochgeometrier (komplett 3D-stridsflygplan).Varje fall har körts med väggfunktionens randvillkorkopplat med tre olika turbulensmodeller: Menter SST, Menter BSL med EARSM och Spalart-Allmaras enekvationsmodell. De övergripande resultaten visar att nya väggfunktionen gerbetydande förbättringar i att beskriva strömningen tillsammans med reducerade krav pånätupplösning, snabbare och djupare konvergens av lösningen och en allmän minskning avberäkningstiden.

Near wake is the region of wake flow just behind the trailing edge of the body where the flow is strongly influenced by the upstream flow conditions and also perhaps by the charac­teristics of the body. The present work is concerned with the study of the development of turbulent near wake behind an infinitely yawed flat plate. The turbulent near wake behind an infinitely yawed flat plate is the simplest of the three-dimensional turbulent near wake flows. The present study aims at providing a set of data on the turbulent near wake behind an infinitely yawed flat plate and also at understanding the development and structure of the near wake. Detailed measurements of mean and turbulent quantities have been made using 3-hole probe, X-wire and 3-wire hotwire probes. Further an asymptotic analysis of the two-dimensional turbulent near wake flow has been formulated for the near wake behind an infinitely yawed flat plate. The feature that the near wake which is dominated by mixing of the oncoming turbulent boundary layer retains, to a large extent, the memory of the turbulent structure of the boundary layer, has been exploited to develop this analysis. The analysis leads to three regions of the wake flow (the inner near wake, the outer near wake and the far wake) for which the governing equations are derived. The matching conditions among these regions lead to logarithmic variations in both normal and longitudinal directions in the overlapping regions surrounding the inner wake. These features are validated by the present results. A computational study involving seven well known turbulence models was also under­taken in order to assess the performance of the existing turbulence models in the prediction of the turbulent near wake behind an infinitely yawed flat plate. In this study all the seven models are implemented into a common flow solver code, thus eliminating the influence of grid size, initial conditions and different numerical schemes while making the comparison. This study shows that the K - e model performs better than other models in predicting the near wake behind an infinitely yawed flat plate.