The present study considers the numerical simulation of the different flow characteristics involved in the conjugate heat transfer analysis of an internally cooled gas turbine blade. Conjugate simulations require full coupling of convective heat transfer in fluid regions to the heat diffusion in solid regions. Therefore, accurate prediction of heat transfer quantities on both external and internal surfaces has the uppermost importance and highly connected with the performance of the employed turbulence models. The complex flow on both surfaces of the internally cooled turbine blades is caused from the boundary layer laminar-to-turbulence transition, shock wave interaction with boundary layer, high streamline curvature and sequential flow separation. In order to discover the performances of different turbulence models on these flow types, analyses have been conducted on five different experimental studies each concerned with different flow and heat transfer characteristics. Each experimental study has been examined with four different turbulence models available in the commercial software (ANSYS FLUENT13.0) to decide most suitable RANS-based turbulence model. The Realizable k-&epsilon / model, Shear Stress Transport k-&omega / model, Reynolds Stress Model and V2-f model, which became increasingly popular during the last few years, have been used at the numerical simulations. According to conducted analyses, despite a few unreasonable predictions, in the majority of the numerical simulations, V2-f model outperforms other first-order turbulence models (Realizable k-&epsilon / and Shear Stress Transport k-&omega / ) in terms of accuracy and Reynolds Stress Model in terms of convergence.

The market of wind power as a sustainable energy source is growing, both on large and small scale. Conventional large scale wind turbines normally operate in uniform areas where expected wind speeds and turbulence characteristics are well investigated and the constructional design of the wind turbines is regulated by standard classes for different external conditions. Small scale wind turbines (SWT), on the other hand, are sometimes placed in more complex environments where the turbulence conditions are rougher. A larger amount of turbulence will generate a larger amount of fatigue loadings on the construction, increasing the risk of breakdown. It is therefore of major concern to perform more measurements and further investigate the turbulence characteristics in complex environments and the effect that these will have on small wind turbine construction. Thus, turbulence is measured with sonic anemometers at two sites with complex environments; at an urban site above a rooftop in a medium sized city (Uppsala, Sweden) and above a forest in Norunda (outside Uppsala) at two heights, near the treetops (z = 33 m) defined as complex and further up (z = 97 m) defined as more uniform. The turbulence data is analyzed and the results are compared to the normal turbulence model (NTM) as it is defined for the standard SWT classes by the International Electrotechnical Commission in the International standard 61400-2: Design requirements for small wind turbines (IEC, 2006). Measurements of  minute standard deviations of longitudinal wind speed (σu) and turbulence intensity (TIu) are reported, as well as the distributions of TIu and of 10  minute mean wind speeds (um) for the different sites and stabilities. The results show that the NTM represents the turbulence at 97 m height above the forest only for light wind speeds, smaller than 10 m/s, but underestimates the turbulence for higher wind speeds.  It should also be noted that the data is scattered and contain a number of occasions with extreme values of σu and TIu. For wind speeds higher than 10 m/s the number of observations is limited but the majority of the observations are more extreme than the NTM. At the complex sites (near the treetops and the rooftop) the NTM clearly underestimates both the magnitude and rate of change of σu with increasing wind speed, although the observed wind speeds close to these rough surfaces are low so the conclusions are limited. Average TIu at 97 m height is 19 %, compared to 41 % close above forest and 43 % above rooftop. Mean values of TIu above forest are generally 10 % lower during stable conditions (z/L > 0.05) while above rooftop, the wind material is sparse and 95 % of the observations had stable stratification so no dependence on stability can be seen. From these results it can be concluded that the turbulence characteristics close above treetops is similar to those above rooftop, but that the NTM, as it is defined for the standard SWT classes, is not valid in these complex and urban terrains and need to be modified to correctly estimate the turbulence intensities, and consequently also the loadings, affecting small wind turbines located at these kinds of sites. / Marknaden för vindkraft som en förnyelsebar energikälla växer snabbt, både stor- och småskaligt. Traditionella storskaliga vindkraftverk placeras normalt på homogena platser där vindklimatet och turbulensens karaktär är ganska väl kartlagda och konstruktionsstandarden regleras av standardklasser utifrån olika externa förhållanden. Små vindkraftverk (SWT) å andra sidan placeras ofta i mer komplex eller urban miljö där turbulensen är mer intensiv. En större andel turbulens genererar större utmattningslaster på konstruktionen vilket ökar risken att vindturbinen går sönder. Det är därför av stor vikt att utföra fler mätningar och ytterligare undersöka turbulensen i komplexa miljöer och vilken effekt den kommer ha på de små vindkraftverkens konstruktion. Med anledning av detta så har turbulensdata analyserats från mätningar med sonicanemometrar. Dels på en urban plats, ovanför ett hustak i en medelstor stad (Uppsala, Sverige). Dels vanför en skog i Norunda (utanför Uppsala) på två höjder, nära trädtopparna (33 m) som anses komplex och högre upp (97 m) som anes mer homogen. Resultaten är jämförda med den normala turbulensmodellen (NTM) så som den definieras för standard SWT klasserna av International Electrotechnical Commission i International standard 61400-2: Design requirements for small wind turbines (IEC, 2006). Mätningar av 10  minuters standardavvikelse av den longitudinella vindhastigheten (σu) och turbulensintensiteten (TIu) redovisas, liksom fördelningen av TIu och 10 minuters medelvinden (um) för olika stabilitet för de olika mätplatserna. Resultaten visar att NTM är representativ på 97 m höjd endast för låga vindhastigheter, under 10 m/s, medan modellen underskattar turbulensen för högre vindhastigheter. Det bör också noteras att spridningen är stor i data och att extrema värden av σu och TIu uppmätts vid flertalet tillfällen. För vindhastigheter över 10 m/s så är antalet mätvärden begränsade, men majoriteten av mätvärdena är högre än NTM. På de komplexa mätplatserna (nära trädtopparna och ovan hustaket) så underskattar NTM avsevärt både storleken av σu och dess förändring med ökad vindhastighet på de komplexa platserna (nära trädtopparna och ovan hustaket). Dock är de observerade vindhastigheterna låga såhär nära de skrovliga ytorna så slutsatserna är begränsade. På 97 m höjd är medelvärdet av TIu 19 %, jämfört med 41 % nära trädtopparna och 43 % ovan hustak. De är generellt 10 % lägre under stabila förhållanden (z/L > 0.05)  över skog, medan ovan hustak där vindmaterialet är begränsat och 95 % av observationerna var stabilt skiktade så ses inte något stabilitetsberoende. Från dessa resultat kan slutsatserna dras att turbulensens karaktär nära trädtoppar liknar den ovan hustak, men att NTM, så som den definieras för standard SWT klasserna, inte gäller vid dessa komplexa och urbana platser och behöver modifieras för att korrekt uppskatta turbulensintensiteterna och därmed också de laster som påverkar små vindkraftverk placerade på den här typen av platser.

An axisymmetric, Navier-Stokes finite volume flow solver, which uses Harten, Lax and van Leer (HLL) and Harten, Lax and van Leer&ndash / Contact (HLLC) upwind flux differencing scheme for spatial and uses Runge-Kutta explicit multi-stage time stepping scheme for temporal discretization on unstructured meshe is developed. Developed solver can solve the compressible axisymmetric flow. The spatial accuracy of the solver can be first or second order accurate. Second order accuracy is achieved by piecewise linear reconstruction. Gradients of flow variables required for piecewise linear reconstruction are calculated by Green-Gauss theorem. Baldwin-Lomax turbulent model is used to compute the turbulent viscosity. Approximate Riemann solver of HLL and HLLC implemented in solver are validated by solving a cylindrical explosion case. Also the solver&rsquo / s capability of solving unstructured, multi-zone domain is investigated by this problem. First and second order results of solver are compared by solving the flow over a circular bump. Axisymmetric flow in solid propellant rocket motor is solved in order to validate the axisymmetric feature of solver. Laminar flow over flat plate is solved for viscous terms validation. Turbulent model is studied in the flow over flat plate and flow with mass injection test cases.

In this thesis we describe the development of Reynolds- averaged Navier Stokes code for the flow past two- dimensional configuration. Particularly, emphasis has been laid on the study of low Reynolds number airfoil aerodynamics. The thesis consists of five chapters covering the back ground history, problem formulation, method of solution and discussion of the results and conclusion. Chapter I deals with a detailed background history of low Reynolds number aerodynamics, problem associated with it, state of the art, its importance in practical applications in aircraft industries. Chapter II describes the mathematical model of the flow physics and various levels of approximations. Also it gives an account of complexity of the equations at low Reynolds number regarding flow separation, transition and reattachment. Chapter III describes method of solution, numerical algorithm developed, description of various upwind schemes, grid system, finite volume discrieti-zation of the governing equations described in Chapter II. Chapter IV describes the application of the newly developed Navier Stokes code for the test cases from GAMM Workshop proceedings. Also it describes validation of the code for Euler solutions, Blasius solution for the flow past flat plate and compressible Navier Stokes solution for the flow past NACA 0012 Airfoil at low Reynolds number. Chapter V describes the application of the Navier Stokes code for the more test cases of current practical interest . In this chapter laminar separation bubble characteristics are investigated in detail regarding formation, growth and shedding in an unsteady environment. Finally the conclusion is drawn regarding the robustness of the newly developed code in predicting the airfoil aerodynamic characteristics at low Reynolds number both in steady and unsteady environment. Lastly, suggestion for future work has been highlighted.

A Computational Fluid Dynamics/Computational Fluid Dynamics (CFD/CSD) coupling interface was developed to obtain aeroelastic solutions of a morphing rotor. The methodology was implemented in Fully Unstructured Navier-Stokes (FUN3D) solver, which communicates aerodynamic forces on the blade surface to University of Michigan’s Nonlinear Active Beam Solver (UM/NLABS) and then imports structural deflections of the blade surface during each time step. Development of this methodology adds the capability to model elastic rotors with flexible airfoils. The method was validated through an aerodynamic work analysis, comparison of sectional blade loads and deflections with experimental data, and two-dimensional stability analyses for pitch/plunge flutter and camber flutter. Computational simulations were performed for a rotor in forward flight with the CFD/CSD solver and with a comprehensive CSD solver using finite-state (F-S) aerodynamics, and results were compared. Prescribed three-per-revolution camber deflections were then applied, and solutions of the CFD/CSD and comprehensive CSD computations indicated that three-per-revolution camber actuation has the potential to minimize hub forces and moments with deflections as small as 0.25%c. In anticipation of active rotor experiments inside enclosed facilities, the capability of CFD for accurately simulating flow inside enclosed volumes was examined. It was determined that URANS models are not suitable for rotor simulations in an enclosed facility, and components that are a distance of two to three rotor radii from the hub were also observed to have a large influence on recirculation and performance.

This dissertation investigates the effect of electromagnetic braking and gas injection on the fluid flow in a continuous casting slab mold numerically and makes verifications on basis of a small Liquid Metal Model for Continuous Casting of steel (mini-LIMMCAST). Numerical calculations were performed by means of the software package CFX with an implemented RANS-SST turbulence model. The non-isotropic nature of the MHD turbulence was taken into account by specific modifications of the turbulence model. The numerical results were validated by flow measurements at the mini-LIMMCAST facility. Numerical simulations disclose the damping effect on the flow closely depending on the wall conductance ratio. In addition, specific modifications of the turbulence model play a crucial role in reconstructing the peculiar phenomenon of an excitation of nonsteady, nonisotropic, large-scale flow perturbations caused by the application of the DC magnetic field.

This study addressed the numerical modelling of flow and diffusion in packed beds of mono-sized spheres. Comprehensive research was conducted in order to implement various numerical approaches in explicit1 and implicit2 simulations of flow through packed beds of uniform spheres. It was noted from literature that the characterization of a packed bed using porosity as the only geometrical parameter is inadequate (Van Antwerpen, 2009) and is still under much deliberation due to the lack of understanding of different flow phenomena through packed beds. Explicit simulations are not only able to give insight into this lack of understanding in fluid mechanics, but can also be used to develop different flow correlations that can be implemented in implicit type simulations. The investigation into the modelling approach using STAR-CCM+®, presented a sound modelling methodology, capable of producing accurate numerical results. A new contact treatment was developed in this study that is able to model all the aspects of the contact geometry without compromising the computational resources. This study also showed, for the first time, that the LES (large eddy simulation) turbulence model was the only model capable of accurately predicting the pressure drop for low Reynolds numbers in the transition regime. The adopted modelling approach was partly validated in an extensive mesh independency test that showed an excellent agreement between the simulation and the KTA (1981) and Eisfeld and Schnitzlein (2001) correlations' predicted pressure drop values, deviating by between 0.54% and 3.45% respectively. This study also showed that explicit simulations are able to accurately model enhanced diffusion due to turbulent mixing, through packed beds. In the tortuosity study it was found that the tortuosity calculations were independent of the Reynolds number, and that the newly developed tortuosity tests were in good agreement with techniques used by Kim en Chen (2006), deviating by between 2.65% and 0.64%. The results from the TMD (thermal mixing degree) tests showed that there appears to be no explicit link between the porosity and mixing abilities of the packed beds tested, but this could be attributed to relatively small bed sizes used and the positioning and size of the warm inlet. A multi-velocity test showed that the TMD criterion is also independent of the Reynolds number. It was concluded that the results from the TMD tests indicated that more elaborate packed beds were needed to derive applicable conclusions from these type of mixing tests. The explicit BETS (braiding effect test section) simulation results confirmed the seemingly irregular temperature trends that were observed in the experimental data, deviating by between 5.44% and 2.29%. From the detail computational fluid dynamics (CFD) results it was possible to attribute these irregularities to the positioning of the thermocouples in high temperature gradient areas. The validation results obtained in the effective thermal conductivity study were in good agreement with the results of Kgame (2011) when the same fitting techniques were used, deviating by 5.1%. The results also showed that this fitting technique is highly sensitive for values of the square of the Pearson product moment correlation coefficient (RSQ) parameter and that the exclusion of the symmetry planes improved the RSQ results. It was concluded that the introduction of the new combined coefficient (CC) parameter is more suited for this type of fitting technique than using only the RSQ parameter. / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2012

[pt] Os modelos mais populares para solucionar escoamentos turbulentos são baseados no esquema RANS (Reynolds Average Navier Stokes) que necessita de fechamento para relacionar o tensor de tensões de Reynolds com os tensores médios cinemáticos. A solução clássica é a aproximação por Bussinesq que assume uma relação linear entre a parte deviatórica do Tensor de Reynolds e o tensor das taxas de deformação. Trabalhos anteriores mostraram que uma relação não linear entre o tensor das taxas de deformação pode melhorar a predição do modelo. No presente trabalho, primeiramente é realizada uma avaliação entre modelos lineares presentes na literatura seguido de uma análise de três modelos de ordem elevada que expandem a base tensorial para incluir tensores ortogonais. Duas adimensionalizações, uma com a energia cinética turbulenta e taxa de dissipação e outra com energia cinética turbulenta e intensidade do tensor de deformação, haviam sido propostas. As previsões dos modelos são comparados com dados DNS para um canal e para uma gama variada de número de Reynolds. Todos os modelos são implementados na plataforma aberta OpenFoam. Predições razoáveis para a componente cisalhante de todos os modelos foram obtidas quando comparadas com os dados DNS. Entretanto, modelos não lineares provaram superioridade na predição das outras componentes. Também foi observado que o modelo não linearmente dependente do tensor taxa de deformação e o tensor não persistencia das deformações foi o que melhor representou os campos providos por DNS. / [en] The most popular models to solve turbulent flows are based on the Reynolds Average Navier Stokes approach (RANS), which needs closure equations to relate the Reynolds stress tensor to the mean kinematic tensors. The classical approach is the Boussinesq approximation that assumes a linear relation between the deviatoric part of the Reynolds stress tensor, and the rate of strain tensor. Previous works have shown, that the non-linear dependence on the rate of strain tensor can improve the model predictions. At the present work, first an evaluation of linear models available in the literature is performed, followed by the analysis of three higher order methods, that expands the tensorial basis to include other objective orthogonal tensors. Two different nondimensionalization, one with the turbulent kinetic energy and dissipation rate and the other one with turbulent kinetic energy and the intensity of the rate of strain, had also been proposed for the models. The performance of the new models is assessed by comparing their numerical predictions to available channel flow and for a broad range of Reynolds Numbers. All models are implemented in the open source platform OpenFOAM. Reasonable predictions of the Reynolds shear component of all models were obtained when compared with the DNS data. However, the non-linear models proved superior in the prediction of the other components. It was also observed that the model which depends nonlinearly with the rate of strain and linearly with the non-persistence of strain was the one that best represented the DNS data field.

As Diretrizes da Política Nacional de Transporte Hidroviário apresentam metas ambiciosas para os próximos anos quanto à construção de eclusas e ao aumento da participação do transporte aquaviário de carga na matriz brasileira. A bibliografia expõe que os custos são otimizados quando um desnível é transposto com a construção do menor número eclusas, o que resulta na busca pela transposição de desníveis significativos com a execução de eclusas com uma única câmara. No entanto, problemas hidráulicos encontrados junto às comportas de enchimento e esvaziamento estão entre as principais limitações para o aumento da altura de queda das eclusas. Os diferenciais de pressão entre as faces de montante e jusante das comportas e a variação do seu grau de abertura durante as operações de enchimento e esvaziamento de eclusas de navegação de média e alta queda geram escoamentos turbulentos, com velocidades e pressões capazes de produzir danos às estruturas. Com o objetivo de analisar os parâmetros hidráulicos do escoamento médio a jusante de comportas dos sistemas de enchimento e esgotamento de eclusas, do tipo segmento invertida, e as pressões instantâneas ao longo do teto e da base do conduto, de forma a identificar e caracterizar padrões de comportamento que auxiliem na elaboração de projetos e no aperfeiçoamento dessas estruturas, foram conduzidas duas investigações complementares, a experimental e a numérica. A investigação experimental, desenvolvida no Laboratório de Obras Hidráulicas do Instituto de Pesquisas Hidráulicas da Universidade Federal do Rio Grande do Sul, proporcionou a geração de dados discretos de pressão instantânea ao longo do teto e da base do conduto para 53 condições de abertura e vazão, para escoamento em regime permanente. A investigação numérica, realizada com o software Flow-3D®, de Dinâmica de Fluidos Computacional, viabilizou a geração de dados do escoamento médio no interior do conduto para 12 condições de abertura e vazão, que reproduziam as simulações experimentais. Os resultados das simulações realizadas no Flow-3D® com modelo de turbulência k- e demonstraram a sua aplicabilidade no estudo do escoamento médio a jusante de comportas de sistemas de enchimento e esvaziamento de eclusas. O modelo numérico reproduziu os dados experimentais de pressão a montante da comporta e os formatos das curvas de pressão ao longo da base e do teto do conduto a jusante da comporta, apresentando resultados mais aderentes para a base. Para as condições operacionais com a comporta parcialmente aberta, as menores pressões ocorreram no teto do conduto próximo à comporta, região de recirculação do escoamento, e junto ao terminal da comporta. A partir da análise dos dados foi possível a caracterização do comportamento das pressões médias, das flutuações de pressão e das pressões máximas e mínimas ao longo da base e do teto do conduto por meio da relação entre coeficientes adimensionais de posição e de pressão. / Brazilian Waterways Policy has ambitious goals for constructing navigation locks and increasing the participation of the cargo transport through waterways in the national transport matrix. Literature states that costs are optimized by the construction of fewer locks for the transposition of water levels by vessels, which results in the search for transposition of significant lifts by using navigation locks with single camera. However, the hydraulic problems in the filling and emptying systems, especially close to the valves, are among the major limitations to increase the lock lift. During filling and emptying operations of medium and high-lift locks, the pressure difference between upstream and downstream sides of lock valve and its opening generate turbulent flows with associated flow velocities and pressures capable of damaging the structures. In the current research, experimental and numerical investigations were conducted in order to analyze the mean flow through lock culvert valves and the instantaneous pressures behavior along the culvert roof and base, and to identify and to characterize hydraulic parameters which could be useful for project development and improvement of these structures. The experimental research was conducted at the “Laboratório de Obras Hidráulicas” of the “Instituto de Pesquisas Hidráulicas” of the “Universidade Federal do Rio Grande do Sul” and provided the generation of discrete data of instantaneous pressure along the culvert roof and base for 53 conditions of flow and valve opening. Experimental simulations were performed with steady state flow. Numerical investigation applied the Computational Fluid Dynamics software Flow-3D® and produced information for the mean flow inside the culvert for 12 valve opening and flow conditions, which reproduced the experimental simulations. valve opening and flow conditions, which reproduced the experimental simulations. The numerical results, obtained by using the k-e turbulence model, demonstrated the applicability of Flow-3D® in the study of the mean flow downstream of lock culvert valves. The numerical model was able to reproduce the experimental data of pressure along the culvert base and roof presenting more accuracy to base data. For partially open gate conditions, the lowest pressures were verified next to the valve lip and at the downstream culvert roof close to the valve, which correspond to the recirculating flow region. From data analysis it was possible to characterize the behavior of the mean pressure, pressure fluctuations and extreme pressures along the culvert base and roof by the relationship between dimensionless coefficients of position and pressure.

Made available in DSpace on 2014-06-11T19:25:27Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-11-06Bitstream added on 2014-06-13T18:26:31Z : No. of bitstreams: 1 fogal_mlf_me_bauru.pdf: 1973940 bytes, checksum: 7fa4d89826d2cfb9214807f1ec353036 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Neste trabalho apresenta-se uma análise teórica e experimental dos resultados comparativos entre as curvas características de um ventilador axial utilizado em um sistema de pulverização agrícola para um ângulo de ataque da pá em 32 graus nas rotações de 1500, 1750, 2600 e 3000 rpm e resultados numéricos da influência da variação do ângulo de ataque da pá em 28, 32 e 36 graus e da otimização do sistema de pulverização ambos para uma rotaç]ao de 2600 rpm. O campo médio turbulento foi obtido com a aplicação da média temporal sendo que o modelo de turbulência exigido para o fechamento do conjunto de equações foi o modelo k-ε de duas equações. A resolução de todos os fenômenos acoplados foi alcançada com o auxílio do código de fluidodinâmica computacional CFX que utiliza a técnica dos volumes finitos como método numérico. Para validação da análise teórica, realizaram-se experimentos em um túnel de vento horizontal de seção circular com diâmetro de 622 mm, usando um tubo de Pitot para as tomadas de pressão de acordo com a norma para ensaios em laboratório. Apresentam-se resultados qualitativos na forma de vetores e mapas de gradiente de velocidade e, quantitativos na forma de tabelas e gráficos para as curvas características. / This paper presents a theoretical and experimental analysis of comparative results the characteristic curves of an axial fan used in an agricultural spraying system for a blade attack angle of 32 degrees at rotations of 1500, 1750, 2600 and 3000 rpm and numerical results for the influence of blade attack angle variation at 28, 32 and 36 degrees and optimization of the spraying system, both for a rotation of 2600 rpm. The average turbulent field was obtained from the application of time average where the turbulence model required for closing the set of equations was the k-ε model for two equations. Resolution of all connected phenomena was achieved with the help of the fluid dynamics computacional, CFX, which uses the finite volumes technique as a numerical method. In order to validate the theoretical analysis, an experiment was conducted in a circular section of a horizontal wind tunnel, 622 mm in diameter and 6220 mm in length, using a Pitot tube for pressure readings according to the norm for laboratory assays. Qualitative results are shown as vectors and gradient maps for speed and quantitative results are shown in tables and graphics for characteristic curves.