This thesis focuses on modelling of wind turbine wakes when they are affected by real complex terrain features, such as hills and forests, and also examines the effect of the rotational momentum imparted to the downstream wake from the rotor blades. Modelling work is carried out using the commercial Computational Fluid Dynamics (CFD) solver FLUENT. Motivation for this project was the fact that there is currently limited knowledge on several issues that affect the operation of a wind farm in a complex terrain environment. Wind developers normally use commercial, easy-to-use software (such as WAsP) to predict the potential wind farm output , which are based on simple linear models to model wakes and wind flow orographic effects and have been calibrated for cases of simple terrain. In cases of complex terrain, they are expected to give errors due to arising non-linearities. After a review of the relevant literature, the chosen CFD procedure is explained. This involves the use of 3-D Reynolds Averaged Navier-Stokes equations using the Reynolds Stress Model for the turbulence closure, in order to account for the anisotropy in atmospheric turbulence. The Virtual Blade Model in FLUENT is demonstrated as a useful tool for modelling the rotor effects without the need of meshing the rotor geometry in detail and avoiding significant computational cost. The approach is initially validated with the widely documented Nibe measurements, which involved full-scale observations of a single wake over at terrain. The model is also tested in the case of a wind turbine operating at the summit of an ideal, Gaussian hill. The wake development is examined in detail and in comparison with another CFD approach. Most notably, a slight divergence is found in the wake path as it evolves downwind. Additionally, the proposed approaches of modelling the neutral atmospheric ow over a real hill and over a forest are validated with full-scale measurements. Ultimately, the work includes the modelling of real wind farms over complex terrain and validating the results with measurements. A coastal complex terrain wind farm is initially examined and results are validated with SCADA measurements and compared with results using the WAsP wind modelling software. Finally, a wind farm over hilly terrain and near forests is also considered and the effect of the forest in the wake is studied. Results are also validated with full-scale measurements.

A comprehensive understanding of high-speed liquid jets is required for their introduction into engine and combustion applications. Their transient nature, short lifetime, unique characteristics and the inability to take many experimental readings, has inhibited this need. This study investigates the outflow of a high-speed liquid jet into quiescent atmospheric air. The key characteristics present are, a bow shock wave preceding the jet head, an enhanced mixing layer and the transient deformation of the liquid jet core. The outflow regime is studied in an experimental and numerical manner. In the experimental investigation, a high-speed liquid water jet is generated using the momentum exchange by impact method. The jet velocity is supersonic with respect to the impinged gaseous medium. The resulting jet speed is Mach 1.8. The jet is visualised with the use of shadowgraph apparatus. Visualisation takes place over a variety of time steps in the liquid jet???s life span and illustrates the four major development stages. The stages progress from initial rapid core jet expansion to jet stabilisation and characteristic uniform gradient formation. The visualisation shows that at all stages of the jet???s life it is axi-symmetric. One dimensional nozzle analysis and a clean bow shock wave indicate that the pulsing jet phenomenon can be ignored. In the numerical investigation, a time marching finite volume scheme is employed. The bow shock wave characteristics are studied with the use of a blunt body analogy. The jet at a specific time frame is considered a solid body. The jet shape is found to have an important influence on the shock position and shape. Analysis of the results indicates a shock stand-off similar to that seen in experimental observations and the prediction of shock data. The jet life span is modelled using a species dependent density model. The transient calculations reproduce the key jet shape characteristics shown in experimental visualisation. The mushrooming effect and large mixing layer are shown to develop. These effects are strongest when the shock wave transience has yet to stabilise. Quantitative analysis of the mixing layer at varying time steps is presented.

The airflow field and particle trajectories inside hard disk drive (HDD) are investigated in this study using commercial software Fluent and Gambit. Three-dimensional grids inside the HDD configuration are built using Gambit taking into account all the components and their geometric details. The airflow field inside HDD is simulated using three incompressible Navier-Stokes equations for various disk rotational speeds. The effects of using the various turbulence models inside the Fluent software such as the standard k - ε , RNG k - ε and Reynolds Stress Method on the computed airflow characteristics are also assessed. Steady flow fields and the effects of rotational speeds are assessed. Based on the computed steady airflow patterns, particle trajectories are computed using routines available in Fluent as well as special particle trajectory functions defined by the user via the user-defined functions. Particles of different sizes and materials are injected at various locations in the computed flow field and the corresponding particle trajectories are studied. Based on the investigation, the trajectory tends to be different according to sizes and materials. The present work forms a basis for further investigation of heat transfer processes inside the HDD to address thermal management issues and also the computation of unsteady flow fields in the HDD due to the movement of the actuator arm during data storage and retrieval / Singapore-MIT Alliance (SMA)

<p>Nuclear reactors release small amounts of radioactivity during their normal operations. The most common method of calculating the dose to the public that results from such releases uses Gaussian Plume models. We are investigating these methods using CAP88-PC, a computer code developed for the Environmental Protection Agency (EPA) in the USA that calculates the concentration of radionuclides released from a stack using Pasquill stability classification. A buoyant or momentum driven part is also included. The uptake of the released radionuclide by plants, animals and humans, directly and indirectly, is then calculated to obtain the doses to the public. This method is well established but is known to suffer from many approximations and does not give answers that are accurate to be better than 50% in many cases. More accurate, though much more computer-intensive methods have been developed to calculate the movement of gases&nbsp / using fluid dynamic models. Such a model, using the code FLUENT can model complex terrains and will also be investigated in this work. This work is a preliminary study to compare the results of the traditional Gaussian plume model and a fluid dynamic model for a simplified case. The results indicate that Computational Fluid Dynamics calculations give qualitatively similar results with the possibility of including much more effects than the simple Gaussian plume model.</p>

The research focus of this thesis is on modelling techniques for river kinetic turbines, to develop predictive numerical tools to further the design of this emerging hydro technology. The performance benefits of enclosing the turbine in a shroud are quantified numerically and an optimized shroud design is developed. The optimum performing model is then used to study river kinetic turbines, including different anchoring systems to enhance performance. Two different turbine numerical models are studied to simulate the rotor. Four different computational fluid dynamics (CFD) turbulence models are compared against a series of particle image velocimetry (PIV) experiments involving highly-separated diffuser-flow and nozzle-flow conditions. The risk of cavitation is briefly discussed as well as riverbed boundary layer losses. This study is part of an effort to develop this emerging technology for distributed power generation in provinces like Manitoba that have a river system well adapted for this technology. / May 2007

Deep knowledge of combustion phenomenon is of great scientific and technological interest due to its presence in a wide range of industrial processes and equipment. Being the most important worldwide energy support provided by combustion of fossil fuels, the goal of developing more efficient and cleaner systems or equipment is clearly justified. In the last decade, the importance of the reduction of pollutant emissions has increased considerably due to both environmental consciousness and to governmental policies, being one of the most important aspects to assure the competitiveness of combustion-related industries.Traditionally, a high number of experimental studies based on trial-and-error analysis were necessary on the optimisation of thermal equipment, where heat and mass transfer and fluid flow have a dominant role. In the last decades, in agreement with the development of computational capabilities, CFD simulations have become a worthful complement to experimental investigations, reducing in this sense production costs and time to market. However, the considerable complexity of combustion phenomena and the strong feedback between the flow and the chemistry, makes more difficult the task of develop accurate, computationally capable and robust numerical codes for combustion phenomena in industrial applications. This goal remains a promising challenge today and for the foreseeable future.The work developed in this thesis contributes to this objective. Rather than assuming less accurate mathematical approaches and consider their application to engineering problems, our main intention has been centred to the development of numerical tools that enable the feasible resolution of combustion problems with the highest level of detail.On the detailed numerical simulation of combustion problems, main difficulties arise from the stiffness of the governing equations, the presence of flame fronts, and the huge number of species and reactions involved in the reaction mechanisms. In order to overcome these numerical difficulties, a parallel multiblock algorithm able to work efficiently with loosely coupled computers, has been developed. The employment of numerical strategies to deal with the commented stiffness, and the use of multiblock techniques to optimise the discretisation and to parallelise the code, are the main attributes that can be pointed out. An excellent ratio between computational time and resources have been obtained.In the analysis of the numerical solutions, special attention is given to their verification. The accuracy of the results has been analysed providing uncertainty estimations. The numerical methodology employed in this thesis to simulate reactive flows is one of the most relevant contributions presented.The numerical infrastructure developed has been applied to the numerical analysis of laminar flames. Although combustion nearly always takes place within a turbulence flow field to increase the mixing process and thereby enhance combustion, laminar flames are considered as an illustrative example of combustion phenomenon and its experimental and detailed numerical analysis is a basic ingredient on the modelling of turbulent combustion processes as well as for pollutant formation. Special attention has been given to co-flow non-premixed and partially premixed methane-air laminar flames. The wide application of these flames in house-hold and industrial heating systems due to both their intense combustion process and the relatively clean nature of natural gas (composed mainly by methane), has motivated extensive research on the experimental and numerical modelling of such flames.Detailed numerical simulations have been performed to analyse fundamental aspects of these flames, and the adequacy of several mathematical approaches employed on their modelling. Available experimental data have been taken into account both on the analysis of the influence of partially premixing to main flame properties and on the mathematical approaches comparison. Special attention has also been given to pollutant formation, NOx and CO emission indexes.

Se ha desarrollado una infraestructura numérica, que permite el estudio de problemas donde están presentes fenómenos periódicos espaciales, haciendo uso de dominios computacionales reducidos con condiciones de contorno periódicas. Se enfoca en particular el estudio de la convección natural del aire, numérica y experimentalmente, en estructuras honeycomb de tipo rectangular, de interés aplicativo en aislamientos transparentes para sistemas solares térmicos. Para abordar el estudio, la tesis se ha estructurado en tres bloques, cuyos contenidos abarcan:1) El estudio del tratamiento numérico de condiciones de contorno periódicas, en base al método de volúmenes finitos, estableciéndose estrategias adecuadas de transferencia de información entre contornos periódicos en una forma explícita. Los tratamientos se sustentan en dos procedimientos: (i) en estrategias que tratan directamente con el valor de las variables del problema sobre nodos de los volúmenes de control (ubicados en los contornos periódicos y en posiciones anexas al contorno) y (ii) en interpolaciones sobre los contornos periódicos utilizadas en el método multibloque: interpolaciones de tipo conservativas e interpolaciones matemáticas. Se proponen tres formulaciones: DIF (Direct Interpolation Formulation), EPF (Exact Position Formulation) y CTF (Conservative Treatment Formulation). En la formulación DIF la transferencia de información se basa en la aplicación de interpolaciones Lagrangianas, en la formulación EPF la información se transfiere nodo a nodo entre posiciones geométricamente semejantes, mientras que en la formulación CTF la transferencia de información se basa en forzar la conservación de los flujos físicos (masa, momento y energía). Las formulaciones son comparadas entre si. Para el análisis comparativo se reproduce un caso de la literatura científica, cuyos campos de velocidad y temperatura presentan un comportamiento periódico espacial. Los criterios de comparación se basan en la verificación de las soluciones numéricas obtenidas para cada formulación. Se resuelven otros casos con la finalidad de presentar nuevos detalles acerca del tratamiento de condiciones de contorno periódicas, en base a las metodologías propuestas.2) Se aborda el estudio numérico del comportamiento periódico del aire en cavidades alargadas e inclinadas 45º, en cuyo interior se ubica una estructura honeycomb de tipo rectangular. Se reproducen casos de la literatura científica, numéricos y experimentales, con la finalidad de verificar y validar el código numérico para geometrías específicas. Aprovechando la naturaleza periódica del flujo, se proponen expresiones matemáticas para representar el comportamiento periódico de las variables velocidad, temperatura y presión dinámica. Dichas expresiones fueron utilizadas como modelos para definir las condiciones de contorno periódicas aplicables a una celda de honeycomb. Se establecen estudios comparativos entre los resultados numéricos conseguidos sobre dominios computacionales completos y los obtenidos aplicando condiciones de contorno periódicas sobre dominios computacionales reducidos a una celda de honeycomb. Mediante un estudio específico, se demuestra la utilidad de las simulaciones numéricas para solucionar geometrías de interés tecnológico, próximas al aislamiento transparente para sistemas solares térmicos, aplicando condiciones de contorno periódicas en dominios computacionales reducidos.3) El estudio numérico de la convección natural del aire en una cavidad rectangular, con estructuras honeycomb en su interior. Se lleva a cabo la validación de los resultados numéricos, contrastando sus valores con resultados experimentales obtenidos en base a técnicas PIV (Particle Image Velocimetry), las cuales permitieron visualizar y cuantificar el campo de velocidades.Las simulaciones numéricas de todo el trabajo se basaron en el método de volúmenes finitos. Las ecuaciones gobernantes discretizadas fueron resueltas en forma segregada, utilizándose el algoritmo SIMPLEC. Las geometrías fueron discretizadas en base a mallas Cartesianas desplazadas. Los resultados numéricos fueron verificados a través de herramientas de post - proceso basadas en la extrapolación de Richardson generalizada y en el concepto del GCI (Grid Convergence Index).

Traditionally Shell-and-tube heat exchangers are designed using correlation based approaches like Kern method and Bell-Delaware method. With the advances in Computational Fluid Dynamics (CFD) software, it is now possible to design small heat exchangers using CFD. In this thesis, shell-and-tube heat exchangers are modeled and numerically analyzed using a commercial finite volume package. The modeled heat exchangers are relatively small, have single shell and tube passes. The leakage effects are not taken into account in the design process. Therefore, there is no leakage from baffle orifices and no gap between baffles and the shell. This study is focused on shell side flow phenomena. First, only shell side is modeled and shell side heat transfer and flow characteristics are analyzed with a series of CFD simulations. Various turbulence models are tried for the first and second order discretization schemes using different mesh densities. CFD predictions of the shell side pressure drop and the heat transfer coefficient are obtained and compared with correlation based method results. After selecting the best modeling approach, the sensitivity of the results to the flow rate, the baffle spacing and baffle cut height are investigated. Then, a simple double pipe heat exchanger is modeled. For the double pipe heat exchanger, both the shell (annulus) side and the tube side are modeled. Last, analyses are performed for a full shell-and-tube heat exchanger model. For that last model, a small laminar educational heat exchanger setup is used. The results are compared with the available experimental results obtained from the setup. Overall, it is observed that the flow and temperature fields obtained from CFD simulations can provide valuable information about the parts of the heat exchanger design that need improvement. The correlation based approaches may indicate the existence of a weakness in design, but CFD simulations can also pin point the source and the location of the weakness.

In this study, the thermal management system of a notebook computer is investigated by using a commercial finite volume Computational Fluid Dynamics (CFD) software. After taking the computer apart, all dimensions are measured and all major components are modeled as accurately as possible. Heat dissipation values and necessary characteristics of the components are obtained from the manufacturer&#039 / s specifications. The different heat dissipation paths that are utilized in the design are investigated. Two active fans and aluminum heat dissipation plates as well as the heat pipe system are modeled according to their specifications. The first and second order discretization schemes as well as two different mesh densities are investigated as modeling choices. Under different operating powers, adequacy of the existing thermal management system is observed. Average and maximum temperatures of the internal components are reported in the form of tables. Thermal resistance networks for five different operating conditions are obtained from the analysis of the CFD simulation results. Temperature distributions on the top surface of the chassis where the keyboard and touchpad are located are investigated considering the user comfort.

Francis type turbines are commonly used in hydropower generation. Main components of the turbine are spiral case, stay vanes, guide vanes, turbine runner and the draft tube. The dimensions of these parts are dependent mainly on the design discharge, head and the speed of the rotor of the generators. In this study, a methodology is developed for parametric optimization by incorporating Matlab codes developed and commercial Computational Fluid Dynamics (CFD) codes into the design process. The design process starts with the selection of initial dimensions from experience curves, iterates to improve the overall hydraulic efficiency and obtain the detailed description of the final geometry for manufacturing with complete visualization of the computed flow field. A Francis turbine designed by the procedure developed has been manufactured and installed for energy production.