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This PhD involved computational fluid dynamic simulations of finned generators cooling under forced convection in an oscillating water column environment. Various design changes to the upstream Wells turbine and its effect on the consequent cooling of the generator were investigated. Simulations were run in steady-state to obtain an initial condition, thereafter, unsteady simulations revealed a steadying of heat transfer over the course of multiple blade rotation cycles. This justified the use of steady-state for the remaining simulations over a range of flow coefficients. The results revealed that the heat transfer from the generator increased for tighter blade tip clearances, thicker blade profiles and greater turbine solidity. The heat transfer was found to increase with rising flow rate coefficient, which was adjusted by increasing the inlet velocity whilst maintaining the angular velocity of the turbine at a constant 2000 RPM. Additionally, the variation of turbine angular velocity at a fixed flow rate coefficient was investigated, the heat transfer was also found to increase with angular velocity, albeit by a far lesser extent. The inclusion of the Wells turbine upstream of the generator was investigated initially and was found to increase heat transfer due to the resulting impingement of airflow across the generator. In all design scenarios in which the heat transfer increases, there is also an observed increase in the mass flow rate of air, radially, towards the generator.

Mediante a crescente necessidade de aumento na oferta de energia elétrica devido à constante elevação na demanda mundial, esta dissertação avalia o desempenho de um sistema conversor de energia de ondas marítimas em energia elétrica. O sistema em análise é o de coluna de água oscilante com turbina de dupla ação instalado na costa. Utiliza-se um modelo regular de ondas como perturbação à dinâmica de uma câmara semi-submersa gerando fluxo de ar através de uma turbina à ar de dupla ação. O sistema final é não linear e com parâmetros variantes no tempo. A dissertação investiga possibilidades para o aumento do rendimento da turbina em diferentes condições de mar através do método de simulação numérica. Após a modelagem física e matemática do sistema escolhido, inicia-se a síntese de um controlador proporcional derivativo para controle da pressão de ar na turbina em torno da pressão ideal de trabalho da mesma. A análise inclui o comparativo entre os resultados do sistema com e sem controlador e a avaliação de robustez utilizando ondas com amplitude variável. O trabalho apresenta ainda propostas de otimização do sistema para trabalhar em condições similares a região de Pecém no Brasil. Pelos resultados obtidos nas simulações, conclui-se que o rendimento e a robustez do sistema podem melhorar utilizando um sistema controlado. O rendimento do sistema poderá ainda ser otimizado para a região de instalação. / Facing the growing necessity in increasing the electrical energy offer due to the constant rise in worldwide demand, this work evaluates the performance of an ocean wave energy converter into electrical energy. The system under analysis is an oscillating water column with dual action turbine installed in a shore. A regular wave model is used as disturbance to the semi-submerged air chamber dynamic generating an air flow through the dual action air turbine. The final system is nonlinear and contains time varying parameters. This work investigates, through numerical simulation, possibilities to increase the turbine efficiency under different ocean conditions. After the physical and mathematical modeling, it is synthesized a proportional derivative controller to control the air pressure in the turbine around its ideal working pressure. The analysis of results includes a comparison between results obtained for the system with and without controller and a robustness evaluation with amplitude variation in ocean waves. The work also presents optimization proposals for the system working in conditions similar to the Pecém region in Brazil. By the results obtained with simulation, it is concluded that the efficiency and robustness were improved for the controlled system. It is observed that the efficiency can be optimized for the installation area.

Mediante a crescente necessidade de aumento na oferta de energia elétrica devido à constante elevação na demanda mundial, esta dissertação avalia o desempenho de um sistema conversor de energia de ondas marítimas em energia elétrica. O sistema em análise é o de coluna de água oscilante com turbina de dupla ação instalado na costa. Utiliza-se um modelo regular de ondas como perturbação à dinâmica de uma câmara semi-submersa gerando fluxo de ar através de uma turbina à ar de dupla ação. O sistema final é não linear e com parâmetros variantes no tempo. A dissertação investiga possibilidades para o aumento do rendimento da turbina em diferentes condições de mar através do método de simulação numérica. Após a modelagem física e matemática do sistema escolhido, inicia-se a síntese de um controlador proporcional derivativo para controle da pressão de ar na turbina em torno da pressão ideal de trabalho da mesma. A análise inclui o comparativo entre os resultados do sistema com e sem controlador e a avaliação de robustez utilizando ondas com amplitude variável. O trabalho apresenta ainda propostas de otimização do sistema para trabalhar em condições similares a região de Pecém no Brasil. Pelos resultados obtidos nas simulações, conclui-se que o rendimento e a robustez do sistema podem melhorar utilizando um sistema controlado. O rendimento do sistema poderá ainda ser otimizado para a região de instalação. / Facing the growing necessity in increasing the electrical energy offer due to the constant rise in worldwide demand, this work evaluates the performance of an ocean wave energy converter into electrical energy. The system under analysis is an oscillating water column with dual action turbine installed in a shore. A regular wave model is used as disturbance to the semi-submerged air chamber dynamic generating an air flow through the dual action air turbine. The final system is nonlinear and contains time varying parameters. This work investigates, through numerical simulation, possibilities to increase the turbine efficiency under different ocean conditions. After the physical and mathematical modeling, it is synthesized a proportional derivative controller to control the air pressure in the turbine around its ideal working pressure. The analysis of results includes a comparison between results obtained for the system with and without controller and a robustness evaluation with amplitude variation in ocean waves. The work also presents optimization proposals for the system working in conditions similar to the Pecém region in Brazil. By the results obtained with simulation, it is concluded that the efficiency and robustness were improved for the controlled system. It is observed that the efficiency can be optimized for the installation area.

Bidirectional air turbines are used in oscillating water column (OWC) power plants for harnessing ocean wave energy. This paper describes the bidirectional aerodynamic and aero-acoustic facility at the University of Siegen for model air turbines performance testing. At least nine test facilities are known worldwide, but their layout, the performance testing procedure and the presentation of performance data are not standardized to this day. The layout of the facility at the University of Siegen follows ideas in ISO 5801 for fan performance testing. The pressurized air supply is bidirectional but steady-state. Achievable values of Reynolds and Mach number of the test turbines are 1,000,000 and 0.5, respectively. In addition, the facility is equipped with acoustic attenuators in the air supply for allowing synchronous determination of aerodynamic and acoustic characteristics of a turbine. A good practice guideline for turbine performance testing and presentation is proposed by showing full sets of non-dimensional aerodynamic and acoustic performance characteristics from two sample model turbines. Eventually, a comparison of in situ data from a full-scale turbine in transient operation with scaled up steady-state model performance measurements underlines the usefulness of steady-state model performance testing.

Several alternative ways of producing energy came up as the world took conscience of the finite availability of fossil fuels and the environmental consequences of its use and processing. Wave and tidal energy are among the so called green energies. Wave energy converters have been under research for the past two decades and yet there hasn’t been one technology that gathered everyone’s acceptance as being the most suitable one. The present work is focused on a self-rectifying turbine for wave energy harnessing. It’s a self-rectifying biplane Wells with an intermediate stator. The main goal is to evaluate the performance of such a turbine. Two different analyses were performed: experimental and computational. The experimental tests were made so that efficiency, velocity profiles and loss coefficients could be calculated. To do so scaled-down prototypes were built from scratch and tested experimentally. The 3D numerical analysis was possible by using a CFD commercial code: Fluent 6.3. Several simulations were performed for different flow coefficients. Three different degrees of mesh refinement were applied and k-ε turbulence model was the one chosen to simulate the viscous behavior of the flow through the turbine. A steady-state analysis is due and two mixing planes were used at the interfaces between the rotors and the stator. In the end comparisons are made between the experimental and numerical results