Thesis (MScIng)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: The effect of topography and terrain on wind is examined in order to ensure that the wind turbine positioning will encourage a greater availability of wind energy to it. Maximum power point tracking methods are presented whereby the loading on the wind turbine is controlled to ensure that the maximum available energy from the wind is captured. The wind turbine system is modelled and used in simulations to evaluate the three proposed maximum power point trackers, named anemometer control, calculation control and constant step control for the purpose of this thesis. An additional analog system is also created whereby the complete wind turbine system is able to be simulated. An inverter is used to replicate the generator and the loading is controlled using an active rectifier since this will be used on the practical system. The results from the simulations and analog system are presented whereby one of the trackers is shown to be inadequate and the other two trackers are shown to be close to ideal. The appeal of the calculation method is in the redundancy of an anemometer making it attractive to less expensive, small-scale systems. / AFRIKAANSE OPSOMMING: Die invloed van die topografie en die terrein op die dinamika van wind word ondersoek om sodoende te verseker dat die posisionering van wind turbienes 'n beter effektiwiteit van wind energie oordrag sal bewerkstellig. Maksimum drywingspunt volger metodes word bespreek sodat die lading op die wind turbiene beheer kan word om sodoende te verseker dat die maksimum wind energie oorgedra kan word. Die wind turbiene stelsel word gemodeleer en geimplimenteer om die drie voorgestelde maksimum drywingspount volgers te evalueer, naamlik windspoedbeheer, berekening-beheer en konstantestap-beheer vir die doeleindes van hierdie tesis. 'n Adissionele analoog stelsel is ontwerp waarmee die volledige wind turbiene stelsel gesimuleer kan word. 'n Omsetter word gebruik om die generator na te boots en die belading word beheer deur middel van 'n aktiewe gelykrigter soos gebruik 'n praktese stelsel. Resultate van die simulasies en die analog stelsel is verskaf om te bewys dat een van die volg-metodes onvoldoende volging bewerkstellig, en die ander twee nabyaan ideale volging bewerkstellig. Dit is getoon dat die berekening metode meer aantreklik is vir kleinskaal stelsels, aangesien 'n windspoedsensor onnodig is.

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This thesis discusses the importance of tidal turbine support structures through analytical and computational modelling. A head-driven analytical channel model was first developed to determine the sensitivity of the flow to the presence and type of support structures. It showed that there was a significant potential reduction in farm power output even when only considering approximate force coefficients for rotor and support structure. To confirm these findings, computational simulations were performed on a full-scale turbine to obtain more accurate force coefficients considering full rotor-support structure interactions. The flow interaction effects between the rotor and its support structure were studied using Computational Fluid Dynamics (CFD) for different support structure shapes for a range of tidal velocities including the power-capping zone. The integrated rotor force coefficients were higher in the presence of the cylindrical support structure than the elliptical support due to the higher opposing thrust from the cylinder in the channel redirecting the flow and increasing the flow velocity over the top half of the rotor. The presence of rotor caused a drop in the stream-wise forces on the support structure. The amplitude of the stream-wise sectional forces along the support structure height was lower in the case of an elliptical than a circular cylinder due to more streamlined shape of the ellipse. At device scale, the computational model was used to study the turbine performance in the power-capping zone by pitching the blades to feather. The influence of pitch-to- feather power-capping strategy was examined by studying the forces and angle of attack on the turbine blades, and the wake at three different blade pitch angles. Increasing blade pitch angle resulted in a significant drop in the average load on the blade. Also since the tidal channel flow has a shear in its velocity profile, the influence of shear on turbine performance was studied by comparing it to the same turbine in a uniform flow. The analytical channel flow model was used to investigate the characteristics of tidal stream energy extraction for large tidal farms deployed in tidal channels with specific focus on the limitations to realizable farm power due to turbine support structure drag and constraints on volume flow rate reduction. The force coefficients dataset from computational modelling was used to obtain a better estimate of the farm power output. Support structures were seen to contribute significantly to the overall resistive force in the channel and thus reduce the overall flow rates in the channel, leading to losses in realizable power. Over a wide range of channel characteristics, realistic levels of support structure drag lead to up to a 10% reduction in realizable power, and an associated reduction in the number of turbines that can be economically installed.

Energy is integral to the quality of life of any society. However, meeting the demand for energy sustainably is the main challenge facing humanity. In general, non-renewable energy resources are used to supply the ever increasing energy demand. However, the extraction and processing of these resources is accompanied by the production of wastes which are a health hazard and impact negatively on climate change. Considering the finite nature of non-renewable sources, the environmental concerns which are associated with their usage and ensuring energy security, renewable energy sources have been brought in the energy supply chain. Wind energy is one of the renewable energy sources which has been supplying electrical energy to the ever increasing energy demand of humanity. Wind energy technology is a mature technology which over and above the bare (conventional) wind turbine technology has seen the development of duct augmented wind turbines. Ducts are used to encase wind turbine rotors to augment the power output of wind turbines especially in low wind speed areas. Though the technology has been under study for decades now, research indicates that there is no known model to estimate the power output of a diffuser augmented wind turbine. This thesis presents the development of the conical Diffuser Augmented Wind Turbine (DAWT) power output estimation model and its validation.

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Made available in DSpace on 2014-06-11T19:30:09Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-02Bitstream added on 2014-06-13T20:00:03Z : No. of bitstreams: 1 tofoli_f_me_guara.pdf: 778310 bytes, checksum: 518b10e7c88d6a576eb683e42128bcd4 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Este trabalho tem como objetivo a análise da influência de parâmetros adimensionais e grandezas dimensionais no projeto de turbomáquinas operando em diferentes situações de pressão, temperatura e vazão mássica de vapor. O trabalho é divido em duas partes principais, sendo que inicialmente são analisados os parâmetros adimensionais e as grandezas dimensionais que influenciam diretamente o valor do rendimento interno das turbomáquinas térmicas que utilizam o vapor como fluido de trabalho. Na segunda parte do trabalho são abordadas as classes de pressão e rotação específica, e sua influência no comportamento de parâmetros adimensionais. A aplicação dos resultados está diretamente ligada a especificação de turbomáquinas em sistemas de cogeração para aproveitamento de fluxos térmicos provenientes de processos, queima de combustíveis ou gases de escape de uma máquina térmica, para os quais os projetistas necessitam estimar o rendimento de tais componentes por ocasião da análise de viabilidade econômica. / This work has as objective the analysis of the influence of dimensionless parameters and dimensional greatness in the project of turbomachinery operating in different pressure situations, temperature and flow steam. This work is shared in two main parts, which are initially analyzed the dimensionless parameters and the dimensional greatness that directly influence the internal efficiency of the thermal turbomachinery that using steam as the working fluid. In the second part of the work are accosted the classes of pressure and specific rotation, and its influence on the behavior of dimensionless parameters. The application of the results is directly linked to the specification of turbomachinery in cogeneration systems for use of heat flows from processes, burning of fuel or the exhaust gases of a thermal machine, for which the designers needs to estimate the efficiency of such components at analysis of economic feasibility.

Made available in DSpace on 2014-06-11T19:30:10Z (GMT). No. of bitstreams: 0 Previous issue date: 2003Bitstream added on 2014-06-13T18:59:52Z : No. of bitstreams: 1 perez_ep_me_guara.pdf: 1116117 bytes, checksum: 2ae25303ba483b9f7ccbf3d2f842125f (MD5) / A turbina Michell-Banki é basicamente uma máquina de ação, sendo que a característica mais importante das turbinas de ação é a não existência do tubo de sucção. A instalação do tubo de sucção numa turbina causa o aumento da queda disponível e como conseqüência, aumenta a potência gerada e a rotação da turbina. No presente trabalho propõe-se a instalação de um tubo de sucção numa turbina Michell-Banki, visando alcançar as melhorias já indicadas acima, lembrando que ao colocar o tubo de sucção aparece um grau de reação na máquina. Foi feito uma análise mecânica-hidráulica da turbina Michell-Banki proposta, com o objetivo de encontrar as equações que permitem calcular os diversos elementos da turbina. Desta maneira o trabalho apresenta uma metodologia para projeto de uma turbina Michell-Banki com tubo de sucção. Também são apresentadas as formas de traçar o rotor, o injetor e a pá diretriz. Finalmente o trabalho apresenta ainda as recomendações para a execução de projeto e construção da turbina. / The turbine Michell-Banki is basically an action machine, and the important characteristic of the action turbines is the no existence of the suction tube. The installation of the suction tube in a turbine increases the available fall and as consequence, it increases the generated power. The rotation of the turbine is also increased by increasing the available fall. In the present work it's proposed the installation of a suction tube in a Michell-Banki turbine, aiming to reach the improvements already indicated above, remembering that when placing the suction tube a reaction degree appears in the machine. It was done an mechanical and hydraulics analysis of the Michell-Banki turbine with the objective of finding the equations that allow to calculate the several elements of the turbine proposed, and thus presenting a methodology for project of a turbine. Finally I described the way of drawing the rotor, the injector and the guideline shovel, as well as it is also recommended the process that should be followed to build the turbine.

Orientador: Anselmo Eduardo Diniz / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-25T10:42:27Z (GMT). No. of bitstreams: 1 Lacerda_RafaelSegantin_M.pdf: 5082934 bytes, checksum: 9288c8f97c6d45416ba8bc96895fc01d (MD5) Previous issue date: 2014 / Resumo: A fabricação de pás de turbinas hidráulicas representa uma das atividades mais importantes no processo de fabricação do rotor de uma usina hidrelétrica e corresponde a uma parcela considerável do custo de produção do mesmo. Devido às características geométricas e requisitos hidráulicos destes componentes, as operações de fresamento em cinco eixos são altamente solicitadas e se destacam pela versatilidade e rapidez que proporcionam para o processo produtivo. Todavia, o fresamento de pás de turbinas hidráulicas apresenta alguns pontos críticos relacionados com a qualidade superficial, qualidade dimensional e os custos da operação de usinagem. A taxa de remoção de material, a variação das condições de fresamento diretamente relacionada com os parâmetros de corte e a necessidade de se reduzir os ciclos de produção são itens que fazem o estudo detalhado desta operação ter importância fundamental para a utilização das modernas tecnologias de usinagem. O objetivo deste trabalho é identificar as condições de corte mais adequadas para o processo de fresamento em cinco eixos de pás de turbinas hidráulicas. Para isto, o processo de fabricação foi monitorado e ensaios foram realizados para comparação entre diferentes estratégias de fresamento e parâmetros de corte. Durante estes ensaios observaram-se os parâmetros elétricos do motor da máquina e também a coloração dos cavacos, para estabelecer uma relação entre estes parâmetros e o real desgaste sofrido pela ferramenta, a fim de se ter um método direto e prático para definição de seu fim de vida. As principais conclusões deste trabalho são que a variável de entrada mais influente na vida da ferramenta dentre as testadas foi a estratégia de corte (concordante ou concordante / discordante) e para estas ferramentas, o desgaste de flanco (VB) foi o principal determinante para o fim de vida da aresta de corte. Em adicional, a observação da potência consumida e da coloração do cavaco realizada pelo operador, mostrou-se adequada para determinar o momento de troca da ferramenta neste tipo de fresamento em desbaste. Palavras chave: fresamento em cinco eixos, pás, turbinas hidráulicas e desgaste de flanco / Abstract: The manufacturing process of blades for hydraulic turbines is one of the most important activities to fabricate a runner for a hydraulic power plant and is responsible for a considerable portion of the production cost thereof. Due to the geometric characteristics and hydraulic requirements in these components, the milling operations in five axis is highly appreciated and offer the versatility and speed for the production process. However, the milling process for blades of hydraulic turbines present some critical issues related to the surface quality, dimensional quality and machining costs. The rate of material removal, the variation of milling conditions directly related with cutting parameters and the need to reduce production cycles are items that make a detailed study of this operation has high importance on the application of the most modern machining technologies. The objective of this work is to identify the most suitable cutting conditions for five axis milling in blades of hydraulic turbines. For this, the manufacturing process was monitored and tests were performed in order to compare different milling strategies and cutting parameters. During these tests was observed the electrical parameters of the machine motor and also the colors of the chips to establish a relationship between these parameters and the actual wear suffered by the tool in order to have a derictly and practical method to define the end of the tool life. The main conclusions are that the most influential variable in the tool life among those tested was the cutting strategy (Up Milling or Up Milling / Down Milling) and for these tools, the main determinant for the end of life is the flank wear (VB) of the cutting edge. In additional, the observation of the power consumption and the colors of the chips performed by the operator, with the goal of determining the exactly time to exchange the tool was adequate for this type of rough milling. Keywords: five axis milling, blades, hydraulic turbines and flank wear / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica

Gas turbine engineering faces many challenges in the constant strive to increase not only the efficiency of engines but also the various stages of development and design. Development of combustors have primarily consisted of empirical or semi-empirical modelling combined with experimental investigations. Due to the associated costs and development time a need exists for an alternative method of development. Although experimental investigations can never be substituted completely, mathematical models incorporating numerical methods have shown to be an attractive alternative to conventional combustor design methods. The purpose of this study is twofold: firstly, to experimentally investigate the physical properties associated with a research combustor that is geometrically representative of practical combustors; and secondly, to use the experimental measurements for the validation of a computational fluids dynamic model that was developed to simulate the research combustor using a commercial code. The combustor was tested at atmospheric conditions and is representative of practical combustors that are characterized by a turbulent, three-dimensional flow field. The single can combustor is divided into a primary, secondary and dilution zone, incorporating film¬cooling air through stacked rings and an axial swirler centred around the fuel atomizer. Measurements at different air/fuel ratios captured the thermal field during operating conditions and consisted of inside gas, liner wall and exit gas temperatures. An investigation of the different combustion models available, led to the implementation of the presumed-PDF model of unpremixed turbulent reaction. The computational grid included the external and internal flow field with velocity boundary conditions prescribed at the various inlets. Two-phase flow was not accounted for with the assumption made that the liquid fuel is introduced into the combustion chamber in a gas phase. Experimental results showed that incomplete combustion occurs in the primary zone, thereby reducing the overall efficiency. Also evident from the results obtained are the incorrect flow splits at the various inlets. Evaluation of the numerical model showed that gas temperatures inside the combustor are overpredicted. However, the numerical model is capable of capturing the correct distributions of temperatures and trends obtained experimentally. This study is successful in capturing detail temperature measurements that will be used for validation purposes to assist the development of a numerical model that can accurately predict combustion properties. / Dissertation (M Eng (Mechanical Engineering))--University of Pretoria, 2007. / Mechanical and Aeronautical Engineering / unrestricted

In this study we conduct wind resource assessment to evaluate the annual energy production of a wind turbine. To estimate energy production of a wind turbine over a period of time, the power characteristics of the wind turbine are integrated with the probabilities of the wind speed expected at a chosen site. The first data set was obtained from a wind farm in Denmark. We propose several probability density functions to model the distribution of the wind speed. We use techniques from nonlinear regression analysis to model the power curve of a wind turbine. The best fit distribution model is assessed by performing numeric goodness–of–fit measures and graphical analyses. Johnson’s bounded (SB) distribution provides the best fit model with the smallest Kolmogorov–Smirnov (K-S) test statistic . 15. The four parameter logistic nonlinear regression (4PL) model is determined to provide the best fit to the power curve data, according to the Akaike Information Criterion (AIC) and the Bayesian Information Criterion (BIC). The estimated annual energy yield is compared to the actual production of the wind turbine. Our models underestimate the actual energy production by a 1 difference. In Chapter Six we conduct data processing, analyses and comparison of wind speed distributions using a data set obtained from a measuring wind mast mounted in Humansdorp, Eastern Cape. The expected annual energy production is estimated by using the certified power curve as provided by the manufacturer of the wind turbine under study. The commonly used Weibull distribution is determined to provide the best fit distribution model to our selected models. The annual energy yield is estimated at 7.33 GWh, with a capacity factor of 41.8 percent.