There is an urgent need for economical, clean, sustainable energy supplies, not only in densely populated areas where electricity grids are appropriate, but also in rural areas where stand-alone power supply systems are often more suitable. Although electrical power supply is very versatile and convenient, it introduces unnecessary complexity for some off-grid applications where direct mechanical shaft power can conveniently be provided by a wind turbine. Wind energy is one of the more promising renewable energy sources. Most wind turbines are of the horizontal axis type, but vertical axis wind turbines or VAWTs have some advantages for direct mechanical drive applications. They need no tail or yaw mechanism to orient them into the wind and power is easily transmitted via a vertical shaft to a load at ground level. Blades may be of uniform section and untwisted, making them relatively easy to fabricate or extrude, unlike the blades of horizontal axis wind turbines (HAWTs) which should be twisted and tapered for optimum performance. Savonius rotor VAWTs are simple and may have a place where the power requirement is only a few Watts, but they are inefficient and uneconomical for applications with larger power requirements. VAWTs based on the Darrieus rotor principle are potentially more efficient and more economical, but those with fixed pitch blades have hitherto been regarded as unsuitable for stand-alone use due to their lack of starting torque and low speed torque. This starting torque problem can be overcome by using variable pitch blades, but most existing variable pitch VAWTs, variously known as giromills or cycloturbines, need wind direction sensors, microprocessors and servomotors to control the blade pitch, making them impracticable for stand-alone, non-electrical applications. A simpler but less well known concept is passive or self-acting variable pitch in which the blades are free to pitch under the combined action of aerodynamic and inertial forces in such a way that a favourable blade angle of attack is maintained without the complexity of conventional variable pitch systems. Several fonns of self-acting variable pitch VAWTs or SAPVAWTs have been described in the literature, several patents exist for variants on the concept, and at least two companies world-wide have attempted to commercialise their designs. However the aerodynamic behaviour of these devices has been little understood and most designs appear to have been based on nothing more than a qualitative appreciation of the potential advantages of the concept. This thesis assesses the potential of both fixed and passive variable pitch vertical axis wind turbines to provide economical stand-alone power for direct mechanical drive applications. It is shown that the starting torque and low speed torque problems of VAWTs can be overcome either by passive variable pitch or by a combination of suitable blade aerofoil sections, either rigid or flexible, and transmissions which unload the rotor at low speeds so that high starting torque is not necessary. The work done for this thesis is made up of a sequence of stages, each following logically from the previous one: 1. Several tasks have been identified which could be performed effectively by a self-starting vertical axis wind turbine using direct mechanical drive. These include, a. pumping water, b. purifying and/or desalinating water by reverse osmosis, c. heating and cooling using vapour compression heat pumps, d. mixing and aerating water bodies and e. heating water by fluid turbulence. Thus it is apparent that such a system has the potential to make a useful contribution to society. 2. A literature survey of existing VAWT designs has been carried out to assess whether any are suitable for these applications. 3. As no suitable existing design was identified, an improved form of SAPVAWT has been developed and patented. 4. To optimise the performance of the improved SAPVAWT, a mathematical model has been developed in collaboration with Mr Leo Lazauskas of the University of Adelaide (see Kirke and Lazauskas, 1991, Lazauskas and Kirke, 1992). As far as the author of the present thesis is aware, this is the only existing mathematical model able to predict the performance of this particular type of SAPVAWT, and one of only two worldwide which model SAPVAWTs. 5. In order to use the mathematical model to predict the performance of a given SAPVAWT, it is necessary to have lift, drag and moment data for the aerofoil profile to be used, over a wide range of incidence and Reynolds numbers. A literature search has revealed large gaps in the existing data. 6. Wind tunnel testing has been carried out to assess the effect of camber on the performance of one set of NACA sections at low Reynolds number, and performance figures for other sections have been estimated by interpolation from existing data. 7. Using the assembled aerofoil data, both experimental and estimated, the mathematical model has been used to predict the performance of both fixed and variable pitch VAWTs. It has been found to predict correctly the performance of known fixed pitch VAWTs and has then been used to predict the performance of fixed pitch VAWTs with cambered blades using newly developed profiles that exhibit superior characteristics at low Reynolds numbers. Results indicate that fixed pitch VAWTs using these blade sections should self-start reliably. 8. To validate the mathematical model predictions for self-acting variable pitch, a two metre diameter physical model has been built and tested in a wind tunnel, and acceptable agreement has been obtained between predicted and measured performance. 9. To demonstrate the performance of a SAP VA WT under field conditions, a six metre diameter turbine has been designed, fabricated, erected and tested. 10. Because a prime mover such as a wind turbine is of no use unless it drives a toad, particular attention has been paid to the behaviour of complete systems, including the wind turbine, the transmission and the load. It is concluded that VAWTs with the improved self-starting and low speed torque characteristics described in this thesis have considerable potential in stand-alone, direct mechanical drive applications.

The kinetic energy present in tidal currents and other water courses has long been appreciated as a vast resource of renewable energy. The work presented in this doctoral thesis is devoted to both the characteristics of the hydro-kinetic resource and the technology for energy conversion. An assessment of the tidal energy resource in Norwegian waters has been carried out based on available data in pilot books. More than 100 sites have been identified as interesting with a total estimated theoretical resource—i.e. the kinetic energy in the undisturbed flow—in the range of 17 TWh. A second study was performed to analyse the velocity distributions presented by tidal currents, regulated rivers and unregulated rivers. The focus is on the possible degree of utilization (or capacity factor), the fraction of converted energy and the ratio of maximum to rated velocity, all of which are believed to be important characteristics of the resource affecting the economic viability of a hydro-kinetic energy converter. The concept for hydro-kinetic energy conversion studied in this thesis comprises a vertical axis turbine coupled to a directly driven permanent magnet generator. One such cable wound laboratory generator has been constructed and an experimental setup for deployment in the river Dalälven has been finalized as part of this thesis work. It has been shown, through simulations and experiments, that the generator design at hand can meet the system requirements in the expected range of operation. Experience from winding the prototype generators suggests that improvements of the stator slot geometry can be implemented and, according to simulations, decrease the stator weight by 11% and decrease the load angle by 17%. The decrease in load angle opens the possibility to reduce the amount of permanent magnetic material in the design.

O presente trabalho apresenta um estudo numérico e experimental sobre o desempenho aerodinâmico de turbinas eólicas de eixo vertical envolvendo rotores Savonius convencional de duplo-estágio e helicoidal. O estudo experimental é realizado no Túnel Aerodinâmico Professor Debi Pada Sadhu, do Laboratório de Mecânica dos Fluidos da UFRGS. As simulações numéricas são realizadas com o software Fluent/ANSYS utilizando o Método dos Volumes Finitos. São comparados os coeficientes de torque estático e dinâmico, o coeficiente de potência, além de uma análise aerodinâmica das duas turbinas. As medições são realizadas empregando Tubos de Pitot, um torquímetro estático digital e um torquímetro simples construído para a medição do torque dinâmico. As turbinas são fabricadas através da técnica de prototipagem 3D, com uma semelhança de dimensões e parâmetros. As soluções numéricas são resolvidas através da equação da continuidade, das equações de Navier-Stokes com médias de Reynolds (RANS) e pelo modelo de turbulência k-ω SST. A qualidade da malha utilizada é avaliada através do método de Índice de Convergência de Malha (GCI), para três diferentes tamanhos de malha. São feitas análises dos rotores na forma estática para diferentes ângulos de incidência e com a turbina em rotação são feitas análises para diferentes razões de velocidades de ponta de pá (λ). Resultados demonstram que a turbina helicoidal apresenta um coeficiente de torque positivo para todos os ângulos do rotor, assim como a turbina convencional de dois estágios. O coeficiente de torque dinâmico da turbina helicoidal é superior ao da turbina de duplo-estágio para a maioria dos casos, e também apresenta menor oscilação de torque ao longo de cada rotação. Por consequência, o coeficiente de potência do rotor helicoidal também se tornou superior, com um valor máximo encontrado na ordem de 11,8% para um λ de 0,65 no caso experimental, e de 8,4% para o mesmo λ no caso numérico, quando comparado com o rotor de duplo-estágio. Os erros relativos entre as simulações numéricas e os resultados experimentais estão entre 2,16% e 13,4%. Uma estimativa de potência gerada é feita para ambos os casos, para uma razão de velocidade de ponta de 0,65, onde a turbina helicoidal apresenta melhores resultados em relação ao rotor de duplo-estágio, na ordem de 13,6% para uma velocidade de 10,4 m/s. / This paper presents a numerical and experimental study of vertical axis wind turbine performance comparison involving two-stage and helical Savonius rotors. The experimental study is conducted in the Aerodynamic Tunnel Professor Debi Pada Sadhu at the Fluid Mechanics Laboratory of the UFRGS. The numerical simulations are performed with the Fluent/ANSYS software using the Finite Volumes Method. The static and dynamic torque coefficients, the power coefficients, and an aerodynamic analysis of the two turbines are compared. Measurements are made using Pitot tubes, a digital static torque wrench and a simple wrench constructed for the dynamic torque measurement. The aerodynamics rotors are manufactured by 3D prototyping technique with similar dimensions and parameters. Numerical solutions are solved by the continuity equation, the Reynolds Averaged Navier-Stokes (RANS) equations and the turbulence model k-ω SST. The quality of the mesh used is evaluated used the Grid Convergence Index (GCI) method, for three different mesh sizes. The rotors analyzes are made in static form for different angles of incidence and for the rotating turbine analyzes are made for differents tip speed ratio (λ). Results show that the helical turbine has a positive static torque coefficient for any rotor angles, as well as conventional two-stage turbine. The dynamic torque coefficient of the helical turbine is higher than the two-stage turbine for most cases and also shows less torque variation along each rotation. Consequently, the power coefficient of the helical rotor also become higher, with a maximum value found on the order of 11.8% for a λ of 0.65 in the experimental case, and 8.4% for the same λ number when compared with the two-stage rotor. The relative errors between the numerical simulations and the experimental results are between 2.16% and 13.4%. A generated power estimate is made for both cases, for a tip speed ratio of 0.65, where the helical turbine provides better results compared to two-stage rotor in order of 13.6% for a velocity of 10.4 m/s.

O presente trabalho apresenta um estudo numérico e experimental sobre o desempenho aerodinâmico de turbinas eólicas de eixo vertical envolvendo rotores Savonius convencional de duplo-estágio e helicoidal. O estudo experimental é realizado no Túnel Aerodinâmico Professor Debi Pada Sadhu, do Laboratório de Mecânica dos Fluidos da UFRGS. As simulações numéricas são realizadas com o software Fluent/ANSYS utilizando o Método dos Volumes Finitos. São comparados os coeficientes de torque estático e dinâmico, o coeficiente de potência, além de uma análise aerodinâmica das duas turbinas. As medições são realizadas empregando Tubos de Pitot, um torquímetro estático digital e um torquímetro simples construído para a medição do torque dinâmico. As turbinas são fabricadas através da técnica de prototipagem 3D, com uma semelhança de dimensões e parâmetros. As soluções numéricas são resolvidas através da equação da continuidade, das equações de Navier-Stokes com médias de Reynolds (RANS) e pelo modelo de turbulência k-ω SST. A qualidade da malha utilizada é avaliada através do método de Índice de Convergência de Malha (GCI), para três diferentes tamanhos de malha. São feitas análises dos rotores na forma estática para diferentes ângulos de incidência e com a turbina em rotação são feitas análises para diferentes razões de velocidades de ponta de pá (λ). Resultados demonstram que a turbina helicoidal apresenta um coeficiente de torque positivo para todos os ângulos do rotor, assim como a turbina convencional de dois estágios. O coeficiente de torque dinâmico da turbina helicoidal é superior ao da turbina de duplo-estágio para a maioria dos casos, e também apresenta menor oscilação de torque ao longo de cada rotação. Por consequência, o coeficiente de potência do rotor helicoidal também se tornou superior, com um valor máximo encontrado na ordem de 11,8% para um λ de 0,65 no caso experimental, e de 8,4% para o mesmo λ no caso numérico, quando comparado com o rotor de duplo-estágio. Os erros relativos entre as simulações numéricas e os resultados experimentais estão entre 2,16% e 13,4%. Uma estimativa de potência gerada é feita para ambos os casos, para uma razão de velocidade de ponta de 0,65, onde a turbina helicoidal apresenta melhores resultados em relação ao rotor de duplo-estágio, na ordem de 13,6% para uma velocidade de 10,4 m/s. / This paper presents a numerical and experimental study of vertical axis wind turbine performance comparison involving two-stage and helical Savonius rotors. The experimental study is conducted in the Aerodynamic Tunnel Professor Debi Pada Sadhu at the Fluid Mechanics Laboratory of the UFRGS. The numerical simulations are performed with the Fluent/ANSYS software using the Finite Volumes Method. The static and dynamic torque coefficients, the power coefficients, and an aerodynamic analysis of the two turbines are compared. Measurements are made using Pitot tubes, a digital static torque wrench and a simple wrench constructed for the dynamic torque measurement. The aerodynamics rotors are manufactured by 3D prototyping technique with similar dimensions and parameters. Numerical solutions are solved by the continuity equation, the Reynolds Averaged Navier-Stokes (RANS) equations and the turbulence model k-ω SST. The quality of the mesh used is evaluated used the Grid Convergence Index (GCI) method, for three different mesh sizes. The rotors analyzes are made in static form for different angles of incidence and for the rotating turbine analyzes are made for differents tip speed ratio (λ). Results show that the helical turbine has a positive static torque coefficient for any rotor angles, as well as conventional two-stage turbine. The dynamic torque coefficient of the helical turbine is higher than the two-stage turbine for most cases and also shows less torque variation along each rotation. Consequently, the power coefficient of the helical rotor also become higher, with a maximum value found on the order of 11.8% for a λ of 0.65 in the experimental case, and 8.4% for the same λ number when compared with the two-stage rotor. The relative errors between the numerical simulations and the experimental results are between 2.16% and 13.4%. A generated power estimate is made for both cases, for a tip speed ratio of 0.65, where the helical turbine provides better results compared to two-stage rotor in order of 13.6% for a velocity of 10.4 m/s.

<p>  </p> <p>In this study, we aimed to explore the potential of integrating wind turbines into tall buildings to harness wind energy in urban areas. Advanced computer simulations will be used to analyze the complex wind patterns and turbulence around tall buildings. We will also study the optimization of wind turbine placement to maximize energy production. We focus on two types of wind turbines, the savonius and a modified savonius, using the Myring formula. We evaluated their performance in turbulent urban areas using computational fluid dynamics simulations. The simulations will also help us understand the wind flow behavior around tall buildings, informing wind turbine placement optimization.</p> <p>Our findings contribute to the understanding of urban wind energy production. This may lead to further advancements in wind turbine design and application in urban environments, promoting sustainable and clean energy production in densely populated areas.</p> <p>We also evaluate the economic feasibility of wind power as an energy source and its potential for commercial applications. Our study's insights are significant for wind energy research, urban planning, and sustainable energy production in cities.</p> <p>To achieve our objectives, we will use state-of-the-art computational tools such as the ANSYS Fluent Student software and the Steady Reynolds Averaged Navier-Stokes (SRANS) K-ε model and K-ω SST models for simulating wind flow around tall buildings.</p> <p>In summary, the goal of this research is to develop a methodology for integrating wind turbines into tall urban buildings to harness wind energy potential. This will contribute to the understanding of urban wind energy production and its economic feasibility for commercial applications.</p>

No description available.

This project is a part of the master thesis for the course Energy smart innovation in the built environment at Halmstad University. This project is done to check the feasibility of VAWT on replacing traditional horizontal axis windmills, costly offshore windmills, and other renewables. As Micro VAWT are smaller, they can be placed where traditional windmills will not be. To stress the point, these can be placed in places like traffic islands and open garden areas.  Lots of such projects are currently ongoing in different parts of the world. Sweden is lagging in this technology diffusion. We concluded that VAWM couldn't alone be used to replace traditional HAWTs or be enough to reach the full renewable target. They can be used in conjunction with HAWT to boost production and efficiency, and we also found other similar uses for VAWM. A business model is suggested so as for the optimal diffusion of VAWT. Our proposal of a micro VAWT of 1.8 million was able to produce 1.41TWh.We found that it was not possible to achieve with VAWT alone.

Wind power is a renewable energy source that is increasingly used all over the world. Most wind turbines have a horizontal axis of rotation but a few have a vertical axis of rotation. The concept presented in this thesis is a straight-bladed vertical axis wind turbine with a direct driven cable-wound permanent magnet synchronous generator. A comparison of the two different types of wind turbines, vertical axis wind turbines and horizontal axis wind turbines, have been performed considering several different aspects. However, the main focus in this thesis is on the generator. Several generators have been modelled with a combined field and circuit model, which has been solved by using the finite element method. A 12 kW generator has been designed, which has a high overall efficiency and a high overload capability. The generator has been constructed at the department and was tested in the laboratory before being mounted in a vertical axis wind turbine. Results from experiments correspond well with results from simulations. The generator has been tested for different loading conditions and the harmonic content of the voltage has been analysed. A 12 kW vertical axis wind turbine was completed and tests have been performed. The results are encouraging and further studies on the prototype will be performed in the future. The simulation method has been used to study electromagnetic losses in several generators. The comparison showed that the average losses should be considered when a variable speed generator for wind power is designed and it concluded that the design optimization process becomes a compromise between lowering the electromagnetic losses and having high overload capability. When constructing a wind turbine, it is important to consider vibrations in the structure. Torsional vibrations in the drive shaft connecting the turbine to the rotor of the generator have been studied. It is shown that a direct driven generator is to prefer over an induction generator with a gearbox when torsional vibrations are concerned. This thesis is based on eight papers all concerning vertical axis wind turbines with three of them focusing on the generator.

This thesis combines measurements with the development of simulation tools for vertical axis wind turbines (VAWT). Numerical models of aerodynamic blade forces are developed and validated against experiments. The studies were made on VAWTs which were operated at open sites. Significant progress within the modeling of aerodynamics of VAWTs has been achieved by the development of new simulation tools and by conducting experimental studies.         An existing dynamic stall model was investigated and further modified for the conditions of the VAWT operation. This model was coupled with a streamtube model and assessed against blade force measurements from a VAWT with curved blades, operated by Sandia National Laboratories. The comparison has shown that the accuracy of the streamtube model has been improved compared to its previous versions. The dynamic stall model was further modified by coupling it with a free vortex model. The new model has become less dependent on empirical constants and has shown an improved accuracy.     Unique blade force measurements on a 12 kW VAWT were conducted. The turbine was operated north of Uppsala. Load cells were used to measure the forces on the turbine. A comprehensive analysis of the measurement accuracy has been performed and the major error sources have been identified. The measured aerodynamic normal force has been presented and analyzed for a wide range of operational conditions including dynamic stall, nominal operation and the region of high flow expansion. The improved vortex model has been validated against the data from the new measurements. The model agrees quite well with the experiments for the regions of nominal operation and high flow expansion. Although it does not reproduce all measurements in great detail, it is suggested that the presented vortex model can be used for preliminary estimations of blade forces due to its high computational speed and reasonable accuracy.

Wind power is a renewable energy source that is today the fastest growing solution to reduce CO2 emissions in the electric energy mix. Upwind horizontal axis wind turbine with three blades has been the preferred technical choice for more than two decades. This horizontal axis concept is today widely leading the market. The current PhD thesis will cover an alternative type of wind turbine with straight blades and rotating along the vertical axis. A brief overview of the main differences between the horizontal and vertical axis concept has been made. However the main focus of this thesis is the aerodynamics of the wind turbine blades. Making aerodynamically efficient turbines starts with efficient blades. Making efficient blades requires a good understanding of the physical phenomena and effective simulations tools to model them. The specific aerodynamics for straight bladed vertical axis turbine flow are reviewed together with the standard aerodynamic simulations tools that have been used in the past by blade and rotor designer. A reasonably fast (regarding computer power) and accurate (regarding comparison with experimental results) simulation method was still lacking in the field prior to the current work. This thesis aims at designing such a method. Analytical methods can be used to model complex flow if the geometry is simple. Therefore, a conformal mapping method is derived to transform any set of section into a set of standard circles. Then analytical procedures are generalized to simulate moving multibody sections in the complex vertical flows and forces experienced by the blades. Finally the fast semi analytical aerodynamic algorithm boosted by fast multipole methods to handle high number of vortices is coupled with a simple structural model of the rotor to investigate potential aeroelastic instabilities. Together with these advanced simulation tools, a standard double multiple streamtube model has been developed and used to design several straight bladed rotor ranging from 2 kW to 20 kW. / Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 704