Tesis: "Vertical axis wind turbines"

1

Waltham, M. R. "Sailwing vertical axis wind turbines." Thesis, University of Reading, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316334.

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2

Rossander, Morgan. "Electromechanics of Vertical Axis Wind Turbines." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-331844.

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Wind power is an established mean of clean energy production and the modern horizontal axis wind turbine has become a common sight. The need for maintenance is high and future wind turbines may need to be improved to enable more remote and offshore locations. Vertical axis wind turbines have possible benefits, such as higher reliability, less noise and lower centre of gravity. This thesis focuses on electromechanical interaction in the straight bladed Darrieus rotor (H-rotor) concept studied at Uppsala University. One of the challenges with vertical axis technology is the oscillating aerodynamic forces. A force measurement setup has been implemented to capture the forces on a three-bladed 12 kW open site prototype. The normal force showed good agreement with simulations. An aerodynamic torque could be estimated from the system. The total electrical torque in the generator was determined from electrical measurements. Both torque estimations lacked the expected aerodynamic ripple at three times per revolution. The even torque detected is an important result and more studies are required to confirm and understand it. The force measurement was also used to study the loads on the turbine in parked conditions. It was discovered that there is a strong dependence on wind direction and that there is a positive torque on the turbine at stand still. The results can assist to determine the best parking strategies for an H-rotor turbine. The studied concept also features diode rectification of the voltage from the permanent magnet synchronous generator. Diodes are considered a cheap and robust solution for rectification at the drawback of inducing ripple in the torque and output voltage. The propagation of the torque ripple was measured on the prototype and studied with simulations and analytical expressions. One key conclusion was that the mechanical driveline of the turbine is an effective filter of the diode induced torque ripple. A critical speed controller was implemented on the prototype. The controller was based on optimal torque control and according to the experiments and the simulations it was able to avoid a rotational speed span. Finally, the optimal torque control was evaluated for multiple turbines with diode rectification to a common DC-link. The setup can potentially reduce the overall complexity of wind farms. The simulations suggest that stability of the system can be obtained by controlling the DC-link load as a semi constant voltage. The thesis is based on nine papers of which six are treated in the thesis summary.

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3

Roynarin, Wirachai. "Optimisation of vertical axis wind turbines." Thesis, Northumbria University, 2004. http://nrl.northumbria.ac.uk/1655/.

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A practical Vertical Axis Wind Turbine (VAWTs) based on a Darrieus rotor has been designed and tested and found to be capable of self-starting at wind speeds above 4m/s. The self-start feature has been achieved by replacing the usual symmetrical aerofoil blade in the VAWT rotor and by using a concentric Savonius rotor or semi-cylinder turbine. A computer program was produced to compute the power coefficient versus tip speed ratio characteristics of a selected aerofoil profile employed in a VAWT. The program accounts for chord length, pitch angle, number of blades, and rotor radius at any wind speed. The published data from 40 aerofoil sections were assessed, taking into account the two main criteria — self-starting and efficiency. Computational fluid dynamics software (ANSYS, Flotran) has been used to investigate the lift and drag performance of a NACA 66-212 and NACA 4421 aerofoils in order to check the computer program predictions. Excellent agreement was obtained for the static aerofoil assessment, but only after special ICEM Computational Fluid Dynamics (CFD) meshing interface routines were utilised. However, agreement between the theoretical and published results was not good for the rotating aerofoils in a VAWT. Thus, further CFD work was not pursued and in preference, an experimental route was initiated. In the first series of wind tunnel tests involving three candidate profiles, good agreement was found between the experimental results and the mathematical models. The aerofoils chosen were the NACA 661-212, the 51223 and the Clark-Y standard aerofoils. A number of prototype VAWTs were fabricated and tested for the influence of the blade pitch angle, the chord length ratio, with 2 or 3 blades. The aerofoil surfaces were made from aluminium sheet with a standard surface finish. The prototype designs were tested in the Northumbria University low speed wind tunnel facility - the models were 0.4 m. high with a 0.4 m diameter. The torque versus wind speed characteristics were recorded and analysed. The S 1223 profile was found to be self-starting with high efficiency. This model generated a high power coefficient of about 0.3 at a tip speed ratio of 1.2. The second series of tests were carried out in field sites in the UK with a 2 m diameter straight—bladed Darrieus rotor prototype with 3 blades using the S1223 blade section. Three field trials were undertaken in the UK to produce realistic performance characteristics for wind conditions of 4-10 m/s. The maximum power coefficient of this machine was found to be 0.18 at a tip speed ratio of 1.2. In addition, an alternative semi-cylinder turbine combined with a Darrieus rotor was fabricated and tested in the UK. It demonstrated the advantage that it could self-start at lower wind speeds, that is 3m/s but delivers approximately 50% less power than that obtained from the first proposed design. A final phase of testing was carried out with an enlarged and modified 3 m diameter prototype installed at a shrimp farm in Thailand to demonstrate how the unit could be used to replace an equivalent 2 HP 2-stroke diesel engine and hence eliminate its inherent emission pollution problems. A Savonius rotor was fitted to the prototype to improve self-start capabilities at a wind speed of 4 m/s for a practical application which by its nature required a high starting torque. The designs are easy to fabricate, low cost, pollution free and have been demonstrated to be ideal for applications in developing countries where there are sufficient wind resources.

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4

Pearson, Charlie. "Vertical axis wind turbine acoustics." Thesis, University of Cambridge, 2014. https://www.repository.cam.ac.uk/handle/1810/245256.

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Increasing awareness of the issues of climate change and sustainable energy use has led to growing levels of interest in small-scale, decentralised power generation. Small-scale wind power has seen significant growth in the last ten years, partly due to the political support for renewable energy and the introduction of Feed In Tariffs, which pay home owners for generating their own electricity. Due to their ability to respond quickly to changing wind conditions, small-scale vertical axis wind turbines (VAWTs) have been proposed as an efficient solution for deployment in built up areas, where the wind is more gusty in nature. If VAWTs are erected in built up areas they will be inherently close to people; consequently, public acceptance of the turbines is essential. One common obstacle to the installation of wind turbines is noise annoyance, so it is important to make the VAWT rotors as quiet as possible. To date, very little work has been undertaken to investigate the sources of noise on VAWTs. The primary aim of this study was therefore to gather experimental data of the noise from various VAWT rotor configurations, for a range of operating conditions. Experimental measurements were carried out using the phased acoustic array in the closed section Markham wind tunnel at Cambridge University Engineering Department. Beamforming was used in conjunction with analysis of the measured sound spectra in order to locate and identify the noise sources on the VAWT rotors. Initial comparisons of the spectra from the model rotor and a full-scale rotor showed good qualitative agreement, suggesting that the conclusions from the experiments would be transferable to real VAWT rotors. One clear feature observed in both sets of spectra was a broadband peak around 1-2kHz, which spectral scaling methods demonstrated was due to laminar boundary layer tonal noise. Application of boundary layer trips to the inner surfaces of the blades on the model rotor was found to eliminate this noise source, and reduced the amplitude of the spectra by up to 10dB in the region of the broadband peak. This method could easily be applied to a full-scale rotor and should result in measurable noise reductions. At low tip speed ratios (TSR) the blades on a VAWT experience dynamic stall and it was found that this led to significant noise radiation from the upstream half of the rotor. As the TSR was increased the dominant source was seen to move to the downstream half of the rotor; this noise was thought to be due to the interaction of the blades in the downstream half of the rotor with the wake from the blades in the upstream half. It was suggested that blade wake interaction is the dominant noise source in the typical range of peak performance for the full-scale QR5 rotor. Different solidity rotors were investigated by using 2-, 3- and 4-bladed rotors and it was found that increasing the solidity had a similar effect to increasing the TSR. This is due to the fact that the induction factor, which governs the deflection of the flow through the rotor, is a function of both the rotor solidity and the TSR. With a large body of experimental data for validation, it was possible to investigate computational noise prediction methods. A harmonic model was developed that aimed to predict the sound radiated by periodic fluctuations in the blade loads. This model was shown to agree with similar models derived by other authors, but to make accurate predictions very high resolution input data was required. Since such high resolution blade loading data is unlikely to be available, and due to the dominance of stochastic sources, the harmonic model was not an especially useful predictive tool. However, it was used to investigate the importance of the near-field components of the sound radiated by the wind tunnel model to the acoustic array. It was shown that the near-field terms were significant over a wide range of frequencies, and the total spectrum was always greater than that of the far-field component. This implied that the noise levels measured by the acoustic array represented an upper bound on the sound radiated to the far-field, and hence that the latter would also be dominated by stochastic components. An alternative application of the harmonic model, which attempted to determine the blade loading harmonics from the harmonics in the sound field was proposed. This inversion method utilised a novel convex optimisation technique that was found to generate good solutions in the simulated test cases, even in the presence of significant random noise. The method was found to be insensitive at low frequencies, which made it ineffective for inverting the real microphone data, although this was shown to be at least partly due to the limitations imposed by the array size. In addition to the harmonic models, an empirical noise prediction method using the spectral scaling laws derived by \citet*{Brooks_1989} was trialled, and was found to be capable of making predictions that were in agreement with the measured data. The model was shown to be sensitive to the exact choice of turbulence parameters used and was also found to require good quality aerodynamic data to make accurate noise predictions. If such data were available however, it is expected that this empirical model would be able to make useful predictions of the noise radiated by a VAWT rotor.

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5

Elmabrok, Ali Mohammed. "The aerodynamics of vertical axis wind turbines." Thesis, University of Manchester, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.629477.

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One of the operational problems encountered with vertical axis wind turbines is their low starting torque. A number of analytical methods were investigated to see whether they could predict the starting performance of vertical axis turbines. The chosen methods used " actuator disc theory" for both single and multiple streamtubes. Two different forms of the multiple streamtube model are applied, one using a single actuator disc and the other using two discs in tandem. The computational analysis of all models simulates the blade aerodynamics throughout the full range of incidence from -180° to 180°. The effects of varying various geometric parameters of the windmill upon the performance of the rotor are investigated to find a design with improved self starting characteristics. The best agreement between theory and experiment was obtained using the multiple streamtube (double disc) method. Savonius rotors have been commonly employed as " starters "for Darrieus turbines. A new analytical method has been developed to model the performance characteristics of the Savonius rotor. In this method the blade is divided up into small elements, and each element is treated as a thin airfoil. The rotor torque and power are computed taking into account the blades' motion, the blade shape and momentum consideration. This method shows good agreement with experimental results for a variety of Savonius rotors.A new experimental technique has been developed to provide information about the variation of torque within a cycle. These results have been used as a check on all the theoretical methods. The agreement between these experimental results and the theoretical methods show that they predict both the time averaged and the instantaneous performance.

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6

D'Ambrosio, Marco, and Marco Medaglia. "Vertical Axis Wind Turbines: History, Technology and Applications." Thesis, Halmstad University, Halmstad University, School of Business and Engineering (SET), 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:hh:diva-4986.

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In this Master Thesis a review of different type of vertical axis wind turbines (VAWT) and a preliminary investigation of a new kind of VAWT are presented.After an introduction about the historical background of wind power, the report deals with a more accurate analysis of the main type of VAWT, showing their characteristics and their operations. The aerodynamics of the wind turbines and a review of different type on generators that can be used to connect the wind mill to the electricity grid are reported as well.Several statistics are also presented, in order to explain how the importance of the wind energy has grown up during the last decades and also to show that this development of the market of wind power creates new opportunity also for VAWT, that are less used than the horizontal axis wind turbine (HAWT).In the end of 2009 a new kind of vertical axis wind turbine, a giromill 3 blades type, has been built in Falkenberg, by the Swedish company VerticalWind. The tower of this wind turbine is made by wood, in order to get a cheaper and more environment friendly structure, and a direct driven synchronous multipole with permanent magnents generator is located at its bottom. This 200 kW VAWT represents the intermediate step between the 12 kW prototype, built in collaboration with the Uppsala University, and the common Swedish commercial size of 2 MW, which is the goal of the company.A preliminary investigation of the characteristics of this VAWT has been done, focusing in particular on the value of the frequency of resonance of the tower, an important value that must be never reached during the operative phase in order to avoid serious damage to all the structure, and on the power curve, used to evaluate the coefficient of power (Cp) of the turbine. The results of this investigation and the steps followed to get them are reported. Moreover a energy production analysis of the turbine has been done using WindPro, as well as a comparison with and older type on commercial VAWT.

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7

Bülow, Fredrik. "A Generator Perspective on Vertical Axis Wind Turbines." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-197855.

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The wind energy conversion system considered in this thesis is based on a vertical axis wind turbine with a cable wound direct drive PM generator. Diode rectifiers are used to connect several such units to a single DC-bus and a single inverter controls the power flow from the DC-bus to a utility grid. This work considers the described system from a generator perspective i.e. the turbine is primarily seen as a torque and the inverter is seen as a controlled load. A 12 kW VAWT prototype with a single turbine has been constructed within the project. The power coefficient of this turbine has been measured when the turbine is operated at various tip speed ratios. This measurement determines both how much energy the turbine can convert in a given wind and at what speed the turbine should be operated in order to maximise the energy capture. The turbine torque variation during the revolution of the turbine has also been studied. A PM generator prototype has been constructed in order to study power loss in the stator core at low electrical frequencies. Heat exchange between the stator and the air-gap between the stator and the rotor has been studied. Heat exchange between the stator and the air-gap is increased by turbulence caused by the rotor. The generator was also used in a demonstration of a DC-grid where two diode rectified PM generators supplied power to a single DC load. An initial study of an inverter suitable for grid connection of the 12 kW PM generator has been performed. Several turbine control strategies are evaluated in simulations. The control strategies only require the parameter "turbine speed" to determine the optimal system load.

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8

Scheurich, Frank. "Modelling the aerodynamics of vertical-axis wind turbines." Thesis, University of Glasgow, 2011. http://theses.gla.ac.uk/2897/.

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The current generation of wind turbines that are being deployed around the world features, almost exclusively, a three-bladed rotor with a horizontal-axis configuration. In recent years, however, a resurgence of interest in the vertical-axis wind turbine configuration has been prompted by some of its inherent advantages over horizontal-axis rotors, particularly in flow conditions that are typical of the urban environment. The accurate modelling of the aerodynamics of vertical-axis wind turbines poses a significant challenge. The cyclic motion of the turbine induces large variations in the angle of attack on the blades during each rotor revolution that result in significant unsteadiness in their aerodynamic loading. In addition, aerodynamic interactions occur between the blades of the turbine and the wake that is generated by the rotor. Interactions between the blades of the turbine and, in particular, tip vortices that were trailed in previous revolutions produce impulsive variations in the blade aerodynamic loading, but these interactions are notoriously difficult to simulate accurately. This dissertation describes the application of a simulation tool, the Vorticity Transport Model (VTM), to the prediction of the aerodynamic performance of three different vertical-axis wind turbines - one with straight blades, another with curved blades and a third with a helically twisted blade configuration - when their rotors are operated in three different conditions. These operating conditions were chosen to be representative of the flow conditions that a vertical-axis wind turbine is likely to encounter in the urban environment. Results of simulations are shown for each of the three different turbine configurations when the rotor is operated in oblique flow, in other words when the wind vector is non-perpendicular to the axis of rotation of the rotor, and also when subjected to unsteady wind. The performance of the straight-bladed turbine when it is influenced by the wake of another rotor is also discussed. The capability of the VTM to simulate the flow surrounding vertical-axis wind turbines has been enhanced by a dynamic stall model that was implemented in the course of this research in order to account for the effects of large, transient variations of the angle of attack on the aerodynamic loading on the turbine blades. It is demonstrated that helical blade twist reduces the oscillation of the power coefficient that is an inherent feature of turbines with non-twisted blades. It is also found that the variation in the blade aerodynamic loading that is caused by the continuous variation of the angle of attack on the blades during each revolution is much larger, and thus far more significant, than that which is induced by an unsteady wind or by an interaction with the wake that is produced by another rotor. Furthermore, it is shown that a vertical-axis turbine that is operated in oblique flow can, potentially, produce a higher power coefficient compared to the operation in conditions in which the wind vector is perpendicular to the axis of rotation, when the ratio between the height of the turbine and the radius of the rotor is sufficiently low.

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9

Möllerström, Erik. "Vertical Axis Wind Turbines : Tower Dynamics and Noise." Licentiate thesis, Högskolan i Halmstad, Energiteknik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-242267.

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Vertical axis wind turbines (VAWTs) have with time been outrivaled by the today common and economically feasible horizontal axis wind turbines (HAWTs). However, VAWTs have several advantages such as the possibility to put the drive train at ground level, lower noise emissions and better scaling behavior which still make them interesting for research. The work within this thesis is made in collaboration between the Department of Construction and Energy Engineering at Halmstad University and the Division for Electricity at Uppsala University. A 200 kW VAWT owned by the latter and situated close to Falkenberg in the southwest of Sweden has been the main subject of the research even if most learnings has been generalized to fit a typical vertical turbine. This particular turbine has a wooden tower which is semi-guy-wired, i.e. the tower is both firmly attached to the ground and supported by guy-wires. This thesis has two main topics both regarding VAWTs: eigenfrequency of the tower and the noise generated from the turbine. The eigenfrequency of a semi-guy-wired tower is studied and an analytical expression describing this is produced and verified by experiments and simulations. The eigenfrequency of the wire itself and how it is affected by wind load are also studied. The noise characteristics of VAWTs have been investigated, both theoretically and by noise measurement campaigns. Both noise emission and frequency distribution of VAWTs has been studied. The work has resulted in analytical expressions for tower and wire eigenfrequency of a semi-guy-wired tower as well as recommendations for designing future towers for VAWTs. The noise emission of VAWTs has been studied and proven low compared to HAWTs. The noise frequency distribution of the 200 kW VAWT differs significantly from that of a similar size HAWTs with for example lower levels for frequencies below 3000 Hz.

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10

Eriksson, Sandra. "Direct Driven Generators for Vertical Axis Wind Turbines." Doctoral thesis, Uppsala : Acta Universitatis Uppsaliensis, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-9210.

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11

Bedon, Gabriele. "Aero-Structural Optimization of Vertical Axis Wind Turbines." Doctoral thesis, Università degli studi di Padova, 2016. http://hdl.handle.net/11577/3424493.

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This Thesis focuses on the aero-structural simulation and optimization of Darrieus Vertical Axis Wind Turbines. Aerodynamic simulation tools based on different techniques are developed, improved with respect to state-of-art tools, and validated against experimental data. The main considered approaches are based on the Blade Element Momentum, Vortex, two- and three-dimensional Unsteady Reynolds-Averaged Navier-Stokes (URANS) Computational Fluid Dynamics (CFD) models. The models are developed keeping in mind the final coupling with an optimization algorithm, therefore with particular emphasis on the computational effort and simulation robustness. A structural simulation tool based on the Euler-Bernoulli beam theory is also developed and validated against experimental data to perform an efficient aero-structural simulation. The validated models are coupled with an optimization algorithm under certain constraints to create an iterative loop able to produce improved designs. Different applications are considered based on the most relevant research topics and real case scenarios. The particular case of a floating Troposkien Vertical Axis Wind Turbine is analysed by improving the baseline aerodynamic design for the 5 MW rotor developed in the FP7 DeepWind project and evaluating the aerodynamic performance under rotor tilted conditions for the 1 kW demonstrator. The airfoil shape for the blade of a 500 kW H-rotor is also subjected to an optimization analysis with the aim to increase the aerodynamic production, obtaining a new geometry different from literature design. Finally, the aerodynamic and structural simulation tools are coupled to perform a complete aero-structural optimization of blade shape and chord distribution for a 500 kW Troposkien rotor. Both aerodynamic production and rotor stress are targeted in the routine and new blade shapes are found and discussed. The Thesis results, beside the increased performance with respect to the baseline case, prove that iterative loops, obtained by coupling a fast simulation tool and an optimization algorithm, can be adopted in the design and test phase of Darrieus Vertical Axis Wind Turbines, by providing the designer an advanced insight on the aerodynamic and structural phenomena experienced by these complex machines. Questa Tesi ha come oggetto la simulazione e l'ottimizzazione aero-strutturale di Turbine Eoliche ad Asse Verticale Darrieus. Strumenti per la simulazione aerodinamica basati su differenti tecniche sono sviluppati, migliorati rispetto allo stato dell'arte, e validati rispetto a dati sperimentali. I principali approcci considerati sono basati sui modelli Blade-Element Momentum, Vortex e Unsteady Reynolds-Averaged Navier-Stokes (URANS) Computational Fluid Dynamics (CFD) bi- e tri-dimensionali. I modelli sono sviluppati tenendo a mente l'accoppiamento con un algoritmo di ottimizzazione, quindi con particolare enfasi sullo sforzo computazionale e sulla robustezza della simulazione. Uno strumento di simulazione strutturale basato sulla teoria della trave di Eulero-Bernoulli è, in aggiunta, sviluppato e validato rispetto a dati sperimentali per effettuare una efficiente simulazione aero-strutturale. I modelli validati sono accoppiati con un algoritmo di ottimizzazione per la creazione di un ciclo per l'ottenimento di configurazioni migliorate. Differenti applicazioni sono considerate, basate sui temi di ricerca più rilevati e scenari reali. Il caso particolare di una Turbina Eolica ad Asse Verticale Troposkiana è stato considerato al fine di migliorare la configurazione aerodinamica di base di un rotore da 5 MW sviluppato nell'ambito del progetto FP7 DeepWind e di valutare le prestazioni aerodinamiche del dimostratore da 1 kW con rotore inclinato. La forma del profilo per la pala di un rotore ad H da 500 kW è oggetto anch'essa di un'attività di ottimizzazione finalizzata all'aumento della produzione aerodinamica, ottenendo una nuova geometria completamente differente da quelle disponibili in letterature. Infine, gli strumenti di simulazione aerodinamica e strutturale sono accoppiati per condurre una completa ottimizzazione aero-strutturale della forma della pala e della distribuzione di corda per un rotore Troposkiano da 500 kW. Sia la produzione aerodinamica che lo stato tensionale sono considerati come obiettivi e nuove forme palari sono individuate e discusse. I risultati della Tesi, oltre all'incremento di prestazioni rispetto alle geometrie di base, provano che i cicli iterativi, ottenuti tramite l'accoppiamento di un veloce strumento di simulazione e un algoritmo di ottimizzazione, possono essere adottati nella progettazione e test di Turbine Eoliche ad Asse Verticale Darrieus, fornendo al progettista un avanzato strumento di analisi dei fenomeni aerodinamici e strutturali agenti in queste complesse macchine.

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12

Ross, Ian J. "Wind tunnel blockage corrections : an application to vertical-axis wind turbines /." Dayton, Ohio : University of Dayton, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1271306622.

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Thesis (M.S. in Aerospace Engineering) -- University of Dayton. Title from PDF t.p. (viewed 06/22/10). Advisor: Aaron Altman. Includes bibliographical references (p. 101-104). Available online via the OhioLINK ETD Center.

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13

Ross, Ian Jonathan. "Wind Tunnel Blockage Corrections: An Application to Vertical-Axis Wind Turbines." University of Dayton / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1271306622.

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14

Deglaire, Paul. "Analytical Aerodynamic Simulation Tools for Vertical Axis Wind Turbines." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-132073.

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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

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15

Kjellin, Jon. "Vertical Axis Wind Turbines : Electrical System and Experimental Results." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-182438.

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The wind power research at the division of Electricity at Uppsala University is aimed towards increased understanding of vertical axis wind turbines. The considered type of wind turbine is an H-rotor with a directly driven synchronous generator operating at variable speed. The experimental work presented in this thesis comprises investigation of three vertical axis wind turbines of different design and size. The electrical, control and measurement systems for the first 12 kW wind turbine have been designed and implemented. The second was a 10 kW wind turbine adapted to a telecom application. Both the 12 kW and the 10 kW were operated against dump loads. The third turbine was a 200 kW grid-connected wind turbine, where control and measurement systems have been implemented. Experimental results have shown that an all-electric control, substituting mechanical systems such as blade-pitch, is possible for this type of turbine. By controlling the rectified generator voltage, the rotational speed of the turbine is also controlled. An electrical start-up system has been built and verified. The power coefficient has been measured and the stall behaviour of this type of turbine has been examined. An optimum tip speed ratio control has been implemented and tested, with promising results. Use of the turbine to estimate the wind speed has been demonstrated. This has been used to get a faster regulation of the turbine compared to if an anemometer had been used.

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16

Soraghan, Conaill Eoin. "Aerodynamic modelling and control of vertical axis wind turbines." Thesis, University of Strathclyde, 2014. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=23210.

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Designing a structure which harnesses energy from the wind offshore is a radically different design challenge compared to that which the industry standard three-blade Danish model horizontal axis wind turbine (HAWT) has evolved to serve. Vertical axis wind turbines (VAWTs) may prove to be suitable candidates for the offshore sector due to the potential to locate heavy and complex mechanical components near the water surface providing ease of access and a low centre of gravity. Unlike their horizontal-axis counterparts, VAWT designs have not benefited from forty years of intense research and development. Therefore many challenges lie ahead for VAWT technology but lessons can be drawn from the development of HAWT technology. The main aims of this thesis are to create a design tool capable of investigating the performance of large scale, variable pitch VAWTs and to provide analyses of rotor design and control systems that would align utility scale VAWTs with aerodynamic performance and operational flexibility of state of the art HAWTs. The design tool developed is based on the double multiple streamtube (DMS) adaptation of blade element momentum theory and it incorporates tip loss effects, flow curvature, dynamic stall, flow expansion and variable pitch. Validation demonstrates good estimation of local wind flow conditions and aerodynamic performance for both fixed pitch and variable pitch rotors. The model has been developed to investigate in particular V-rotor performance and the potential of variable pitch for VAWTs. A contribution is made to DMS modelling, which involves capturing the effects of varying degrees of streamtube expansion occurring along the blade. This contribution is referred to as fanning and is particularly significant when implementing or designing pitch regimes. Three novel investigations are provided that contribute to fixed pitch VAWT rotor design and control. Firstly, a method for applying lift to drag ratio to VAWTs is introduced, which accounts for azimuthal variation in aerodynamic performance. Secondly, the impact of wind shear on V-rotor rotor design is analysed. Thirdly, a solution for smoothing power fluctuations from aggregated VAWTs is proposed, which is based on controlling the phase of each rotor so peaks in individual generated power do not occur simultaneously. A holistic approach to the way in which cyclic variable pitch can benefit VAWT operation is provided. Five control objectives are identified that span the entire operating envelope for any wind turbine, namely providing high torque during start-up, maximising power coefficient in below rated conditions, alleviating cyclic loading, power limiting in above rated conditions and aerodynamic braking in extremely high winds. Two test case turbines are designed, a similarly rated H-rotor and V-rotor, and for each turbine and each objective, a cyclic pitch regime is developed and analysed.

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17

Gonzalez, Campos Jose Alberto. "Design and Experimentation of Darrieus Vertical Axis Wind Turbines." Case Western Reserve University School of Graduate Studies / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case1594690510943748.

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18

Robotham, Antony John. "The aerodynamic control of the V-type vertical axis wind turbine." n.p, 1989. http://ethos.bl.uk/.

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19

Pawsey, N. C. K. Mechanical &amp Manufacturing Engineering Faculty of Engineering UNSW. "Development and evaluation of passive variable-pitch vertical axis wind turbines." Awarded by:University of New South Wales. School of Mechanical and Manufacturing Engineering, 2002. http://handle.unsw.edu.au/1959.4/18805.

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Vertical-axis wind turbines do not need to be oriented to the wind direction and offer direct rotary output to a ground-level load, making them particularly suitable for water pumping, heating, purification and aeration, as well as stand-alone electricity generation. The use of high-efficiency Darrieus turbines for such applications is virtually prohibited by their inherent inability to self-start. The provision of blade-articulation (variable-pitch blades) has been demonstrated by a number of researchers to make Darrieus turbines self-starting. One aim of this thesis is to evaluate the various concepts manifested in the numerous specific passive variable-pitch designs appearing in the literature, often without theoretical analysis. In the present work, two separate mathematical models have been produced to predict the performance of passive variable-pitch Darrieus-type turbines. A blade-element/momentum theory model has been used to investigate the relationships between the key parameter values and turbine steady-state performance. A strategy for parameter selection has been developed on the basis of these results. A free vortex wake model for passive variable-pitch turbines has been developed, allowing the study of unsteady performance. Significant reduction of average ef- ficiency in a turbulent wind is predicted for a Darrieus turbine. The improved low-speed torque of passive variable-pitch turbines is predicted to significantly improve turbulent wind performance. Two new design concepts for passive variable-pitch turbines are presented that are intended to allow greater control of blade pitch behaviour and improved turbulent wind performance. A prototype turbine featuring these design concepts has been designed, constructed and tested in the wind tunnel. As part of this testing, a technique has been developed for measuring the pitch angle response of one of the turbine blades in operation. This allows comparison of predicted and measured pitch histories and gives insight into the performance of turbines of this type. Results have demonstrated the usefulness of the mathematical models as design tools and have indicated the potential of one of the new design concepts in particular to make a vertical axis wind turbine self-starting.

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20

Parker, Colin M. "An Investigation into the Aerodynamics Surrounding Vertical-Axis Wind Turbines." Thesis, The George Washington University, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10687173.

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The flow surrounding a scaled model vertical-axis wind turbine (VAWT) at realistic operating conditions was studied. The model closely matches geometric and dynamic properties—tip-speed ratio and Reynolds number—of a full-size turbine. The flowfield is measured using particle imaging velocimetry (PIV) in the mid-plane upstream, around, and after (up to 4 turbine diameters downstream) the turbine, as well as a vertical plane behind the turbine. Ensemble-averaged results revealed an asymmetric wake behind the turbine, regardless of tip-speed ratio, with a larger velocity deficit for a higher tip-speed ratio. For the higher tip-speed ratio, an area of averaged flow reversal is present with a maximum reverse flow of –0.04U∞. Phase-averaged vorticity fields—achieved by syncing the PIV system with the rotation of the turbine—show distinct structures form from each turbine blade. There are distinct differences in the structures that are shed into the wake for tip-speed ratios of 0.9, 1.3 and 2.2—switching from two pairs to a single pair of shed vortices—and how they convect into the wake—the middle tip-speed ratio vortices convect downstream inside the wake, while the high tip-speed ratio pair is shed into the shear layer of the wake. The wake structure is found to be much more sensitive to changes in tip-speed ratio than to changes in Reynolds number. The geometry of a turbine can influence tip-speed ratio, but the precise relationship among VAWT geometric parameters and VAWT wake characteristics remains unknown. Next, we characterize the wakes of three VAWTs that are geometrically similar except for the ratio of the turbine diameter (D), to blade chord (c), which was chosen to be D/c = 3, 6, and 9, for a fixed freestream Reynolds number based on the blade chord of Rec =16,000. In addition to two-component PIV and single-component constant temperature anemometer measurements are made at the horizontal mid-plane in the wake of each turbine. Hot-wire measurement locations are selected to coincide with the edge of the shear layer of each turbine wake, as deduced from the PIV data, which allows for an analysis of the frequency content of the wake due to vortex shedding by the turbine. Changing the tip-speed ratio leads to substantial wake variation possibly because changing the tip-speed ratio changes the dynamic solidity. In this work, we achieve a similar change in dynamic solidity by varying the D/c ratio and holding the tip-speed ratio constant. This change leads to very similar characteristic shifts in the wake, such as a greater blockage effect, including averaged flow reversal in the case of high dynamic solidity (D/c = 3). The phase-averaged vortex identification shows that both the blockage effect and the wake structures are similarly affected by a change in dynamic solidity. At lower dynamic solidity, pairs of vortices are shed into the wake directly downstream of the turbine. For all three models, a vortex chain is shed into the shear layer at the edge of the wake where the blade is processing into the freestream.

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21

Shaheen, Mohammed Mahmoud Zaki Mohammed. "Design and Assessment of Vertical Axis Wind Turbine Farms." University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1439306478.

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22

Krysiński, Tomasz. "Mathematical modelling and shape optimisation of vertical axis wind turbines blades." Rozprawa doktorska, ISBN 978-83-61506-47-8, 2018. https://repolis.bg.polsl.pl/dlibra/docmetadata?showContent=true&id=53466.

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23

Krysiński, Tomasz. "Mathematical modelling and shape optimisation of vertical axis wind turbines blades." Rozprawa doktorska, ISBN 978-83-61506-47-8, 2018. https://delibra.bg.polsl.pl/dlibra/docmetadata?showContent=true&id=53466.

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24

Kirke, Brian Kinloch, and n/a. "Evaluation of Self-Starting Vertical Axis Wind Turbines for Stand-Alone Applications." Griffith University. School of Engineering, 1998. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20050916.120408.

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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.

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25

Kirke, Brian. "Evaluation of Self-Starting Vertical Axis Wind Turbines for Stand-Alone Applications." Thesis, Griffith University, 1998. http://hdl.handle.net/10072/366205.

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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. Thesis (PhD Doctorate) Doctor of Philosophy (PhD) School of Engineering Science, Environment, Engineering and Technology Full Text

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26

Goude, Anders. "Fluid Mechanics of Vertical Axis Turbines : Simulations and Model Development." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-183794.

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Two computationally fast fluid mechanical models for vertical axis turbines are the streamtube and the vortex model. The streamtube model is the fastest, allowing three-dimensional modeling of the turbine, but lacks a proper time-dependent description of the flow through the turbine. The vortex model used is two-dimensional, but gives a more complete time-dependent description of the flow. Effects of a velocity profile and the inclusion of struts have been investigated with the streamtube model. Simulations with an inhomogeneous velocity profile predict that the power coefficient of a vertical axis turbine is relatively insensitive to the velocity profile. For the struts, structural mechanic loads have been computed and the calculations show that if turbines are designed for high flow velocities, additional struts are required, reducing the efficiency for lower flow velocities.Turbines in channels and turbine arrays have been studied with the vortex model. The channel study shows that smaller channels give higher power coefficients and convergence is obtained in fewer time steps. Simulations on a turbine array were performed on five turbines in a row and in a zigzag configuration, where better performance is predicted for the row configuration. The row configuration was extended to ten turbines and it has been shown that the turbine spacing needs to be increased if the misalignment in flow direction is large.A control system for the turbine with only the rotational velocity as input has been studied using the vortex model coupled with an electrical model. According to simulations, this system can obtain power coefficients close to the theoretical peak values. This control system study has been extended to a turbine farm. Individual control of each turbine has been compared to a less costly control system where all turbines are connected to a mutual DC bus through passive rectifiers. The individual control performs best for aerodynamically independent turbines, but for aerodynamically coupled turbines, the results show that a mutual DC bus can be a viable option.Finally, an implementation of the fast multipole method has been made on a graphics processing unit (GPU) and the performance gain from this platform is demonstrated.

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27

Awan, Muhammad Rizwan. "Feasibility Study of Vertical Axis wind turbines in Urban areas of Sweden." Thesis, KTH, Kraft- och värmeteknologi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-129410.

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28

Dyachuk, Eduard. "Aerodynamics of Vertical Axis Wind Turbines : Development of Simulation Tools and Experiments." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-260573.

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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.

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29

Danao, Louis Angelo. "The influence of unsteady wind on the performance and aerodynamics of vertical axis wind turbines." Thesis, University of Sheffield, 2012. http://etheses.whiterose.ac.uk/2928/.

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Interest in small-scale wind turbines as energy sources in the built environment has increased due to the desire of consumers in urban areas to reduce their carbon footprint. Vertical axis wind turbines (VAWTs) have shown to be potentially well suited within the urban landscape. However, there is a large gap in the fundamental understanding of VAWT operation in turbulent, unsteady wind that is typical of the built environment. This dissertation investigates the aerodynamics and performance of VAWTs in fluctuating wind through experiments and numerical simulations. All experimental investigations utilise a low-speed open section wind tunnel. The use of a shutter mechanism that generates unsteady wind in the wind tunnel is detailed. Performance measurements for turbine power use a validated method previously developed in the same laboratory with slight modification for unsteady wind performance. Both steady and unsteady power performance tests results are presented. Near–blade flow physics during steady wind operation is scrutinised using Particle Image Velocimetry (PIV). Complementing the findings in experiments, numerical simulations using Unsteady Reynolds Averaged Navier–Stokes Computational Fluid Dynamics (URANS CFD) are employed. The numerical model is validated using experimental data. Blade force measurements that are not available from experiments are extracted from the numerical models to provide additional insight for performance analysis. A survey of varying unsteady wind parameters is conducted to examine the effects of various unsteady wind conditions on the performance of the VAWT. The aerodynamics is inspected through vorticity visualisations alongside blade force metrics to link performance to blade stall. Results show marginal improvement on VAWT performance (CP) with small wind speed fluctuations versus steady wind CP. Operating the VAWT at tip speed ratios (λ) higher than steady wind peak CP λ also improve performance. Conditions other than the stated above reduce VAWT CP.

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30

Rastegar, Damoon. "Modification of Aeroelastic Model for Vertical Axes Wind Turbines." Thesis, Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-3388.

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In wind turbines, flow pressure variations on the air-structure interface cause aerodynamic forces. Consequently the structure deforms and starts to move. The interaction between aerodynamic forces and structural deformations mainly concerns aeroelasticity. Since these two are coupled, they have to be considered simultaneously in cases which the deformations are not negligible in comparison to the other geometric dimensions. The purpose of this work is to improve the simulation model of a vertical axis wind turbine by modifying the structural model from undamped Euler-Bernoulli beam theory with lumped mass matrix to the more advanced Timoshenko beam theory with consistent mass matrix plus an additional damping term. The bending of the beam is then unified with longitudinal and torsional deformations based on a fixed shape cross-section assumption and the Saint-Venant torsion theory. The whole work has been carried out by implementing the finite element method using MATLAB code and implanting it in a previously developed package as a complement. Finally the results have been verified by qualitative comparisons with alternative simulations.

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31

Ferrari, Gareth Marc. "Development of an aeroelastic simulation for the analysis of vertical-axis wind turbines." Thesis, University of Auckland, 2012. http://hdl.handle.net/2292/13039.

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Like their horizontal-axis counterparts, as the blades of vertical-axis wind turbines increase in size they typically become relatively more flexible so a better understanding of their aeroelastic behaviour is required. This research addresses the challenges of large, flexible, vertical-axis wind turbines using methods previously unavailable, or impractical due to limited computational resources. A weakly-coupled aeroelastic simulation was developed to investigate the dynamic behaviour of vertical-axis wind turbines. The aeroelastic simulation comprised a free vortex wake model to represent the aerodynamics, and a multibody systems model to represent the structural dynamics, with the models coupled together via an interface. A modified version of the Beddoes- Leishman dynamic stall model was used to account for unsteady aerodynamic effects on the blades. The modal characteristics of the structural model were extracted using the Eigensystem Realisation Algorithm. The aerodynamic aspects of the simulation were validated against a wide range of experimental data. The structural aspects of the simulation were verified against an industry-standard multi-body systems package, and validated against a combination of analytical, numerical and experimental data. An extensive set of tests were conducted on the aerodynamic and structural models demonstrating that quite computationally undemanding methods for the computational parameters, including the time-step sizes and levels of blade discretisation, were capable of producing results very similar to those predicted using much more computationally demanding values. The aeroelastic simulation was used to conduct a number of numerical experiments designed to aid an investigation into how the aeroelastic behaviour of a large-scale baseline turbine configuration changed in response to various parameters. It was shown that the asymmetric loading along the blades, caused by a combination of the gravitational loads and the vertical variation in height of the wind speed, results in a periodic vertical rocking motion of the blades. This rocking motion occurred at a frequency of twice per revolution. It enabled new insight into the dynamic motion of VAWT blades. It was also found that the periodic rocking motion could be reduced by increasing the stiffness of the blades and reducing the linear density of the blades.

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32

Menon, Ashwin. "Numerical investigation of synthetic jet based flow control for vertical axis wind turbines." Thesis, Rensselaer Polytechnic Institute, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=1568426.

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This numerical study focuses on the implementation of active flow control using synthetic jets on vertical-axis wind turbine (VAWT) blades. This study demonstrates that synthetic-jet based flow control improves the efficiency of the turbine and reduces the risk of structural fatigue. In VAWTs, the blades experience a significant variation in the angle of attack over each rotation cycle and associated with it are sudden changes in the flow-induced loading on the blades. For example, a sudden variation in blade loading is experienced due to the detachment of the leading edge vortex at high angles of attack. This is in-turn reduces the axial force and hence the overall power output of the turbine. Additionally, such force variations lead to structural fatigue and possibly failure. Current simulations consider a cross-section of a three-blade VAWT model (with straight blades). VAWT models with two different airfoils, NACA 0018 and DU 06-W-200, are considered at tip-speed-ratios of 2 and 3. In these simulations, unsteady, Reynolds-averaged Navier-Stokes equations along with the Spalart-Allmaras turbulence model are employed, where stabilized finite element method is utilized along with an implicit time-integration scheme. The idea of using synthetic jets is to control the variation in flow-induced loading during each rotation cycle. At first the dominant location of the flow separation is determined for both airfoils. The jets are then placed at this location. Jet parameters of blowing ratio and reduced frequency are specified within a range (i.e., O(0.5-1.5) and O(1-10), respectively) and their effects on jet performance are studied. The jets are activated only in a selected portion of the rotation cycle. This is referred to as the partial cycle control in contrast to the full cycle (the latter is found to be detrimental). For given jet parameters, simulations results are used to determine whether the jets improve axial force, flow separation and blade-vortex interaction. At blowing ratio of 1.5 and reduced frequency of 5, we observe above 12% increase in the average axial force over the rotation cycle for both airfoils.

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33

Carper, Christopher T. "Design and construction of vertical axis wind turbines using dual-layer vacuum-forming." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/59899.

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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010. Cataloged from PDF version of thesis. Includes bibliographical references (p. 23). How does one visualize wind? Is it the way trees bend in a strong gust or the way smoke is carried in a breeze? What if wind could be visualized using design, technology, and light? This thesis documents the design of a large scale display of vertical axis wind turbines that can be used to visualize wind. The intent is to build a matrix of several hundred turbines at MIT as part of the 150th anniversary celebration in 2011. The main focus is the appearance of the turbines, which are fabricated using a novel dual-layer vacuum-forming process. In it, one layer of pre-cut plastic is sandwiched between a polyurethane foam mold and a top layer of plastic which is heated and forms the seal for the vacuum. The top layer is subsequently removed and discarded leaving a formed part with clean, smooth edges. In order to optimize the manufacturing process and achieve repeatable results, variables such as heating time and material alignment had to be controlled. PETG and polystyrene were tested in a variety of configurations to maximize the respective strengths of each material and minimize their weaknesses. Each turbine is also designed to power its own LEDs. Potential designs for the necessary electronics are also included. by Christopher T. Carper. S.B.

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34

Edwards, Jonathan. "The influence of aerodynamic stall on the performance of vertical axis wind turbines." Thesis, University of Sheffield, 2012. http://etheses.whiterose.ac.uk/4988/.

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There is currently an increasing desire for local small-scale sustainable energy generation. This has lead to increased interest in the concept of the vertical axis wind turbine (VAWT), which is potentially well-suited to operation within the built environment. This study investigates the performance and flow physics of a small-scale VAWT using experimental and computational methods. The experiments utilise the University’s low-speed open-section wind tunnel. The design and use of a variety of existing and newly developed methods and apparatus is detailed, this includes the development of an entire VAWT-testing rig and associated measurement equipment. Also included, is a new method for the experimental determination of the power performance. A full performance curve is shown to be determined using a short test taking a few minutes. The near-blade flow physics of the rotating blades were interrogated using particle image velocimetry (PIV) as part of a measurement campaign which goes beyond the existing literature in both the range of measurements taken and the subsequent analysis which is presented. Details of the effect of changes in azimuthal position, tip speed ratio and fixing angle on the flow physics are presented. Comparable CFD simulations are first validated against the PIV measurements before they are used to provide additional information for the performance analysis. A new methodology for determining flowfield-corrected lift and drag polars from a CFD solution allows detailed examination of the performance-impact of the changes in the aerodynamic forces with azimuthal position and tip speed ratio.

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35

Tourn, Cremona Silvana Cecilia. "Characterization of a New Open Jet Wind Tunnel to Optimize and Test Vertical Axis Wind Turbines." Doctoral thesis, Universitat Rovira i Virgili, 2017. http://hdl.handle.net/10803/461079.

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Basat en el creixent interès en les tecnologies ambientals urbanes, l'estudi de turinas d'eix vertical de petita escala mostra desafiaments motivadors. En aquesta tesi, es presenten els criteris de disseny, les característiques i potencialitats d'un nou túnel de vent de secció de prova oberta. Té un àrea de sortida i la broquet del túnel de 1,5 x 1,5 m2, i es pot operar amb velocitats de sortida de 3 m / s a 17 m / s. La caracterització del flux s'ha dut a terme amb tubs pitot calibrats, anemòmetres de cassoletes i anemòmetres de fil calent. Es consideren dues configuracions diferents de l'àrea de prova, amb i sense sostre. Els mesuraments en el rang de velocitats de sortida disponibles mostren que la secció transversal, on les intensitats de velocitat i turbulència mostren un nivell acceptable d'uniformitat, té una àrea de 0,8 x 0,8 m2 i una dimensió de 2 m des de la sortida del broquet del túnel. En aquesta secció de treball, la intensitat màxima de la turbulència és del 4%. La caracterització detallada del flux realitzat indica que el túnel de vent es pot utilitzar per provar models a d'aerogeneradors de petita escala. Basado en el creciente interés en las tecnologías ambientales urbanas, el estudio de turinas de eje vertical de pequeña escala muestra desafíos motivadores. En esta tesis, se presentan los criterios de diseño, las características y potencialidades de un nuevo túnel de viento de seccion de prueba abierta. Tiene un área de salida e la boquilla del túnel de 1,5 x 1,5 m2, y se puede operar con velocidades de salida de 3 m/s a 17 m/s. La caracterización del flujo se ha llevado a cabo con tubos pitot calibrados, anemómetros de cazoletas y anemómetros de hilo caliente. Se consideran dos configuraciones diferentes del área de prueba, con y sin techo. Las mediciones en el rango de velocidades de salida disponibles muestran que la sección transversal, donde las intensidades de velocidad y turbulencia muestran un nivel aceptable de uniformidad, tiene un área de 0,8 x 0,8 m2 y una dimensión de 2 m desde la salida de la boquilla del túnel. En esta sección de trabajo, la intensidad máxima de la turbulencia es del 4%. La caracterización detallada del flujo realizado indica que el túnel de viento se puede utilizar para probar modelos a de aerogeneradores de pequeña escala. Based on the increasing interest in urban environmental technologies, the study of small scale vertical axis wind turbines shows motivating challenges. In this thesis, we present the design criteria, characteristics and potentials of a new open jet wind tunnel. It has a nozzle exit area of 1.5 x1.5 m2, and it can be operated with exit velocities from 3 m/s to 17 m/s. The characterization of the flow has been carried out with calibrated pitot tubes, cup anemometers, and hot wire anemometers. Two different configurations of the test area, with and without a ceiling, are considered. Measurements in the range of available exit velocities show that the cross section, where the velocity and turbulence intensities show an acceptable level of uniformity, has an area of 0.8 x 0.8 m2 and a streamwise dimension of 2 m from the nozzle exit of the tunnel. In this working section, the maximum turbulence intensity is 4%. The detailed characterization of the flow carried out indicates that the wind tunnel can be used to test small scale models of wind turbines.

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36

Bah, Elhadji Alpha Amadou. "Numerical investigation on the use of multi-element blades in vertical-axis wind turbines." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53501.

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The interest in sustainable forms of energy is being driven by the anticipated scarcity of traditional fossil fuels over the coming decades. There is also a growing concern about the effects of fossil fuel emissions on human health and the environment. Many sources of renewable energy are being researched and implemented for power production. In particular, wind power generation by horizontal- and vertical-axis wind turbines is very popular. Vertical-axis wind turbines (VAWTs) have a relative construction simplicity compared to horizontal-axis wind turbines (HAWTs). However, VAWTs present specific challenges that may hinder their performance. For instance, they are strongly affected by dynamic stall. A significant part of the kinetic energy contained in the oncoming wind is lost in swirl and vortices. As a result, VAWTs have lower power production compared to HAWTs. First, the present work is aimed at the study of the aerodynamics of straight-bladed VAWTs (SB-VAWTs). Empirical calculations are conducted in a preliminary work. Then a two-dimensional double multiple streamtube (DMST) approach supported by a two-dimensional numerical study is implemented. The dynamic stall and aerodynamic performance of the rotor are investigated. A VAWT-fitted dynamic stall model is implemented. Computational fluid dynamics (CFD) simulations are conducted to serve as reference for the DMST calculations. This three-pronged approach allows us to efficiently explore multiple configurations. The dynamic stall phenomenon is identified as a primary cause of performance loss. The results in this section validate the DMST model as a good replacement for CFD analysis in early phase design provided that a good dynamic stall model is used. After having identify the primary cause of performance loss, the goal is to investigate the use to dual-element blades for alleviating the effect of dynamic stall, thereby improving the performance of the rotor. The desirable airfoil characteristics are defined and a parametric analysis conducted. In the present study the parameters consists of the size of the blade elements, the space between them, and their relative orientation. The performance of the rotor is calculated and compared to the baseline. The results highlight the preeminence of the two-element configuration over the single-element provided that the adequate parametric study is conducted beforehand. A performance enhancement is obtained over a large range of tip speed ratios. The starting characteristics and the operation stability are also improved. Finally, an economic analysis is conducted to determine the cost of energy and thus the financial viability of such a project. The Great Coast of Senegal is selected as site of operation. The energy need and sources of this region are presented along with its wind energy potential. The cost evaluation shows the economic viability by comparing the cost of energy to the current energy market prices.

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37

Korobenko, Artem. "Advanced Fluid--Structure Interaction Techniques in Application to Horizontal and Vertical Axis Wind Turbines." Thesis, University of California, San Diego, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=3670451.

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During the last several decades engineers and scientists put significant effort into developing reliable and efficient wind turbines. As a wind power production demands grow, the wind energy research and development need to be enhanced with high-precision methods and tools. These include time-dependent, full-scale, complex-geometry advanced computational simulations at large-scale. Those, computational analysis of wind turbines, including fluid-structure interaction simulations (FSI) at full scale is important for accurate and reliable modeling, as well as blade failure prediction and design optimization. In current dissertation the FSI framework is applied to most challenging class of problems, such as large scale horizontal axis wind turbines and vertical axis wind turbines. The governing equations for aerodynamics and structural mechanics together with coupled formulation are explained in details. The simulations are performed for different wind turbine designs, operational conditions and validated against field-test and wind tunnel experimental data.

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38

Weiss, Samuel Bruce. "Vertical axis wind turbine with continuous blade angle adjustment." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/65178.

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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010. This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. Cataloged from student submitted PDF version of thesis. Includes bibliographical references (p. 26). The author presents a concept for a vertical axis wind turbine that utilizes each blade's entire rotational cycle for power generation. Each blade has its own vertical axis of rotation and is constrained to rotate at the rate of one half of a revolution per full revolution of the rotor. For a rotor of radius r and blades of width b, a technical analysis predicts a theoretical maximum power coefficient of CP = b 2r+b, neglecting wind flow interference by upwind blades. This theoretical power coefficient is generally greater than the efficiency of a typical Savonius wind turbine (CP ~~ 0.15), and it reaches CP = 0.5 at the limiting blade width, b = 2r. The analysis also predicts a static torque and optimal tip-speed ratio that are both greater than those of a Savonius wind turbine with similar blade dimensions. Design considerations for implementing the kinematic constraint and for blade adjustment to account for changes in wind direction are discussed, and the author's prototype is presented. Testing of the prototype demonstrated that implementation of the kinematic constraint is feasible, and that efficiencies greater than those achievable by a Savonius turbine are plausible. In 4 m s wind conditions, the prototype yielded an estimated CP of 0.15, with much room for improvement through design changes and blade optimization in future iterations of this style of turbine. by Samuel Bruce Weiss. S.B.

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39

Rynkiewicz, Mateusz. "Design of PM generator for avertical axis wind turbine." Thesis, Uppsala universitet, Elektricitetslära, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-177309.

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The task in this project is to design a generator for a vertical axis wind turbine withpower rated to 20kW at a wind speed of 10m/s. The project is conducted at theDivision of Electricity at Uppsala University with collaboration from ElectricGeneration AB. The design has just a few moving parts, which decreases maintenancecosts and increases its toughness. The turbine absorbs wind from every direction butits rotation speed ratio is lower than horizontal axis wind turbines. It means that thegenerator must be bigger and therefore more expensive. Price is an importantcriterion for the generator. Neodymium magnets are expensive so the amount of thismaterial must be limited.Several designs have been simulated but one final design has proven the mostpromising. It fulfills all specifications such as efficiency above 95%, 20kW outputpower and it also has a relatively low amount of hard magnetic material.A design with a single row of cables per slot was decided upon to eliminate heatpockets between cable rows, which can occur in designs with two cable rows perslot. It would be interesting to study designs with two or more cable rows per slot, asit could lead to a smaller and more efficient machine.

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40

Eboibi, Okeoghene. "The influence of blade chord on the aerodynamics and performance of vertical axis wind turbines." Thesis, University of Sheffield, 2013. http://etheses.whiterose.ac.uk/4730/.

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The climate change due to emissions from the combustion of fossil fuel to meet the ever increasing energy demands of the growing world population has roused the attention of governments and individuals to protect the environment. The formulated policies to protect the environment have aroused interest in wind turbines as an alternative source of energy. The suitability of the vertical axis wind turbines (VAWTs) in harnessing energy from the wind in the built areas have been shown, but there still exists a large knowledge gaps in the aerodynamics and performance of the VAWT especially in the design and selection of an appropriate blade chord. This thesis studied the influence of the blade chord on the aerodynamics and performance of vertical axis wind turbines through experimental and computational fluid dynamics methods. Two VAWT configurations of blade chords 0.04m (AR = 15) and 0.03m (AR = 20) with corresponding solidities of 0.34 and 0.26 were used for the investigations. The performance and the flow fields of the two configurations were measured experimentally through the use of performance measurement method and Particle Image Velocimentry (PIV) measurement techniques. All the experimental tests were conducted in a low-speed open suction wind tunnel and the results are presented. Computational fluid dynamics modelling based on the Unsteady Reynolds Average Navier-stokes (URANS) was employed to simulate the two configurations at the same wind tunnel test conditions to complement the revelations from the experimental tests. The developed CFD models after a parametric study that enabled the selection of the model’s features were validated against experimental data by comparing both forces and the flow physics. Vorticity of the CFD flow visualisation and blade forces provided an additional and penetrating insight into the aerodynamics and performance of the VAWTs by linking flow physics, and performance to the aerodynamics. The VAWT flow physics, aerodynamics and performances have been shown to depend on the Reynolds numbers that ranges from 1.27x103 to 1.1x105, the blade chord (solidity), the azimuth angle blade stall is initiated and the dynamic stall associated with the flow fields around the blade. At 6m/s test condition, the C = 0.04m VAWT attained peak CP = 0.165 at λ = 4, while the C = 0.03m VAWT performed in the negative region at all the λ. The better performance attained by the C = 0.04m VAWT over the C = 0.03m VAWT was repeated at all other wind speeds tested in the experiments and also in the computational fluid dynamics investigations. The C = 0.04m VAWT attained a higher peak CP = 0.326 at 8m/s at λ = 3.75 indicating increased performance with increases in Reynolds numbers. This trend was equally seen with the C = 0.03m VAWT in the experiments and also the computational fluid dynamics results. The VAWT with σ = 0.34 performed better than σ = 0.26 VAWT in all the conditions tested due to its higher Reynolds numbers and solidity differences that influence the nature of the dynamic stall phenomenon associated with the flow fields around the blades.

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41

Norström, Parliden Jonas, and Mateusz Rynkiewicz. "Design of PM generator for a vertical axis wind turbine." Thesis, Uppsala universitet, Elektricitetslära, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-180910.

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The task in this project is to design a generator for a vertical axis wind turbine withpower rated to 20kW at a wind speed of 10m/s. The project is conducted at theDivision of Electricity at Uppsala University with collaboration from ElectricGeneration AB. The design has just a few moving parts, which decreases maintenancecosts and increases its toughness. The turbine absorbs wind from every direction butits rotation speed ratio is lower than horizontal axis wind turbines. It means that thegenerator must be bigger and therefore more expensive. Price is an importantcriterion for the generator. Neodymium magnets are expensive so the amount of thismaterial must be limited.Several designs have been simulated but one final design has proven the mostpromising. It fulfills all specifications such as efficiency above 95%, 20kW outputpower and it also has a relatively low amount of hard magnetic material.A design with a single row of cables per slot was decided upon to eliminate heatpockets between cable rows, which can occur in designs with two cable rows perslot. It would be interesting to study designs with two or more cable rows per slot, asit could lead to a smaller and more efficient machine.

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42

Colley, Gareth. "Design, operation and diagnostics of a vertical axis wind turbine." Thesis, University of Huddersfield, 2012. http://eprints.hud.ac.uk/id/eprint/17547/.

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The need for sustainable energy sources becomes greater each year due to the continued depletion of fossil fuels and the resulting energy crisis. Solutions to this problem are potentially in the form of wind turbines which have been receiving increased support at a micro level. At present a number of wind turbines are being developed that are of cross-flow vertical axis operation which have shown significant increases in performance compared to existing technologies. From an extensive literature review a number of key issues have been highlighted which are concerned with design, operation and diagnostics of this new wind power technology which have been used to formulate the scope of this research. A design procedure for a cross-flow machine that features both a multi-blade rotor and fixed outer stator guide vanes has been derived in which both rotor and stator blade profiles have been generated for a low wind speed urban application. Using these blade profiles a prototype wind turbine has been fabricated and used for full scale development testing. In the presented work both experimental and numerical investigations have been carried out to determine the operational characteristics of this new technology. The experimental data obtained under controlled laboratory conditions has been used to validate a Computational Fluid Dynamic (CFD) model which has been used throughout. A flow field analysis of the machine has highlighted large asymmetries in both pressure and velocity about the central axis of the machine in both stationary and rotating frames of reference. This has identified primary inefficiencies within the design which limit the torque generating capability of the rotor due to blockage effects and downstream blade interactions. This asymmetry has been quantified in the form asymmetry ratio and used to determine downstream rotor effects and the optimum location of multiple wind turbines which is seen to be x/D >10 in order to minimize performance reductions. The torque and power generation capabilities of the machine have been characterised at both 'design' and ‘offdesign' conditions in which individual blade torque contributions have been quantified. This has highlighted specific energy transfer zones within the turbine namely at a few key blades on the windward side of the rotor. It has also shown counter-rotating torques generated on the leeward side of the machine at specific blade positions during the cycle. Overall performance has been quantified in which a maximum CT = 1.7 and CP = 0.24 has been observed which has some similarities to the Savonius rotor. Geometric effects on torque and power response have been quantified in which a strong dependence on stator blade number is noticed. Further, maximum performance output of the machine is generated at the baseline design condition. Using torque response data a multiple regression model has been developed in which a design equation for crossflow rotor torque has been derived which can be used during the conceptual design phase. Finally, the effectiveness of a two-dimensional transient CFD model to predict cross-flow wind turbine rotor blade loss has been evaluated against full scale experimental data. It has shown that from analysis in the frequency domain specific blade faults can be recognised which agrees well with experimental data obtained. The use of this model for wind turbine performance emulation has been described.

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43

Christoffer, Fjellstedt. "Simulations of vertical axis wind turbines with PMSG and diode rectification to a mutual DC-bus." Thesis, Uppsala universitet, Institutionen för teknikvetenskaper, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-323735.

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Transient simulations were performed with MATLAB Simulink on a mutual wind park topology, where three vertical axis wind turbines equipped with permanent magnet synchronous generators were connected to a mutual DC-bus through passive diode rectification. The aim with the work was to show the effects of two different kinds of loads on the system in respect to generator torque, rotor speed, produced power by the generators and the power on the DC-bus. The loads were a variable voltage source and a resistance with the value 2.0 Ω. It was shown that the transient behavior of the system in respect to both kinds of loads exhibited a high level of stability when the wind speed was altered. It was also shown that the system when equipped with a voltage source load began to oscillate with the natural frequency of a two mass rotating spring system if a sudden increase of the voltage made the DC-bus voltage larger than the peak of the internal induced voltage of the generators. Small variations of the DC voltage however exhibited a stable behavior.

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44

Imamura, Erik. "Vertical Axis Wind Turbines : A Mechanical Design Project and a Feasibility Study for Microgrids in Tanzania." Thesis, KTH, Maskinkonstruktion (Inst.), 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-168726.

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Detta arbete behandlar vindkraft med vertikal axel, att användas utanför ordinarie elnät, främst i byar och småföretag på landsbygden i utvecklingsländer. Två fristående projekt ingår. Det första handlar om konstruktion, med målet att utveckla ett koncept för att hålla kraftverkets vingar. En särskild egenskap är att de ska vara hopdragbara, så svepta arean kan följa rådande vindstyrka. Kraftverket monteras och reses på plats, med hopfällda vingar. Tornet kan fällas för att underlätta underhåll. Infällbara vingar förenklar även om kraftverken ska tas ur drift eller flyttas. Arbetet inleddes med problemdefiniering och funktionsanalys, varefter systematisk idégenerering användes för att ta fram koncept. En stor del av projektet upptogs av studier av krafter och hållfasthet med analytiska metoder. Kartongprototyper, handskisser och CAD-modeller användes flitigt för utveckling och utvärdering. Slutligen valdes en fyrledsmekanism. I skrivande stund håller en storskalig prototyp på att byggas, som kommer använda en modifierad version av den föreslagna konstruktionen.Det andra projektet var en övergripande genomförbarhetsstudie, utförd i Tanzania där marknads-lanseringen är tänkt att ske. Exjobbets uppdragsgivare har tidigare arbetat i landet, så det finns lokalkännedom och affärskontakter har behållits. Undersökningen baserades på intervjuer, observationer och en omfattande litteraturstudie. Särskilt fokus låg på intäktsmöjligheterna på bynivå. Flera parametrar kartlades och rekommendationer utformades. Finansiering, tillgång på vind, sociala utvecklingseffekter, existerande elmarknad och vissa andra frågor behandlades också i någon mån. Det finns indikationer på ekonomisk potential för elektrifiering, men frågan är komplex och det gick inte att dra några definitiva slutsatser. Affärsidén är lovande, men vissa specifika risker bör beaktas. This thesis treats vertical axis wind turbines for off-grid applications, primarily for villages and small enterprises in rural regions of developing countries. Two separate projects are incorporated. The first one is about mechanical engineering, with the aim to develop a concept design to hold the turbine wings. A special feature is that the wings will be contractible, allowing variable swept area, to adjust to shifting wind conditions. The tower with the turbine is assembled and raised on-site with contracted wings. Maintenance, as well as decommissioning and relocation of the equipment, is also facilitated by contractible wings. After problem definition and function analysis, concepts were generated by systematic ideation methods. A large part of the project was dedicated to a study of loads and forces, using analytical methods. Cardboard prototypes, hand sketches, and CAD models were also used for development and evaluation. Finally, a four-bar linkage was presented. At the time of writing, a large-scale prototype is under construction, which will use a modified version of the suggested design.The second project could be labeled a pre-feasibility study. It was performed in Tanzania, which will be the first market. The commissioning company has previously worked in the country, so there is local know-how, and business contacts have been maintained. The research was based on interviews, observations, and an extensive literature study. Special focus was put on village level profitability. A number of parameters were mapped and some recommendations drafted. Funding options, availability of wind, social development effects, national electricity markets, and other issues were also covered to some extent. Some indications were found regarding the economic potential of rural electrification, but the issue is complex and no certain conclusions could be made. The project was found promising, but there are certain risks that should be considered.

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45

Dunne, Reeve. "Dynamic Stall on Vertical Axis Wind Turbines." Thesis, 2016. https://thesis.library.caltech.edu/9140/2/Dunne_thesis_edit.pdf.

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In this study the dynamics of flow over the blades of vertical axis wind turbines was investigated using a simplified periodic motion to uncover the fundamental flow physics and provide insight into the design of more efficient turbines. Time-resolved, two-dimensional velocity measurements were made with particle image velocimetry on a wing undergoing pitching and surging motion to mimic the flow on a turbine blade in a non-rotating frame. Dynamic stall prior to maximum angle of attack and a leading edge vortex development were identified in the phase-averaged flow field and captured by a simple model with five modes, including the first two harmonics of the pitch/surge frequency identified using the dynamic mode decomposition. Analysis of these modes identified vortical structures corresponding to both frequencies that led the separation and reattachment processes, while their phase relationship determined the evolution of the flow. Detailed analysis of the leading edge vortex found multiple regimes of vortex development coupled to the time-varying flow field on the airfoil. The vortex was shown to grow on the airfoil for four convection times, before shedding and causing dynamic stall in agreement with 'optimal' vortex formation theory. Vortex shedding from the trailing edge was identified from instantaneous velocity fields prior to separation. This shedding was found to be in agreement with classical Strouhal frequency scaling and was removed by phase averaging, which indicates that it is not exactly coupled to the phase of the airfoil motion. The flow field over an airfoil undergoing solely pitch motion was shown to develop similarly to the pitch/surge motion; however, flow separation took place earlier, corresponding to the earlier formation of the leading edge vortex. A similar reduced-order model to the pitch/surge case was developed, with similar vortical structures leading separation and reattachment; however, the relative phase lead of the separation mode, corresponding to earlier separation, necessitated that a third frequency to be incorporated into the reattachment mode to provide a relative lag in reattachment. Finally, the results are returned to the rotating frame and the effects of each flow phenomena on the turbine are estimated, suggesting kinematic criteria for the design of improved turbines.

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46

Molina, Andreu Carbó. "Wind tunnel testing of small Vertical-Axis Wind Turbines for urban areas." Doctoral thesis, 2019. http://hdl.handle.net/2158/1179097.

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The implementation of small vertical-axis wind turbines (VAWTs) in urban environments is being studied by the scientific community to complement large wind farms in wind energy generation. The technology is, however, far from maturity due to the complexity of urban flows and the lack of knowledge in the field. This thesis focuses on turbulence, one of the main characteristics of urban flows, and its influence on VAWT performance. Its objective is to generate turbulent wind conditions inside a wind tunnel and testing a VAWT to determine how turbulence intensity (Iu) and integral length scale (Lux) affect its operation. The first part of the research was devoted to obtaining highly-turbulent wind profiles in the wind tunnel with the use of different configurations of square grids. Gathering experience from previous studies and literature, a careful study and validation of this technique was done, in order to obtain uniform wind conditions with the adequate values of turbulence intensity and length scales to model the urban flows. Then, a H-Darrieus VAWT prototype was tested under these turbulent conditions in two different wind tunnels (VUB in Belgium, and CRIACIV in Italy). Those campaigns allowed to evaluate the crossed effect of Iu, Lux and Reynolds numbers on the VAWT performance, and quantify the effect of wind tunnel blockage in the measurements. Further tests with the same set-up included the study of the near wake of the VAWT and the aerodynamic characteristics of the individual blades, always focusing on the effect of incoming turbulence. Finally, a short campaign was done at the large VKI L1-B wind tunnel to observe the effect of a shear flow with high levels of Lux (impossible to model in smaller wind tunnels). The tests on the VAWT revealed an important increase of performance for low to moderate Iu values (5-15%) in low chord-based Reynolds numbers (Rec < 100000), while the effect of Lux was negligible. Iu also proved to cause a positive effect by providing faster wake recovery and by mitigating the negative effect of the turbine shaft. The study of the effect of turbulence on the aerodynamic coefficients of different typical VAWT aerofoils showed that turbulence considerably delays the stall in the blades, which was linked the increase of turbine performance. The tests at VKI proved that this positive effect of turbulence is also evident in shear flows. The possibility of testing in three different wind tunnels strengthens the results of this study, which have been already used in combination with CFD simulations, and present good agreement with literature. The findings of this thesis contribute to expand the knowledge of how turbulent flows interact with VAWTs, and provide a useful insight for the optimization and combination of several VAWTs inside urban environments.

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47

Chang, Ken-Hao, and 張根豪. "Numerical Analysis of H-type Vertical Axis Wind Turbines." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/44222968940061830385.

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碩士 清雲科技大學 電機工程研究所 98 Vertical axis wind turbines (VAWT) has the advantages of low running noise, simple structure and easy to integrate with the living environment. It has become more popular in the green energy market. To develop wind turbines with higher efficiency, the computational fluid dynamics (CFD) method has been applied to study the static characters and dynamic performance of one 200W H-type VAWT. Cross section profile of blades and a two-dimensional space has been created first. Numerical simulations are then performed by CFD software CFdesign. Simulation results show that the wind turbine under the same inlet wind speed had run to approach the same angular velocity even they started with different initial angular velocities. Wind turbines with different moment of inertia are found to have the same equilibrium angular velocity for the same inlet wind speed and initial rotational speeds. Blades with larger elevation angles tangential to the rotating circle are found to increase the turbine performance significantly in our simulation results. Blades which are hold at 1/2 chord length with tangential elevation angles 5°~10° and hold at 1/4 chord length with angles 10°~15° have the highest equilibrium rotating speed. It indicates these kinds of setup for blades are optimized. Static torque analysis results show that one peak curves have better acceleration effect to wind turbine rotors. This phenomenon may support a new evidence for theoretical study of wind turbine aerodynamics.

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48

Liou, Jia-Lun, and 劉家綸. "Investigations of Aerodynamic Characteristics of Vertical-axis Wind Turbines." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/32653314723281255881.

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碩士 淡江大學 航空太空工程學系碩士班 101 The thesis studies the aerodynamic characteristics of vertical-axis wind turbines, which is divided into two parts. The first part of this study experimentally investigates the effects of rotor geometries on the turbine Power output, including the airfoil type, blade weight, rotor diameter, airfoil chord length. The results show that the rotor with symmetric airfoil, chord length of 15 cm, blade length of 30 cm and rotor radius of 30 cm exhibits the highest Power output among the test rotors. The second part of this thesis investigates the effects of stator on the drag-type rotor Power output, which is placed around the rotor. The stator includes top and bottom circular plates, and a number of flat plates placed between them. These flat plates are arranged equal-angled and tangent to a circle, which direct some air into the interior of the stator, and block some air from the stator. In this way, a vortical flow is able to be created inside the stator, which always forces the drag-type blades rotated during their rotation motion. Numerical investigations of the 4-, 6-, 8-, and 12-plate stators indicate that vortical flows are generated inside the stators. The experimental investigations show that the 4-plate and 12-plate stators have the highest and lowest effects on rotor Power output, while they are the most and least sensitive to the wind direction, respectively. In summary, the 6-plate stator exhibits the optimum effect on rotor Power output.

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49

Pawsey, N. C. K. "Development and evaluation of passive variable-pitch vertical axis wind turbines /." 2002. http://www.library.unsw.edu.au/~thesis/adt-NUN/public/adt-NUN20030611.092522/index.html.

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50

Chen, Yen-Yu, and 陳彥佑. "Performance Studies of Horizontal-axis and Vertical-axis Wind Turbines with Shrouds." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/41148792605970191481.

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碩士 淡江大學 航空太空工程學系碩士班 102 The thesis studies of horizontal-axis and vertical-axis wind turbines with shrouds, which is divided into two parts. Part 1 investigates the aerodynamic characteristics of horizontal-axis wind turbine (HAWT) with different flanged diffusers and blades. Results show that larger power output is obtained when the pitch angle of the blades is fixed at 30°, and the chord length ratio between the blade root and tip is fixed at 0.3. Flanged diffuser diffusion angle of 30° have larger power output. Part 2 investigate a vortical stator assembly (VSA) which was developed to improve the rotor performance, surrounding a drag-type, vertical-axis wind turbine (VAWT). The design was created to generate vortical flow inside the VSA; thus, the rotor blades always generate positive torque because they rotate in the same direction as the vortical flow. A numerical simulation was performed to verify the flow structures around and inside the VSAs. The experimental results indicated that VSAs can substantially augment the rotor performance, depending on the number and length of the guide vanes used. The augmentation ratios of the rotor power outputs with the VSA were between 7 and 10 under the investigated wind speeds 6 m/s, and wind directions between 0° and 50°. The diameter of the rotor integrated VSA increased by less than 80%. Results also show that the rotor starting speed was reduced to approximately 1 m/s.

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