Dissertations / Theses on the topic 'Turbine fluid-structure'

The dynamic motion of floating wind turbines is studied using numerical simulations. Floating wind turbines in the deep ocean avoid many of the concerns with land-based wind turbines while allowing access to strong stable winds. The full three-dimensional Navier-Stokes equations are solved on a regular structured grid, using a level set method for the free surface and an immersed boundary method for the turbine platform. The tethers, the tower, the nacelle and the rotor weight are included using reduced order dynamic models, resulting in an efficient numerical approach which can handle nearly all the nonlinear wave forces on the platform, while imposing no limitation on the platform motion. Wind is modeled as a constant thrust force and rotor gyroscopic effects are accounted for. Other aerodynamic loadings and aero-elastic effects are not considered. Several tests, including comparison with other numerical, experimental and grid study tests, have been done to validate and verify the numerical approach. Also for further validation, a 100:1 scale model Tension Leg Platform (TLP) floating wind turbine has been simulated and the results are compared with water flume experiments conducted by our research group. The model has been extended to full scale systems and the response of the tension leg and spar buoy floating wind turbines has been studied. The tension leg platform response to different amplitude waves is examined and for large waves a nonlinear trend is seen. The nonlinearity limits the motion and shows that the linear assumption will lead to over prediction of the TLP response. Studying the flow field behind the TLP for moderate amplitude waves shows vortices during the transient response of the platform but not at the steady state, probably due to the small Keulegan-Carpenter number. The effects of changing the platform shape are considered and finally the nonlinear response of the platform to a large amplitude wave leading to slacking of the tethers is simulated. For the spar buoy floating wind turbine, the response to regular periodic waves is studied first. Then, the model is extended to irregular waves to study the interaction of the buoy with more realistic sea state. The results are presented for a harsh condition, in which waves over 17 m are generated, and linear models might not be accurate enough. The results are studied in both time and frequency domain without relying on any experimental data or linear assumption. Finally a design study has been conducted on the spar buoy platform to study the effects of tethers position, tethers stiffness, and platform aspect ratio, on the response of the floating wind turbine. It is shown that higher aspect ratio platforms generally lead to lower mean pitch and surge responses, but it may also lead to nonlinear trend in standard deviation in pitch and heave, and that the tether attachment points design near the platform center of gravity generally leads to a more stable platform in comparison with attachment points near the tank top or bottom of the platform.

A high fidelity approach coupling the computational fluid dynamics method (CFD) and multi-body dynamics method (MBD) is presented for aero-servo-elastic wind turbine simulations. The approach uses the incompressible CFD dynamic overset code CFDShip-Iowa v4.5 to compute the aerodynamics, coupled with the MBD code Virtual.Lab Motion to predict the motion responses to the aerodynamic loads. The IEC 61400-1 ed. 3 recommended Mann wind turbulence model was implemented in this thesis into the code CFDShip-Iowa v4.5 as boundary and initial conditions, and used as the explicit wind turbulence for CFD simulations. A drivetrain model with control systems was implemented in the CFD/MBD framework for investigation of drivetrain dynamics. The tool and methodology developed in this thesis are unique, being the first time with complete wind turbine simulations including CFD of the rotor/tower aerodynamics, elastic blades, gearbox dynamics and feedback control systems in turbulent winds. Dynamic overset CFD simulations were performed with the benchmark experiment UAE phase VI to demonstrate capabilities of the code for wind turbine aerodynamics. The complete turbine geometry was modeled, including blades and approximate geometries for hub, nacelle and tower. Unsteady Reynolds-Averaged Navier-Stokes (URANS) and Detached Eddy Simulation (DES) turbulence models were used in the simulations. Results for both variable wind speed at constant blade pitch angle and variable blade pitch angle at fixed wind speed show that the CFD predictions match the experimental data consistently well, including the general trends for power and thrust, sectional normal force coefficients and pressure coefficients at different sections along the blade. The implemented Mann wind turbulence model was validated both theoretically and statistically by comparing the generated stationary wind turbulent field with the theoretical one-point spectrum for the three components of the velocity fluctuations, and by comparing the expected statistics from the simulated turbulent field by CFD with the explicit wind turbulence inlet boundary from the Mann model. The proposed coupled CFD/MBD approach was applied to the conceptual NREL 5MW offshore wind turbine. Extensive simulations were performed in an increasing level of complexity to investigate the aerodynamic predictions, turbine performance, elastic blades, wind shear and atmospheric wind turbulence. Comparisons against the publicly available OC3 simulation results show good agreements between the CFD/MBD approach and the OC3 participants in time and frequency domains. Wind turbulence/turbine interaction was examined for the wake flow to analyze the influence of turbulent wind on wake diffusion. The Gearbox Reliability Collaborative project gearbox was up-scaled in size and added to the NREL 5MW turbine with the purpose of demonstrating drivetrain dynamics. Generator torque and blade pitch controllers were implemented to simulate realistic operational conditions of commercial wind turbines. Interactions between wind turbulence, rotor aerodynamics, elastic blades, drivetrain dynamics at the gear-level and servo-control dynamics were studied, showing the potential of the methodology to study complex aerodynamic/mechanic systems.

The depletion of fossil fuel and the increase of fuel consumption globally create an increased demand for the use of renewable energy. Vertical axis tidal turbines are a promising renewable energy device which needs to be improved. One problem appears in its operation is the structural instability and noise coming from the vibration of the long slender vertical axis blades. The vibration is a result of fluid structure interaction between turbine blades and the unsteady tidal current. This interaction of the tides and the blade generates vortical features which can excite the turbine blades to vibrate and causes a tonal noise known as singing. The aim of this work is to predict the blade response and locked-in condition by controlling the vortex shedding. The vortex is controlled by modifying blade’s trailing edge shape. The modifications include truncated, sharp and rounded trailing edge shapes. The response is modeled by vibrations using a spring damper system. A 2D numerical model of a vertical axis tidal turbine blade is developed to resolve the vibration using OpenFOAM 2.2. The blade has 0.75 m chord length and 3.07×106 Re. The model employs the equivalence incoming velocity method which represents the actual unsteady tidal current by time varying velocity magnitude and angle of attack of the model incoming flow. The problem is examined by observing the force applied to a static blade, and a rotating three bladed vertical axis turbine primarily. This is to confirm that the mesh topology and selected boundary conditions are sufficient and robust to resolve the blade response model. The locked-in condition is clarified by the blade main frequencies, pressure distribution, displacement, and force coefficients. In addition to the reference trailing edge, three different trailing edge shapes were studied. From the results it can be seen that the response is sensitive to pitching motion, high blade initial angle of attack, high tidal velocity and low spring and damping constant blade material. The results also show that the blunt (conventional truncated) foil has the largest ability to control the turbine blade response which is demonstrated by the smallest amplitude and the least frequent turbine blade’s vibration. For all three trailing edge shapes, along with a more limited investigation of an asymmetric trailing edge all are shown to be able to shift the frequency of the resonant response. This will allow the designer to study the likely behaviour of their design. Overall, the developed methodology using a two-dimensional, three degree of freedom solution of the unsteady CFD around the foil is shown to provide useful insight to the tidal turbine designer at a reasonable computational cost.

Ce travail porte sur la mise en œuvre de simulations sur des pales de machines tournantes. Une première partie de la thèse porte sur l’amélioration des performances du couplage fluide-structure. Des nouveaux algorithmes sont présentés. Une nouvelle méthode de déformation de maillage est évaluée. Les développements sont validés à partir de plusieurs cas tests. La deuxième partie porte sur l’application des avancées à des machines tournantes. Une première validation est faite sur une hydrolienne. La vibration d’une pale au passage du mat est étudiée. Enfin, des résultats sur une hydrolienne industrielle sont exposés
A methodology to simulate blades of turbines is developed. A first part is dedicated to improving the performance of the fluid-structure coupling. New algorithms are presented. A new mesh morphing solution is shown. Developments are validated on many test cases. A second part is dedicated to applying the developments on turbines. A first validation is made on a water turbine. The vibration of a blade interacting with a mast is studied. Finally, some results of an industrial water turbine are shown

Le sujet de la thèse est le développement d'un outil numérique qui permet de modéliser l'écoulement autour des pales d'éoliennes. Nous nous sommes intéressés à la résolution des équations de Navier-Stokes en incompressible sur des maillages de type octree où les échelles plus petites en proche parois ont été modélisées par la méthode dite des wall functions. Un procédé d'adaptation automatique du maillage (AMR) a été développé pour affiner le maillage dans les zones où la vorticité est plus importante. Le modèle de structure d'une pale d'éolienne a été également implémenté et couplé avec le modèle fluide car une application de l'outil numérique est l'étude des effets des rafales de vent sur les pales d'éolienne. Un travail expérimental a été mené sur une éolienne avec une mesure de vent en amont. Ces données permettent ainsi de calibrer et valider les modèles numériques développés dans la thèse
The subject of the thesis is the development of a numerical tool that allows to model the flow around wind blades. We are interested in the solving of incompressible Navier-Stokes equations on octree grids, where the smallest scales close to the wall have been modelled by the use of the so-called Wall Functions. An automatic Adaptive Mesh Refinement (AMR) process has been developed in order to refine the mesh in the areas where the vorticity is higher. The structural model of a real wind blade has also been implemented and coupled with the fluid model. Indeed, an application of the numerical tool is the study of the effects of wind gusts on blades. An experimental work has been conducted with an in-service wind turbine with the measurement of wind speed upstream. This data will allow to calibrate and validate the numerical models developed in the thesis

Um dos grandes desafios enfrentados pelos fabricantes de turbinas hidráulicas é prevenir o aparecimento de vibrações induzidas pelo escoamento nas travessas do pré-distribuidor e pás do rotor. Considerando apenas as travessas, e atribuídos a tais vibrações, foram relatados 28 casos de trincas ou ruídos anormais nas últimas décadas, que acarretaram enormes prejuízos associados a reparos, atrasos e perda de geração. O estado da arte na prevenção destes problemas baseia-se na utilização de sofisticados, e caros, programas comerciais de dinâmica dos fluidos computacional para o cálculo transiente do fenômeno. Este trabalho faz uma ampla revisão bibliográfica e levantamento de eventos de trincas ou ruídos ocorridos em travessas nos últimos 50 anos. Propõe, então, um enfoque alternativo, baseado exclusivamente em ferramentas de código aberto. A partir de hipóteses simplificadoras devidamente justificadas, o problema é formulado matematicamente de forma bidimensional, no plano da seção transversal da travessa, levando em conta a interação fluido-estrutura. Nesta estratégia, as equações de Navier-Stokes são resolvidas pelo método dos elementos finitos por meio da biblioteca gratuita oomph-lib. Um código especial em C++ é desenvolvido para o problema de interação fluido-estrutura, no qual o fenômeno de turbulência é levado em consideração por meio de um algoritmo baseado no modelo de Baldwin-Lomax. O método proposto é validado por meio da comparação dos resultados obtidos com referências e medições disponíveis na literatura, que tratam de problemas de barras retangulares suportadas elasticamente. O trabalho finaliza com a aplicação do método a um estudo de caso envolvendo uma travessa particular.
One of the biggest challenges for hydraulic turbine manufacturers is to prevent vortex-induced vibration on the stay vanes and runner blades. Only regarding stay vanes, 28 cases of cracks or unusual noises attributed to such vibrations were reported in the past decades leading to huge costs due to repair, delays and lack of generation. The state of the art today is to use powerful and expensive commercial computational fluid dynamics software to address the required transient phenomena. The present work carries out a comprehensive survey on occurred events in stay vanes during the last 50 years. Then, an alternative approach, based only on free open-source tools, is proposed. From due justified simplifying assumptions, the problem is formulated two-dimensionally, in the stay vane cross section plane, taking the fluid-structure interaction into account. In such a strategy, the Navier-Stokes equations are solved using oomph-lib, an object-oriented, finite-element library. A special C++ computational code is developed to deal with the fluid-structure interaction problem, in which turbulence is considered through a special algorithm, based on the Baldwin-Lomax model. The proposed method is validated through comparisons with an aerodynamics benchmark and an experimental measurement of oscillating rectangular bars both available in the literature. The method is finally applied to a case study of a particular stay vane. Keywords: Hydraulic turbine. Fluid-structure interaction. Vortex-induced vibration.

The marine current turbine (MCT) is an exciting proposition for the extraction of renewable tidal and marine current power. However, the numerical prediction of the performance of the MCT is difficult due to its complex geometry, the surrounding turbulent flow and the free surface. The main purpose of this research is to develop a computational tool for the simulation of a MCT in turbulent flow and in this thesis, the author has modified a 3D Large Eddy Simulation (LES) numerical code to simulate a three blade MCT under a variety of operating conditions based on the Immersed Boundary Method (IBM) and the Conservative Level Set Method (CLS). The interaction between the solid structure and surrounding fluid is modelled by the immersed boundary method, which the author modified to handle the complex geometrical conditions. The conservative free surface (CLS) scheme was implemented in the original Cgles code to capture the free surface effect. A series of simulations of turbulent flow in an open channel with different slope conditions were conducted using the modified free surface code. Supercritical flow with Froude number up to 1.94 was simulated and a decrease of the integral constant in the law of the wall has been noticed which matches well with the experimental data. Further simulations of the marine current turbine in turbulent flow have been carried out for different operating conditions and good match with experimental data was observed for all flow conditions. The effect of waves on the performance of the turbine was also investigated and it has been noticed that this existence will increase the power performance of the turbine due to the increase of free stream velocity.

Behaviour prediction of hydraulic steel structures with the view to surrounding influences in various design dispositions is a fundamental condition for operational reliability assessment of the analyzed construction. Reliable characteristics of construction behaviour defined by the specification of its movement within changes caused by time and environmental influences is of great importance. In currently used engineering mechanics formulation it concerns setting the response of the defined construction or its part to the given time variable mechanic load. Required response values, which are necessary for evaluation terminal dispositions of capacity and usability of the construction, are trans-location and tension, or values thence derived. Calculation is basic means for response prediction of construction. The thesis presented deals with complex multi-physical behaviour problems of water supply constructions in fluid structure interaction. There are presented various approaches to calculations of static and dynamic qualities of constructions. These approaches are divided into so called “direct method”, which is based on direct connection between two physical fields and the calculation is performed by the method of final elements, and so called “indirect method” , which is based on connection of two physical fields by means of various interfaces, which are described in this thesis. In case of indirect method, the calculation of running liquid is performed by the method of final volumes and the construction calculation is performed by the method of final elements. Within the scope of this thesis, static and dynamic responses of water supply constructions have been solved with the use of the above mentioned approaches. The results of the calculations in the scope of this thesis have been compared with the findings of performed experiments. The final part of the thesis describes the results and generalized findings gathered from the tasks by various approaches.

Dans un scénario de transition énergétique où la production et les grands réseaux de distribution d’électricité sont remis en cause, le potentiel de production au niveau des écoulements à faible vitesse est important et reste encore peu exploité. Cette thèse étudie un concept novateur d’hydrolienne permettant de répondre en partie à cette problématique : le système hydrolien à aile oscillante passive. Bioinspiré de la nage d’animaux aquatiques, ce dispositif de récupération de l’énergie cinétique des courants consiste en une aile décrivant des mouvements périodiques de pilonnement et de tangage, entièrement induits par les interactions fluide-structure. Une première partie du travail a porté sur la construction d’un modèle numérique permettant de reproduire fidèlement le comportement du système. Un prototype d’aile oscillante passive à échelle réduite a ensuite été conçu et testé dans un canal hydraulique. Grâce à une technique de réglage dynamique des paramètres structuraux, le système a pu être étudié expérimentalement sur une large gamme de paramètres mécaniques et hydrauliques. L’étude des performances énergétiques du prototype a permis d’identifier des conditions de fonctionnement optimales. Dans ces conditions, des rendements hydrauliques supérieurs à 30% ont été obtenus. Les résultats de ce travail de thèse permettent d’envisager maintenant l’installation d’un système hydrolien à aile oscillante passive en milieu naturel. En effet, les configurations optimales identifiées à l’échelle réduite peuvent s’étendre naturellement à des conditions hydrauliques réelles
Given the current energy transition conjuncture, where the electricity production and the electricity grid are challenged, the hydraulic potential of low current sites is relevant and remains under-exploited. In such context, this thesis studies a novel concept of an energy harvester device: the fully passive flapping foil turbine. Bioinspired from aquatic animals swimming technique, this hydrokinetic energy harvester consists of an oscillating foil describing periodic heaving and pitching motions, entirely induced by fluid-structure interactions. The first part of this thesis deals with the development of a numerical model for accurately simulating the harvester behavior. Then, a reduced scale prototype of the fully passive flapping foil has been designed and tested in a water channel. Thanks to an original dynamic tuning strategy of the structural parameters, experiments have been conducted for a wide range of configurations of the harvester. The investigation of the harvesting performances of the prototype helped identifying several optimized parameters sets. In such cases, hydraulic efficiencies as high as 30% have been reached. The main results of this thesis allow to consider a full scale fully passive flapping foil harvester in realistic conditions. As a matter of fact, the optimized cases identified for the reduced scale prototype can be naturally extended to real operating conditions

Due to the increase of rotor size in horizontal axis wind turbine (HAWT) during the past 25 years in order to achieve higher power output, all wind turbine components and blades in particular, have to withstand higher structural loads. This upscalingproblem could be solved by applying technologies capable of reducing aerodynamic loads the rotor has to withstand, either with passive or active control solutions. These control devices and techniques can reduce the fatigue load upon the blades up to 40% and therefore less maintenance is needed, resulting in an important money savings for the wind farm manager. This project consists in a study of load control techniques for offshore wind turbines from an aerodynamic and aeroelastic point ofview, with the aim to assess a cost effective, robust and reliable solution which could operate maintenance free in quite hostile environments. The first part of this study involves 2D and 3D aerodynamic and aeroelastic simulations to validate the computational model with experimental data and to analyze the interaction between the fluid and the structure. The second part of this study is an assessment of the unsteady aerodynamic loads produced by a wind gust over the blades and to verify how a trailing edge flap would influence the aerodynamic control parameters for the selected wind turbine blade.
På grund av ökningen av rotorstorleken hos horisontella vindturbiner (HAWT) under de senaste 25 åren, en design som har uppstod för att uppnå högre effekt, måste alla vindkraftkomponenter och blad stå emot högre strukturella belastningar. Detta uppskalningsproblem kan lösas genom att använda metoder som kan minska aerodynamiska belastningar som rotorn måste tåla, antingen med passiva eller aktiva styrlösningar. Dessa kontrollanordningar och tekniker kan minska utmattningsbelastningen på bladen med upp till 40 % och därför behövs mindre underhåll, vilket resulterar i viktiga besparingar för vindkraftsägaren. Detta projekt består av en studie av lastkontrolltekniker för havsbaserade vindkraftverk ur en aerodynamisk och aeroelastisk synvinkel, i syfte att bedöma en kostnadseffektiv, robust och pålitlig lösning som kan fungera underhållsfri i tuffa miljöer. Den första delen av denna studie involverar 2D- och 3D-aerodynamiska och aeroelastiska simuleringar för att validera beräkningsmodellen med experimentella data och för att analysera interaktionen mellan fluiden och strukturen. Den andra delen av denna studie är en bedömning av de ojämna aerodynamiska belastningarna som produceras av ett vindkast över bladen och för att verifiera hur en bakkantklaff skulle påverka de aerodynamiska styrparametrarna för det valda vindturbinbladet.

As one of the fastest growing renewable energy sources, wind energy is playing an increasingly important part in addressing the climate change and energy crisis issues the world is currently facing. The abundance of wind resource in offshore areas makes them a popular choice for turbine installation. In the past few years, several floating wind projects have emerged where wind turbines are installed far offshore in deepwater sites on moored platforms. Compared to land-based or offshore fixed-bottom wind turbines, an FOWT is a fully coupled system where the wind turbine with flexible blades and the floating platform with its mooring system interact with each other in wind and waves, which makes old design tools inadequate. This work aims to develop a fully coupled high-fidelity aero-hydro-mooring-elastic analysis tool, and to better understand the sophisticated fluid-structure interactions for FOWTs. The numerical tool developed in this work takes advantage of the open source CFD toolbox OpenFOAM to accurately solve wind turbine aerodynamics and floating platform hydrodynamics, and utilises the open source MBD code MBDyn for structural dynamics within a multibody framework while modelling flexible bodies based on a nonlinear beam theory. Coupling of these two solvers is achieved by establishing an interface library to exchange data with the help of the TCP/IP protocol. Additionally, to tackle the complex mesh movement in FOWT simulations, a mesh motion solver is developed in OpenFOAM by combining the sliding mesh technique and the dynamic mesh morphing method. A mooring system analysis module comprising a quasi-static method and a lumped-mass based dynamic approach is also implemented to simulate mooring lines in an FOWT system. A series of test cases is firstly studied to validate the various features of the tool, including basic fluid flow solving, modelling of wind turbine aerodynamics, hydrodynamic analysis of a floating structure with its mooring system, dynamic analysis of a riser or mooring line and coupled analysis of flow induced vibration of a flexible beam. The developed tool is then applied to analyse FSI problems of FOWTs under three different scenarios. Firstly, a coupled aero-hydro-mooring analysis is carried out for the OC4 semisubmersible FOWT under regular waves and uniform wind speed. Blade flexibility is ignored, and mooring lines are solved using the quasi-static method. Interactions between the moored platform and the wind turbine are investigated, focusing on of platform motion on the aerodynamic performance of the wind turbine and the impacts of wind turbine aerodynamics on the responses of the floating platform and its mooring system. Subsequently, an aeroelastic analysis is conducted for the NREL 5-MW offshore wind turbine with flexible blades under uniform wind speed. Effects of blade flexibility on wind turbine aerodynamics and structural responses are studied using the developed CFD-MBD tool. The floating platform supporting the turbine is not directly modelled for simplicity and the influence of platform motion responses on the turbine are analysed via imposing a prescribed surge motion to the turbine base. Fully coupled aero-hydro-mooring-elastic analysis is lastly carried out for the OC4 semi-submersible FOWT under a combined wind/wave condition to demonstrate the capabilities of the developed CFD-MBD tool. Responses of the floating system are investigated in terms of platform hydrodynamics, mooring system dynamics, wind turbine aerodynamics and blade structural dynamics. Interactions between the FOWT and fluid flow are analysed by visualising results obtained via the CFD approach.

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.

FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico
Among the new-found data about the availability of fossil fuels, which affirms that oil and natural gas sources will be almost depleted in the next century and the coal in the following two centuries. There is a global pursuit about new ways to produce energy. Another important fact that ratify this quest, lies at rise of the environment imbalance arouse from the burn of fossil fuels which, through the greenhouse effect, leads, for instance, to melting glaciers and increasing the temperature in the earth. The wind power, already used to move ships since antiquity is a relevant alternative way to produce energy, since it dispose of, at least, two great advantages, namely, it is endless and produce low negative consequences to environment. A place is considered to be good to receive the wind power engines called wind turbines, which convert the wind kinetic energy in electricity, if it is a ground plane with little amount of barriers. The sea, especially the regions far from the coast, satisfy the two latter requirement, and, furthermore, it is a place in which there are less obstructions about the noise pollution from the offshore wind turbines and there is not concern about deceases arouse in people who leave near of wind farms. In order to install the wind turbines in those spots away from the seashore, is required that its towers must be attached at the sea floor or must be develop a system that allow the turbine to float. Therefore the objective of the present work is to develop a structural modelling of the Monopile, TLP (Tension Leg Platform) and Spar type wind turbines subject using Finite Element Methods with the coupling method accomplished by Localized Lagrange Multipliers, jointly with the software SolidWorks and Autocad (drawing creation), ANSYS (mesh development) and Matlab (solver). The obtained results are relevant since such models are those which are most commonly used in offshore wind power plants. Lastly, due to the use of the latter coupling method, there is not the requisition to develop the study using meshes that agree each other. On the contrary, the analysis can be performed with non match meshes adjusting them with the Zero Moment Rule described in this present study.
Diante dos mais recentes dados com respeito a quantidade de combustÃveis fÃsseis ainda disponÃveis na natureza, os quais atestam que nÃo hà mais nem um sÃculo sequer para que o petrÃleo e o gÃs natural sejam praticamente extintos e que as reservas de carvÃo mineral suprirÃo somente mais 2 sÃculos de consumo, levando em conta o gasto atual. A preocupaÃÃo quanto a novas formas de extraÃÃo de energia se tornam necessÃrias e urgentes. Outro importante fator que ratifica o imediatismo de se buscar diferentes fontes de energia em detrimento de combustÃvel fÃssil, à o fato de que as emissÃes intrÃnsecas à sua queima estÃo gerando desequilÃbrio no clima global pela intensificaÃÃo do efeito estufa, apontado como um dos principais contribuidores do derretimento de geleiras e aquecimento da temperatura da terra. A energia eÃlica, jà utilizada desde a antiguidade para auxÃlio de locomoÃÃo de embarcaÃÃes e em moinhos de vento, se mostra uma alternativa de extrema relevÃncia, jà que, ela nÃo à portadora dos dois problemas crÃticos citados anteriormente. A saber, ela à infindÃvel e tem baixa consequÃncia negativa ao meio ambiente. Quanto aos locais que oferecem maior rendimento e produÃÃo para instalaÃÃo dos aerogeradores, responsÃveis pela conversÃo da energia cinÃtica do vento em energia elÃtrica, sÃo os que dispÃem de terreno mais plano e ausente de barreiras que impeÃam a continuidade do fluxo de vento. O mar, sobretudo as regiÃes mais distantes da costa, satisfazem Ãs duas necessidades citadas anteriormente, e, ainda se tratam de um local no qual nÃo hà a preocupaÃÃo quanto a poluiÃÃo sonora gerada pelos aerogeradores e nem com distÃrbios e doenÃas que possam ser desencadeadas em pessoas que residam pertos de grandes parques Ãolicos. A utilizaÃÃo de aerogeradores no mar (offshore) distantes da costa, e por conseguinte, em grandes profundidades, requer torres de sustentaÃÃo fixadas ao solo ou um sistema que proporcione que a turbina flutue. Diante do exposto, o trabalho em questÃo tem por objetivo realizar a modelagem estrutural do aerogerador flutuante (Spar), do portador de torre de tripà e do modelo monopile, sujeitos a carregamentos decorrentes de situaÃÃes normais e extremas, utilizando os mÃtodos dos Elementos Finitos juntamente com o MÃtodo de Acoplamento por Multiplicadores de Lagrange Localizados, atrelados aos softwares SolidWorks e Autocad (criaÃÃo do desenho), ANSYS (malha) e Matlab (solver). E, em decorrÃncia do fato da utilizaÃÃo do mÃtodo de acoplamento, nÃo hà necessidade de que as malhas dos subdomÃnios envolvidos sejam coincidentes. Pelo contrÃrio, pode-se utilizar malhas nÃo encaixantes para discretizar o sistema e, nas regiÃes onde hà contato entre malhas que nÃo coicidem, aplica-se a Regra do Momento Zero, descrita no presente trabalho. Nesse tipo de abordagem, pode haver uma separaÃÃo dos cÃdigos computacionais utilizados para o fluido e para a estrutura, os quais sÃo inicialmente tratados como entidades individuais e sà apÃs terem sido discretizados à que a informaÃÃo sobre suas malhas à recebida pela parte do cÃdigo responsÃvel por realizar o acoplamento dos subdomÃnios. Problemas de malhas que nÃo se encaixam podem surgir por diversos motivos, dentre eles, o fato de um subdomÃnio requerer uma malha mais refinada do que outros para que dele resultem resultados acurados. Pesquisadores de diferentes Ãreas podem gerar malhas separadas de distintos subdomÃnios e desejarem unÃ-los pelo mÃtodo abordado nesse trabalho em uma simulaÃÃo, ou a conformidade das malhas pode requerer muito tempo dispendido devido ao grande esforÃo computacional para a geraÃÃo de malhas conformes. Por fim, a aplicaÃÃo do mÃtodo produz resultados de grande relevÃncia, visto que, os modelos a que dizem respeito sÃo os mais comumente utilizados em projetos de aproveitamento de energia eÃlica offshore.

The aim of this diploma thesis is to determine and compare modal properties of four swirl turbine wheels, each with a different geometry. Natural frequencies and mode shapes were obtained based on computer modelling using Ansys software and they were compared with experimental modal analysis' results. The computer modelling and the experimental modal analysis were carried out for different boundary conditions and in different environments. The beginning of the thesis is dedicated to a brief overview of literature with similar issues. Then a brief introduction of a dynamics theory is mentioned in which equations of motion for a damped and an undamped single degree of freedom system are derived. The creation of a geometry model which is obtained by a reverse engineering is shown in the second part of the thesis. The geometry model was subsequently used for the computer based modelling of the modal parameters. In the third part an experimental equipment, setting, measurement and processing of data are described. The conclusion of the thesis is dedicated to the comparison of the results obtained by the experimental modal analysis and the computing modelling is presented. Moreover, influence of boundary conditions and influence of the environment on the natural frequencies are evaluated.

Grades da tomada dágua de usinas hidroelétricas são equipamentos de grande importância porque são responsáveis pela proteção das turbinas hidráulicas contra impacto de corpos flutuantes. Tais estruturas estão submetidas à ação de cargas dinâmicas oriundas do escoamento da água através das barras. O objetivo do presente trabalho é analisar grades submetidas à ação de fluxo de água. Ou seja, analisar as respostas da estrutura e o comportamento do escoamento da água utilizando os cálculos de dinâmica de estruturas acopladas às técnicas de dinâmica de fluidos computacional (CFD). Para a elaboração destas análises, foi utilizado o software comercial CFX versão 14. Tais análises foram elaboradas mediante o processo de interação fluido-estrutura. Primeiramente, um modelo estrutural simplificado das barras verticais das grades é elaborado a partir de dados de projetos conhecidos. A partir deste modelo define-se um volume de controle que representa o escoamento do fluido. Devido ao número de Reynolds calculado, utiliza-se o modelo de turbulência para obtenção dos resultados tais como tensões e deslocamentos nas barras verticais, e perfil de velocidades do escoamento. Considerando o modelo proposto, foram elaboradas análises com sete diferentes valores de velocidade de modo a comparar os dados calculados numericamente através do método de elementos finitos com valores obtidos experimentalmente. A partir do modelo verificado, é apresentada uma análise de uma grade inclinada submetida a um fluxo paralelo.
Trashracks are very important equipment because they are responsible for protecting turbines of hydroelectric plants against floating bodies. These structures are subjected to the action of dynamic loads due to the water flow through the vertical and horizontal bars. The objective of this study was to analyze trashracks submitted by action of water flow. In other words, to analyze the responses of the structure and the behavior of water flow using dynamic of structures calculations coupled with computational fluid dynamics techniques (CFD) for a turbulent regime, through the use of commercial software CFX version 14. This analysis is elaborated by the process of fluid structure interaction. First of all, a simplified structural model of vertical bars is defined from other similar projects. For this model is defined a volume of control that represents fluid flow. Due to the Reynolds number calculated, it is utilized a turbulence model in order to obtain the results. These results are: stresses and displacements of vertical bars; and profile of velocities of flow. The results are analyzed and discussed. After that, considering the simplified model, analyzes with seven different values of speed are executed in order to compare the results between the data calculated numerically by finite elements method, and the values obtained experimentally. Considering the model verified, an analysis, of an inclined trashrack subjected to a parallel flow, is presented.

Elementos de materiais flexíveis são empregados em diversas aplicações na engenharia, como por exemplo, em pás de turbinas eólicas. O comportamento do escoamento é afetado pela alteração na forma da estrutura. Muitas vezes, seu movimento e deformação são induzidos pelas próprias forças fluidodinâmicas. O trabalho apresenta o estudo de escoamentos externos envolvendo a interação fluido-estrutura, com o interesse voltado ao comportamento de pás de turbinas eólicas. Simulações numéricas são realizadas com o intuito de avaliar o efeito que a deformação da estrutura, devido à resposta elástica às forças oriundas do escoamento, tem nas próprias forças fluidodinâmicas. A plataforma ANSYS Workbench é utilizada, combinando o software ANSYS CFX para a análise do fluido e o ANSYS Mechanical para a análise da estrutura. Como validação do método, o escoamento laminar sobre um cilindro apoiado elasticamente é estudado e comparado com dados da literatura. O caso escolhido para o presente trabalho é o de um escoamento turbulento sobre um elemento de pá, fixo em uma das suas extremidades e livre na outra. A geometria da pá é retangular com o perfil NACA 0012 e o modelo de turbulência utilizado é o k-ω SST. Os resultados demonstram a influência significativa que a deformação da estrutura tem nas forças fluidodinâmicas de sustentação e arrasto e concordam com a literatura existente.
Elements of flexible materials are employed in several engineering applications, for instance, in wind turbine blades. The flow behavior is affected by any change in the shape of the structure. Often, its displacement and deformation are induced by the fluid-dynamic forces themselves. This paper presents the study of an external flow using fluid-structure interaction (FSI), focused on the behavior of wind turbine blades. Numerical simulations are performed in order to evaluate the effect that the deformation of the structure, caused by the elastic response to the flow forces, has on the fluid-dynamic forces themselves. The ANSYS Workbench platform is used, combining the software ANSYS CFX for the fluid analysis and ANSYS Mechanical for the structural analysis. As a form of validation of this method, the laminar flow over an elastically mounted cylinder is studied and compared with literature data. The chosen case for this work is a turbulent flow over a 3D blade element, fixed at one end and free at the other. The blade geometry is rectangular with the NACA 0012 profile and the turbulence model used is the k-ω SST. The results demonstrate the significant influence that the deformation of the structure has on the fluid-dynamic lift and drag forces, leading to an agreement with the existing literature.

L’objectif de ce travail porte sur le développement d’un modèle d’interaction fluide-structure adapté à la dynamique des éoliennes de grandes tailles avec des pales flexibles qui se déforment de manière significative sous l’effet de la pression exercée par le vent. Le modèle développé est basé sur une approche efficace d’IFS partitionnée pour un fluide incompressible et non visqueux en interaction avec une structure flexible soumise a des grandes transformations. Il permet de fournir une meilleure estimation de la charge aérodynamique et de la réponse dynamique associée du système (pales, mat, attachements, câbles) avec un temps de calcul raisonnable et pour des simulations sur des longues périodes. Pour la modélisation structurale, un élément fini de type solide 3D est développé pour l’étude dynamique des pales d’éolienne soumises à des grands déplacements et des grandes rotations. Une amélioration du comportement en flexion est proposée par l’introduction des degrés de liberté en rotation et l’enrichissement du champ de déplacements afin de décrire plus précisément la flexibilité des pales. Cet élément solide est apte de capter des modes de hautes fréquences qui peuvent s’avérer néfastes pour la stabilité du calcul. Deux techniques sont donc proposées pour les contrôler : la régularisation de la matrice masse et le développement des schémas d’intégration robustes de conservation et de dissipation d’énergie. Les chargements aérodynamiques sont modélisés en utilisant la Panel Method. Il s’agit d’une méthode aux frontières, relativement rapide par rapport à la CFD mais suffisamment précise pour calculer la distribution de la pression exercée sur la pale. Les modèles fluide et structure interagissent via un algorithme de couplage partitionné itératif dans lequel des considérations particulières sont prises en compte dans le contexte des grandes transformations. Dans un effort visant à instaurer un indicateur de fatigue dans la méthodologie proposée, des câbles précontraints sont introduits reliant le mat de l’éolienne au support. Une nouvelle formulation complémentaire en termes de contraintes est ainsi développée pour l’analyse dynamique des câbles 3D en comportement élasto-visco-plastique. Chaque méthode proposée a été d’abord validée sur des cas tests pertinents. Par la suite, des simulations numériques d’éoliennes avec des pales flexibles sont effectuées en vue d’affiner la compréhension de leur comportement dynamique et l’intérêt que la flexibilité des pales peut apporter à leur fonctionnement
In this work, a numerical model of fluid-structure interaction is developed for dynamic analysis of giant wind turbines with flexible blades that can deflect significantly under wind loading. The model is based on an efficient partitioned FSI approach for incompressible and inviscid flow interacting with a flexible structure undergoing large transformations. It seeks to provide the best estimate of true design aerodynamic load and the associated dynamic response of such system (blades, tower, attachments, cables). To model the structure, we developed a 3D solid element to analyze geometrically nonlinear statics and dynamics of wind turbine blades undergoing large displacements and rotations. The 3D solid bending behavior is improved by introducing rotational degrees of freedom and enriching the approximation of displacement field in order to describe the flexibility of the blades more accurately. This solid iscapable of representing high frequencies modes which should be taken under control. Thus, we proposed a regularized form of the mass matrix and robust time-stepping schemes based on energy conservation and dissipation. Aerodynamic loads are modeled by using the 3D Vortex Panel Method. Such boundary method is relatively fast to calculate pressure distribution compared to CFD and provides enough precision. The aerodynamic and structural parts interact with each other via a partitioned coupling scheme with iterative procedure where special considerations are taken into account for large overall motion. In an effort to introduce a fatigue indicator within the proposed framework, pre-stressed cables are added to the wind turbine, connecting the tower to the support and providing more stability. Therefore, a novel complementary force-based finite element formulation is constructed for dynamic analysis of elasto-viscoplastic cables. Each of theproposed methods is first validated with differents estexamples.Then,several numerical simulations of full-scale wind turbines are performed in order to better understand its dynamic behavior and to eventually optimize its operation

碩士
國立宜蘭大學
機械與機電工程學系碩士班
99
This research uses finite element analysis software ANSYS, CFD software CFX and three-dimensional computer-aided design software SolidWorks analyzes the flow field of the wind turbine. First, the model of large wind turbine is designed, then the fluid analysis is performed the fluid-structural analysis is also used to find the stress and strain distribution of the wind turbine. In this research, the flow field analysis for the upwind turbine and downwind turbine are considered. The results can find the higher velocity of the blade surface is observed. The stream lines are denser near the blade surface. That represents the velocity change is fast. Behind the rotating blade, the stream lines are not so dense that indicated the fluid has to travel long distance to blade to the original velocity value. The vortex distribution for the downwind turbine is more significant than that of the upwind turbine because the wind route is different for both of the wind turbine that they also have the different tilt angle rotor of shaft design. Through the fluid-structural coupling analysis for the wind turbine, the stress distribution of the structure can be observed, then the new design can be proposed, the transient fluid analysis is also performed, the force and torque variation based on the time can be obtained to see their differences.

碩士
國立宜蘭大學
機械與機電工程學系碩士班
98
In this research, aerodynamic characters of the wind turbine blade will be designed. Blade Element Theory and CAD software Blade Calculator are used to design two-dimensional shape curves of the wind turbine blades. Pro/E used to draw three-dimensional model of blades bused on two-dimensional curves. The finite element analysis software ANSYS and the computational fluid dynamics software CFX are used to perform, the fluid flow analysis to get the noise, blade surface pressure power with different wind speed. Through these analysis, we can combine the blade efficiency, noise, and angle adjustment devise to design a blade that will obtain the lower noise and avoid the blade stall. Fluid-structure coupling analysis is also performed. The maximum stress and strain are observed at the center line of the windward blade side. Blade deformation is similar to that of the cantilever beam, because the maximum deformation is observed at the blade terminal. Finally the natural frequencies with prestress and without prestress for the blade are analyzed. The vibration results showed that three is no much difference between these two cases.

碩士
中華大學
機械工程學系
105
In recent years with the country's active development of renewable energy and development and research, and wind power is a kind of renewable energy, but also the world is committed to the development of renewable energy. Taiwan's western coastal and outer islands have considerable wind resources, the average annual wind speed of up to 5 ~ 6 m/s above the density of 250 w/m2, showing that China has a wind turbine development of shallow power. In this study, the structural analysis software ANSYS was used to analyze the structural mechanics behavior of the 660 kW Vestas V47 trilobalic horizontal shaft fan at the wind speed (15 m/s). In the study, Workbench under ANSYS was used to analyze the fluid-structure coupling, that is, the computational fluid dynamics software CFX and ANSYS structural mechanics software were combined with each other. And according to the relationship between different pitch angle, tilt angle and wind speed, different terrain corresponds to the ground roughness coefficient α. In addition to the general external flow field, the portion of the flow field region establishes a circular rotational domain flow field in the blade rotor section, since the setting of the blade portion during the calculation of the fluid analysis is to rotate, The wind speed is based on the wind velocity distribution method of IEC61400-1. The formula is Vinlet = Vhub (Z / Hhub) α, and the response of the blade to the fluid-solid coupling is discussed. The results are analyzed. Part of the speed in the first model has the maximum value, YZ plane under the maximum value will appear in the third model, the rotation field pressure field and YZ plane pressure field maximum is appear in the third model, Structural stress maximum value In addition to the first model is present on the left side of the blade, the other two models are present on the right side of the blade, and the maximum value appears on the first model. This study hopes to study the distribution of the flow field, the distribution of the pressure field and the stress distribution of the structure, and then the noise problem is discussed.

碩士
國立宜蘭大學
機械與機電工程學系碩士班
104
A wind turbine is one of widely used green power generation devices at present. Since most of the turbine blades are made of composite materials, the effect of ply-angle need to be considered. 2 MW onshore wind turbine is studied in this paper, and ANSYS Composite PrepPost (ACP) was used to input the laminated composite properties for the wind turbine blades. The failure of the composite structure is investigated through fluid-structure interaction analysis and Tsai-Wu failure criterion. The results show that the structure of the wind turbine blade during abnormal operation (wind speed = 11.5 m/s, pitch angle = 0°) is safe, even under negative attack angle conditions. The results for normal operation (wind speed = 25 m/s, pitch angle = 0°) indicates that the tower may be hit by the blade due to tip deformation. The highest stress is observed at the blade root due to significant deformation, but the blade structure is not expected to fail because the maximum Tsai-Wu failure indicators is only 0.875 (<1). In contrast, stress concentration is observed at 30 m from the blade root. It is caused by the structural weakness in the area with the least number of plies in the blade. Since the highest Tsai-Wu failure indicator is up to 1.1696, the composite laminates are expected to be damaged. Layers 5, 11 and 12 will fail according to the values of failure indicator. These findings will be useful to improve the design of composite wind turbine blades in the future.

碩士
國立高雄應用科技大學
機械與精密工程研究所
96
The low-pressure blades crack near root location occurs occasionally in steam turbine. A possible occurrence of the blade failure is due to the interaction between unsteady flow and blades. The interaction between fluid field and structure should not be ignored for the low-pressure turbine blades with high aspect ratio. In this paper, solid-fluid interaction analysis of numerical simulated for the L-1 low-pressure turbine blades by using commercial software ANSYS with ALE (Arbitrary Lagrangian-Eulerian) method. The results showed that the blade vibration comes from the fluid flow generated impact pressure wave, and the maximum stress of blades occurred at the trail 15 mm from the root, and the largest displacement points at the top of the tail.

博士
國立臺灣大學
工程科學及海洋工程學研究所
99
Wind turbine blades are long, thin, composite structures and therefore will have bending deflection in the flapwise direction as well as foil-section twist during rotational motion. The twist phenomenon accompanies the change of flow filed around blades and then leads to the change of loading condition on blades. The blade design without considering the aerodynamic and aeroelastic effect makes a wind turbine could not performance the best power generation efficiency. Otherwise, blades are usually built by the vacuum assisted resin transfer molding method. The successful manufacture depends on the proper infusion strategy and well realization of permeated characteristics of various laminates. Large-scale blades make the complicated permeated behavior of laminates and increase the infusion difficulty. First, the study confirmed the relationship between fiber orientation angle and structural response by the bend-twist experiments of small wind turbine blades. Then the calculating procedure of fluid-structure interaction with considering the aerodynamic effect was established by calculating attack angles of a blade (BEM), pressure distribution on the foil sections (2D flow field analysis), and structural analyses (FEM). The fluid-structure coupling effect was specifically discussed by calculating the power efficiency of a wind turbine. The adjustment of fiber orientation angle in the blade laminates was also utilized to improve the operating efficiency of wind turbines. The mold-flow manufacturing analyses focused on discussing the permeating characteristics of composite laminates under the VARTM process. The operation of 3D model composed of 1D pipe elements and laminates simulated the groove-flowing behavior of sandwich laminates and then substituted for complicated infusion experiments. The idea of equivalent thickness contributed to derive the permeability of sandwich laminates. The permeability predictive equations that were derived on the basis of the infusion experiments produced permeability of various laminates conveniently and were beneficial for the numerical analyses of large structures manufactures under the VARTM process.

碩士
國立虎尾科技大學
航空與電子科技研究所
98
Wind turbines have being attracted a lot of interest in engineering applications as the requirement for clear energy increases. Appropriate blade design has a significant effect on the efficiency of a wind turbine. To design an efficient wind turbine, it is necessary to understand the interaction between wind loads and blades. Many present studies focus on these two topics separately because highly dissimilar characteristics between them. The present study aims to investigate the coupling effect of wind loads and 2D blades for a small scale wind turbine. The present study applies the analysis software ANSYS and the computational fluid mechanics software CFX to conduct a two-way fluid structural analysis of a 2D blade. The effect of factors, include angle of attack, wind speed and Young modulus of blades, on the drag and lift are covered in the study. The information of displacement and force along the fluid structural interface are hand-shaked through stagger iteration between the fluid solver and the solid solver that individual calculation of field variables are carried out in the fluid solver and the solid solver until the displacement and force along the interface of fluid and structure are convergent. The analysis results show a blade with a flexible material under a high wind speed can reduce the drag coefficients by2.05 % and the lift coefficient by63.79%. This study provides a good insight for the design of blades for a small scale wind turbine.

碩士
國立臺灣科技大學
機械工程系
102
This study predicts the aerodynamic performance of the NREL 5MW offshore wind turbine via a two-way fluid-structure Interaction (FSI) approach. This simulations are performed under the rated wind velocity 11.4 m/s and rated rotor speed 12.1 rpm at full scale. The flow field around the wind turbine is computed by solving the Navier–Stokes equations incorporated with the k-Omiga turbulence model, where air is assumed as an incompressible viscous fluid. The equations are discretized using a finite volume method. In this study STAR-CCM+ and Abaqus are employed to solve the FSI problem, where a weak coupling approach is used. A remeshing process is adopted to obtain the required grid quality of sliding grid system as well as the mesh around the deformed blades. The simulation suggests that the deformation of reference point for flexible blade is about 6.45% of the total blade length. while the wind turbine with flexible blades delivers a power decrease by 9.56% when compared with the power delivered by rigid blades.

碩士
國立臺灣科技大學
機械工程系
101
This study investigates the aerodynamic characteristics of a 2MW three-blade horizontal wind turbine in operation condition via flow simulation with taking the fluid-structure interaction into account. The incompressible flow field around wind turbine is obtained by solving the continuity and momentum equations incorporated with a k-? turbulence model, and the forces and moments exerted on the wind turbine by wind can be then calculated. Two approaches, i.e. moving reference frame and sliding mesh method are adopted to find their differences in predicting aerodynamic performance, where the measured power is employed to validate the numerical result. Five different fiber reinforced plastic materials for blades under isotropic assumption are used to study their effects on the aerodynamic characteristics. The results suggest that the former method is less accurate than the later one, where the error in power prediction is about 5% for investigated cases. The deformation of blade tip varies from 0.2 m and 0.8 m for the studied materials, while the predicted power gives 2% difference between the wind turbines with flexible and rigid blades, which is mainly due to the small deformation of blades.

碩士
中華大學
機械與航太工程研究所
94
In this study we performed the solid-fluid coupling for radial-inward cutback shape turbine impeller with STAR-CD package software. The interactive analysis of structure and flow field for the impeller has been studied. In this research, the impeller outer diameter is 380mm, the axial length is 155 mm, and the analysis of structure and flow field changes are carried under the rotational speed of 30000RPM. The results of simulation analysis are as follows: The three-dimensional flow field analysis changed by multiple loads (temperature, centrifugal force) show 20MPa decrease in stress, 3.195mm increase in displacement. Flow field analysis shows 19Psi decrease in inlet pressure and no defect in pressure concentration at the bottom of the blades. Flow field velocity shows obvious vortex generation at shifted flow channels between two blades. The temperature of shifted flow field entering rotary zone is 56K higher than the temperature downstream of middle section before changing. The pressure drop ratio of flow field before shifting is 5.5, and is 3.77 after changing. The vibration and noise can be reduced by this 45% reduction in pressure drop. Traditional structure and flow field analysis can only be discussed solely. The discussion of solid-fluid coupling effect is to investigate the interactive impact between solid and surrounding flow field, so as to demonstrate a more realistic analysis and research when a turbine works. This study discusses the most important factor (temperature, displacement) in the interaction between impeller and flow field. The results for the varied effect of impeller and flow field has been obtained.

Oscillating-foil hydrokinetic turbines have gained interest over the years to extract energy from renewable sources. The influence of the sweep angle on the performance of a fully-passive oscillating-plate hydrokinetic turbine prototype was investigated experimentally in the present work. The sweep angle was introduced to promote spanwise flow along the plate in order to manipulate the leading edge vortex (LEV) and hydrodynamically optimize the performance of the turbine. In the present work, flat plates of two configurations were considered: a plate with a 6° sweep angle and an unswept plate (control), which were undergoing fully-passive pitch and heave motions in uniform inflow at the Reynolds numbers ranging from 15 000 to 30 000. The resulting kinematic parameters and the energy extraction performance were evaluated for both plates. Planar (2D) particle image velocimetry (PIV) was used to obtain patterns of the phase-averaged out-of-plane vorticity during the oscillation cycle. The circulation in the wake was then related to the induced-forces on the plate by calculating the moments of vorticity of the LEV with respect to the pitching axis of the plate. Tomographic (3D) PIV was implemented in evaluating the influence of the spanwise flow on the dynamics of the vortex structure in three-dimensional space. The rate of deformation of the vortex length was quantified by calculating the deformation terms embedded in the vorticity equations, then linked to the stability of the vortex. The results show evidence of delay of the shedding of LEV and increased vortex stability, in the case of the swept plate. The manipulation of the LEV by the spanwise flow was related to the induced kinematics exhibited by the prolonged heave forces experienced by the swept plate, which led to the higher power extraction performance at high inflow velocities. In the presence of spanwise flow, positive vortex stretching along the vortex line increased the stabilization of the vortex core and prevented the onset of helical vortex breakdown, observed in the case of the unswept plate. The use of the sweep profile on the plate has led to the improvement of energy extraction performance of the fully-passive hydrokinetic turbine.
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