One of the main drawbacks of offshore wind energy is its high levelized cost of electricity (LCOE). One explanation for these high costs arises from the large amount of uncertainties that come with such complex projects. As a result of this complexity, it’s difficult to foresee the course of events in advance. Decisions made during the preliminary design phase are often based on limited data while having a great impact on project outcome. A tool is needed to assist engineers during these early stages of design. This tool should deliver good results using limited input data and require little computational time. An example of such a tool is TeamPlay; an engineering model that evaluates offshore wind farm design using automated optimization techniques. In its current state, only a monopile type foundation is analyzed within this process. Since the current trend in the industry is to build larger farms further from shore, this foundation type will become less popular in the future. A jacket type foundation is better suited for far-­‐shore application. In this thesis, a new stand-­‐alone engineering model is created which can be added to TeamPlay’s functionality to extend future use...

The main purpose of this project was the creation of a tool, based on the research performed by Scheldbergen [25] and Roscher [24], capable of performing Finite Element Analysis (FEA) on a Horizontal Axis Wind Turbine (HAWT) blade and minimize its weight by altering the various thicknesses locally, always satisfying a number of structural constraints. The first goal was the development of a geometry creation algorithm based on a Non Uniform Rational Basis Splines (NURBS) algorithm developed by Ferede [14], with a more complex spanwise/chordwise discretization technique in order to more accurately design a discretized HAWT blade. The second goal was the alteration of the material creation algorithm developed by Scheldbergen [25], so that different stacks at various blade locations can be assigned. Moreover, the aerodynamic loads generation algorithm of Scheldbergen [25] was modified to apply for different airfoils along the blade span. Also, Blade Element Momentum (BEM) theory was used for the calculation of the aerodynamic loads and the software XFOIL was used for the aerodynamic analysis of the airfoils (pressure distribution on the airfoil at corresponding angles of attack and Re numbers). An initial HAWT blade design was created, matching the SANDIA 5 MW wind turbine blade [23] geometry and materials. Furthermore, the apwise/edgewise stiffness, moments of inertia, mass and mode shapes were also validated. Additionally, the SANDIA blade was analyzed in DNV GL Bladed in order to validate the aerodynamic loads on the blade. Following, the tool was designed to process the geometry, the materials and the gravitational/ centrifugal/aerodynamic loads of the blade and translate them to an input for the FEA software MSC Nastran for Linear Static Analysis (SOL 101), Buckling Analysis (SOL 105) and Modal Analysis (SOL 103). The post processing algorithm of Scheldbergen [25] was modified to apply for a HAWT (instead of a VAWT), transforming the results of the FEA analysis into optimization constraints (ultimate load, buckling, tip deflection and fatigue). The final part of the algorithm involved the minimization of the blade's mass by altering the thickness at various locations, using the MATLAB function fmincon. Concluding, a case study of a smart rotor blade equipped with trailing edge ap (TRF) was examined. A _ 2 flap was used at 90-100% of the chord and 78-98% of the span. Two kinds of optimization were performed for the HAWT and smart rotor scenarios; one that included ultimate stress, tip deflection and fatigue constraints (UL-TD-FA) and one that also included buckling constraints (UL-BU-TD-FA). It was found that the buckling constraint was the limiting factor of the optimization and the fatigue constraint was the least dominant. The initial design of the smart rotor blade showed a 16.5% decrease of the maximum fatigue damage and a 2% decrease in the maximum stress. The optimized smart rotor blade mass was 0.5 % lower in the UL-TD-FA scenario and 2.5% in the UL-BU-TD-FA scenario compared to the HAWT blade. The tool created is capable of creating a flexible and fairly accurate representation of a HAWT and smart rotor blade. It also provides the ability to structurally analyze the blade under the most significant structural criteria and minimize the blade's weight under specific loading conditions. The tool constitutes a good starting point for more detailed structural analysis of smart rotors and more complex structural optimization of HAWT and smart rotor blades.

Energy demand from wind greatly increases, as such more remote sites need to be explored in order to find good wind resources. These remote sites are driving the industry further offshore and therefore into extreme wind and sea conditions. This push towards extreme conditions requires technological advancements concerning the wind turbine loads, power production and installation. The levelised cost of wind energy is strongly dependent on the capital expenditures and thus on the installation and logistics of erecting a wind turbine offshore. Improving the robustness of the installation to higher wind velocity and turbulence will increase the weather window and therefore drastically decrease the levelised cost of energy (LCoE). This thesis will focus on one particular technique of wind turbine installation: Horizontal Single Blade Mounting (HSBM). HSBM is a wind turbine blade lifting technique performed by Siemens Wind Power (SWP). This technique is currently limited to low wind speeds, which contradicts the fact that the industry is targeting high wind speed offshore sites. This technical problem is the basis of the thesis study. This thesis study will answer three research questions in order to improve future lifting methods. In a nutshell these questions are: one, how to model the aerodynamic forces and dynamic behaviour of a hoisted wind turbine blade?, two, what are the critical parameters affecting the blade response? and three, how can single blade mounting be improved for higher wind speeds?.

A wind turbine is designed to produce a maximum amount of energy at minimum cost while it withstands any possible wind condition. In the wind conditions with the highest wind speeds the wind turbine has to cope with the most extreme loads. In these most extreme cases the wind turbine is parked, the blades do not rotate, and the blades deform elastically under these wind loads. An increase in the flexibility of the blades results in higher elastic blade deformations. The main objective of this project is to design blades in a way that the extreme loading on the blades reduces with more than 10 % without compromising the energy yield by making use of flexible materials and the corresponding increased deformations. The reason to focus on load reduction is that a wind turbine can be made cheaper if these loads are reduced. The research methodology is a three-step approach: Firstly a modelling tool is created to design and evaluate blades with new flexible materials at different locations in the blade. Secondly a verification procedure is performed to check the accuracy of the modelling tool. Thirdly this tool is used to design blades with highly flexible materials and to perform an iteration procedure to design the best flexible blade design. The modelling tool is based on the cross sectional software BECAS to design new flexible blades and on the aeroelastic software HAWC2 to analyse the behaviour. This BECAS-HAWC2 modelling tool is based on the existing XANT M-21 wind turbine of which only the blade materials are variable parameters, the rest of the wind turbine remains as it is. A verification procedure compares the modelling tool with two other models of the same blade. The minor differences between several modelled parameters increase the confidence in the BECASHAWC2 model. A material with unidirectional fibres and a highly flexible matrix material is stacked in different orientations to design different blade materials. These flexible materials are introduced in specific locations of the blade. The design exploration approach makes it possible to design and evaluate many different blades using different flexible materials at different locations. The current results show that the best option is to use the flexible material with fibres only in longitudinal and transverse direction in the skin of the blade. Not replacing the full skin but only the part of the root up to the middle of the blade results in the best flexible design. This best design has a reduction in maximum thrust force and maximum root bending moment of respectively 23 % and 26 % compared with the original blade, easily exceeding the predefined goal of 10 %. This significant load reduction is due to a significant blade twist rotation thereby reducing the area exposed to the wind. The annual energy yield is not compromised, it even shows a considerable 11 % increase due to a stall delay effect in the higher wind regimes which is also caused by an increase in blade twist. The best flexible design is a preliminary design that shows promising results. These results show that by using flexible materials in the blade skin a significant load reduction is combined with an increase in energy. This indicates an untapped potential for future wind energy which makes further research on this topic recommended.

The reduction of the Levelised Cost of Electricity (LCoE) in wind energy, and offshore in particular, is among the main objectives of research in the academia nowadays, and a demanding task as well. Offshore wind farms are capital intensive investments and lowering uncertainties and costs throughout design, planning, installation and operational phases will offer cheaper electricity production and a more competitive nature against fossil fuel powered energy. Of course, a big part of the total cost of a wind farm is the wind turbines themselves. Innovations in the design and manufacturing processes are always welcome in order to further advance within the learning curve of the technology and achieve efficient economies of scale. Furthermore, the blades of the wind turbine rotor are its most important component because they express the most basic operation of the turbine, aerodynamics and energy capture. Yet they pose structural challenges. There are efforts to maximise energy output while keeping their mass low, which should subsequently drive down secondary costs. Additionally, another important factor is the increase of energy output in the farm level that can lead to a larger cost reduction. This thesis aims to investigate the performance and feasibility of lightweight, low power density rotors. This investigation is made by acquiring a performance baseline with the reference rotor of the 10 MW INNWIND machine and comparing it with the proposed alternative rotor designs by means of parametrical modifications. The reference machine rotor radius is 89.166 m, with a blade mass of 41.7 tn and a rated power output of 10 MW operating at an optimal lambda of 7.5. All the new designs include an increase in rotor radius to 103 m. They also include differences in operational parameters such as rated rotational speed, blade slenderness and tip speed, while rated power stays the same. These designs result in different blade masses and allocation of energy production...

Big wind farms with big wind turbines are more cost effective and produce greener electricity compared to smaller ones. This is one of the reasons for the growth of wind turbine size during the last 3 decades. However, as wind turbines become bigger, their blades become longer, thicker and heavier. This results in larger unsteady loads on blades which is an important limitation for their life time and their size growth. Flow control has emerged as the promising solution both for improving the aerodynamic efficiency and controlling the unsteady loads on wind turbine blades. DBD plasma actuator is an active flow control mechanism that has shown high potentials for unsteady load control with the capability to change lift coefficient to a significant amount with a very fast response time. The current research first intends to identify the variations of angle of attack and lift coefficient on wind turbine blades as a result of gravitational loads, mass and aerodynamic imbalances, turbulence, wind shear, yawed inflow and tower shadow and investigate their corresponding frequencies and the fatigue damage from the blade root bending moments. Then, (single and multi) DBD plasma actuator with different configurations will be used on three different trailing-edge shapes (round, half-round and sharp) of modified version of ’NACA64-2-A015’ airfoil to control the aerodynamic loads via circulation control. This is managed either by manipulation of Kutta condition or acting as a virtual Gurney flap. Furthermore, it is intended to investigate the correlation between the frequency of actuation, frequency of vortex shedding and the amount of lift enhancement.

Wind turbine design is subject to load calculation standards. These determine material use which in turn affects wind turbine costs. Wind turbine cost reductions are important as they contribute to the economic feasibility of wind turbines. Therefore careful evaluation of the load standards is paramount for wind turbine design. This thesis offers an evaluation of 50-year ultimate load estimates described in the IEC 61400-1 standard and a tool for wind turbine designers to manage the estimates...

The continued grow of the wind industry has resulted in an increase in turbine cluster density in wind farms. This has made the topic of wind turbine and wind farm wake aerodynamics more relevant than ever. Wind turbine wake models are used to predict the deficit and recovery of the wind velocities in the wake. The currently used wake models in the industry contain a relatively simple approach to model the near-wake of the turbine, assuming an initial hat or Gaussian deficit profile at a fixed location in the wake. This thesis presents an alternative near-wake model based on discrete, inviscid, perfectly circular vortex rings for use in conjuncture with existing far-wake models.

Wind energy is one of the fastest growing types of renewable energy. Today, offshore wind represents 14% of the EU wind energy market, and has a huge potential for further growth [1]. Operations and Maintenance (O&M) accounts for 18-23% of the total lifetime cost in offshore wind farms, compared to 12% onshore [2]. The offshore O&M tasks are more costly, being influenced by distance offshore, harsh offshore conditions, wind farm size, wind turbine reliability and maintenance strategy [2]. Exchanges of main components, also known as major interventions, causes significant costs and has been indicated as the largest uncertaintywhen predicting O&M costs [3]. Major interventions are characterized by the need for a jack-up vessel to perform the exchange. No studies have been found on offshore major interventions. Echavarria has previously performed an analysis on the exchange rates of main components based on the onshore WMEP population, which had an average rated power of 233 kW [4]. Blades and generator were identified as most critical components, but it is not known how this reflects current exchange rates for larger turbines. The goal of this research is therefore to determine future failure rates and predict the cost of offshore major interventions.

In order to be more competitive with conventional, polluting energy resources, the levelised cost of energy (LCoE) of wind turbines has to decrease significantly [1]. A method to achieve this goal is to reduce the amount of parts in a wind turbine and more specifically avoid the use of expensive and failure-prone pitch systems. Using blades which passively deform under high aerodynamic loading and effectively reduce the peak, design-driving loads on the turbine structure might offer an interesting alternative to the pitch system. However, the conventional material for construction of blades, glass-fibre reinforced plastics, does not allow for such large deformations during normal operating conditions. Prior to this project, a study to incorporate more flexible materials has been carried out in the design of the current XANT-21 wind turbine in order to increase the flexibility of the blades. However, introducing a high degree of flexibility in the wind turbine blades might increase the risk of aeroelastic instabilities. These aeroelastic instabilities often result, in combination with a non-linearity in the aerodynamics or structure, in limit cycle oscillations (LCOs). The need to identify the key structural parameters which play a role in the initiation of the aeroelastic instabilities has led to the objective of this thesis: Investigate the influence of the critical structural parameters on the onset velocity and the behaviour of high-amplitude limit cycle oscillations of a wind turbine airfoil by means of numerical simulations.

Wind turbines are operating under very complex and uncontrolled environmental conditions, including atmospheric turbulence, atmospheric boundary layer effects, directional and spatial variations in wind shear, etc. Over the past decades, the size of a commercial wind turbine has increased considerably. All the complex and uncontrolled conditions mentioned above result in uncertainties of aerodynamic loads calculation on very large wind turbine blades and thus better numerical codes are needed for predicting the loads in the design phase. With the aim to eliminate these uncontrolled effects and improve the aerodynamic models, in last decades, several important experimental campaigns of different wind turbine models have been performed in large wind tunnels. The objective of such experiments (e.g. using the NREL wind turbine and the MEXICO rotor) is to provide high quality measurement data which can be used to validate numerical models and improve different fidelity numerical codes, particularly for predicting wind turbine aerodynamic loads. @en

Ducted Wind Turbines (DWTs) are one of the many concepts that have been proposed to improve the energy extraction from wind in comparison to bare wind turbines. In reviewing the DWT studies, investigations based on the combined use of theoretical, computational, and experimental techniques have been presented. Although indicated in these studies that the power output of wind turbines can be significantly increased by using surrounding ducts, the factors influencing this power increase, like the duct shape, augmentation add-on’s and yawed inflow conditions, need further investigation. These topics have been addressed in this doctoral thesis. The study presents a computational investigation of DWTs, employing two-dimensional and three-dimensional CFD simulations. To this intent, solutions obtained using panel, RANS, URANS and LB-VLES methods are shown. For reliable solution accuracy, verification and validation assessments are performed when possible. Through parametric investigation, it is found that the aerodynamic performance of the DWT can be improved by increasing the duct cross-section camber and a correct choice of turbine thrust force coefficient, whilst maintaining the same duct-exit-area ratio. The aerodynamic performance improvement for a DWT directly corresponds to the dimensionless duct thrust force coefficient. Flow analysis showed that flow separation when detected inside of the duct, reduces the duct thrust force coefficient and ultimately the aerodynamic performance of the DWT model. In an effort to further improve on the aerodynamic performance of the DWT, the effect of multi-element ducts and Gurney flap on the existing DWT models are investigated. The aerodynamic performance improvement with multi-element ducts strongly depends on the installation settings of the secondary duct element with respect to the primary DWT geometry. On the other hand, a Gurney flap retrofitted at the trailing edge of the duct improves the aerodynamic performance of the DWT model by delaying inner duct wall flow separation, thus increasing the mass flow rate at the turbine. Finally, the effects of yawed inflow condition on the aerodynamic and aeroacoustic performance of DWT models are studied in detail. The analysis showed that DWTs can demonstrate yaw insensitivity up to a specific yaw angle. The yaw insensitivity for the DWT model, however, strongly depends on the aerodynamic mutual interaction between the duct and turbine, which changes with the duct geometry, turbine configuration and yaw angle. While assessing the aeroacoustic performance of the DWT models, it is found that the DWT model xiii xiv Summary with highly cambered duct cross-section generates higher broadband noise levels, which results from the turbulent flow structures convecting along the surface of the duct. @en

Airborne wind energy (AWE) is an emerging renewable energy technology that harnesses wind energy using tethered flying systems. The extra degrees of freedom allow these systems to harvest wind resources at altitudes currently unrealisable by conventional turbines. These flying devices, often resembling kites or drones, are typically divided into two classes. The first converts kinetic energy into electricity using onboard generators and transmits it to the ground via a conductive tether. The second class transfers aerodynamic forces via the tether to the ground, where the mechanical energy is converted into electrical energy using an electrical machine.As the tether’s length constrains the system, once the flying device reaches this tether length limit, some energy must be used to retract it back to its initial position. This cycle of traction and retraction is known as a pumping cycle. Therefore, AWE systems must be designed to maximise the harvesting or traction phase while minimising the retraction phase to ensure a net positive power output. From the AWE system landscape, this thesis is based on tethered aircraft-style fixed-wing systems. Typically, such systems utilise composite structures owing to their high stiffness-toweight ratios. Designing these composite structures demands special attention due to their anisotropic nature, which results in complex load-deflection couplings. Here, a multi-disciplinary simulation framework for tethered composite aircraft wings is developed. The research focuses on methods used during the iterative phases of initial (conceptual and preliminary) design that are commonly employed in a spiral system engineering approach. The proposed framework integrates computational methods for the design of the aerodynamic A, bridle B, and structural S domains. The bridle is a system of segments of tether and pulleys that distribute the tether forces into the wing structure. The aerodynamic and structural domains are divided into 2D and 1D models, which are then integrated to determine the 3D response of the wing. A nonlinear vortex-lattice method (VLM) is utilised for the aerodynamic domain. For the structural domain, an anisotropic 1D finite element (FE) model is developed that is coupled with a 2D FE sectional solver. In addition, methods are proposed that enable detailed topology optimisation. For tailless swept-wings, like those used by EnerKíte, the aero-structural-bridle interactions are crucial. The developed framework is used to investigate the impacts of different wing and bridle configurations to determine the sufficient level of fidelity required at the initial design phases. Typically, such aeroelastic phenomena are captured during detailed design stages wherein full 3D structural and aerodynamic simulations are employed. However, this mandates design knowledge typically unknown at the initial design stages. This motivates a multi-fidelity modelling approach to include these coupling effects while abstracting the composite ply level details during the design exploration. This is achieved by combining geometric discretisation approaches with lamination parameters. Thus, the framework aims to provide viable design options during the initial stages while considering aero-structural-bridle couplings.@en

Society is finally entering a new age of renewable energy development. For the first time it is truly conceivable to power a vast majority of global energy use with a combination of wind, solar, and other forms of low carbon, renewable power. The rise of electrification and so called ”Power to X”, where renewable energy is used to create other more condensed and potentially storable sustainable fuels, will require a significant increase in the capacity of electrical grid networks worldwide in the coming decades. One of the largest growing sectors in renewable energy is offshore wind power. With farms in operation for over two decades, offshore wind has been predominately deployed in relatively shallow water in the North Sea of Europe. While expanding to global markets is possible with fixed bottom machines, the resource is relatively limited based on the strict seabed requirements. Moving to floating offshore wind platforms, demonstrated in pilot projects like Hywind Scotland, has the potential to vastly expand the potential wind resource and open markets in the Americas and Asia which would otherwise be unreachable....@en

The contribution of sustainable Wind Energy (WE) to the global energy scenario has been steadily increasing over the past decades. In the process, Horizontal Axis Wind Turbines (HAWT) became the most widespread and largest WE harvesting machines. Nevertheless, significant challenges still lie ahead of further expansion of HAWT, namely concerning systemrobustness and cost-of-energy(COE) competitiveness. This dissertation studies aHAWT design concept termed modern Active Stall Control (ASC). With this concept HAWT power regulation is achieved using flowcontrol actuators to trim the aerodynamic loads across the operational envelope. The underpinning idea is that as the aerodynamic loads are trimmed by flowcontrol actuatorswithout pitching the blades, the pitch system may be mitigated. In turn, this might lead to decreased failure-rates and down-time, and thus eventually present a more cost-effective solution than state-of-the art HAWTs. Going specifically into ASC, if aerodynamic load trimming is performed it is necessary to employ a flow control actuator. From different flow control actuator types, since the aim is to reduce the maintenance and operational costs of ASC machines, actuators with few mechanical parts become more interesting. As such the present research also focuses on the Alternating Current Dielectric Barrier Discharge (AC-DBD) plasma actuator, owing among other things to its absence of moving parts, negligible mass and virtually unlimited bandwidth of actuation. A preliminary study on the feasibility of active stall control to regulate HAWT power production in replacement of the pitch system is conducted. By taking the National Renewable Energy Laboratory 5MWturbine as reference, a simple blade element momentum code is used to assess the required actuation authority. Considering half of the blade span is equipped with actuators, the required change in the lift coefficient to regulate power is estimated in ¢Cl Æ 0.7. Concerning actuation technologies, three flow control devices are investigated, namely Boundary Layer Transpiration, Trailing Edge Jets and Dielectric Barrier Discharge plasma actuators. Results indicate the authority of the actuators considered is not sufficient to regulate power, since the change in the lift coefficient is not large enough. Especially if a pitch-controlledmachine is used as baseline case. Active stall control of Horizontal AxisWind Turbines appears feasible only if the rotor is re-designed from the start to incorporate active-stall devices. Regarding AC-DBD plasma actuators, three specific topics are investigated. The different studies aim at DBD performance characterization, namely at the influence of external flow on DBD plasma momentum transfer and on the frequency response of actuator flow region characteristic of DBD pulse operation. Both these topics are important to bridge the gap between academic-laboratory employment of DBD and large-size industrial applications. Finally regarding DBD plasma actuator modeling, a method is developed to describe plasma actuation effects in integral boundary layer formulation, and coupled to a viscous-inviscid panel code (similar to XFOIL), while an experimental campaign is carried to validate the predictions. The three DBD plasma studies are further described below. Addressing cross-talk effects between DBD plasma actuators and external flow, a study is carried out in which an actuator is positioned in a boundary layer operated in a range of free stream velocities from 0 to 60m/s, and tested both in counter-flow and co-flow forcing configurations. Electrical measurements and a CCD camera are used to characterize the DBD performance at different external flow speeds, while the actuator thrust is measured using a sensitive load cell. Results show the power consumption is constant for different flow velocities and actuator configurations, while the plasma light emission is constant for co-flow forcing but increases with counter-flow forcing for increasing free stream velocities. The measured force is constant for free stream velocities larger than 20m/s, with same magnitude and opposite direction for the counter-flow and co-flow configurations. In quiescent conditions the measured force is smaller due to the change in wall shear force by the induced wall-jet. In addition to the experimental study, an analytical model is presented to estimate the influence of external flow on the actuator force. It is based on conservation of momentum through the ion-neutral collisional process while including the contribution of the wall shear force. Model results compare well with experimental data at different external flow velocities, while extrapolation to larger velocities shows variation in actuator thrust of at least 10% for external speedU Æ 200m/s. Concerning the response of DBD actuator region flow to pulsed operation, a methodology is provided to derive the local frequency response of flow under actuation, in terms of the magnitude of actuator induced velocity perturbations. The method is applied to an AC- DBD plasma actuator but can be extended to other kinds of pulsed actuation. For the derivation, the actuator body force termis introduced in the Navier-Stokes equations, from which the flow is locally approximated with a linear-time-invariant (LTI) system. The proposed semi-phenomenologicalmodel includes the effect of both viscosity and external flow velocity, while providing a system response in the frequency domain. Experimental data is compared with analytical results for a typical DBD plasma actuator operating in quiescent flow and in a laminar boundary layer. Good agreement is obtained between analytical and experimental results for cases below the model validity threshold frequency. These results demonstrate an efficient yet simple approach towards prediction of the response of a convective flow to pulsed actuation. Future application of the methodology might include actuation scheduling design and optimization for different flow control scenarios. The third study specifically addressing DBD plasma actuators presents a methodology to model the effect of DBD plasma actuators on airfoil performance within the framework of a viscous-inviscid airfoil analysis code. The approach is valid for incompressible, turbulent flow applications. The effect of (plasma) body forces in the boundary layer is analyzed with a generalized form of the von Kármán integral boundary layer equations. The additional terms appearing in the von Kármán equations give rise to a new closure relation. The model is implemented in a viscous-inviscid airfoil analysis code and validated by carrying out an experimental study. PIV measurements are performed on an airfoil equipped with DBD plasma actuators over a range of Reynolds number and angle of attack combinations. Balance measurements are also collected to evaluate the lift and drag coefficients. Results show the proposed model captures the magnitude of the variation in IBL parameters from DBD actuation. Additionally the magnitude of the lift coefficient variations (¢Cl ) induced by plasma actuation is reasonably estimated. As such, this approach enables the design of airfoils specifically tailored for DBD plasma flow control. Transitioning into ASCrotor design, and building on the previously presented, a methodology is introduced for designing airfoils suitable to employ actuation in a wind energy environment. The novel airfoil sections are baptized WAP (Wind Energy Actuated Profiles). A genetic algorithm based multiobjective airfoil optimizer is formulated by setting two cost functions, one for wind energy performance and the other representing actuation suitability. The wind energy cost function considers ’reference’ wind energy airfoils while using a probabilistic approach to include the effects of turbulence and wind shear. The actuation suitability cost function is developed for HAWT active stall control, including two different control strategies designated by ’enhanced’ and ’decreased’ performance. Two different actuation types are considered, namely boundary layer transpiration and DBD plasma. Results show that using WAP airfoils provides much higher control efficiency than adding actuation on reference wind energy airfoils, without detrimental effects in non-actuated operation. The WAP sections yield an actuator employment efficiency that is 2 to 4 times larger than obtained with reference wind energy airfoils. Regarding geometry, WAP sections for decreased performance display an upper surface concave aft-region compared to typical wind energy ’reference’ airfoils,while retaining common sharp nose and S-tail (characteristic aft-loading) features. Results show there is much to gain in designing airfoils from the beginning to include actuation effects, especially compared to employing actuation on already existing airfoils, which ultimately might pave theway for novelHAWT control strategies. Finally addressing the complete rotor planform design, an optimization study tailors a HAWT rotor to ASC operation, in a aero-structural-servo formulation. The study considers the aerodynamic and structural loads are in static equilibrium, and as such no unsteady effects are taken into account. The optimization includes planformgeometry design but also actuation scheduling, rated rotational speed and spanwise laminate skin thickness. Results show that, compared to variable-pitch turbines, ASC planform displays increased chord at inboard stations with decreased twist angle towards the tip, resulting in increased AOA. Actuation is employed to trim the (static) loads across the operational wind speed envelope and hence reduce load overshoots and associated costs. Comparing with state-of-the-art pitch machines, the expected COE of the ASC rotor does not indicate a significant decrease, but appears to be at least competitive with pitch-controlled HAWTs if the pitch system is effectively mitigated. Additionally, and though not explicitly considered in the present work, it is foreseen ASC might become interesting if the actuation system allows for further OM cost reduction via fatigue load-alleviation, since the actuation trimming load system is anyhow included in an ASC machine. @en

The airborne wind energy (AWE) technology aims to utilise tethered wings to harvest wind energy at altitudes conventional wind turbines cannot reach. There are two distinct methods to harvest airborne wind energy: onboard and ground-based generation. The onboard generation is achieved through flying fast manoeuvres driving propellers attached to the tethered wing, while the generated electricity is conducted through the tether. On the other hand, the ground-based generation utilises the tether tension of the kite to unwind it from a drum, driving a generator. When the tether is fully extended, it is reeled in by the generator, which consumes energy. Since the traction phase is a lot longer and produces a lot more electricity than electricity needed in the reel-in phase the net energy of such a cycle is positive. SkySails Power is one of the leading companies developing a ground-based AWE generator driven by a large ram-air kite. This thesis describes the development of a methodology for simulating their wing.@en

There is a growth in the energy consumption of the world, leading to rapid depletion of natural resources, such as fossil fuels. Added to that, the environmental impact of fossil fuels (e.g. global warming) makes a renewable source of energy a better alternative for power generation. Among renewable energy sources, generating energy from wind is becoming more popular. Although the number of, installed, wind turbines is increasing rapidly, there are still many challenges ahead for making the cost of generating energy from offshore wind competitive with other energy sources. One method for making the Cost of Energy from wind competitive is to reduce the operational and maintenance cost of wind turbines. The operational and maintenance cost of wind turbines may be reduced by eliminating, as much as possible, rotating components of the turbine which are prone to wear and tear. An alternative way to regulate power is to use stall control scheme, thereby eliminating the need to use the pitch mechanism. With recent advances in composite technology for tailoring the structural response of composite structures, it is possible to apply the technique to the conventional passive stall control scheme. Particularly, the use of twist coupling for regulating (passively) the angle of attack, thus also the torque and power of the wind turbine, shows a promise to design adaptive blades for stall regulated wind turbines, with improved performance in terms of power and load control, as well as in terms of cost reduction. Most of the research conducted so far investigates the benefit of twist coupled blades for power and/or load regulation; either based on a parametric study using few design variables or using simplified models for analysing the aeroelastic response of adaptive blades. In this thesis, a detailed optimization study is performed using variable stiffness laminates, to evaluate the potential of twist coupled blades to enhance the aerodynamic performance of stall controlled wind turbines. Furthermore, detailed structural and aerodynamic constraints are included in the optimization study, while using an analysis tool with sufficient complexity to accurately capture the aeroelastic response of twist coupled blades.@en

Vortex generators have become a ubiquitous sight on the modern wind turbine blade. These small, passive devices can increase the energy extraction potential of a rotor, but their subtle footprint disguises the technical difficulties associated with designing and integrating them onto wind turbine blades. The complexity of rotor inflow and the blade-bound flow present specific challenges for the design of vortex generators. Flow three dimensionality effects along the blades have conventionally been factored into design tools using correction factors for two-dimensional airfoil performance characteristics. However, the introduction of local perturbations in the form of streamwise vortices adds an additional layer of complexity. Indeed, the interaction of the vortex generator and flow three-dimensionality is ill-understood, and thus, so are its design implications. Furthermore, the passive nature of vortex generators means that a lot of variables influence their performance, making design optimisation a costly process. This thesis aims to improve the physical understanding of vortex generator physics in the context of wind energy applications, paving the way for more effective engineering tools. The objective is tackled by reviewing the state of the art, benchmarking existing tools and experiments, defining, measuring and simulating relevant test cases, and developing a new design tool. A measurement campaign is conducted in a boundary layer wind tunnel using non-intrusive PIV measurements for assessing the details and dynamics of streamwise vortices. A second measurement campaign maps the performance of the DU-97-W300 airfoil section with vortex generators in a conventional closed-loop wind tunnel. Inviscid vortex theory is employed for modelling vortex dynamics. Xfoil features throughout as a design tool and itself as the subject of an improved airfoil design tool incorporating vortex generators. @en