In the present thesis the wake flow behind wind turbines is analyzed numerically using large-eddy simulations. The wind turbine rotors are modeled by using either the actuator disc method or the actuator line method in which the blades are represented by body forces computed with airfoil data. Using these models, the boundary layers of the turbine blades are not resolved and most of the computational power is preserved to simulate the wake flow. The actuator disc method is used for the wake interaction studies of the Lillgrund wind farm. In this study the power production is simulated for two different wind directions and compared to measurements. A grid sensitivity study and a turbulence intensity study are also performed. As a last step the front row turbines are derated in an attempt to increase the total production of the farm. The results show that it is important to impose atmospheric conditions at the inlet in the simulations, otherwise production will be unrealistically low for some turbines in the farm. The agreement between the simulated and measured power is very good. The study based on derating the front row turbines does not show any positive increase on the farm production. The actuator line method is used for near wake analysis of the MEXICO rotor. In this study the near wake is simulated for five different flow cases and compared with particle image velocimetry (PIV) measurements. The analysis is performed by comparing size and circulation of the tip vortices, the radial and streamwise velocity distributions, the spatial expansion of the wake and the axial induction factor. The simulations and measurements generally are in agreement. In some cases, however, the measurements are affected by tunnel effects which are not captured in the simulations. In connection to the actuator disc method a power control strategy for operating conditions below rated power is implemented and tested. The strategy is first validated using an in-house developed blade element momentum code and then is implemented in the actuator disc method used in the EllipSys3D code. The initial tests show that the strategy responds as expected when changing the moment of inertia of the rotor and when varying the inlet conditions. Results from the implementation of the strategy in the actuator disc method in EllipSys3D show that the turbine adapts to the conditions it is operating in by changing its rotational velocity and power output when the inlet conditions are varied. / <p>QC 20130111</p>

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

When it comes to design a wind turbine rotor, several parameters have to be taken into account. The present work focuses on the inclination of the blades with respect to the rotor plane, namely the pich angle. The main goal of the project was to design a small-scale wind turbine rotor for wind tunnel tests and in this thesis the optimization of a first prototype is presented. The characterization of the performances was carried out by coupling two different approaches: an experimental and a numerical one. For the experimental part, a proper setup was built and the wind turbine model was tested in a wind tunnel. The results were compared with a Blade Element Momentum theory code developed in Python, that involved also CFD simulations to assess the aerodynamic properties of the blade sections. The analysis characterized the performances at variable collective pitch in terms of power and thrust coefficient, showing that the intitial blade design was not the optimal one. Therefore, the optimal pitch angle that maximize the power porduction was found for variable conditions. The second part of the experiments focused on the case of pitch unbalanced and the potential risks connected to it. As a result, the analysis demonstrated that any kind of pitch unbalance generates losses in the power production and may lead to a possible increase of the thrust. To compare the results, a modified BEM code was developed by assuming an axisymmetric axial induction factor. Finally, an additional analysis on the wind turbine oscillations was made, finding a connection between lateral vibrations and rotor unbalance and revealing the resonance frequency of the structure.

Wind energy is one of the most promising sources of renewable energy. Unfortunately, therapid growth in wind turbine technology is not equally at par with the improvement in itsreliability. Wind turbine systems tend to fail before their design life and hence result in asizeable amount of failure cost. A lack of reliable data has plagued the reliability and risk assessment of wind turbines in the scientific community. Many efforts have been made to estimate the failure probability of these systems and highlight the critical failure modes. However, there is a knowledge gap in quantifying the effect of the root cause of failure. This thesis work bridges this gap by developing a reliability analysis tool that quantifes the impact of a root failure cause, based on the resultant cost of failure. Furthermore, an attempt to quantify the importance of tribology in wind turbines is made. The model uses two independent reliability estimation methods - Fault Tree Analysis and Failure Mode and Effect Analysis. The two resulting approaches are used to prove the model's versatility and ease of adaptation of the model in the industry. Furthermore, with the inclusion of 'Reliability Influencing Factors', this model can calculate the overall potential economic gain from improving one or multiple properties of a component. The report then illustrates one of the industrial use cases of the model. With wind turbine gearbox as a representative assembly, tribology's quantitative importance is depicted against the Levelised Cost of Energy. It is concluded that a 2.5% decrease in energy cost can be achieved with just a 5% improvement in wind turbine gearbox tribology. / Vindenergi är en av de mest lovande källorna för förnybar energi. Tyvärr matchas inte den hastiga utvecklingen i vindturbinteknologi med en likvärding utveckling i dess pålitlighet. Vindturbinsystem tenderar att fallera tidigare än designats för, vilket resulterar i en betydande falleringskostnad. En avsaknad av tillförlitlig data har hindrat utvärderingen av påalitlighet och risk för vindturbiner. Många ansträngningar har gjorts för att estimera sannolikheten att dessa system ska fallera och att lyfta fram de kritiska fellägena. Däremot finns det en kunskapsbrist när det kommer till att kvantifiera effekten av den grundläggandeorsaken till fallering. Denna avhandling minskar denna brist genom att utveckla ett verktyg för pålitlighetsanalys som kvantifierar effekten av en falleringsorsak baserat på den resulterande kostnaden för fallering. Vidare görs ett försök att kvantifiera vikten av tribologi i vindturbiner. Modellen använde två oberoende metoder för estimering av pålitlighet - Fault Tree Analysis and Failure ode and Effect Analysis. De två resulterande angreppssätten används för att påvisa hur anpassbar modellen är och hur lätt modellen kan användas i industrin. Vidare, med inklusionen av 'Reliability Influencing Factors' kan modellen beräkna den övergripande potentiella ekonomiska vinningen från att förbättra en eller flera delar av en komponent. Rapporten illustrerar sedan en av de industriella användningsområdena av modellen. Med en vindturbins växellåda som representativt exempel påvisas den kvantitativa vikten av tribologi mot 'the Levelised Cost of Energy'. Slutsatsen dras sedan att en 2.5% minskning i energiförbrukning för konsumenten kan nås med endast en 5% förbättring av tribologin i en vindurbins växellåda.

The object of this thesis is to develop a cost effective direct-driven wind generator suited for offshore wind turbines. As the generator price is a complicated function dependent on many parameters, the emphasis is mainly put on reduction of the weight of active materials, such as copper, laminated steel, permanent magnets, and electrical insulation. The higher specific torque and power density of a transverse flux permanent magnet (TFPM) machine in comparison to conventional radial-flux machines make it a promising solution for direct-driven wind turbine generators. The novel TFPM generator investigated in this work due to its possibly more compact construction would allow a better utilization of the available nacelle space. The analytical model, including evaluation of the synchronous inductance, is developed and applied in parametric study of a 5 MW wind turbine generator. The influence of the design variables with respect to the analyzed characteristics is investigated. A number of machines that have approximately the same performances are found. These machines are compared and the optimal ranges for the main parameters are suggested. One possible design topology is presented in more details with dimensions and main characteristics. This generator is compared with radial-flux generators with surface-mounted and tangentially-polarized magnets. It is found that the analyzed TFPM generator would favor a smaller outer diameter, reduced total active weight, and reduced weight of the magnet material. The TFPM would however require a longer axial length. TFPM generators with a broader range of output power have also been investigated. Generators rated 3, 5, 7, 10, and 12 MW are analyzed and their characteristics with respect to the output power are compared. The novel transverse flux topology has been found to be promising for low-speed hightorque applications, such as direct-driven wind turbines in the multi-megawatt range. / QC 20101118