Design of wind turbine blades with respect to stability

Abstract: In the 21st century, wind power has emerged as a strong candidate in fulfilling societies goals of achieving carbon-free energy energy production. Windpower has evolved along with other technological developments, giving rise to larger turbines, but with the overall design trend remaining largely unchanged. Winfoor, a Swedish company based in Lund,aims to break that trend. With their new Triblade design, Winfoor hopes to change the way wind turbine blades. Here, the traditional single airfoil is replaced by three smaller foils, utilizing a truss system to retain structural integrity. The truss-design also allows for a modular assembly, as opposed to the traditional design which is constructed as a single piece. This allows for a simpler production(construction), transport and erection process. The design also has the potential to be significantly lighter than its conventional counterparts. This thesis studies the possibility of using steel as opposed to more conventional materials such as carbon and glass fiber reinforced polymers. Specifically, the stability of the structure with respect to global and local buckling is examined during hurricane-force winds, when the wind turbine is not producing electricity. Thepossibilityofimprovingstructuralstabilityusingcorrugatedbeamsisstudiedusingfinite element software, where a combination of linear and non-linear procedures is used. The impact of changes to the overall design, such as connection methods and distance between the blades, is also studied. The analysis consists of two parts; a linear buckling analysis of the structure, followed by a general static analysis of the structure under load, where the calculated buckling modes are applied as initial imperfections in order to capture any post-buckling behavior. From this thesis it was concluded that corrugated beams significantly improve the stability of the structure while also allowing for the use of steel, as opposed to more expensive conventional materials.