ABSTRACT
This book has hopefully provided an insight into wind turbine aerodynamics and aeroelasticity. To model the steady performance of a given wind turbine in order to calculate the annual energy production for an actual site, the classical steady BEM method has been outlined. The loads on a real wind turbine construction are, however, very dynamic, mainly due to gravity and the varying inflow conditions from wind shear, tower shadow and, not least, atmospheric turbulence. All the theory and equations needed to write an unsteady BEM code are given in this book, including all necessary engineering models, such as dynamic inflow, dynamic stall and yaw/tilt models. A method to build a structural model of a wind turbine construction has also been outlined in order to allow the calculation of the dynamic structural response of the different components when exposed to unsteady loads. The vibrations couple directly to the aerodynamic loads through the angle of attack since, when estimating the local velocities seen by the blade, the velocities from the vibrations must be subtracted from the wind speed. The aerodynamics and structural dynamics are therefore strongly coupled and comprise a so-called aeroelastic problem in which both models must be solved simultaneously in a time marching procedure. During an aeroelastic simulation the aerodynamic model must be solved many times (one time per time step) and a fast model is thus required. The BEM method is simple but very fast and will therefore very likely be used for many years to come. However, more advanced tools such as CFD (computational fluid dynamics) have made huge progress in recent years, not least due to advances in processor speed and storage capacity of modern computers.
