Wind turbine blades have significantly increased in length over the last few decades and are being operated in increasingly complex inflows such as the wake of other wind turbines or on floating platforms. This is increasing the unsteady and three-dimensional aerodynamic effects and the nonlinear structural dynamics that are neglected by the industry-standard Blade-Element Momentum and linear structural theories, respectively. In this dissertation, we employ Unsteady Vortex-Lattice Method for the aerodynamics and nonlinear Geometrically-Exact Beam Theory for the structural dynamics computations to describe these phenomena and their role on wind turbine aeroelasticity. We show that, Unsteady Vortex-Lattice Method fails to provide accurate drag estimation that we overcome with a semiempirical correction to include drag from steady-state tabulated data. We also show that, in cases of yaw, Blade-Element Momentum theory predicts accurate root-bending moments and rotor coefficients up to about ten degrees of yaw, for larger yaw angles, it over estimates the loads decay with the yaw angle. Furthermore, the interaction between radial sections of the blade under turbulent inflow is significant but not accounted for by Blade-Element Momentum theory so we study this phenomenon with Unsteady Vortex-Lattice Method and propose a correction to include the interaction between blade sections in Blade-Element Momentum theory that improves the prediction of loads along the span. We also reduce the computational cost of the Unsteady Vortex-Lattice Method by proposing a new wake discretisation scheme of the wake convection equation. We study the change in aerodynamic surface orientation in long flexible blades and conclude that capturing the twist degree of freedom is important for loads and power estimation. Moreover, we describe the influence of the platform pitch and roll motions in the unsteady character of the aerodynamic loads. Finally, we redesign the controller of the blade pitch to account for nonlinear structural dynamics and unsteady aerodynamics showing a reduction in the fluctuations of the main platform motions and energy production around the equilibrium position.Open Acces
