In a world in which climate change is at the centre of public debate, most of the CO2 emissions come from energy. Increasing attention is being paid to clean generation, and wind energy still represents one of the leading solutions. In this field, new trends raise new issues, which especially stem from the great dimensions of the wind turbines. Technological limitations force designers to deal with increasingly flexible blades and so the interaction between fluid and structure is expected to play a central role in the design process of wind turbines. The computational study of Fluid-Structure Interaction (FSI) will thus need refined modelling to obtain sound physical insights. The current project aims to propose a novel FSI model for wind energy applications, where the Large Eddy Simulation (LES) approach for fluid treatment is coupled with a modal approach for the study of the structural dynamics. In the proposed method, the Actuator Line Model (ALM) provides a representation of the rotor, as well as an interface between fluid and structure. Our approach is expected to start from a linear description of the blade motion to consider then the thorough motion of the blades, including torsion and other changes in airfoil orientation due to elastic deformation. This novel tool would be able to study complex inflows, wake and yawed operations that are critical for the wind turbines of the near future.
Implementing the method presented and performing coupled simulations, we will be able to carry out state-of-the-art wake and fatigue loads analyses that will take into account fully non-linear fluid dynamics. Moreover, to the author's knowledge, this would be the first work in literature to thoroughly assess the effect of the deformability of the structure on the performance and the flow features for a large modern wind turbine. In fact, Jonkman et al., 2005, Meng et al., 2018 and other derived works do not focus their analyses on the effect of the deformability on the flow field, but rather they concentrate on the effects of other factors such as atmospheric turbulence or structural design. Moreover, our code is able to model the presence of the tower and the nacelle by means of the Immerse Boundary Method (IBM), which can have important effects on the structural dynamics, such as tower shadowing (Santoni et al., 2017).
A successful implementation of the model could allow us to deal with several problems revealed by the literature and to include progressively additional complexity in the model. For example, many studies suggested that the adoption of a dynamic stall for FSI is fundamental to avoid non-physical results (Leishman & Beddoes, 1989). Besides, the use of a generalized rotor disk model is a well-documented strategy to simulate efficiently large wind farms in wake operation with advanced fluid solver. A two-way coupling that is computationally affordable could be the key to representing aeroelasticity in wake operation in wind farms. Furthermore, even with a standalone turbine, yawed operations could be considered. When the flow is not aligned with the horizontal axis of the wind turbine, loads are known to cause more fatigue, since they are high in module and highly non-symmetrical (Jiménez et al., 2010). Moreover, important wake modifications can occur, leading to performance drop.
In all these cases, an advanced aeroelastic model, with a sophisticated fluid solver, could offer interesting insights into physical phenomena that have important effects on the design of the wind turbines and even of the wind farms.