A two-way coupling method for the study of aeroelastic effects in large wind turbines

The relevant size of state-of-the-art wind turbines suggests a significant Fluid-Structure Interaction. Given the difficulties to measure the phenomena occurring, researchers advocate high-fidelity numerical models exploiting Computational Fluid and Structural Dynamics. This work presents a novel aeroelastic model for wind turbines combining our Large-Eddy Simulation fluid solver with a modal beam-like structural solver. A loose algorithm couples the Actuator Line Model, which represents the blades in the fluid domain, with the structural model, which represents the flexural and torsional deformations. For the NREL 5 MW wind turbine, we compare the results of three sets of simulations. Firstly, we consider one-way coupled simulations where only the fluid solver provides the structural one with the aerodynamic loads; then, we consider two-way coupled simulations where the structural feedback to the fluid solver is made of the bending deformation velocities only; finally, we add to the feedback the torsional deformation. The comparison suggests that one-way coupled simulations tend to overpredict the power production and the structural oscillations. The flapwise blades vibration induces a significant aerodynamic damping in the structural motion, while the nose-down torsion reduces the mean aerodynamic forces, and hence the power, yet without introducing a marked dynamical effect.