Impact of rotor size on the aeroelastic behavior of large turbines: a LES study using flexible actuator lines

This paper investigates the impact of rotor size on the structural displacements and loads of large wind turbines during power production. The actuator line method is used in Large Eddy Simulations and is coupled to a structural solver for the blades. The latter consists either of a linear solver based on the Euler-Bernoulli beam theory, or uses BeamDyn to account for the non-linearities. The effects of upscaling are investigated for three reference wind turbines of various sizes: the NREL-5 MW, the DTU-10 MW and the IEA-15 MW. The study reveals that the larger turbines exhibit higher bending relative to the radius and a significant torsion angle. The torsion angle is primarily linked to the structural non-linearities and substantially affects the mean blade loads of the largest turbines. Consequently, the power and thrust coefficients predicted using the linear structural model differ from those obtained using BeamDyn. However, the variations of the root bending moments are predicted similarly using both structural solvers; also suggesting that a linear structural solver is still sufficient for the fatigue analysis. Finally, the fatigue analysis is extended to the shaft loads due to the entire rotor, and empirical scaling trends are derived.