On the effect of blade deformations on the aerodynamic performance of wind turbine rotors subjected to yawed inflow

This work is aimed to investigate the effects of elastic blade deformations on the aerodynamics of large wind turbine rotors subjected to yawed inflow. Due to the increasing rotor size and advanced light weight blade designs, significant blade deflections can be observed on a regular basis for modern wind turbines. However, especially for complex flow situations like yawed inflow, the role of blade deformations is still not completely understood. In this paper, numerical simulations are conducted on the DTU 10 MW reference wind turbine to gain a better understanding of the involved phenomena. Results are obtained by two numerical methods of different fidelity. First, by the aero-elastic simulation tool FAST, which is based on the low fidelity Blade Element Momentum Theory (BEM) and makes use of common skewed wake correction models. Secondly, by a high-fidelity framework which couples the open-source Computational Fluid Dynamics (CFD) toolbox OpenFOAM with the in-house geometrically non-linear beam solver BeamFOAM. The evaluation of the results is based on the analysis of azimuthal variations of the sectional forces along the blade span and reveals a generally good agreement between the used numerical approach in terms of force amplitudes and variation phases. However, especially for cases of larger yaw angles, the BEM models clearly over-predict the variation amplitudes of the forces up to 40% in the outer blade part.