1 Wind Energy Division, Risø National Laboratory for Sustainable Energy, Technical University of Denmark2 Risø National Laboratory for Sustainable Energy, Technical University of Denmark3 unknown4 Department of Wind Energy, Technical University of Denmark
The problem of the aeroelastic stability of wind turbine blades is addressed in this report by advancing the aerodynamic modelling in the beam element type codes from the engineering-type empirical models to unsteady, 2D or 3D, Navier-Stokes solvers. Inthis project, structural models for the full wind turbine blade have been combined with 2D and 3D unsteady Navier-Stokes solvers. The relative disadvantage of the quasi-3D approach (where the elastic solver is coupled with a 2D Navier-Stokes solver) isits inability to model induced flow. The lack of a validation test case did not allow for quantitative comparisons with experimental data to be carried out; instead the results of the advanced aeroelastic tools are qualitatively cross-compared. Allinvestigated methods predicted qualitatively similar results. They all resulted in positive aerodynamic damping values for the flap mode, in a decrease in damping with the increase of wind speeds and in a minimum value for the damping for wind speedaround 15~m/s. The eigenvalue analyses resulted in steeper distributions for this mode. The agreement in aerodynamic damping decrease with the increase of wind speed is also observed in the distributions for the lead-lag mode. In perspective, theuncoupled, linear method results in higher values of aerodynamic damping compared to the 3D aeroelastic tool. The quasi-3D tool results in lower aerodynamic damping values in the higher wind speeds and in lower damping values in the lower wind speedregime. Apart from the computations for the full blade, 2D computations for the so-called “typical section” have been carried out. The 2D aeroelastic tools resulted in similar aerodynamic damping values. Qualitative agreement was better for the lead-lagmode. The presence of roughness tapes has a small, rather negligible impact on aeroelastic stability as depicted by the results of both aeroelastic tools. On the other hand, in conformity to the inability of the adopted computational model to successfullypredict the corresponding test cases under work package 2 of the project, the aeroelastic tools are not capable to predict the correct physical trends when the blade is equipped with stall strips. The resulting decrease in damping in the computations byboth tools is not in accordance with experience.