Fast trailed and bound vorticity modeling of swept wind turbine blades

Passive load alleviation can be achieved through geometric bend-twist coupling, for example, by sweeping the blade backwards. The influence of the blade sweep on the trailing vorticity and bound vorticity is not modelled in the current fast aeroelastic wind turbine codes suitable for certification. A near wake trailed vorticity model which was coupled with a blade element momentum theory based aerodynamic model has been modified to take into account the blade sweep. The extended model is compared with the original near wake model, a blade element momentum (BEM) model and full rotor computational fluid dynamics (CFD) results for the modified IEA 10MW reference wind turbines. The steady-state loadings calculated from the extended model are in better agreements with CFD compared to the original model and the BEM for four different swept blades. It is also shown that the influence of the blade sweep on normal loading is not correctly modelled by BEM and this error will be inherited to the near wake model results. Thus, further modification to BEM will likely improve the predicted normal loading for swept blades, even if no near wake model is used. (paper)