Prediction of the unsteady aerodynamic characteristics of horizontal axis wind turbines including three-dimensional effects

An unsteady aerodynamic model for horizontal axis wind turbine performance prediction has been extended to consider three-dimensional (3D) rotational effects. The method couples a prescribed wake vortex scheme with a semi-empirical unsteady aerofoil model to provide the unsteady response of the blades due to the cyclic variation of incidence. The wake geometry of the turbine and the basic aerodynamic parameters required by the unsteady aerofoil model are calculated from the prescribed wake model using two-dimensional aerofoil data. The 3D rotational effects are then taken into account by a series of corrections to the unsteady aerofoil model. Application of these corrections has yielded substantial improvements in the prediction of aerodynamic force and moment coefficients on inboard blade sections. This is illustrated by a series of comparisons with field data. In general, the method is shown to give accurate predictions over a range of operating conditions and inflow angles.