Simulations of a rotor with active deformable trailing edge flaps in half-wake inflow: Comparison of EllipSys 3D with HAWC2

Various research projects have focused on active aerodynamic load control of wind turbines using control devices on the blades, for example flaps. The aerodynamic load predictions of utilized aeroelastic codes have not yet been fully validated with full rotor CFD or experimental results. In this study, a comparison between aerodynamic predictions of the aeroelastic code HAWC2 and the Navier-Stokes code EllipSys3D for the NREL 5MW reference wind turbine rotor in a stiff configuration equipped with a deformable trailing edge flap is performed.

A case where the half rotor plane experiences an inflow resembling the wake from an upstream wind turbine is investigated, which is appropriate for comparing the predictions of the two codes related to the abrupt aerodynamic response and the influence of the controllable flap. The trailing edge flap is actuated to alleviate the added loads from a non-uniform inflow mimicking a half-wake situation, using different control methods and maximum flap angles.

Three different control inputs are simulated: a prescribed flap angle based on the a priori knowledge of the inflow velocity, a controller based on the blade root flap-wise moment feedback, and finally a controller based on a Pitot tube velocity feedback measured at flap mid-span. Good agreement is found between EllipSys3D and HAWC2 in the prediction of the dynamic blade loads, considering the high complexity of the flow case.