Test of an active flap system on a 4.3 MW wind turbine

This article describes a field test performed on a 4.3 MW wind turbine with one blade equipped with an active flap system. The results presented focus primarily on the steady state and periodic characterization of the active flap system in different deflection states. The tests were performed between 2020 and 2021 on a test turbine in northern Denmark in close-to-shore conditions. The active flap system is primarily characterized based on the load response of the flapwise bending moment of the blades. Flap actuations are performed both as open-loop on-off swaps (shifting between two different flap positions at fixed time intervals) and as closed-loop 1P activations (cyclic activation of the flap both in phase and counterphase with the blade azimuthal position). For the steady state swap tests, the impact on flapwise bending moment ranges between 3% and 20% depending on the flap actuation level and the wind speed. For the cyclic flap tests, the load impact is based on blade-to-blade fatigue load comparison, showing a potential load reduction of approximately 13%.