Investigation of the theoretical load alleviation potential using trailing edge flaps controlled by inflow data

A novel control concept for fatigue load reduction with trailing edge flaps based on the measurement of the inflow locally on the blade was presented. The investigation was conducted with the aeroelastic code HAWC2. The aerodynamic modelling in the code is based on blade element momentum theory. The simulations were carried out for the NREL 5MW reference wind turbine, and the mean wind speed at hub height was 8 m s−1. The turbine was operated with fixed rotational speed. The energy at the blade is concentrated in spectral bands centred at multiples of the rotational frequency up to three times the rotational frequency. The highest fatigue load reduction was achieved when the inflow sensor was placed at the outer parts of the blade. In the best case, the reduction of the local fatigue loads induced by the blade sectional normal force was 60%. The control method gave the highest fatigue load reductions in conditions with strong wind shear. The demands for the flap actuator in terms of deflection angles was ±10°. The requirements in terms of the flap deflection velocity depend mainly on the inflow turbulence intensity. The maximum value was ±40°s−1 for 20% inflow turbulence intensity. Unsteady aerodynamic effects seem to be negligible.