Load Reduction of Wind Turbines Using Trailing Edge Flaps

Abstract

Horizontal axis wind turbines have become an attractive renewable energy source due to their low carbon foot print. It was the aim of this study to reduce fatigue inducing variations of the blade root bending moment and thus enable the construction of lighter structures which further reduces the carbon footprint. Within the Smart Blades project the IWT-7.5-164 wind turbine has been used to investigate the feasibility of using trailing edge flaps as active control mechanism for load reduction. The analysis has been conducted using the German Aerospace Center’s in-house comprehensive rotor simulation code S4 to simulate the aerodynamics as well as the structural deformation. For a tilted rotor without flaps the blade root bending moment acting perpendicular to the rotor plane has been observed to undergo a characteristic cyclic variation due to the tilt and gravity. Adding trailing edge flaps with a constant deflection alters the mean bending moment of the cyclic variation. A following study addressed the effect of using a sinusoidal flapping motion for a range of flapping amplitudes and phases. As a result a configuration has been identified that eliminates the cyclic variation of the blade root bending moment.