This paper presents an investigation of the potential for reduction of fluctuating loads on wind turbine blades with the use of flaplike deflectable trailing edges. More specifically, the aeroelastic response of an elastically mounted airfoil section with a deflectable trailing edge is investigated. This is done by coupling a model for the aerodynamic forces on a deforming airfoil with a linear spring/damper model for the elastic deformation of a rigid airfoil to which the forces associated with the deflection of the trailing edge are added. The analysis showed that when the airfoil experienced a wind step from $10to12m∕s$ the standard deviation of the normal force could be reduced by up to 85% when the flap was controlled by the reading of the airfoil flapwise position and velocity, while reductions of up to 95% could be obtained when the flap was controlled by the reading of the angle of attack. When the airfoil experienced a turbulent wind field, the standard deviation of the normal force could be reduced by 81% for control based on measured angle of attack. The maximum reduction using a combination of flapwise position and velocity was 75%. The maximum deflection of the trailing edge geometry was, in all the considered cases, small enough to justify the use of a potential flow code for calculation of the aerodynamic forces. Calculations showed that the effect of a time lag in the actuators and sensors may drastically reduce the efficiency of the control algorithm. Likewise, the effect of a low maximum actuation velocity reduces the efficiency of the control algorithm. The analysis of the two-dimensional (2D) aeroservoelastic system shown in this paper indicates that the potential of using trailing edge flaps for reduction of fluctuating loads is significant.

This paper presents the design and experimental verification of the Risø-B1 airfoil family for MW-size wind turbines with variable speed and pitch control. Seven airfoils were designed with thickness-to-chord ratios between 15% and 53% to cover the entire span of a wind turbine blade. The airfoils were designed to have high maximum lift and high design lift to allow a slender flexible blade while maintaining high aerodynamic efficiency. The design was carried out with a Risø in-house multi disciplinary optimization tool. Wind tunnel testing was done for Risø-B1-18 and Risø-B1-24 in the VELUX wind tunnel, Denmark, at a Reynolds number of 1.6×106. For both airfoils the predicted target characteristics were met. Results for Risø-B1-18 showed a maximum lift coefficient of 1.64. A standard case of zigzag tape leading edge roughness caused a drop in maximum lift of only 3.7%. Cases of more severe roughness caused reductions in maximum lift between 12% and 27%. Results for the Risø-B1-24 airfoil showed a maximum lift coefficient of 1.62. The standard case leading edge roughness caused a drop in maximum lift of 7.4%. Vortex generators and Gurney flaps in combination could increase maximum lift up to 2.2 (32%).