“Experimental Assessment of the Effectiveness of Active Flaps to Reduce the Blade Root Bending Moment of Wind Turbine Blades”

Sammanfattning: This thesis intends to asses the application of local flow control to wind turbines blades, in order to demonstrate that the normal root benging moment on the blades can be reduced, with the aim of increasing wind turbines life span, reducing regular maintenance and further to make a contribution to current research on wind turbines. It develops the subject by first assessing the flow characteristics of the Großer Windkannal (GroWiKa) in the Hermann-Föttinger Institute (HFI) at the Technical University of Berlin and continues with establishing the effectiveness of local flow control on the Reasearch Wind Turbine (BeRT) designed by the institute. It is divided into six chapters; the first chapter gives an overview of the literature review required, to study the different methodologies used during the experiments. In following the different experimental set-ups used will be explained, which will lead to the presentation of the different characteristics of the flow into the settling chamber of GroWiKa, so that its effects on the wind turbine can be evaluated by means of pitot tubes and hot-wires. Chapter 4 reflects the different effects of blockage calculated during the experiments and its corrections for a blockage of 40%, while chapter 5 gives an overview on the system dynamics of the flaps, where three servos has been used and compared with each other, in order to give an assesment on its effectiveness for the rotative system. The final chapter analyses the normal bending at the blade root, by yawing the wind turbine and setting the flaps into a simple prescribe motion, in pursuance of creating a 1 period disturbance and show how the normal bending at the root of the blade can be reduced by the action of local flow control. To this end it was found that the servo system was not effective enough to respond to sudden changes in the flow field. However, it will be shown that after accounting for the servos delay, it is possible to reduce the blade normal to rotor plane root bending moment up to 31%, when the correct phase shift is applied to the flap’s prescribed motion.