Investigation of passive root flaps on HAWT

Abstract

Passive root flaps and in particular the Gurney flaps have been employed for improving aerodynamic characteristics for various applications since the 1970's. The effects of passive flaps on two dimensional airfoils have therefore been studied extensively, however, research on their application to Horizontal axis wind turbine blades (HAWT) is lacking and scarce. This research is a part of ongoing efforts at the Delft University of Technology to fill this missing gap. The blade of a HAWT is generally divided into three different regions for aerodynamic analyses. The region closest to the rotational axis is defined as the root region (r/R=0 - 0.3) . This region experiences the lowest rotational speeds and requires higher structural strength, resulting in a thick airfoil section. Although this section does not contribute significantly to the power generation of the whole turbine, the flow from this region does however effect the performance of the rest of the blade. Improving the aerodynamic flow characteristics of this region, therefore increases the performance of the whole turbine. For this research, passive (i.e. stationary) flaps were considered to enhance the flow at the root region and experimental analyses carried out at the Open Jet Facility (OJF) wind tunnel of TU Delft. An LM388 wind turbine blade (of Nordex N80 wind turbines) was used as a reference to create a scaled blade. The Analyses consisted of load (power and thrust) measurements and calculations for various flap configurations on a scaled wind turbine model. Furthermore, to understand how the flow is effected by the augmentation of flaps a Stereoscopic Particle Image Velocimetry (SPIV) was carried out for the most effective flap configuration and also no-flap configuration for the sake of comparison.