Comparative Measurements of the Effect of a Winglet on a Wind Turbine
A 3.3 m diameter variable speed wind turbine and rotor has been designed, fabricated and tested with exchangeable blade tip capability. This rotor was custom designed utilizing the NREL S83X series airfoils for the University of Waterloo Wind Energy (UWWE
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Abstract. A 3.3 m diameter variable speed wind turbine and rotor has been designed, fabricated and tested with exchangeable blade tip capability. This rotor was custom designed utilizing the NREL S83X series airfoils for the University of Waterloo Wind Energy (UWWE) research facility with blades allowing the outer 10% of the blade to be exchanged. The winglet was found to have a bell-shaped power augmentation profile, with a broad peak between 6.5 m/s and 9.5 m/s where power was increased by 5% to 8%. These power augmentation figures matched closely with the findings in the literature that suggested increases of 2% to 8% are possible.
1 Introduction The designs of current horizontal axis wind turbine (HAWT) blade tips vary depending on scale but are for the most part simple shapes within the blade plane. Simple alterations to the standard tip have been found to produce desirable bending load alleviation[1]; out of plane shapes, such as the endplate and winglet, can possibly augment the power output. Studies on small-scale rotors have found that the power produced by a wind turbine can be increased by 4 to 9% using such devices [2, 3]. Computational studies have also been performed on large rotors (MW-scale), and predict that power can be augmented by 2 - 3% at such a scale [4, 5, 6, 7, 8, 9]. Three-dimensional effects are significant on real airfoils and rotating airfoils such as wind turbine blades where the production of a tip vortex reduces the lift and induces drag. The majority of effort on wing tip losses have been directed at aircraft wings, and altering the geometry of the tip changes the effect of tip vortices. A geometric description of a winglet is shown in Figure 1 and is defined by the cant angle, height, twist, sweep, toe, and is also influenced by the chord distribution or Drew Gertz · David A. Johnson · Nigel Swytink-Binnema Wind Energy Group, Department of Mechanical and Mechatronics Engineering, University of Waterloo, Ontario, Canada e-mail: {dpgertz,da3johns,nswytink}@uwaterloo.ca M. H¨olling et al. (eds.), Wind Energy – Impact of Turbulence, Research Topics in Wind Energy 2, c Springer-Verlag Berlin Heidelberg 2014 DOI: 10.1007/978-3-642-54696-9_18,
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Fig. 1 (left) Geometric definition of winglet (right) Winglet Geometry (Dimensions in mm)
planform (rectangular, tapered, elliptical, etc.), airfoil, and location (pressure or suction side of wing). Prior wind turbine winglet studies The majority of published studies on wind turbine winglets have been numerical in nature. The consensus seems to be that it is possible to augment the power production of a turbine using winglets by means of a reduction in induced drag and hence greater torque. Table 1 summarizes the relevant studies and their results. The winglet designs outlined differ greatly, but there are some general trends. The power augmentation due to the winglet, Paug , defined as the percentage change in the maximum power coefficient, has been predicted
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