Winglets for wind turbines: an experimental study on aerodynamic performance and tip vortex behavior

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2017

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Ostovan, Yaşar

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This study experimentally investigated the effects of winglets on power performance and tip vortex behavior of two interacting similar model horizontal axis wind turbines. Power performance of both turbines positioned in-line was measured with and without winglets attached to the blade tips of the upstream turbine. Results showed that power coefficient of upstream turbine increased about 3% operating with winglets around rotor design TSR. Downstream turbine produced less energy while operating in the wake of the “wingletted” upstream turbine. However, the overall efficiency of two turbines increased with winglets. Trajectories of three vortex structures shed from three consecutive blades of the rotor were captured in Phase-locked PIV measurements covering 120 degrees of azimuthal progression of the rotor. The impact of using winglets on the flow field near the wake boundary as well as on the tip vortex characteristics were investigated. Results showed that winglets initially generated an asymmetric co-rotating vortex pair, which eventually merged together after about 10 tip chords downstream. Mutual induction of the initial double vortex structure caused a faster downstream convection and a radially outward motion of tip vortices. The wake boundary was shifted radially outwards, and velocity gradients were diffused. Vorticity and turbulent kinetic energy levels were significantly reduced across the wake boundary and within the vortex core. The vortex core sizes were tripled. Results showed consistency with various vortex core and expansion models. The estimated induced drag reduction was about 15% with winglets. Meandering analysis showed that the meandering amplitude increased as the vortices aged.

Subject Keywords

Wind turbines., Vortex-motion., Particle tracking velocimetry

URI

http://etd.lib.metu.edu.tr/upload/12621684/index.pdf
https://hdl.handle.net/11511/26979

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Graduate School of Natural and Applied Sciences, Thesis

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Citation Formats

Y. Ostovan, “Winglets for wind turbines: an experimental study on aerodynamic performance and tip vortex behavior,” Ph.D. - Doctoral Program, Middle East Technical University, 2017.