Effect of winglet geometry on horizontal axis wind turbine performance

Abstract

Winglets (WLs) have recently been used to improve the performance of horizontal axis wind turbine (HAWT). The WL geometry is a key parameter for diverging blade tip vortices away from turbine blades and reducing induced drag. The present study focuses on the effect of winglet height (H) and toe angle ( w ) on the turbine performance. The performance of a three-bladed rotor of 1 m diameter with SD8000 aerofoil is numerically investigated using ANSYS 17.2 CFD on a polyhedral mesh. The model is hence validated by comparing results for power coefficient (C pw ) with experimental values available in the literature. Four different values of H are considered while keeping w constant at 0 • . H of 0.8%R is proved to be the best height for performance enhancement. It increases C pw by 2.4% at tip speed ratio = 7. The toe angle effect is studied for upwind and downwind WLs. The results show that C pw increases as w increases up to w = +20 • at all values of . C pw increases by 6% at = 7. Downwind WL always reduces C pw . The present results are well explained by the resulting vectors map near the blade tip. Using WL with the optimum H and w , causes 6% increase in C pw as compared to rotor without WL. K E Y W O R D SCFD, toe angle, wind turbine, winglet, winglet height INTRODUCTIONGlobal warming and fossil fuel emissions are the main drive and motivation for finding alternative sources of energy. Wind energy is one of the most viable alternative energy sources. It is expected to support the global electricity by more than 20% by 2030. 1 Many researchers have studied the aerodynamics behavior of the flow around wind turbines in order to understand the wind kinetic energy extraction by rotor. The flow around wind turbine is very complicated due to turbulence generation and vortices. Experimental studies need sophisticated measurements techniques and equipments. Verified numerical modeling has been widely used in order to better understand the flow within the turbine and in its wake.Blade Element Momentum Theory (BEMT) and Computational Fluid Dynamics (CFD) are the most common approaches that are used to calculate the aerodynamic forces. 2 BEMT is the basic theory of wind turbine blade design by combination between momentum theory and blade geometry. It solves set of equations at each blade element by balancingThis is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

CFD-based curved tip shape design for wind turbine blades

“…1. Many works (Hansen and Mühle, 2018;Khalafallah et al, 2019;Khaled et al, 2019;Mourad et al, 2020;Papadopoulos et al, 2020;Aju et al, 2020) are focusing on smaller turbines whereas only three other works (Kalken and Ceyhan, 2017;Matheswaran et al, 2019;Zahle et al, 2018) focus on larger MW turbines as is the case in the present study. Furthermore, as will be evident in Sections 2.2-2.3 there are few available actual optimizations whereas the majority of works are parametric studies and thus better performing tips could very likely be found in the vicinity of the selected parameter settings for these rotor configurations.…”

“…They find that both winglet length and cant angle are amongst the most important design variables for improving performance. Mourad et al (2020) use an initial literature survey covering 10 references to conclude that i) there is no agreement on optimum winglet configuration, ii) height is the most effective winglet parameter, and iii) that upstream directed winglet should be preferred over downstream configurations. Since they found no study covering toe angle, i.e., the angle of attack between tangential velocity component and winglet profile, they carry out a parameter study using height and toe angle as their two parameters.…”

“…The analysis showed that of the winglet heights ranging from 0.8-8.0 % d/R it was the smaller winglet height of 0.8 % d/R that gave the largest power increase. Furthermore, Mourad et al (2020) winglet is not useful for wind turbine rotors. The poor performance of the winglet with 8% height is not easily aligned with previously reported results by Gertz and Johnson (2011) and Gertz et al (2012) stating a 5% increase in power for that winglet height -albeit for different overall parametrization.…”

“…Flapwise displacement can also be found to be favoured slightly over sweep (Zahle et al, 2018, Fig. 4) but both are used heavily to displace the tip vortex in numerous works (Hansen and Mühle, 2018;Sy et al, 2020;Mourad et al, 2020). Few works also include twist and chord design variables for the winglet planform where the expected trends of a reduced chord distribution towards the tip and an initial increase in twist distribution followed by a sharp decrease at the very end of the blade can be observed (Zahle et al, 2018).…”

The Influence of Winglet Pitching on the Performance of a Model Wind Turbine: Aerodynamic Loads, Rotating Speed, and Wake Statistics

“…They reported that an optimized winglet design can improve the energy extraction as well as accelerate the recovery of turbulent kinetic energy in the wake by quicker tip vortex interaction. Mourad et al [31] computationally explored the effects of winglet geometry on horizontal axis wind turbines. They found that downwind winglets with toe angles from 10 ○ to 30 ○ can reduce power outputs compared to rotors with no winglets.…”