Winglet design for vertical axis wind turbines based on a design of experiment and CFD approach

• Published in: Energy conversion and management 2019-09, Vol.195, p.712-726
• Main Authors: Zhang, Tian-tian, Elsakka, Mohamed, Huang, Wei, Wang, Zhen-guo, Ingham, Derek B., Ma, Lin, Pourkashanian, Mohamed
• Format: Article
• Language: English
• Subjects: Aerodynamics; Blade tips; Computational fluid dynamics; Computer applications; Computer simulation; Design of experiments; Design parameters; Experimental design; Orthogonal experimental design; Power efficiency; Tip speed; Turbines; VAWT; Vertical axis wind turbines; Vortices; Wind power; Wind turbines; Wing tip vortices; Winglet design; Winglets
• ISSN: 0196-8904; 1879-2227
• DOI: 10.1016/j.enconman.2019.05.055

•The twist angle has the most significant effect on the winglet of VAWTs.•The winglet’s influence increases along the blade span towards the tip.•A winglet can weaken the tip vortex and enhance the power coefficient of the VAWT. Vertical axis wind turbines (VAWTs) have been attracting an increasing attention in recent years because of their potential for effectively using wind energy. The tip vortices from the VAWT blades have a negative impact on the power efficiency. Since a winglet has been proved to be effective in decreasing the tip vortex in the aerospace field, this paper numerically studies the aerodynamic effect of appending a winglet on the blade of a VAWT. Based on the theoretical motion pattern of the VAWT blade, this paper simplifies the three-dimensional full-scale rotor simulation to a one-blade oscillating problem in order to reduce the computational cost. The full rotor model simulation is also used in validating the result. The numerical approach has been validated by the experimental data that is available in the open literature. Six parameters are applied in defining the configuration of the winglet. The orthogonal experimental design (OED) approach is adopted in this paper to determine the significance of the design parameters that affect the rotor’s power coefficient. The OED results show that the twist angle of the winglet is the most significant factor that affects the winglet’s performance. A range analysis of the OED results produces an optimal variable arrangement in the current scope, and the winglet’s performance in this variable arrangement is compared with the blade without a winglet. For the single blade study, the comparison result shows that the optimal winglet can decrease the tip vortices and improve the blade’s power performance by up to 31% at a tip speed ratio of 2.29. However, for the full VAWT case, the relative enhancement in the power coefficient is about 10.5, 6.7, and 10.0% for TSRs of 1.85, 2.29, and 2.52, respectively. The winglet assists in maintain the pressure difference between the two sides of the blade, thus weakening the tip vortex and improving the aerodynamic efficiency of the surface near the blade tip.