Aerodynamic Enhancement of Vertical-Axis Wind Turbines Using Plain and Serrated Gurney Flaps

In light of the escalating demand for renewable energy sources, vertical-axis wind turbines have emerged as a pivotal technical solution for addressing the challenge of clean energy supply in residential and urban areas. As a simple and feasible passive control method, the plain Gurney flap (PGF) is widely applied to improve turbine aerodynamic performance. In this paper, the influence of a novel serrated gurney flap (SGF) with different flap heights is studied on the NACA0021 airfoil by numerical simulations. The findings demonstrate that, compared with the PGF, the SGF reduces the trailing edge reverse vortices from a pair to a single vortex and possesses lower drag. When the flap height reaches 6% of the chord (6%c), the lift-to-drag ratio of SGF surpasses that of PGF. A turbine rotor is equipped with an SGF and a PGF to compare their performances. The result confirms the flap effect depending on the rotor's tip speed. At a low tip speed ratio (TSR), the PGF works better than the SGF. The SGF is preferred over the PGF for a higher tip speed ratio (TSR > 2.5). With the 6%c flap height, the performance of the SGF rotor surpasses the PGF by 13.9% at TSR = 2.62.