A Preliminary Assessment of the Impact of Gurney Flaps on the Aerodynamic Performance Augmentation of Darrieus Wind Turbines

Gurney Flaps (GFs) can enhance the aerodynamic performance of airfoils, making them generate more lift and delaying the onset of stall. Since their potential was discovered in the early ’70s, GFs have been applied in several fields, including wind turbines. Here, the research has been focused mostly on the use of GFs in Horizontal Axis Wind Turbines (HAWTs), whereas a lack of studies involving the application of these devices on Darrieus Vertical-Axis Wind Turbines (VAWTs) is apparent in the literature. The benefits induced by GFs could actually be particularly interesting for this type of wind turbines, which are presently receiving a renewed attention from the industry. In the present study, the possible benefits of mounting GFs on a VAWT have been evaluated. The aerodynamic behavior of a single rotating NACA0021 airfoil equipped with different GF configurations has been investigated by means of unsteady CFD simulations. The effect of varying the size of the GF, as well as the different effects of this device at two different functioning regimes of the rotor were also analyzed. The results clearly suggested that properly-mounted GFs could notably improve the performance of a Darrieus VAWT (up to more than +20% for the 1-blade test case), especially at low tip-speed ratios.