In the recent years, a renewed interest has arisen towards Vertical Axis Wind Turbines (VAWTs), due to their advantages in non-conventional installations, e.g. the built environment or off-shore floating platforms, with respect to the well-established horizontal axis architecture (HAWT). The main obstacle to their diffusion is currently represented by the lower peak efficiency achievable by these machines, when compared to their horizontal-axis counterparts; their complex and unsteady rotor aerodynamics in fact not only results in an overall performance penalty, but also hinders their proper design and optimisation. In such perspective, an attractive solution is represented by Power Augmentation Devices (PADs), i.e. auxiliary systems, either active or passive, designed to improve the control of the flow developing around turbine blades, as well as their aerodynamic performance. Among the various PADs under study, Gurney Flaps (GFs) stand out as one of the most interesting solutions to be implemented on VAWTs. These passive devices in fact, by altering the vortex pattern developing around the airfoil trailing edge, are able to increase the profile efficiency and resistance to stall, considerably improving the overall turbine performance at the low/medium tip-speed ratios.

Moving from this background, the research group is carrying out an extended numerical investigation of the effects of Gurney Flaps on VAWTs behaviour. High-fidelity 2D CFD simulations are being performed on both static and rotating profiles. For the purpose, the symmetric NACA0021 airfoil, typically used in VAWTs design, was chosen. In order to gain a better understanding of the device behaviour and eventually maximise its performance, several configurations, obtained by varying the flap length and its inclination with respect to the airfoil chord, are under testing and will be critically compared.

The scope of the research is to provide the scientific community with a deeper insight into the potential benefits offered by Gurney Flaps to VAWTs performance, possibly providing some guidelines for their design and optimisation.