Aerodynamic upgrades of a Darrieus vertical axis small wind turbine

Wind energy conversion is contributing significantly to the new clean energy transition but, up to now, such contribution is mainly driven by large multi-MW windfarms. On the other hand, the recent needs in terms of distributed energy production are revealing a new interest in small-scale wind energy conversion technologies for residential and urban applications. In this context, vertical axis wind turbines (VAWT) are often the most valid choice from the point of view of building integrating possibilities, but it is well known that they suffer a considerable gap in performance when compared to horizontal axis technologies. Based on these premises, in the present work some innovative solutions for improving the performance of a Darrieus vertical axis wind turbine are investigated through numerical and engineering approaches. The investigated interventions include rotor hybridization by the use of an inner Savonius section for improving the machine's start-up and the possible application of dimples for improving the NACA 0021 airfoil performances on the outer rotor section. Results demonstrate the effectiveness of the interventions in obtaining a rotor with stable performances in a very wide range of wind regimes.