RoDaVi – a mixed drag-lift wind turbine: experimental investigation on performances and flows

In this paper, wind tunnel measurements are reported on a model of a novel vertical axis wind turbine (VAWT), which combines drag and lift contributions. The turbine is a modified Savonius rotor, which aims optimizing performances in medium-low wind regimes, by using a careful design of geometry and shape of the turbine. Specifically, it consists of a double helix, with conical shape, taking inspiration by “vite aerea” of Leonardo Da Vinci and here identified as RoDaVi (ROtor DA VInci). To this end, the dynamically scaled turbine model is tested in wind tunnel to derive mechanical and electrical power coefficients, in order to derive global performances, efficiency and best working conditions. Data are compared to those obtained using a conventional Savonius turbine in the same working conditions. Global performance results are also combined with instantaneous and averaged velocity fields obtained by means of Particle Image Velocimetry (PIV), which allows deriving near wake details and specific fluid flow phenomena. The parameters which are changed during experiments are the freestream velocity and the angle of inclination of the rotational axis of the turbine in respect to the axial direction. The proposed system is able to work with good performances (power coefficients in the range 0.2–0.3, depending on inclination angle), on an extended range of operative conditions, i.e. for tip speed ratios between 0.5 and 2.5, in comparison to the ranges 0.5–1 typical of a Savonius rotor. Motivations for the increased performances and working ranges reached by the proposed turbine are related to flow behavior in the wake as derived from detailed PIV velocity measurements.