Numerical performance assessment of an innovative Darrieus-style vertical axis wind turbine with auxiliary straight blades

Vertical axis wind turbines (VAWTs) are receiving growing interest for small scale power generation at low wind speed condition, in particular for off-grid, home applications. VAWTs are mainly composed of two typologies: drag-based Savonius, and lift-based Darrieus turbines. Between the two, the Darrieus turbine is the most promising since it is characterized by higher efficiency, even if for applications at higher wind speeds with respect to Savonius VAWTs. A lot of research is made in order to enhance the aerodynamics of the Darrieus rotors, making them applicable for lower wind speeds without significantly affecting efficiency. One of the developments of standard Darrieus configuration is proposed in our previous paper, adopting three couples of blades for the rotor, each composed by a main and an auxiliary aerofoil. A scaled model of such rotor configuration is tested in the wind tunnel available at the Department of Civil and Mechanical Engineering (DICEM) of the University of Cassino, showing good performances in terms of power and torque coefficients, especially at the lower wind speeds. In the present paper, a Reynolds Averaged Navier-Stokes-based CFD model is used in order to investigate the performance of an innovative, real scale double-bladed wind turbine. The CFD model is validated on the basis of the wind tunnel data, and the real scale wind turbine performance is analysed by numerically evaluating the power and torque coefficients. The results of the simulations confirm the capabilities of the proposed configuration to give valuable performance even for wind speeds below 4 m·s-1