Semi-empirical Methods for the Analysis of Vertical Axis Wind Turbines with Helical Blades

The Vertical Axis Wind Turbine (VAWT) was not successful for large size installations but it is suitable for small size applications. It is likely to integrate better in an urban environment due to its architectural features and its intrinsic capability to exploit winds from any direction without an orientation system. The performances of these machines can be evaluated with enough accuracy by means of the semiempirical models that allow to explore various configurations in a straightforward way. They need the support of experimental investigations for aerodynamic coefficients and they have to refer to a limited class of airfoils. However they can be matched with CFD tools usefully to enlarge the field of investigation keeping the above advantages. In the paper the performance of the H type (giromill) configuration as well as of the helical rotors are calculated and compared. The latter geometry has received recently a special attention on account of some aspects that are discussed.