Wind Energy

236 J.-L. Menet
Fig. 43.1. 3D representation
U
θ
d
e
e’
Fig. 43.2. Savonius rotor
U
θ β
e
e9
Fig. 43.3. Modified rotor
43.2 Description of the Savonius Rotors
The Savonius rotor is made from two vertical half-cylinders running around
a vertical axis (Figs. 43.1, 43.2).
A modified rotor (Fig. 43.3) is also studied, which is just an extrapolation
of the Savonius rotor, using three geometrical parameters: the main overlap
e, the secondary overlap e ′ , and the angle β between the paddles.
In the following, we name conventional Savonius rotor the one for which
the geometrical parameters e and e ′ are, respectively, equal to d/6 and 0. The
characteristic curves of such a rotor (values of the power coefficient Cp and of
the torque coefficient Cm towards the speed ratio λ) are presented in Fig. 43.4.
43.3 Description of the Numerical Model
The model used in this study is a mono-stepped rotor of infinite height. This
hypothesis has allowed to carry out the calculations on the two-dimensional