Wind Energy

43 Aerodynamic Behaviour of a New Type of Slow-Running VAWT 237
Aerodynamic coefficients
0.45
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
C m
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8
Fig. 43.4. Aerodynamic performances of the conventional Savonius rotor [8]
model represented in Fig. 43.2. The three geometric parameters e, e ′ and θ
are selected for the numerical study.
The influence of the dynamic parameter, namely the Reynolds number
ReD, based on the rotor diameter D of the rotor, has also been investigated [7].
Only the influence of the overlap is presented in this paper.
The finite volume mesh obtained is about 50,000 cells large and made
of quadrilaterals. First-order discretisation schemes have been used for the
pressure and the velocity computations of an incompressible flow, together
with a high Reynolds number two equations turbulence model.
The calculations have been realised using a static calculation (rotor supposed
to be fixed whatever the wind direction θ) and also a dynamic calculation.
Only the static calculation is presented here.
43.4 Results
For the present calculation, the Reynolds number corresponds to the nominal
conditions for the prototype [6]: ReD = 1.56 × 10 5 .
43.4.1 Optimised Savonius Rotor
A static simulation of the flow around few Savonius rotors, allowed to determine
the pressure distribution on the paddles for different values of the wind
direction θ. (c.f. example on Fig. 43.5). Then the static torque is calculated as
a function of θ (Fig. 43.6).
The present simulation gives satisfactory results since the differences between
the numerical simulation and the experimental data [9] are inferior to
10% for most angles θ. The optimal value for the relative overlap ratio e/d
C p
λ