Wind Energy

306 L. Battisti et al.
57.2 Analysis of the Results
The investigation was focused on assessing the magnitude of the thermal
anti-icing power, varying the size and type (1, 2 or 3 blades) of the wind
turbine. In the latter case, the number of blades was changed keeping the
rotor diameter and solidity constant. Under such an assumption, the velocity
triangles change only because so does the Prandtl tip loss factor that explicitly
depends on the number of blades. The rotors used were generated by means
of a BEM code, which showed that for all the study cases considered, the
angle of attack ranged between 2 ◦ and 12 ◦ from the middle to the tip. The
environmental data reported in Table 57.1 were used to compute the anti-icing
heat flux requirement for the chosen rotors. A temperature of 2 ◦ Cwasseton
the blade’s outer surface to create a running wet condition over the external
heated surface.
57.3 Anti-Icing Power as a Function of the Machine Size
Four 3-bladed turbines with different rated power output were selected (see
Table 57.2). The heated spanwise length along the blade radius L, and the
width H of the heated zone are shown in Table 57.2.
Trials on ice accretion suggested keeping the same width of the heated
zone for all wind turbines. In fact as the turbines size decreases, the chord
length decreases as well, while the water collection increases. L corresponds
to the profiled length of the blade for all cases. The anti-icing heat flux qt,
averaged on the heated blade’s area, is reported in Fig. 57.1a. A larger heat
flux has to be supplied to the bigger rotors since the heated area lies close to
the leading edge where the heat exchange reaches a peak. Such a behaviour
is emphasized for blades working at high AoA since higher convective heat
exchange coefficient and water collection occur onto the blade’s surface. The
overall thermal power Qt = qt ∗ Nblades ∗ Aheated (Fig. 57.1b) increases with
the turbine size as a consequence of the increase of the area to be heated.
Table 57.1. Site variables used for the simulations
Ts ( ◦ C) T∞ ( ◦ C) p∞ (Pa) Rh (–) LWC (g m −3 ) MVD
Table 57.2. Turbine data used for a comparison of the anti-icing thermal power
with respect to machine size
Pr (kW) D (m) Z (–) Nr (rpm) Vr (m s −1 ) NACA airfoil L (m) H (m)
M1 726 40.76 3 33.21 12.5 44xx 16.1 0.32
M2 1,630 61.12 3 22.15 12.5 44xx 24.1 0.32
M3 3,668 91.68 3 14.76 12.5 44xx 36.2 0.32
M4 6,522 122.24 3 11.06 12.5 44xx 48.2 0.32