Environmental Engineering Reference
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Figure 9-8. Signal scattering efficiency of scale-model HAWT blades compared to flat
metal plates.
[data: Sengupta and Senior 1978, 1980]
Figure 9-9. Signal scattering efficiency of a Darrieus VAWT blade compared to a flat
metal plate of the same planform area.
[data from Sengupta
et al.
1981b]
The airfoil and material factors, h
A
and h
M
, are the same as those for a HAWT blade and
are given in Equations (9-22b) and (9-22c). Equation (9-24) should be considered to be
preliminary until verified by scattering tests on Darrieus blades of other lengths.
Effective Number of VAWT Blades
Equation (9-20c) can be applied to VAWT rotors by assuming that coning angles are
determined by the angles between blade chords at the rotor equator. Thus, the coning angle
is zero for a two-bladed VAWT and 60 deg for a VAWT with three blades. In the infre-
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