Environmental Engineering Reference
In-Depth Information
Vertical Axis Systems
Several vertical-axis concepts have been proposed for wind turbines that are driven by
lift forces, rather than the drag forces that turn a panemone. These include the
Darrieus
rotor
which has been the most successful, and this VAWT coniguration is discussed in the
following section. The
giromill
, another lift-driven vertical-axis machine, has been deve-
loped by several manufacturers. Giromills use straight vertical blades whose pitch angles
vary cyclically during rotation and are independently controlled. The 40-kW prototype built
and tested by the
McDonnell Aircraft Company
was discussed previously (Fig. 3-15). The
mechanical complexity of the blade support and pitch-change systems has usually prevented
giromill designs from being cost-effective.
An innovative VAWT rotor,
invented by Peter Musgrove at
Reading University in England,
is the
Arrow
coniguration
shown in Figure 3-18. This
prototype at Carmarthen Bay,
South Wales, is 25 m in
diameter and rated at 130 kW
[Musgrove and Clare 1987]. Its
vertical turbine shaft and a
horizontal crossarm form a
rotating “T”. Two blades are
attached to the ends of the
crossarm by struts, and each is
hinged at its mid-length. Below
the rated wind speed the blades
are vertical, but at wind speeds
above rated they are furled or
“reefed” to an arrow-head shape
by hydraulic actuators in the
crossarm. This reduces their
swept area and limits both the
output power and blade loads.
Figure 3-18. The 125-kW,
25-m diameter Musgrove
Arrow VAWT at Carmarthen
Bay, South Wales.
(a) Blades
vertical for maximum swept
area (b) Blades furled.
(Courtesy of
Vertical Axis Wind
Turbines Ltd.
)
(b)
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