Environmental Engineering Reference
In-Depth Information
Figure 1: An example of VAWTs in the Sistan Basin in the border region of Iran
and Afghanistan. Note in the right hand image how the upstream wall is
used to expose only one half of the rotor to the wind (photographs taken
in 1971 near Herat, Afghanistan, copyright: Alan Cookson).
review articles have been published in the past detailing the historical development
of wind turbines of all types [1, 2]. Virtually all of these reviews suggest that the very
earliest wind turbines were indeed VAWTs and it is thought that these were fi rst
used in Persia for milling grain more than 2000 years ago. These early wind tur-
bines were essentially drag devices with a rotor comprising a number of bundles of
reeds, or other simple blades, on a timber framework. The rotor was housed within
a walled enclosure that channelled the fl ow of wind preferentially to one side of
the rotor thereby generating the torque necessary to rotate the millstone. This type
of device was still in use during the latter half of the 20th century and an example
located in the border region of Afghanistan and Iran is shown in Fig. 1 [3].
The Persian and Sistan VAWTs had rigid vanes to generate torque whereas
other designs have used sails that can effectively pitch with respect to their align-
ment on the rotor and thus can potentially increase effi ciency. An example of a
Chinese VAWT of the type used for many years for pumping applications, and which
was described by King [4] for pumping brine for salt production, is illustrated
in Fig. 2.
2.2 VAWT types
A wide variety of VAWTs have been proposed over the past few decades and a
number of excellent bibliographies on VAWTs have been published that sum-
marise research and development of these devices, including the survey by
Abramovich [5]. Some of the more important types of rotor design are highlighted
in the following sections.
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