Savonius wind turbine
The turbine consists of a number of aerofoils, usually—but not always—vertically mounted on a rotating shaft or framework, either ground stationed or tethered in airborne systems.
[1][2] Europeans had earlier experimented with curved blades on vertical wind turbines for many decades.
The earliest mention is by the Bishop of Csanád County, Fausto Veranzio, who was also an engineer.
He wrote in his 1616 book Machinae novae about several vertical axis wind turbines with curved or V-shaped blades.
None of his or any other earlier examples reached the state of development achieved by Savonius.
He experimented with his rotor on various small rowing craft on lakes in Finland.
No results of his investigations are known, but the Magnus effect is confirmed[clarification needed] by Felix van König (1978).
[6] Looking down on the rotor from above, a two-scoop machine might resemble the letter "S" in cross section.
In practice, much of the swept area of a Savonius rotor may be near the ground if it has a short mount without an extended post, making the overall energy extraction less effective due to the lower wind speeds found at lower heights.
[7] According to Betz's law, the maximum power that is possible to extract from a theoretical ideal rotor is
However, in practice the extractable power is about half that[8] (one can argue that only one half of the rotor — the scoop co-moving with the wind — works at each instant of time) and depends also on the efficiency of the given rotor.
Most anemometers are Savonius turbines for this reason, as efficiency is irrelevant to the application of measuring wind speed.
Design is simplified because, unlike with horizontal axis wind turbines (HAWTs), no pointing mechanism is required to allow for shifting wind direction and the turbine is self-starting.
Savonius and other vertical-axis machines are suited to pumping water and other high torque, low rpm applications, and are not usually connected to electric power grids.
In the early 1980s, Risto Joutsiniemi developed a helical rotor (wiki:fi) version that does not require end plates, has a smoother torque profile and is self-starting in the same manner as is a crossed pair of straight rotors.
[citation needed] The most ubiquitous application of the Savonius wind turbine is the Flettner ventilator, which is commonly seen on the roofs of vans and buses[where?]
This rotor was developed for ventilation by the German aircraft engineer Anton Flettner in the 1920s.
[11] Specifically constructed Savonius wind turbines have been used to provide power to autonomous neutrino detector stations of the ARIANNA experiment on the Ross-Ice Shelf in Antarctica.
[12] In Europe, small Savonius wind turbines can sometimes be seen used as "animated" advertising signs in which the rotational movement helps to draw attention to the item advertised.
