savonius wind turbine

Savonius wind turbine

Savonius wind turbineFrom Wikipedia, the free encyclopedia

Savonius wind turbines are a type of vertical-axis wind turbine (VAWT),used for converting the force of the wind into torque on a rotating shaft. Theturbine consists of a number of aerofoils, usually—but not always—verticallymounted on a rotating shaft or framework, either ground stationed ortethered in airborne systems.

Contents1 Origin2 Operation3 Power and rotational speed4 Use5 Tethered airborne Savonius turbines6 Gallery7 References8 External links

OriginThe Savonius wind turbine was invented by the Finnish engineer Sigurd Johannes Savonius in 1922.However, Europeans had been experimenting with curved blades on vertical wind turbines for many decadesbefore this. The earliest mention is by the Italian Bishop of Czanad, Fausto Veranzio, who was also anengineer. He wrote in his 1616 book Machinae novae about several vertical axis wind turbines with curvedor V-shaped blades. None of his or any other earlier examples reached the state of development made bySavonius. In his Finnish biography there is mention of his intention to develop a turbine-type similar to theFlettner-type, but autorotationary. He experimented with his rotor on small rowing vessels on lakes in hiscountry. No results of his particular investigations are known, but the Magnus-Effect is confirmed byKönig.[1] The two Savonius patents: US1697574 (https://www.google.com/patents/US1697574), filed in 1925by Sigurd Johannes Savonius, and US1766765 (https://www.google.com/patents/US1766765), filed in 1928.

OperationThe Savonius turbine is one of the simplest turbines. Aerodynamically, it is a drag-type device, consisting oftwo or three scoops. Looking down on the rotor from above, a two-scoop machine would look like an "S"shape in cross section. Because of the curvature, the scoops experience less drag when moving against thewind than when moving with the wind. The differential drag causes the Savonius turbine to spin. Becausethey are drag-type devices, Savonius turbines extract much less of the wind's power than othersimilarly-sized lift-type turbines. Much of the swept area of a Savonius rotor may be near the ground, if ithas a small mount without an extended post, making the overall energy extraction less effective due to thelower wind speeds found at lower heights.

Savonius wind turbine - Wikipedia, the free encyclopedia https://en.wikipedia.org/wiki/Savonius_wind_turbine

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Schematic drawing of atwo-scoop Savonius turbine

Combined Darrieus-Savonius generator inTaiwan

Power and rotational speedThe maximum power of a Savonius rotor is given by , where andare the height and radius of the rotor and is the wind speed.

The angular frequency of a rotor is given by , where is a dimensionless factor called the

tip-speed ratio. The range λ varies within is characteristic of a specific windmill, and for a Savonius rotor λ istypically around ≈1.

For example, an oil-barrel sized Savonius rotor with h=1 m and r=0.5 m under a wind of v=10 m/s, willgenerate a maximum power of 180 W and an angular speed of 20 rad/s (190 revolutions per minute).

UseSavonius turbines are used whenever cost or reliability is much more importantthan efficiency.

Most anemometers are Savonius turbines for this reason, as efficiency isirrelevant to the application of measuring wind speed. Much larger Savoniusturbines have been used to generate electric power on deep-water buoys, whichneed small amounts of power and get very little maintenance. Design issimplified because, unlike with horizontal axis wind turbines (HAWTs), nopointing mechanism is required to allow for shifting wind direction and theturbine is self-starting. Savonius and other vertical-axis machines are good atpumping water and other high torque, low rpm applications and are not usuallyconnected to electric power grids. They can sometimes have long helical scoops,to give smooth torque.

The most ubiquitous application of the Savonius wind turbine is the FlettnerVentilator, which is commonly seen on the roofs of vans and buses and is usedas a cooling device. The ventilator was developed by the German aircraftengineer Anton Flettner in the 1920s. It uses the Savonius wind turbine to drivean extractor fan. The vents are still manufactured in the UK by Flettner Ventilator Limited.[2]

Small Savonius wind turbines are sometimes seen used as advertising signs where the rotation helps to draw


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Wikimedia Commons hasmedia related to Savoniuswind turbines.

attention to the item advertised. They sometimes feature a simple two-frame animation.

Tethered airborne Savonius turbinesAirborne wind turbinesKite typesWhen the Savonius rotor axis is set horizontally and tethered, then kiting results. There are scores ofpatents and products that use the net lift Magnus-effect that occurs in the autorotation of the Savoniusrotor. The spin may be mined for some of its energy for making noise, heat, or electricity.

Gallery

Operation of aSavonius turbine

A Savonius rotorbladed WECS

ReferencesFelix van König (1978). Windenergie in praktischer Nutzung. Pfriemer. ISBN 3-7906-0077-6.1.Flettner (http://www.flettner.co.uk/home.htm)2.

External linksBuild your own model Savonius wind turbine (http://www.re-energy.ca/wind-turbine)Windside Savonius Type Wind Turbines for use in ExtremeEnvironments (http://www.windside.com/)Forgen low power Savonius Type Wind Turbines for Marine Applications(http://forgenrenewables.com/buy-products/wind-turbines/vertical-axis/)HelixWind Savonius Type Wind Turbine (http://jason.wells.me/blog/?page_id=722)Savonius turbines for dynamic environments www.spinpower.org (http://www.spinpower.org)How to build a Savonius wind generator (http://www.amics21.com/laveritat/savonius_generator_english.pdf)

Notions of Wind Energy for the Complete Idiot (http://www.amics21.com/laveritat/notions_of_wind_energy_for_the_complete_idiot.pdf)

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Categories: Vertical axis wind turbines Finnish inventions


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savonius wind turbine

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