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The Savonius

The principle of the Savonius rotor as a resistance runner is like it is at the Persian Windmill. But here it is foregone to the shielding. Instead the profiles are aquiline. The resistance value of a ball or cylinder hull is low outside and high inside the hull. Therefore there is a difference between the pressure of the wind. This makes the Savonius (named after the inventor) turn round when the wind starts.

Savonius rotor
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archetypal version

Due to the movement in the direction of the wind the virtual wind is lower and also due to the movement against the real wind the windmill is braked. And therefore the Savonius rotor has an humble efficiency.

In its archetypal version the Savonius rotor has some other disadvantages. too. The sheets must be thick, the turning moment pulses, the rotor can stutter if wind slows.

Better are the open-Savonius and the Trivonius.

If the Savonius is closed there will always be some whirls in the hulls and whirls at a windmill lower the efficiency except at the Tirajator. At the open-Savonius and Trivonius the wind can pass the middle. Therefore the efficiency is higher.

A variation of the Savonius rotor is the hull anemometer.

hull anemometer
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It finds its usage as a measurement device for the windspeed.