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The Darrieus



The Darrieus is a pure buoyancy runner. Buoyancy runners are living by the fact, that the buoyancy always has a component in the direction of the movement.

Darrieus
Bild "Home:Darrieus.GIF"

At the Darrieus (named after the inventor) the blades of the rotor turn so fast, that the head wind is much higher than the real wind. Therefore the virtual wind changes two times the sides of the profile each circulation (therefore the Darrieus needs symmetric profiles), but it still remains in a window of about +20° and -20° towards the vector of the movement.

wind- and force-vectors
on a Darrieus profile

Bild "Home:anigif_Darrieus.gif"
animated picture

The picture above shows the principle. In the box is shown a turning Darrieus profile for a dormant observer (the wind comes form left). The picture shows a profile with a with-turning observer (that means the film of a camera that is fixed above the profile). Blue are the head wind and real wind, which vector-pike circulates on a circle, cyan stands for the virtual wind. Orange is the buoyancy force, it has two components: one in the direction of the movement (green) and one perpendicular (red) that only delivers a constraint force.


Advantages:
  • due to its symmetry the Darrieus in independent of the direction of the wind
  • because it uses the buoyancy the efficiency factor is OK.
  • less shadow

Disadvantages:
  • it cannot start by itself at upcoming wind
  • the buoyancy force pulses with each turning
  • extreme changes of the load; only a little component of the force is usable; the material must be very high tech and is therefore expensive
  • the profile on the lee side must go through the air turbulence caused by the profile on the windward side
  • animals have no chance; dead flies stick on the profiles and reduce the efficiency

So it is clear, that the Darrieus is more a plaything for freaks and not for the production of energy.

There is an attempt to improve the Darrieus by a misalignment of the profiles while turning. But this makes the Darrieus more interference-prone for just some percent more efficiency. And the Darrieus loses the advantage of being independent of the direction of the wind.

The Darrieus has an efficiency factor up to 40%. But this is not the chief thing. It is far more important how much surface a windmill holds in the wind! Because of the high needs towards the material this surface is very low at the Darrieus.


  • Bottom line: take the Tirajator, much better.