now when I refer to the Savonius I am talking about those vawts with bucket-shaped vanes (essentially drag turbines, although there are certainly some lift characteristics in more advanced versions) that specifically direct the outgoing airflow onto the opposite vane, forcing it INTO the oncoming wind, as shown on the left,
as opposed to that on the right, which strangely enough seems to appear mainly in HAWT articles in a dismissal of VAWTs - shows how much they have thought about things - note the lack of the reverse-thrust effect.
A cut-down version as shown below left may be even more efficient , with perhaps the ultimate version being this Benesh profile , ( below right)
|Optimised Benesh rotor|
I havent found comparative data, although somewhere i have seen research that shows that a three-blade savonius is actually LESS efficient, contrary perhaps to expectations.
but before I go further, i thought that this furling savonius idea ingenious.
The Savonius type VAWT seems suitable for my planned application (mechanical pond pump) because of its low-speed, high-torque nature.
But electricity generation requirements move in the other direction, to high-rpm relatively low-torque designs, using lift-based aerofoil-blade designs (Darrieus type).
|Quiet Revolution helical turbine.|
Most of the latest machines, more than a few coming from China which seems to be where all commercial offerings are originating, use the same blade type in a simpler vertical arrangement of 3 and more blades, also known as a giromill.
I plan to investigate the giromill type further, if I get as far as an electrical pump, but for the moment I'll go with the Savonius types - more in the next post.