Wednesday, 9 November 2011

Some Variations on the Savonius VAWT


Looking at the benesh rotor, it occurred to me that if I removed the flat parts, I could insert another rotor at right angles. This would look very much like that furling rotor design that I linked to in my first post, with the added advantage of the thrust from the exiting airstream that is a feature of the standard Savonius.

So the rotor would look like this (left)

and the airflow would  look like this (below; green arrows show rotational direction)

I set the blade offset as for the optimum offset for the Savonius, which has been shown to be between .15d and .2d, where d is the DIAMETER ie twice the radius, of the blade arc. The blades are 1/4 of a cylinder, so arcs are 90 degrees.

But wait, theres more! I further wondered what would happen if I removed the offset - see diagrams below

The orange arrows are my prediction of wind flow, with much less thrust on the far side of the flow, but that blue arrow shows the lift that I hypothesise would be generated.

SO I would expect pattern 2 to be inferior at low speeds but could it catch up and even surpass pattern 1 at higher speeds?  Only one way to find out - build 'em and measure!

Doing this lead me into new fields of measuring turbine rpm at various wind speeds.
Doesnt look like the wind powered pump will be going this summer  -apparently Lao Tzu said that a good traveller has no fixed plans and is not intent on arriving - I suspect that he would be more impressed by my journey than the missus.

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