Message-ID: <Pine.SOL.3.96L.980411195300.27129A-100000@fox.ksu.ksu.edu> Date: Sun, 12 Apr 1998 10:43:42 -0500 From: kerryo <mailto:astingsh@ksu.edu> Subject: Re: Savonius rotor and water well To: mailto:DEVEL-L@AMERICAN.EDU
Hi Uwe,> ... one of my concerns is, how to pump water from a (to be drilled)
> well. As you can see from the subject line, I'm thinking about a
> Savonius rotor, connected to a pump with a vertical shaft.
>
I don't want to talk you out of rotors altogether, but the situation is more complex than you might think. As far as I know, shaft-driven pumps are likely to require much higher rpm than Savonius provides, even if all else is equal.
But a rotor of any size will reveal that its essential problem is that its one of three-dimensional dynamic balance (bad enough in ~2D: ever try to balance your own tires?) and the rectangular cross section of a cylindrical Savonius is made to order for a design that throws itself out of balance once its rotating.
Take the classic oil drum, cut it in half, fasten the halves to hubs (offset about a foot) and string it up on a shaft. Then wait and watch as it gets to rolling. The central space *open up* and youll be able to see the shaft - stoboscopically so to speak. What this tells you is that centripetal forces are deforming the surface -- in each vertical section, from a straight line to a catenary curve. Moreover, the distortion is different on the downwind side from the upwind side: i.e., the machine is *inherently* out of balance. Add to that the fact that the top bearing is never going to be as securely anchored as the bottom - Guy wires don't do it - and it's only a matter of time before something gives way, and the whole thing topples over (ruining your pump shaft in the process).
Now, having damped your enthusiasm, here's a possible solution: hang the axis *horizontally*.: both bearings are equally rigid (or floppy if you want to look at it that way) plus you can draw your power off from *both* ends. The axis is of course transverse to the prevailing winds. (Dont worry about omnidirectionality. That was S's big idea, because he thought it would work as a sail for water craft which go all directions - but when you find a place that has good consistent wind from all directions, let me know, OK?) The rotor will respond well to wind even 45 off-axis, in any case.
Secondly, since you're now bringing the power (by rocking wire, say) down to ground level, youre already well set to _offset the mill from the wellhead. That is, you can drill the well where the water is, and put the mill where the wind is - no small consideration ;-)
Finally, forget the drums; make your own windcatcher with (doubly) curved skins. Fabric over basketry is one way to at least approximate this, with the further advantage that when the wind finally takes it (nothing manmade yet that's put up against nature stays put forever) its only a few yards of cloth blowing into the neighbors yard rather than a serious piece of metal plate.
> Now, my questions are:
> - does anyone know where to get these pumps?
> - anyone knows an efficient and cheap design?
for shallow wells, consider a diaphram pump. With a bit of tinkering, you can make your own out of pipe fittings and inner tubing. (Getting it down a borehole might take a bit of study, if you're going below 4m or so, which I hope you are.)
> - how should I calculate the surface area of the rotor?
>
Savonious rotors are not terribly efficient, but the best _developmental way to proceed is to build a modest one, see what it will do, and go on from there.> Any help is greatly appreciated.
>
> Uwe
> (Uwe Bruenjes, mailto:uweb@megalink.net.mx, Calle 29 # 808, Chihuahua, Chih., =
> Mexico)
>
Hope this helps!kerry miller mailto:astingsh@ksu.edu