Minimun speed for a savonius

[miglesia]

After my posts asking for a simple (the simplest) rotor, I've read that in low winds, a savonius is very disappointing.

That doesn't agree with articles like:

LINK

What are the real facts?

Thank you

Manuel

PD: Forgive if I make basic questions, but searching the site I can't find it

[vawtman]

Im thinking he was testing a hawt at ground level in swirling winds and they dont work there.His sav would win in that environment.Things havent changed much since then.Lets go boys.1974 fun year.

[thefinis]

The fact is that all wind machines have poor performance in low winds. It has to do with the wind power formula that has wind speed cubed in it. Even my old areomotor windmill had hard times in light breezes. It had to find the wind and then overcome the load(water weight and friction) to start turning. Just like most wind turbines once it started spinning it could keep spinning with less wind than it took to start it. That is one of the problems with light breezes if the wind dies to a point that the load is too great then the turbine stops and must wait for a gust to start it again even if the wind picks back up to where it was working before.

Anything less than 5 mph isn't going to do much work and around 10 mph is usually considered where you start having usable winds. For me enough wind to make it spin would make it interesting even if it did no work but I am easily entertained. I like the yard spinners made from square milk cartons or plastic bottles.

If all you are trying to do is make it lift water 3 meters then you can load it lightly and gear it down to where all it needs is enough wind to make it turn probably around 5 mph. Remember all factors in a wind turbine affect output. Wind speed is the most important factor but airfoil design, size, bearings, gearing, load, tower , trees, type of wind(gusty, turblent, smooth), etc. all affect it too.

Finis

[Kwazai]

I haven't put this one on a pivot yet, but I'm getting it to spin in only the slightest of breezes. (2mph +/- best guess).

http://www.fieldlines.com/story/2006/1/30/143452/124

L8r

Mike

[Bruce S]

Manuel;

   That is one of the on-going questions.

There are many answers and little to no current real facts. EXCEPT for Ed's VAWTs

Do a search for Eds diaries and read on. He's got some decent power coming out of these, and has done some real research into these.

Basically the "S" is more of a torque machine than high RPM. So if you build an "S" for low RPMs by say using setup gearing (Which is what MENS did) then you can make very good use of low wind speeds.

Norm on here constantly comes up with low winds devices and though they don't put out high numbers he's knows that. If like me, you can't put up so much as a 1 meter unit due to living in the city. These little beauties can be added.

The minimum speed? good question. I believe that would depend on what you build it out of, the size to capture enough to start it turning and what you want to do with it.

Cheers!

Bruce S

 

[ghurd]

Hi Manuel,

Ed goes by the name 'windstuffnow' and has a website under the same name. Excellent reading.

G-

[Norm]

   You're not going to be able to do too much

with a 3mph (wind?)...even a 6mph wind would

give you 8times the power but if you're lucky

enough to live where you can put up even a small

savonius.

   One step at a time ...put up little windmills

and observe where you're getting the most wind.

   A dozen little spinners charging a couple of

of AA rechargable batteries each....in the right

places is better than the best highest speed

savonius in the wrong place...It's more fun

too !  

   Yet to be tried is a 6x8 tarp diverting a

3 or 4mph wind against the downwind side of

a 3ft high x  4 inches wide 'spinner'

               (  :>) Norm.

[Norm]

   Something like this...



stacked 3 units high 60 degrees apart from each

other ....starts in the slightest breeze 2mph ?

spins very fast ....by using a threaded rod for

the shaft you can use the old threaded rod and nut

method to determine the rpm...about 10 or 15 AOL

disks stacked on the bottom make a good flywheel.

   Once it gets 'reved up', you grasp the nut

and see how far it travels in 10 seconds.

        Now wasn't that Fun ?

                  ( :>) Norm.

[viron]

There is an "optimum Savonius" (google those words and you should come up with a pdf file on the 3rd or so hit hit) that is not a drag motor.  It has a TSR of 1.8 and improved torque over previous Savonius designs.  That is still a far cry from TRS or 8 for a HAWT, but torque is good and it responds well in gusts.  The efficient as tested by NASA and UC-Long Beach is 40%.  Not bad!  I am planning on building one in a few weeks.  Right now I am trying to settle on alternator details.

For me I think it should work well.  I live in Merritt Island, FL  where the Kennedy Space Center is located.  My average windspeed is 8mph.  June thru August the wind is pretty dead except for big windys (hurricanes).  My GUESS is that the optimum Savonius will self regulate its speed after 35-40mph due to wing stall, which with a small diameter of 1.0-1.5 meters means I can use lightweight construction.  Brown foam and fiberglass.