My new VAWT

[paulc]

hello FOlks,

I went the scrap yard to look for some aluminum for a VAWT,  By the grace of God I the 3 pieces that you see in the mill pictures.

Each piece is 3' tall and has and the cupped end is 7" in diameter.  This gives the mill a an over all height of 36" by  19" almost a 2 to one ratio H to Dia.

The wood blocks that hold it together are made of Ironwood, but are not permanant.

The bearing at the base is actually a motor that turns very freely and does not cog at all.

I have a couple questions.  There was not much wind at ground level to day and the fastest it turned was about 80 RPM.

Here are the questions

1. do the top and bottom of the cups need to be covered?  I did this with duct tape and the mill seemed to turn faster.  Does the air just blow out the top and bottom of the cups if they are noy sealed?
   
2. In the picture Rotornut showed me there was no air space in the center of the of the mill. On mine there is.  COuld this be hurting me? Might sealing it off help efficiency?
   
   

To ne fair I need to get the mill up in the air, and add a top bearing and axle support,

3) I wondered if spreading out the cups would and supporting them by the center would help?  I have seen some built that way..

Please any comments good or bad would be appreciated

Thank you

PaulC

W1VLF

[electrondady1]

hey man, welcome to the party!! thats a nice three bladed drag unit you've made. the vane tips travel about the same speed as the wind. the wider you space them the more torque or leverage you get but the less rpm. and vice versa , the tighter to the center the faster it will spin. your probably right about the ends being covered. congratulations!

[RP]

PaulC,

Nice work!

1.  Yes the ends need to be closed for the reason you gave and it can be a simple disc the same diameter as the mill.  Hint, check discount store for cheap stainless steel pizza pans!
   
2.  As to the gap:  Consider that any wind that blows around the convex side of the upwind cup toward the axis simply leaks through the gap.  It COULD be caught by the concave side of the next cup and put to work if there was no gap.
   
   

For my Savonius I studied the Sandia labs papers (on the internet) and elected to go with a two blade rather than three and I overlapped the two cups by about 10%.  I believe the theory is that some of the air caught in one cup shoots around the inside of the S shaped overlap and jets out the other cup thus helping to push it forward as well.  In reality I suspect its a very complicated matter of vortex shedding, reynolds numbers and a whole bunch of calculus and differential equations but the simple theory is easier for me to get my arms around.  :-)

When you do a two blader like mine you have to stack two rotor sets with a 90° offset to smooth the output torque.  Its not so critical with the three blader.

Hope this helps

[rotornuts]

Hey Paul, nice score and nice job of setting it up. You'll be happy when you get a center shaft in there. If I were you I would keep the present layout exactly because to me for a three blade it looks good. The open center reduces pressure drag on the upwind blade by providing a source of air to feed the low pressure area behind the blade reducing the pressure differential and thereby reducing "pressure drag". Like RP siad a circular top an bottom plate would work very well in my opinion because of the added structural stiffness and it also reduces "induced drag" or drag caused by vortices of air created at the top and bottom as air "escapes" around the ends of the blades. My last suggestion I don't recommend doing without a long pause and a bit of a head scratch but I'll give the general idea. On my last two models I used a zigzag trailing edge for a few reasons two of which are a reduction in induced drag cause by long straight trialing edges and also this in my opinion also seems to help reduce "pressure drag"(it's a long story). I would hate to see you cut up those very nice chunks of aluminum so I'd save that for an experiment.

Good job and 80 rpm in not much wind at ground level with only a bottom bearing and duct taped ends is pretty good I'd say.

Have fun and if your into the experimenting keep it so you can try different configurations without too much trouble.(same end plates and bearings but maybe a two blader or different spacings on the three blader for example)

Mike

[windstuffnow]

  Nice work!  How does your genny work with it?

[Nando]

PAUL:

Good effort indeed !!.

The Cups need to interface with each other to gain ( in a 2 cups about 15 to 20 % additional power).

Using 3 cups I do not remember how much one can get additional power but it is a bit less.

Place an upper support or your generator bushing may not last or the shaft may bend with high winds.