Author Topic: 2 cylinder VAWT (Read 12658 times)

rotornuts · « **Reply #33 on:** June 09, 2005, 11:28:37 PM »

I did these up the day I made the model.

streamlined version

Two blade large cord

Three blade large cord

I think the evolutionary process has begun. I'm just trying to remember deadly simplicity was one of my motivations. I tried the two cylinder without the flaps and it only work in high winds so the flaps stay for sure so I guess whether it's two or three some streamlining is in order.

I will say though that at first my flaps were an inch and a half longer and it worked better after I cut them down so a wide(large)cord may not be the answer. I guess we'll see. At the moment 'I'm thinking the three blader with a narrow cord.

Mike

XRay · « **Reply #34 on:** June 10, 2005, 12:44:25 AM »

Good morning to you Mike,

Creating eddies introduces drag (no free ride). Because this drag part in one side of the cylinder (one trip wire) the drag component is unbalanced, creating more startup torque.

Maybe you can lose those flaps!

Including a Lenz separates the cylinders making the rotor diameter bigger increasing torque:

Ray

XRay · « **Reply #35 on:** June 10, 2005, 12:56:51 AM »

O jee, me like the streamlined version.

The others look like my old paper models, only the cannels are a bit narrow. Remember I ended up making a Ropatec rotor.

He they look like negative scoop-rotors to, maybe thats positive.

Greetings,

Ray

Kwazai · « **Reply #36 on:** June 10, 2005, 06:45:28 AM »

how bout one that could be cut out of a drum with a tube or trapezoid in the center (darieus?savonius?

) the outer edge of the drum is already a foil of sorts. The problem with the darrieus ,they way I understand it, is self starting and they have added a savonius to get it started. from a practical standpoint- I'm thinking two concentric circles- the outer one with the foils cut in it, the inner one with an offset set of foils-darrieus outside, savonius inside?

forgive my rambling...

electrondady1 · « **Reply #37 on:** June 10, 2005, 07:00:41 AM »

about twenty years ago there was a fad around here. every retired guy had a bunch of bleach containers cut up and spining on there front yard some guys had dozens of them. thats what got me thinking about wind power in the first place.how about a version of this design on every lanp post . how about one on every fence post in a farmers field. these little vawts work and are almost indestructable. the problem for me is to scale down a pmg enough to be compatible with the torque the mills generate.carry on roto your doing good work!

XRay · « **Reply #38 on:** June 10, 2005, 07:52:38 AM »

Hey electrondady1,

Cool idea, placing one on every fence post in a farmers fields.

Use the barbwire to conduct the current. I wonder what happens when lightning strikes on one of the fence post. :-o

Ray

electrondady1 · « **Reply #39 on:** June 10, 2005, 07:58:34 AM »

i beleave that's when the magic smoke escapes!!

windstuffnow · « **Reply #40 on:** June 10, 2005, 07:59:10 AM »

The first diagram above looks better, I think the more you close off the air flow between the blades the more the pressure will increase as wind speed increases turning the turbine into a solid round cylinder. This could defeat the power production. I might be overlooking something but that's the way I see them.

For a drag machine the 1/2 cylinder produces the highest downwind Cd of around 2.3, unfortunately the upwind side sees a Cd of around 1 so just under half of the power gained is lost to drag on the upwind side. A drag machine extracts its highest power at around a TSR of .33, although, it will continue to produce power up to a TSR of around .7-.8 and after it reaches a TSR of 1 there is no longer any power extraction. Once you exceed the TSR of 1 your dependant on extracting power primarily from the upwind side as lift although the downwind side will add to that somewhat. The faster its spins the better. There is alot of energy that can be extracted in the upwind side, for instance if the machine is in a 15mph wind and the rotor is traveling at a TSR of 1 the upwind blade sees 30mph winds, the downwind see's nothing and is just along for the ride. The big trick is to get the machine running above 1 and preferably 2 or higher where you can start collecting from both sides as well as front and back. That's the big advantage the HAWT's have over the VAWT's. The original idea of the Lenz turbine was to cancel the upwind side drag by using lift allowing the full extraction of the downwind side. Once I realized there was more power on the upwind side I headed in that direction but only was able to get it to a TSR of around 1.7 so the downwind side still has problems adding much to the extraction. I wasn't completely satisfied with the results although what I ended up with was a reasonably efficient VAWT with good start up torque. It still has to be proven in winds above 12mph which is the limit to my home brewed wind tunnel.

I think mike is on to something and hopefully will surpass the results of my turbine... I agree with mikes statement of keeping it dangerously simple also...

Great work mike! I'm following your project with great expectations. If I wasn't so busy right now I'd be building one to test myself!

Hav eFun

Windstuff Ed

wildbill hickup · « **Reply #41 on:** June 10, 2005, 08:05:13 AM »

I'm going to try a 3 blader with a couple of ideas of my own. I'll let you know how it turns out. Question to any of the folks that calculate things I don't even begin to understand. Based on roto's very first drawing. With 8" total dia., if I use 3" dia tubes, 2 feet long,and the wings are 3" wide and 2' long of course, can anyone come up with a swept area figure or would that be hard to apply in this case. I'm trying to come up with some rough ideas on power output(at say a 10MPH wind) it'd great to get 50-100 watts to start. My plan is to mount it on a ametec PM motor and see what happens.

Thanks

Wildbill

XRay · « **Reply #42 on:** June 10, 2005, 08:13:47 AM »

I think if you want to use a drum effectively just make a Savonius its also the most easiest windmill to make.

Myself was thinking about a combination Darrieus Savonius but then the Savonius placed on one site of the roof ridge electrically kick starting the Darrieus placed on the other side of the ridge.

Greetings,

Ray

kitno455 · « **Reply #43 on:** June 10, 2005, 08:23:30 AM »

bill- swept area of a vawt is how big it looks from the front if it was a solid cylinder- in your case, its 2 feet tall and the disks are 8 inches across. that looks like a rectangle 2 x .67 feet, or 1.33 square feet.

allan

rotornuts · « **Reply #44 on:** June 10, 2005, 08:34:09 AM »

Morning Ed. I believe your feelings about the solidity of the center are correct. Of the above three images I think only the top one is practical. The lower two were done before I constructed the first model and I have since learned that a shorter flap/cord worked better. I'm considerind what may happen if I added a third cylinder to the top drawing but I'm also afraid it may confuse the airflow through the center. The only thing that is directing the air the right way is the interaction between the two cylinders and I can visualize but not say for sure what will happen with three.

I would also agree but can't say definitively that the center should be left open and if I could with such a small fragile model I'd eliminate the rod through the center as well.

I'm off to try a three cylinder model

Mike

kitno455 · « **Reply #45 on:** June 10, 2005, 08:38:00 AM »

ok, this is maybe a crazy idea, but what if the 'lenz' shape in the middle was shaped more flat, and its angle was controlled by a tail, instead of it rotating. then it may be possible to use more cylinders or airfoils, and not have them disturb each other as much?

allan

monte350c · « **Reply #46 on:** June 10, 2005, 08:57:14 AM »

Hi All,

Would it be a stretch to compare the 2 cylinder model to Ed's 700 rpm coffee can?

It looks like there is something interesting going on when the two cylinders or wing shapes are fairly close to each other. Ed mentioned in a post on the Lenz turbine a while back that the effect disappeared when he up-sized the unit and the two wings became further apart.

Sandia Labs did an extensive set of tests on 2 and 3 bucket Savonius machines, that included varying the center gap. There are locked rotor torque measurements taken at various angles of rotation, in numerous configurations.

http://infoserve.library.sandia.gov/sand_doc/1976/760131.pdf

There's an interesting read about a 5 meter Darrieus unit:

http://infoserve.library.sandia.gov/sand_doc/1980/800179.pdf

and some info on torque ripple in VAWT's:

http://infoserve.library.sandia.gov/sand_doc/1978/780577.pdf

Obviously not exactly pertinent to this new design but some of the ideas might work when put together. Like torque output at various points in rotation. Perhaps the venturi effect could be applied where needed in the rotation, ie with some stationary elements that end up at 3 and 9 o'clock and yaw to remain in those places with varying wind direction. As Ed pointed out, things are pretty good in VAWT's at the front and back, but the upgoing blade can use some help. I did a bunch of playing around with lift type VAWT's and the TSR seems to be directly related to solidity and the ability to self-start. Ie. low solidity units will run happily at TSR's of 4 or better, but don't like to self-start. High solidity units (let's say .3 or better) like to start but don't run fast.

The rest of the collection on VAWT technology is here:

http://www.sandia.gov/wind/topical.htm#VAWTARCHIVE

and makes for some interesting reading at least.

Ted.

rotornuts · « **Reply #47 on:** June 10, 2005, 09:24:42 AM »

Morning Ted. I'll read the links in a minute. this thing definitely has shades of the coffe can in it. I'm trying three cylinders with a low solidity but I'm thinking two will be the ticket. I think of solidity like stability in an aircraft. Aircraft that have a reduced wing size and a planform that compimizes stability have better manuverability and speed performance than the same aircraft with a wing that is shaped to provide stability. This kinda flies goes against the way I was thinking in the recent past so I'm reassessing my thoughts on it. I always try to remember that each application has it's own issues so a uniform theory doesn't apply but it's hard to not let opinion from one project influence another. In the transition from Hawt's to Vawt's I've had to dismiss alot of what I thought I knew because of the unique conditions of a Vawt.

I am very curious now to see what sandia has to say so I'm off to do some reading.

Thanks for the links.

Mike

rotornuts · « **Reply #48 on:** June 10, 2005, 09:56:08 AM »

Well, It's seems that sandia was disapointed enough in the three bucket configuration they didn't even publish the results. They say that other than start torque the two bucket is superior. I think the trip wires on my model may compensate for that. Ok then is it going to be two or three? two, three, two, three, maybe I should draw straws. Allright I'll do thre three just to say I did but, again, I think it's going to be back to two in a low solidity.

Mike

electrondady1 · « **Reply #49 on:** June 10, 2005, 10:14:49 AM »

thanks very much for those links

electrondady1 · « **Reply #50 on:** June 10, 2005, 10:26:54 AM »

roto, i know your doing pure research but something to bear in mind as you go on, the profiles your coming up with are very compatible with extrusion tech. extrusion dies are relatively inexpensive. imagine any old plastic junk going in one end and fully formed vanes coming out the other. just slice it at whatever lengh you want. good luck!

monte350c · « **Reply #51 on:** June 10, 2005, 10:33:05 AM »

Yes, and if the start becomes problematic, as the article suggests you can just have two units stacked one on top of the other, the top rotated 90 degrees with respect to the bottom unit. The charts on the Savonius then show positive torque all the way around, and so should self-start no problem.

It's a pity they didn't continue down that road a bit - it looks like the idea behind all those tests was to examine the possibilities of using a Savonius to start a Darrieus.

You're picking up where they left off all those years ago. That report was from 1976!

Sure would be nice to have a wind tunnel to play with...

Ted.

electrondady1 · « **Reply #52 on:** June 10, 2005, 10:37:45 AM »

oops! the thanks was for monte 350 for the sandia links.

rotornuts · « **Reply #53 on:** June 10, 2005, 10:44:14 AM »

Hello again guys.

Electron daddy, this thing is a cinch to build for sure and ted, I regret to inform that I increased the diameter to 7" added an third cylinder and used the same flaps and to my dismay it's defying expectation by working very well so far. I haven't seen high winds yet but it seems to be beating the two cylinder(again from a visual perspective bearing in mind that more points on something that rotates will make it look like it's going faster, these days I mark a point on the rim to refrence rotation speed.

Clearly something interesting is happening in the center so I think I should leave it alone and avoid any flow manipulating thingies.]

Slightly confounded, Mike

monte350c · « **Reply #54 on:** June 10, 2005, 11:32:19 AM »

Wow - don't be sorry! Sounds like you're on to something.

There's lots of approaches to rpm counting - I did a simple one by hot glueing some magnets to the bottom disk of my vawt models and putting one coil about 120 turns of 22 guage wire nearby. Attach the output wires to my Fluke meter on the hertz setting and voila, a rough and ready tach.

Good luck and this keeps getting more interesting!

Ted.

wildbill hickup · « **Reply #55 on:** June 10, 2005, 02:20:28 PM »

Ok now where did I put that wind/watt formula.....I know it's here somewhere.....maybe in that pile...no that one....it's bound to be in there somewhere :-> HELP!!!!!

windstuffnow · « **Reply #56 on:** June 10, 2005, 02:49:40 PM »

Mike, I found the same thing when I went to the 3 wing design, it gained speed as well as torque. Also, it started much easier. I think you'll find that your start up torque will go up significantly if you open a slot to the inside of the tubes on the backside of each wing, this also helps create the turbulant energy that will keep the air stuck to the wing reducing drag.

Man, your having way to much fun... wish I was there! You've got my blood boiling, I want to go out and play with some stuff. Unfortunately I can't gotta keep my nose to the grindstone at least for a few more days... Then I can play a little.

windstuffnow · « **Reply #57 on:** June 10, 2005, 02:55:07 PM »

Mike, I think you need to start a new thread on this diary, its getting hard to follow... Lots of interest!!!

Norm · « **Reply #58 on:** June 10, 2005, 06:42:57 PM »

They look a lot like yours because thats were

I got the idea...thanks woof...and the cupped

ends do seem to make it work better.

This little toy is getting lost amongst all

this tech stuff about RN, vortex, venturis, and

stuff!

Fun!

( :>) Norm.

electrondady1 · « **Reply #59 on:** June 10, 2005, 08:48:15 PM »

well if you could post the graphic for the three pillar unit be for you change anything.....

nothing to lose · « **Reply #60 on:** June 10, 2005, 09:38:29 PM »

Sorry I did not have time to read all of this, very interested in it though.

I leave soon for my summer trips, so just last minute surfing stuff, see everyone later this year on here.

Anyway, on this funny little thing in the first picture. I like it.

I remember when I was a kid (many years ago) I had an odd ball kite. It had sort of a body and wings as I recall. The wings were similar to what is on that post in the first picture, best as I remember. So I would think your on the right track with the lift Idea here. That kit was great. When the wind blew past the wings they spun, when they spun they created lift, faster the wind the faster they spun the more lift they made.

Why or how it worked I have no idea really, but that thing would fly better than any normal kite.

As experements (playing) way back then, I do recall toy glider planes. My kite plane tied to the end of a string would fly in the wind with the spinning wings, but a glidder plane would fall to the ground in the same winds with it's stationary wings.

The glider plane would glide if thrown though, my kite plane I don't think did or not very well.

Anyway, I hope this works well, I know that old toy did, and those wings would really get to spinning too. Very fast in a good kite flying wind!

Too bad we can't buy decent stuff like that now adays

Kwazai · « **Reply #61 on:** June 13, 2005, 07:04:14 AM »

ditto...

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Author Topic: 2 cylinder VAWT (Read 12658 times)