windgen.org vawt discussion

wiboater wrote:

---

 I see what your saying but isn't the curve the wrong way for producing lift? His C rotor is smaller than the lenz , it will be interesting to see the bigger one.  I actully put a curve on that flat side of one of my lenz turbines, to make more of an airplane wing shape, I think it helps.It's hard to compare the two I have though because one is bigger in wing diameter and cup length and width.

-- Edited by wiboater on Tuesday 9th of February 2010 05:38:44 PM

---

That's what I thought as well- the radius of the c-part should be the same as the Lenz blade LE, for comparatives.  That's where I'm using the ABS to form the two components... the "C" and the air-foil leading edge.  Glue 'em together and fill out the back fin with somethin'...

Turtle,  slow

 

-- Edited by keithturtle on Wednesday 10th of February 2010 12:34:24 AM

 I see what your saying but isn't the curve the wrong way for producing lift? His C rotor is smaller than the lenz , it will be interesting to see the bigger one.  I actully put a curve on that flat side of one of my lenz turbines, to make more of an airplane wing shape, I think it helps.It's hard to compare the two I have though because one is bigger in wing diameter and cup length and width.

-- Edited by wiboater on Tuesday 9th of February 2010 05:38:44 PM

wiboater wrote:

---

I think because the C rotor has openings on both sides at the front the wind can escape more easily out both sides. That probably makes a difference since the Lenz traps the wind more. the difference in size should definately make a difference. the 2 turbines I have the one on the dock that is larger in radius at the cup of the wing is putting out more power today than the one on the roof.

---

But if you think about air moving in the forward direction going around that crotor curve and coming out going in the backwards direction, from a change in momentum perspective, that's as good or better than just stopping the air dead in a scoop.

I think the Lenz has the advantage because the flat part helps funnel air across the outside of the curved part and that causes a lot of lift in the forward direction.


-- Edited by sjh7132 on Tuesday 9th of February 2010 03:56:53 PM

I think because the C rotor has openings on both sides at the front the wind can escape more easily out both sides. That probably makes a difference since the Lenz traps the wind more. the difference in size should definately make a difference. the 2 turbines I have the one on the dock that is larger in radius at the cup of the wing is putting out more power today than the one on the roof.

Hello Steve

" Well it's good to see that air in Germany also works with the Lenz. :-)"

And not bad, but the Lenz is not as fast spinnig than in america. :)

" We have a tendency to talk about the radius being the distance from the center to the center of the front cylinder but that's not really correct for swept area. "

Yes that a good point to talk about. I saw that Ed seems to measure the radius from center to the greatest distance,
i think thats better than i handle it until now.
Before the test i measured like you wrote, to the center of the wing, to the cord line.
To get usefull comparing results, i built both rotors with the same outer diameter.
So both rotors got before testing around 56cm from center to outer point of the rotor.
Thats the reason why i enlarge the Lenz before testing from 50cm to 56 cm, to get correct results. (german correctness) :))
The "new" diameter also changes the TSR value of the C-Rotor from 0,82 to 0,92.
The Lenz was nearly on the line with around 0,96 unloaded.
In the future i will test the unloaded TSR  of the lenz into my garden, but i think it will be the same like
comparing the C-Rotor TSR on teststand and garden, it was the same value.

Today i bought some material to build another test C-Rotor with dimensions like Ed's blades.
If this test wouldn't increase the results for the C-Rotor signifikant, than the lenz has win this match. To be honest i think so... :)
We will see.

Bernd



-- Edited by Bernd on Monday 8th of February 2010 09:02:40 PM

Well it's good to see that air in Germany also works with the Lenz. :-)

You might want to normalize the two power measurements for the actual radius of the turbines.  (center to most distant point from the center.)   We have a tendency to talk about the radius being the distance from the center to the center of the front cylinder but that's not really correct for swept area.

About the solidity.  My simulations have shown that you can increase the radius by 30% and use the same blade size with very little or no  loss in efficiency.  Ed has confirmed in email that he has seen this in real life.  (Although I'm not sure if he's tried a 30% enlargement)

Thanks for posting those measurements.

Like i wrote before, we build a Lenz 2 rotor with over all 56,5 cm diameter and 50cm height.
I chose this size because i had a complete C-Rotor with the same size, that i made some month ago.

Comparing to the Lenz2 the C-Rotor has much less solidity and the Lenz blades have much more volume.
Here some pictures of my test candidates.





We had build the Lenz 2 blades from 10cm half Tube an the side is made of a 3mm alloy sandwich plate, witch is used for advertising panel.
The top and bottom is made of 4mm plywood.
The gap between plate and half tube was closed with some white tape.
All dimensions i took from Ed's site for the Lenz 2 design for a diameter of 50cm.
Because of the 56cm C-rotor diameter i mounted the lenz blade's with 56 cm too.
The angle of attack was 9 degree.



You can see the different dimensions. Maybe thats one of the reasons for the suprisingly results of the lenz.







On the next picture you can see the lenz on my teststand.
This teststand i put in front of two 40cm Fan's.
If you want to see more of this teststand, than look here:

http://www.daswindrad.de/forum/viewtopic.php?f=10&t=12

There is also a video available where i explain in german how the measuring is working:

http://www.vallstedt-networks.de/diverses/bremse_1.avi






Than i measured the mechanical torque at different rpms.
I did the same with the C-Rotor and put all results in two diagram's.
The result of the Lenz power was shocking me.
Never before i measured such a high power on my teststand.
Here are the results:



The difference at highest peak is around 65% !!  Unbelievable...
Before testing i though that the difference could be around 10% ore may be 20%,
but never so much.

So now there is the point for me to search for the reasons.
Could the difference in blade volume lead to this extreme result ?
The C-Rotor also has much lower solidity.
I think the next days i'll try another test, using C-Rotor blades with the same dimensions as the lenz blades.

Never the less i would like to express Ed my greatest admiration for this simple but powerfull turbine.

Oh i forgot to post the rpm without load.
For the C-Rotor i measured 135 rpm without load and for the lenz it was 143 rpm.
So i can say that the unload TSR of my lenz is a little bit higher than the TSR of the C-Rotor, but not much.
The undload TSR of my Lenz 2 was around 0,96 and the one of the C-Rotor was around 0,92.
The loaded optimum TSR was for the Lenz at 0,56 and for C-Rotor at 0,59.

Bernd


-- Edited by Bernd on Monday 8th of February 2010 06:49:20 PM

-- Edited by Bernd on Monday 8th of February 2010 07:13:50 PM

That's pretty much what I'm up to with a smallish Lenz-type 3 bade turbine.

I just did the initial spin testing on the one with the balsa blades- 48rpm in front of the 20" box fan.  Took it outside in a 20 mph wind and it spun like madness, surprisingly balanced, but the tach wouldn't read, probably for bright sky and too much background light.

I will be fashioning my c-rotor blade from 0.065" sheet ABS plastic, heat forming two components to start with, the airfoil leading edge, and the c-shape, bonded to the airfoil.  The trailing vane will probably be aluminum for now, though I'd like to fashion a ribbed ABS curved fin soon.

I'll cut and sand pine 2x4 stock for the airfoil form, and use a pipe for the c-part.

Turtle, slow

-- Edited by keithturtle on Monday 8th of February 2010 05:54:38 AM

I look forward to some measurements.

Thanks for explanation. I'm just happy if i understand english without pun. :)

Bernd

lenze2 by a guy named lenz =lenz2x2

lenz2 "kariert"

-- Edited by electrondady1 on Sunday 7th of February 2010 02:23:34 PM

I think it got lost in the translation. :)

Sorry bad pun... a "Lenz 2" built by a "Lenz too" = Lenz 2 Squared....Ill keep my day job. 

Sorry, i don't know the meaning of " 2 Sq'd "

Bernd

Does that make it a Lenz 2 Sq'd?

hello friends
Today i build a 50cm Lenz 2 Turbine for comparison with a 50cm C-rotor on my teststand.
The funny thing is that a friend of mine was helping me to build the turbine, and his last name is Lenz too, no joke. :)

For now i can say that the turbine is working very well.
Fotos and comparing test results will follow.

Bernd


-- Edited by Bernd on Sunday 7th of February 2010 12:12:12 AM