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Lenz turbine
By rotornuts, Section Wind Posted on Fri May 20, 2005 at 08:40:46 PM MST
Ok, maybe I'm fickle

I recently decided to drop the single blade for a while because I wanted to build a working unit and the single needs too much work yet. So I come to the conclusion I can't go very big due to my location and have since determined the output of a 30" machine is uninspiring. I got to thinking about VAWT's because they seem more compact. I started working on the theory and different designs and it dawned on me the brilliance of the lenz turbine because of it's ability to prodice power on the upwind and downwind sides so I drew a two blade version to see if I'm understanding the theory correctly.

Ed, can you see a problem with this?
I dropped one blade and introduced a circular center as I'm not sure I understand the need for a delta center unless it is itself producing lift and I've missed it. The circular center as you can see still provides for the venturi effect and my only concern is that i've misunderstood what's going on and have reversed the venturi.
As I uderstand it in the above diagram the unit should rotate in a clockwise direction.
Is this correct or have I overlooked something or made a critical error?
Mike

Lenz turbine | 13 comments (13 topical)

Re: Lenz turbine (3.00 / 0) (#1)
by Norm on Fri May 20, 2005 at 04:09:48 PM MST

Rotornuts:
Interesting I'm anxious to what Ed has to
say about this...Don't mind me I'm just reading
postings.
( :>) Norm.
( :>) Norm

Re: Lenz turbine (3.00 / 0) (#2)
by windstuffnow on Fri May 20, 2005 at 06:21:45 PM MST

Hi Rotornuts,
Some of the problems I was trying to overcome with the Lenz turbine was the pulse or lag between power points. This is the only problem I see with the 2 blade design. As the blades pass the center of the direct wind the blade in the rear gets blanked the front blade stalls as it passes center. With the 3 blades the power pulse is reduced because there is always one blade making power. The two bladed units seem to have 2 40 degree lags where the 3 blade has 3 10 degree lags. The biggest portion of drag is on the front wing passing center. Also the two blade units have 2 positions where they don't want to start or catch the wind to begin rotation. You can offset the startup by making the center a bit smaller than the wing chord, this will allow the air to flow over the core and catch a wing, but you'll end up loosing some of the venturi effect. The venturi actually creates a low pressure zone behind the turbine and the air flowing around the unit tries to fill the void, in doing so it changes the direction of the air flow enough to start creating lift before the blade actually sees the direct wind.

I've never taken the Lenz turbine out in the "real world" as yet. It's only been tested in a wind tunnel environment. In the tests it proves to be quite efficient and makes reasonable power. I need to dig it out, set it up outside and monitor the data. I've been slightly diverted from the project though, while I was digging out the journal with all my numbers on the unit I found some drawings of my old free wing unit and an idea hit me. The free wing is a VAWT that utilizes the entire frontal area to extract power but the answer to getting to work eluded me until I looked at the drawings the other day and the problem stood out like a sore thumb. The solution seemed simple at the time and it will work but the mechanism will be a bit complicated. I've been working out design problems on it ever since. I believe I've beaten it and I'm at a point where I need to build the machine. I'm quite hyped about this one, it should be quite impressive. Or... another historic failure to add to my collection...

Have Fun with it, I fired up the tunnel and blew the dust off the Lenz the other day, in a 12 mph wind with no load it was running at 260 rpm. My wind tunnel is quite primitive built from a very large fan with plywood around it. It has reverse curve inserts to help straighten out the wind before it hits the turbines but doesn't straighten it out enough to remove all the turbulance. My next one will be built behind a couple thousand 1" tubes with a larger power unit.

Have Fun

Windstuff Ed

Have Fun! Windstuff Ed

Re: Lenz turbine (3.00 / 0) (#3)
by rotornuts on Fri May 20, 2005 at 07:17:20 PM MST

Thanks for the commentary Ed. I realize the pulse effect is more significant with a two blade design I just considered it this way for simplicity and I was also wondering what kind of effect "solidity" as a factor of circumfrence may have. I do think the Coanda effect may significantly reduce the pulsing effect and the wide cord has the effect of put wing in the wind almost all the time. I was wondering also if you can see a problem with the round center as apposed to the delta center thats tailored to the three blade design. I considered an oval in the center to match the two blades but couldn't see an advantage. I'd love to play with this some as I can now see the beauty in it's design. Maybe a dimpled surface on the center would help the Coanda effect by delaying separation such as with a golf ball.

[ Parent ]

Re: Lenz turbine (3.00 / 0) (#4)
by rotornuts on Fri May 20, 2005 at 07:23:43 PM MST

I should say that the coanda effect is the reason I wanted to adopt a round center.

[ Parent ]

Re: Lenz turbine (3.00 / 0) (#6)
by windstuffnow on Fri May 20, 2005 at 08:43:46 PM MST

Actually the "dimples" might help. As long as you can keep the air flowing over the surface your fine, but you will be breaking the air from the drum each time the wing passes. This creates turbulance and will break the coanda effect. If its running fairly fast it won't have time to reorganize effectivly.

There was another one that used the venturi effect but to a lesser degree, a 2 blade unit with a Football shape in the center. Suposedly, they run fairly efficiently. It was patented back in the early 80's... its called a Ropatec

I started the Lenz turbine project shortly after a guy sent me an email about another one that used the venturi effect, also patented back in the early 80's. After building one from the specs he sent I wasn't impressed with it at all but was intrigued by the idea. Below is a patent drawing of the venturi turbine emailed to me...

Below is the one I originally built as a test machine...

Then of course the infamous 700 rpm coffee can ...

I made up a mini dyno to check the locked rotor torque at any angle of rotation while in the wind and found all the failings of the machine. Decided to start from scratch with some new ideas out of the results and that's how the Lenz turbine was born. 1 machine and several tweeks later it ran ( runs ) quite well but still has several bugs that need to be worked out before I'm satisfied with it...

Fun little machines!
Winstuff Ed

Have Fun! Windstuff Ed
[ Parent ]

Re: Lenz turbine (3.00 / 0) (#7)
by rotornuts on Fri May 20, 2005 at 10:55:29 PM MST

I gotta say Ed I'd love to read your notes! I'll fiddle with my above variation and see what happens. I'learn the most from seeing what doesn't work so I'll make no modifications till I try it.

Thanks for sharing

Mike

[ Parent ]

Re: Lenz turbine (3.00 / 0) (#5)
by bob golding on Fri May 20, 2005 at 07:45:51 PM MST

hi ed , it would be good to see some more progress on the lenz turbine. i built one out of copper sheet which worked after a fashion but was far too heavy. i started to make one with pvc tubes and foam covered with thin aluminium but never finished it. its still sitting here waiting for me to get round to finishing it. i have the airfoil sections shaped but have only skinned up one so far. even cleared the bench to do it, that didnt last.

bob golding

[ Parent ]

Dedicated endevor (3.00 / 0) (#9)
by Norm on Sat May 21, 2005 at 05:26:52 AM MST

even cleared the bench to do it, that didnt last.
I hear you ...Bob! LOL !
There's a common bond for all of us!
You made my day!

Havin Fun in NE Ohio!
( :>) Norm.
( :>) Norm
[ Parent ]

Re: Lenz turbine (3.00 / 0) (#8)
by zap on Sat May 21, 2005 at 12:50:03 AM MST

Hey Mike I like the design but I have a Q for you and Ed about the coanda effect

I don't know much about the effect except what I read years ago when Hughes was testing the notar. From what I know about it... won't the lift that it creates just want to pull your center column to the outside? I can see how it would create a low pressure and I assume that low would be reacting 90° to the wind direction? If I have that correct, how does this impart a rotative force? Or is the low used to "pull" air between the airfoil and column? Thanks,

zap

Re: Lenz turbine (3.00 / 0) (#10)
by rotornuts on Sat May 21, 2005 at 10:40:21 AM MST

I'm thinking/hoping it will pull air between the airfoil and the column effectively increasing how many degrees of rotation the unit will produce power and reducing drag and downwind turbulence but as Ed has pointed out It's questionable how much benefit it may have as the wind shadow from the upwind blade occurs at almost the same time as you want the effect. I'm building a model right now so I can get a better visualization.

http://www.absoluteastronomy.com/encyclopedia/C/Co/Coanda_effect.htm

I'm thinking keeping the two blade confiquration but reducing the cord width in proportion to the center.

[ Parent ]

Re: Lenz turbine (3.00 / 0) (#11)
by windstuffnow on Sat May 21, 2005 at 11:53:57 AM MST

Sounds Fun! I'm looking forward to seeing and reading about your outcome with it!

So much fun... so little time...

Windstuff Ed

Have Fun! Windstuff Ed
[ Parent ]

Re: Lenz turbine (3.00 / 0) (#12)
by hvirtane on Thu May 26, 2005 at 02:08:05 AM MST

What about putting
inside a savonius turbine
instead of the solid
cylinder?

Maybe something like
the 'picoturbine'.

Some time ago I made
a draft drawing like this:

Some time later
I started tom play with
ideas similar as
the 'Gorlow turbine'.

This first draft uses for the blade
construction blank wooden boards,
which can be cut into suitable shape,
which might be something like
the well-known K2 airfoil.

You might also use steel tubes and
cover them with wooden or polyurethane
pieces:

What do you think?

- Hannu

Re: Lenz turbine (3.00 / 0) (#13)
by rotornuts on Fri May 27, 2005 at 03:00:48 PM MST

I like your idea for replacing the solid center on the first diagram. I'll have to consider what would happen if that modification was made.

Mike

[ Parent ]

Lenz turbine | 13 comments (13 topical)

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