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And again and again with the Lenz turbine variation
By rotornuts, Section Wind Posted on Sun May 22, 2005 at 07:54:39 AM MST
New drawings of the next learning experience

Well the first worked.
http://www.fieldlines.com/story/2005/5/21/204220/623
http://www.fieldlines.com/story/2005/5/20/204046/109
But not very well. Wouldn't self start and it ran at a TSR of about .7
It wanted to go but there was to much drag and negative pressure behind the unit I think.
Anyhow I think I'm going to try and change the shape of the venturi so the lowest pressure occurs hopefully along the leading edge of the blade instead of at the apex. I'd also like to see if I can keep the aiflow to the outside of the rotor on the down wind and the first 90 degrees if the upwind side using the center.
Here's a drawing with some speculation on airflow and lift areas. It's a three blade design. I've changed the inside shape considerably and It's starting to look more like that delta shape I couldn't see the purpose for. Hmmm...

All opinions welcome as long as you realize I don't care to build a proven design. Oh and it's late and I'm going bugeye from drawing that image.
Mike

And again and again with the Lenz turbine variation | 11 comments (11 topical)

Diary (3.00 / 0) (#1)
by wdyasq on Sun May 22, 2005 at 07:26:28 AM MST

This discussion sure would be a lot easier to follow in a diary format.

But while I am here, what you have forgotten on your diagram is the rotation. Once the surface speed of the rotor achieves the speed of the wind, it, to use an old sailing term, 'starts making its' own wind'.

Lots of things going one here - might even get a ltiile of the Magnus effect.

Ron
Adventure is just bad planning." -- Roald Amundsen

Re: Diary (3.00 / 0) (#2)
by rotornuts on Sun May 22, 2005 at 01:35:23 PM MST

Your right, Diary format would work better. I have to confess the dynamics of a vawt, espessially one where your attempting to manipulate the airflow, can be a bit hard to follow. I doubt I fully understand what's going on during all portions of a rotation.

The rotation of the above is clockwise.

Thanks for putting a name to distortion of the global airflow around a rotating cylinder, I didn't know it was the magnus effect but I realized something must be happening I just didn't realize it was as profound as the magnus effect describes.

Hawt's are much easier to visualize.

Mike

[ Parent ]

Re: And again and again with the Lenz turbine vari (3.00 / 0) (#3)
by rotornuts on Sun May 22, 2005 at 05:31:42 PM MST

You know, I was fooling arund with my model today and I think all this time I've been visualizing the action in the venturi backwards not realizing most of the power is being produced on the downwind side. The shape of the venturi I've drawn would likely deminish the pressure differential on the downwind side stealing away power!

Re: And again and again with the Lenz turbine vari (3.00 / 0) (#4)
by rotornuts on Sun May 22, 2005 at 08:05:40 PM MST

I drew another version with what I think would be corrected venturi's. I looks strangly familiar don't ya think Ed.

Well any additional thoughs?

Can someone with a better understanding than I tell me if I indeed was misunderstand the venturi thing?

Mike

[ Parent ]

Re: And again and again with the Lenz turbine vari (3.00 / 0) (#5)
by rotornuts on Sun May 22, 2005 at 10:42:33 PM MST

I just overlayed the origional patent, Ed's unit and what I came up with after playing with my original and here's what it looks like.

Both Ed's and mine are different than the origional patent but I've come to the same place as Ed did a long time ago.

[ Parent ]

Re: And again and again with the Lenz turbine vari (3.00 / 0) (#6)
by XRay on Mon May 23, 2005 at 07:29:40 AM MST

Our on the right track, the venturi locks good. It absolutely must self-start this way. Did you (un)intentionally add buckets to the venturi (dents in the venturi) that helps self-start to. You find those buckets back in windstuffs rotor blades. Correct me if I am wrong.
My version is self-starting torque is very weak, but kicks in after a definite RPM.

Greetings
Ray

---------------------
You dont know how little you know.
till you know enought to know that you still know nothing
[ Parent ]

Re: And again and again with the Lenz turbine vari (3.00 / 0) (#7)
by rotornuts on Mon May 23, 2005 at 04:21:20 PM MST

I was thinking it may help to try and deflect the airflow around the downwind blade. It hard to visualize and consider what going to happen with these things because it's so different for at various rpm and even during a single rotation at various rpm. I'm trying to understand it better but till I model the above I'm only speculating.

[ Parent ]

Re: And again and again with the Lenz turbine vari (3.00 / 0) (#8)
by XRay on Tue May 24, 2005 at 03:30:05 AM MST

Ok, I zoomed in on your drawing and here are my thoughts:
I think that this deflection you draw is creating a restriction or a wall of wind, notice first picture. This only happens while rotation speed is slower than wind speed. When rotation and wind speed match this down wind effect is gone (TRS=1)
Then notice the first picture again and see a other miner problem, the air coming out of the Lenz is forced to expand premature, and the air loses velocity already in the Lenz.
So to tackle these problems I sharpened the ventu, like the second picture.
Correct me if I am wrong.

fist picture.

second picture.

Greetings,
Ray
---------------------
You dont know how little you know.
till you know enought to know that you still know nothing
[ Parent ]

Re: And again and again with the Lenz turbine vari (3.00 / 0) (#9)
by XRay on Tue May 24, 2005 at 07:18:22 AM MST

This sharpened venturi will also contribute to a quicker self-start. I think :))
---------------------
You dont know how little you know.
till you know enought to know that you still know nothing
[ Parent ]

Re: And again and again with the Lenz turbine vari (3.00 / 0) (#10)
by rotornuts on Tue May 24, 2005 at 08:49:08 AM MST

Hello Ray, Thanks for the input. I see what your getting at but I'm thinking it would work both ways although I'm not sure what would work best.

This is how I'm visualizing the air flow above and below tsr 1.

Below tsr 1 there should be little air flow through the venturi so that the space in the venturi is at a higher pressure than the space downwind from the wing so, if most of the air is divered around the venturi we would get a low pressure area at the outside of the wing area and downwind producing good starting torque. The area in blue is around where I see the low pressure area.

Above tsr 1 I think we want the air flow to shift into the venturi to increase airspeed in the venturi area to make it the low pressure area. Now we are producing lift on the inside of the wing rather than the outside and the swail or "dent" serves to seperate air flow on the center and create drag rather than lift. The area in blue on the second diagram is a drag area which I think is better than it being a lift area. If there was no swail and the center had a simple delta shape then I think the area in blue would be producing lift which would counter rotation more than drag. Unfortunately I can't see a better way to treat this area so I've settled for drag.

I could easily be mistaken on this but at this time this is my best understanding of what's happening.

[ Parent ]

Re: And again and again with the Lenz turbine vari (3.00 / 0) (#11)
by XRay on Wed May 25, 2005 at 04:11:41 AM MST

Well, how about some paper models? I had some interesting learnings from paper models. I had an experience with a silly paper model: I was fooling around with a 2-blade version folded a few different venturi types; the best was the sharpest one like my second picture.

Yes I understand and agree on your visualization, but just before tsr=1 pressure builds up in the venturi and is almost equal to the downside pressure. Pressure builds up because the rotor spines around and the leading site of the venturi gasp air. This means that the wall of wind is there, but it is the last stage before tsr=1. Maybe if you sharpen the swail the rotor exceeds tsr=1 just a bit faster.

You already mentioned "It hard to visualize and consider what going to happen with these things because it's so different for at various rpm and even during a single rotation at various rpm." We need someone who can make a computer simulation for this type of problem.

Did you noticed that we where actually making a sequence movie with our pictures?

: your below tsr 1 picture
: my first picture
: your above tsr 1 picture
: my second picture

have lots of fun, I think I need to make a few paper models.
Ray

---------------------
You dont know how little you know.
till you know enought to know that you still know nothing
[ Parent ]

And again and again with the Lenz turbine variation | 11 comments (11 topical)

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