| T O P I C R E V I E W |
| BushWhacker |
Posted - 16/03/2008 : 06:02:01
Hi People;
Does anyone here have any good links to darrieus wind turbines design?
Perhaps someone has played with a darrieus design of some sort?
I've got a half dozen airfoils I picked up for a song and was trying to think of an effective way to use them.
http://i228.photobucket.com/albums/ee276/KonaKia/P9250380.jpg
If memory serves they are about 3 ft. long and taper from about 16 in. to about 13 in. They are in fact a true airfoil with a convex and a concave side. I realize I'll have to put the convex (lift) side inboard but have no idea of what radius to set the wings out at, nor the angle of pitch. I will be building an adjustment to be able to alter the pitch to some degree but having a rough reference point would be a good start.
Any input would be appreciated.
TIA,
BW
Everything should be made as simple as possible, but not one bit simpler. - Albert Einstein |
| 13 L A T E S T R E P L I E S (Newest First) |
| MattM |
Posted - 22/03/2008 : 02:40:41
Well, I set out to see today if narrow or wide would spin easier.
It turns out that wide ones work well, but only for about a 1/6th of a turn. For some reason it races that 1/6th of a turn and then slows down to the point where it just cannot seem to keep up its velocity, causing it to move in a pulsating rhythm. It probably had to do with the fact that the arms were 28" (with 6" wide blades) out from dead center and only contained 1 ft^2 of surface area. The rotation was only consistently smooth when wind speed reached above 15 mph. I have a strong feeling if it had been six bladed rather than three then it would have been more successful.
Earlier in the day I tested a narrow version with the same surface area but with the same size blades mounted directly on the hub. In the direct output of a fan it made the thing spin fast enough to literally disappear. But when I took it outside the 15-20mph gusts barely budged it.
I just don't see how he gets so much energy out of the vertical design. What Ed Lenz is doing really has my respect.
Go Huskers! |
| BushWhacker |
Posted - 20/03/2008 : 22:12:51
The snow has melted away and I got a good look at my air foils again. The back (under?) side of the foil is concave from about 3" behind the leading edge. Think of an elongated, bent teardrop. All the same I think it's going to be a fun and frustrating adventure into wind power. I had a look on youtube and saw an interesting 5 or 6 blade design that seemed to be pretty busy making power. Things that make me go "HMMmmm?".
Something else I saw that was pretty interesting is this hybrid
http://uk.youtube.com/watch?v=CkIX3_O8sWg&feature=related
I won't go to the trouble of trying to make one as noise is something I'm trying to avoid but it's interesting all the same. The owner claims 33% efficiency. I find that a hard to swallow. All the same if it make 1.5 KW on such a small footprint I'm impressed!
Cheers!
BW
Everything should be made as simple as possible, but not one bit simpler. - Albert Einstein |
| ghurd |
Posted - 19/03/2008 : 21:52:54
If Ed changed something, it was NOT related to ease of manufacturing. |
| chris_psmith |
Posted - 19/03/2008 : 20:53:33
I don't know the pro's and cons of the benefit from the back face having an aerofoil form Vs being open like a bucket to catch the wind. When you read the description of the lenz2 he used a rough aerofoil shape early on but then changed as it got bigger, i don't know if this was due to a thought process or ease of making the turbine. Must be some others who have made a 3 blade version of this.
Chris |
| MattM |
Posted - 19/03/2008 : 14:35:47
The Lenz 2 seems to be the reverse of your link, where it has ridges top and bottom facing away from the airfoil to grab wind as it moves downwind whereas the airfoil in your link faces the wind. The airfoil in the Lenz 2 seems more positioned akin to the leading edge of the airfoil cutting the wind force when moving upwind. The ridges of the Lenz 2 act as vertex generators while moving upwind, which should help it break some of the drag. In your link the airfoil faces headwind as it moves downwind, right?
edit: The outside ridge seems to be in pretty good relationship just as it passes the top dead center of its rotation, the point closes to the approaching wind. The inner ridge appears to be optimized for the point when it is perpendicular to the top dead center point, that is the point at which it reaches the first quarter turn. Kind of brilliant idea if you asked me.
Go Huskers! |
| chris_psmith |
Posted - 19/03/2008 : 07:44:30
Not sure if 9 degrees is best for a proper aero profile, the lenz is a one sided blade, i am trying the angle at the bottom of the link, about 6 degree.
http://club.cycom.co.uk/vertAxis.html |
| gholt |
Posted - 17/03/2008 : 09:42:09
Hello BW,
hmmmmm ... if this doesn't put you to sleep nothing will -
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19810005410_1981005410.pdf
In all honesty, you'll need to do a down and dirty fast mock up with at least three (3) of your airfoils bound at the two ends between round discs of plywood perhaps on a lazy susan turntable and let 'er fly and evaluate your results. If the airfoils are as large as they appear, you may actually have to weld up arms to suspend them and figure out a method to adjust the angle of attack until you have a good number to work with. The 9 degree number is NOT a magic number. It works for the Lenz profile and you're on your own with whatever airfoil you have.
If one examines the Lenz profile and/or the Delta II blade profile for the system Jay Leno had installed, you may notice there is a combination (dual purpose) configuration to the profile serving both lift and drag components depending on where the blade is positioned within it's rotational cycle - very clever.
http://www.popularmechanics.com/automotive/jay_leno_garage/4216780.html
It's somewhat safe to say that the first 30-40% of an airfoil provides the lift characteristics, anything after that serves another purpose (a PVC wind genny prop demonstrates this quite well). In the image above, look at the end of the blade where you can actually see the profile. The inside, about 60% and the outside about 70% are devoted to drag configuration while the remainder forward to the leading edge is devoted to producing lift on either side of the wind cycle.
Clark Y, Eppler and Wortman airfoils are noted for their low speed, high lift flight characteristics.
I'm not sure that's exactly what you wanted to know, but let's hope it gets you started. It looks like you've got a project.
G. |
| MattM |
Posted - 17/03/2008 : 05:29:16
quote:
Originally posted by BushWhacker
As you increase diameter you reduce RPM but gain torque.
While the Savonius and Lenz 2 are both VAWT's the Savonius works on drag and the Lenz 2 is a lift type turbine. Apples and oranges I'm afraid.
Adding torque isn't so bad when you think about it; the motors attached to vawt's are typically geared. If you use the arms on the rotor as additional scoop area then its yet another bonus.
I'm curious what people mean by the drag and lift explanations. If the airfoil is rigid - at least the arm it attaches to is fixed - then the lift does nothing. In order to use the lift you'd have to have a flexible arm or free floating wing to gain anything from the lift. Otherwise the lift has nothing to move. After all, lift is a force perpendicular to the wing's movement. I must be missing something in the designs because mostly just the darieus designs seem to use moving parts on the airfoil.
Now if you could get your airfoil to act like a whale tail, where it actually uses the lift to move outward from the center and effectively increase your diameter on the downwind wide then it would boost the rotational speed of the rotor when it comes back in due to it moving at the same relative speed as it was at its furthest point. But moving parts just add to complexity which becomes counter indicative to cost efficiency at that point.
Go Huskers! |
| BushWhacker |
Posted - 17/03/2008 : 04:53:25
Hi gholt;
BANG ON! Thank you!
That Eppler 664 extended is about 95% correct to the airfoil profile I have. I was worried about the concave surface screwing up the flow in a darrieus/lens type turbine. Could you please provide a link that would lead me to the source of that information? I think I have more reading to do.
MattM;
As you increase diameter you reduce RPM but gain torque.
While the Savonius and Lenz 2 are both VAWT's the Savonius works on drag and the Lenz 2 is a lift type turbine. Apples and oranges I'm afraid.
Cheers!
BW
Everything should be made as simple as possible, but not one bit simpler. - Albert Einstein |
| MattM |
Posted - 17/03/2008 : 02:50:35
Has anyone explored the benefits of increasing the diameter of the vawt?
I see most of the vawt's tend to be a fairly tight diameter. From my little brother's expiriments with 2- and 3-blades savonius types, short and fat scoops are no advantage. I'd think you could get away with an extreme diameter without being too dangerous, especially considering that the thing should be up off the ground just like any other wind turbine. Perhaps that is why the Lenz2 design works so well, all the material is pretty much concentrated at the tangent.
Go Huskers! |
| gholt |
Posted - 17/03/2008 : 02:27:07
Hello BW,
The 9 degree angle we're talking about here is known as the "angle of attack". The angle of attack is measured between the cord line of the airfoil and the relative wind angle. Here's a quick image to save a thousand words ...
Since you have an existing airfoil, you can simply form something around it to get the airfoil contour (yours are tapered, so an average will do just fine). This "something" can be paper with tabs, a piece of wire (clothes hanger) or any other thing you can think of which will conform to the shape. After you get the shape, connect the leading edge and the trailing edge with a straight line - that's the cord line.
Next in a plan view draw a line from the center of your arbor to where the airfoil will sit. Place the cord line at 90 degrees to the radius you've just drawn. Now pull the trailing edge in until you have a 9 degree angle of attack ... This is where you will want to start your testing.
G. |
| BushWhacker |
Posted - 16/03/2008 : 22:40:20
Thanks gholt;
The 9 degree pitch is definitely a step in the right direction, but I guess I'm in uncharted waters concerning the enclosed foil with a concave surface. It must be time for some good old fashioned trial and error.
Cheers!
BW
Everything should be made as simple as possible, but not one bit simpler. - Albert Einstein |
| gholt |
Posted - 16/03/2008 : 18:55:06
Hello BushWhacker,
Ed Lenz continues to do a great deal of development in this area and you can find some very valuable background information here -
http://www.windstuffnow.com/main/vawt.htm
He continues by describing the 9 degree pitch angle he derived here -
http://www.windstuffnow.com/main/lenz2_turbine.htm
Garland
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