The use of fixed, lift-type blades is a waste of time. The Sicard/Bayly-Kentfield VAWT and the Sharp VAWT demonstate that passive, infinitely variable pitch control based on centrifugal pendulum spring blades, is far superior. Annually, about 50% more energy can be converted (based on a letter to me from Professor Emeritus J.A.C. Kentfield at the University of Calgary). And the VAWT are actually easier to build.
You keep talking about these designs that were studied decades ago. My question is why haven't they been pursued? Are there commercial versions out there? Please do not ridicule the work of people in this forum; we are learning and we are having fun. If you have a better way, by all means show us with a working model.
I don't believe that one solution fits all circumstances. You mentioned on another thread that drag turbines are good for pumping because of their low speed and high torque. I like simple designs because fewer moving parts usually means more reliable. For the wind conditions I'm designing in, I don't want high power in high winds because that would force me to build a large alternater for that twice-a-year wind.
-- Edited by Caleb on Wednesday 18th of August 2010 02:04:19 AM
The use of fixed, lift-type blades is a waste of time. The Sicard/Bayly-Kentfield VAWT and the Sharp VAWT demonstate that passive, infinitely variable pitch control based on centrifugal pendulum spring blades, is far superior. Annually, about 50% more energy can be converted (based on a letter to me from Professor Emeritus J.A.C. Kentfield at the University of Calgary). And the VAWT are actually easier to build.
Steve Would it be possible for you to run sims on this if I gave you the proper overlay and spacing for a paid of 24 inch chord length foils based off of the drawing in this article.
Sure if you want to make things easy on me (which means quicker results) this is what you need to give me.
1) X,Y coordinates of your blade shape with the mounting point defined as (0,0). The blade moves in the -X direction. +Y is the outside of the VAWT, -Y is towards the center. Define it with no angle of attack (or angle of attack 0 degrees) I usually use about 60 points.
[If the mounting point of 0,0 is really hard, I can shift the blade without too much extra work.]
2) The radius you want to use (center of VAWT to blade mounting point)
3) Number of blades
4) Angle of attack you want to use, (please also tell me nose in or nose out so I don't get confused.)
5) Wind speed you want to run.
The sim will be 2d, and if you want I can use my new software to allow it to spin itself up from still if you want to see how it starts. (Although remember sim shows my VAWT spins up, and it really doesn't.) Torque and power will be 'per meter of blade length'
The bulk of the work is in defining the blade. Once that's done changing the AOA, radius, wind, etc are just a few numbers and waiting a few days for a new sim to complete.
If you find a good blade, I'll put it on my frame.
By the way, my simulation is laminar flow, which seems to work pretty well for small turbines. Your 24 inch cord and ??? diameter might be pushing the Re to the point where laminar flow isn't valid. Is that 24 in for a 60in diameter VAWT?
-- Edited by sjh7132 on Monday 9th of August 2010 04:34:20 PM
Steve Here is a reference work that is driving my new Sav blade design. It should be posible to achieve TSR 1.6 with a pair of these blades. Notice the bump that helps eliminate delamination allowing the TSR 1.6. I have also found research into the perfect blade spacing and in another blade over lap. This other research should improve on the articles design. Would it be possible for you to run sims on this if I gave you the proper overlay and spacing for a pair of 24 inch chord length foils based off of the drawing in this article. The new numbers even take into effect the diameter of the center shaft and the shaft needs to be in the Sim. The blade thickness is about 1/4 inch and the 24 inch measurment is from tip to tail. The nice thing about this design is at the point of rotation where a normal Sav losses power and may even create negative power ( blades inline with wind flow) the lift part kicks in and generates even more power. The spacing changes maximise the power added from one blade dumping wind into the other. My concern is at TSR 1 and greater what happens to the drag part of the power curve.
Steve Do you think the starting problem with larger diameter Vawts is because of incorrect solidity? The other side to the problem is identical TSR on a small diameter Vawt is faster rotation than a large diameter. It could be that a small Vawt looks to be spun-up but is still at too low of a TSR. The key is the amount of power available from large diameter although you could just make the smaller one taller (windspire). I'm still stuck on creating a 60 inch for home use because of some articles I've read about minimum diameter caused by distubances created by the windward blade movement and useable power extraction. The bigger the diameter the bigger the chord length can be for the same solidity. Most of these formulas don't even consider what blade style is used because there based on power extraction maximums. It's up to us to find the proper blade style for a given sized Vawt to achieve the highest level of this maximum power extraction. Most researchers have given up on the 5-10 MPH range do to the small amount of power available. I'm starting to sway towards a low wind speed Sav that has partial lift taking it to TSR 1.6. At least I know it can generate power in low winds and a natural stall at 1 1/2 wind speed making it safer. They are also easier and cheaper to make.
In my experiments with the elliptical blades (these were real life by the way), I scaled the blades to diameter to keep the solidity the same. I don't have a good explaination. Maybe Re makes a big difference? Rotation Inerta tends to go up with the size ^2, but torque is only linear with size. Maybe that's part of the problem.
Edit: Looking back at my notes, I had some restrictions on the size of foam I could find. The larger diameters had larger blades, but they weren't perfectly scaled, so the solidity on the larger diameters did drop.
-- Edited by sjh7132 on Monday 9th of August 2010 04:06:47 PM
Steve Do you think the starting problem with larger diameter Vawts is because of incorrect solidity? The other side to the problem is identical TSR on a small diameter Vawt is faster rotation than a large diameter. It could be that a small Vawt looks to be spun-up but is still at too low of a TSR. The key is the amount of power available from large diameter although you could just make the smaller one taller (windspire). I'm still stuck on creating a 60 inch for home use because of some articles I've read about minimum diameter caused by distubances created by the windward blade movement and useable power extraction. The bigger the diameter the bigger the chord length can be for the same solidity. Most of these formulas don't even consider what blade style is used because there based on power extraction maximums. It's up to us to find the proper blade style for a given sized Vawt to achieve the highest level of this maximum power extraction. Most researchers have given up on the 5-10 MPH range do to the small amount of power available. I'm starting to sway towards a low wind speed Sav that has partial lift taking it to TSR 1.6. At least I know it can generate power in low winds and a natural stall at 1 1/2 wind speed making it safer. They are also easier and cheaper to make.
Lynx Steam wrote:Going to bigger diameter seems not to work for self start. Smaller diameter lessens the power output.
I found that same thing when playing with my elliptical blades. Small diameter would take right off. Larger diameter would need a push start, and even larger I couldn't push fast enough to make it work.
I can atest that a symetrical blade works. The combined chord length of my two blades is 15% of the circumference. Diameter of the circumference (through center of wings) is 2.0 X one chord length, or roughly 1 x combined chord length of both blades. The profile of the blades I am using are roughly 0020 NACA, with one trick, which some of you may have picked up on. I just don't want to share it with the world. The paper model below will provide for the trick.
Going to bigger diameter seems not to work for self start. Smaller diameter lessens the power output.
Make a paper model. Take an 11 x 17 chunk of stiff paper and brings the edges together without creasing the leading edge for a 8.5" x 11" wing. Tape the trailing edge. Now you will have a NACA 0020. Make two of these. Get a 3 foot long piece of wood, 1" x 1/4". Accurately slot the paper for this wood 1/3 back of the leading edge, 0 degree AOA. Hot melt glue or elmers both sides of the paper in the shape of the airfoil. The stick will act to hold the airfoil shape somewhat by attaching at inner surface and outer surface of the wing. Drill a small hole at the center of the stick for a nail. Use a small washer or two. If you want to try three of these wings go to 4 foot diameter, use a small wood disk and three spokes nailed and glued. Balance with three is critical, so add or subtract weight til no part of the turbine is heavier. Balance through the disc with a piece of wire held horizontal. Add a brass tubing bearing for better stability and speed. Now you can bend the trailing edge in or out and see the change to speed. You can add shaped foam to hold the airfoil shape at ends (ends only), shape and glue inside the paper at wing tips. Add winglets to add horizontal stability with stiff paper glued to the foam inserts. Even up with leading edge, 1" extension off trailing edge. This will prevent yawing of the blades. Try it and report back what rpm you get.
At this point two different people have gotten the same results with the cambered blades. It appears to be a bad choice no mater what direction the blades are mounted. The industrial one's spin them up to TSR 5 or so and they may be working purely from simulated wind do to rotation. I think at this point we should try and stick with symetrical blades because several people have had good results. Finding the right size for the choice of blade style and length seems to be the next logical step. I found and posted some stuff for chord length and solidity which is based on power extraction and not blade style. Has anyone seen any papers on blade length or height. Is there even a restiction for such things other then mounting and weight.
Well, there is middle ground between the highly cambered S1223 and a symmetrical foil like a NACA0018. emagnets on youtube seems to have had some luck with an asymmetric blade (that's still convex on both sides.) It's interesting because he build 2 VAWTs, one with the most convex on the outside and one with it on the inside. Inside works much better.
If he doesn't post on this forum in a day or two, I'll post the videos because they are worth seeing.
I think in general the longer the blade the better, as long as you can support it and keep it from bending.
At this point two different people have gotten the same results with the cambered blades. It appears to be a bad choice no mater what direction the blades are mounted. The industrial one's spin them up to TSR 5 or so and they may be working purely from simulated wind do to rotation. I think at this point we should try and stick with symetrical blades because several people have had good results. Finding the right size for the choice of blade style and length seems to be the next logical step. I found and posted some stuff for chord length and solidity which is based on power extraction and not blade style. Has anyone seen any papers on blade length or height. Is there even a restiction for such things other then mounting and weight.
Steve, what problems did you have with the s1223? Did you figure out what went wrong could you overcome the problem?
Watch the videos in 'Another VAWT attempt from Steve' It's in the video called 'More wind turbine experiments.' Basically I just couldn't get it to spin with or without a push. Although it might have spun if I could have pushed it faster. I had a 9 degree offset to the AOA which I think didn't help.
After it didn't spin, I simulated the turbine and got the same results.
May be their is the chance to add flaps like on areoplanes.
Or you can shift the whole blade, using something like "voith schneider". The switzerland company "envergate" has build a very nice VAWT with shifting blades. For me until now its the best VAWT i have ever seen.
Interesting to see that the 300 watt VENCO model has a TSR of just 1,5 and the middle model has a TSR of only 2,3. Into theoretical discussions about lift type VAWTs they ever talk about much higher TSRs. May be thats the different between theorie and reallity. :)
Joesan. The forklift makes a great test rig. If you are making any more blades you might want to have a look at the S1223 which is a further development and has 20-30% more lift than the S1210 and still avoids the dead band at low speeds, although Steve had some problems with it. Great to see the revs at that windspeed- was that on the trailer or forklift? Allan
I did not get any measurements. That model was only made so I could proof to myself that using this blade profile would be a good start. I had a hell of a time trying to stop it though. It was mounted on a small car trailer which nearly took off, partly because of the inballance. Got the idea from Durham university. Below is the link to the report that I based my decision on. You probably know it already. http://homepage.ntlworld.com/julien.dourado/zeph_tech_web/academic_research/6_performance_mains_connected.pdf
joesan wrote:The 3m model hit about 1 rev/sec at maybe 5 or 6m/s very disturbed wind. Again, no load on it.
The blades were wet laid fiber glass epoxy, 50 cm chord and 7kg ea. I used wooden laminated arms and the lot was not very well balanced. The camber was pointing towards the inside.
It sounds like your 3m model was one of the more successful lift type VAWTs on the this board. Did you get any power measurements?
The 3m model hit about 1 rev/sec at maybe 5 or 6m/s very disturbed wind. Again, no load on it.
The blades were wet laid fiber glass epoxy, 50 cm chord and 7kg ea. I used wooden laminated arms and the lot was not very well balanced. The camber was pointing towards the inside.
I really appreciate your advise and your interest in my ordeal.
A earlier three bladed model at 3m diameter really did self start and went into lift mode. Currently I have three blades mounted with this new model, so first I will change them for the curvature to face outwards. Going for two blades means that I will have to take everything apart and re-drill the holes for the arms. So, if three don't work then I will try two. Thanks for the advice, Marcus.
One thing I am worried about is the diameter. I want to reach 200+ rpm because I have a certain alternator in mind. Can this be achieved at say 10 - 12m/s?
Looking at the photos and your airfoil orientation I would surmise that the turbine will almost act as though in a stalled position. The forces acting on all five blades at any given time almost cancel. Lift might overcome this at 80-100 rpm if you could get it there. Try just two blades opposed. There are points where the forces nearly cancel, but the rest of the rotation is either lift or drag. What you are looking for is increasing rpm and increasing lift forces. If you get results from two blades, try three.
Klyde wrote:The reason is the lift direction for a rotating Vawt is towards the center and slightly forward.
With a symmetric air foil I know that's not true, the lift is in half the time and out half the time. (Thus the stress on the pole problem.) Are you saying this foil is so asymmetric that the lift is always inward? That's hard to believe given the virtual AOA from the circular path and mounting position.
Still the results are the same. If you want max lift in the front of the VAWT they need to be mounted concave side out.
Thanks for that. I have read and heard about this theory and I shall try this next week. I will let you know how it goes. Luckily i have designed the blade attachments so that they can easily be changed round.
Someone was writing about a 9deg angle. should this be tried too, and if, then which way would the blade have to be pioted? Leading edge towards the centre or away from it?
Joesan Although there is limited discussion on the subject from the few papers I've read the suggested mounting is with the curved side (chamber) out not in. If it's possible to remount them this would be good test of that theory. The reason is the lift direction for a rotating Vawt is towards the center and slightly forward. The windside of the Vawt removes some of the power thus slowing the wind down and the downwind side therefore see slower wind. The negative effect of the downside is less than the positive gain on the windside which makes cambered blades useful.
The blade attachment is at approximately 15cm from the leading edge. appr. 33%.
I have tried spinning it up by hand to about 1 rev every 2 sec. It does not hold the speed but will slow down slowly. Again this was in a 4m/s undisturbed wind.
I tried same with 3 blades with the same result.
Previously I made three 50cm blades s1210 too. I mounted them on a rover wheel hub at 3m diameter. this worked fine, but the blades did look a little big.
When I then got the offer of thees 5 blades, I just jumped at the chance.
Hi Friends of VAWT's, I am from Ireland, new here and am surprised about the accumulated knowledge in this forum.
I have recently aquired 5 blades s1210 with a chord of 400mm and a length of 2000mm.
I have mounted them using 2 x40mm steel box section arms on a home made hub diameter 4.5m (no alternator yet) with 2 angular contact ball bearings. Hardly any friction at all. The total weight is around 85kg.
The blade angle is 0 deg and the camber line is pointing inwards.
The turbine starts rotating in a very light breeze, say 1m/s but only very slowly. At 4 m/s it does not exceed a rotational speed of 1 rev every 12 seconds.
What am I doing wrong? Any help would be greatly appreciated.
Steve Ignore the time when it's traveling against the wind and with the wind which basicaly does not add or subtract power and focus on the up and downwind cross paths. The AOA is the combination of the real wind and your forward motion. When you are seting still and are in th upwind cross path the wind is hitting the side of the blade which is extreme AOA. If you are seting slightly before then you have a more moderate AOA. So under these circumstances then yes you have High AOA. As you transition form upwind downwind you will enter small areas of the correct AOA and this is how startup begins. With a three bladed Vawt one of the blades should be in the right spot. As you increase speed the AOA of the crosswind points get lower and at the same time you start getting an increase from zero in the upwind and down wind sides. After you speed up past TSR 1 you get an AOA all the way around with the power sections comming down and what were the dead zones now producing power because of the vitual AOA. This average AOA is what most papers are discussing. By TSR1.7 the stall generated by the extreme AOA in the power sections is overcome by virtual AOA and the Vawt is free to spinup till it stalls without the need af additional wind power. These are lift based and therefore travel many times the speed of the real wind and most articles are about them while they are running because most are power spun up.. This AOA at low speed which is high in two spots but zero everywhere else is what makes it hard to start. Most the time at low speed the extreme AOA in the power spots is added to the roataion by drag not lift and pushes the blade around. As you increase speed the AOA on average around its rotation increases until it exceeds the blades stall angle all the way around and then no lift is generated.
At some point the power sections lowering and the dead zones comeing up will meet and you will have a virtual AOA thats even almost all the way around. If you design a vawt with this in mind you choose the TSR that fits this perfectly. Once you choose the correct TSR to run in this virtual AOA you can calculate all the other design qualities that make it happen and if done correctly it will not run away. This is how most professionals do it. They start with TSR but keep in mind that everything varies with wind speed and they can still get out of hand. So look for your average wind speed then choose a TSR for that speed or what rpms you want for that speed and then design everything to achieve that TSR.
-- Edited by Klyde on Saturday 24th of July 2010 04:05:21 PM
Steve The AOA is low at low speeds because it is the combination of real wind and virtual wind. It increases as rotational speed increases and tops out at whatever AOA is generated by the mounting point of the blade along its chord.
That sounds backwards to me. Do the thought experiment. If the VAWT it spinning at 1 RPM then the virtual wind is negligible. The real wind will hit the blade at AOA's anywhere from 0 to 360 degrees.
As you speed the blade up, the AOA's will be reduced, oscillating around that virtual AOA caused by the mount point. If you spin very fast the real wind is negligible and the AOA is the one caused by the mount point.
Steve The AOA is low at low speeds because it is the combination of real wind and virtual wind. It increases as rotational speed increases and tops out at whatever AOA is generated by the mounting point of the blade along its chord.
From what I understand once you hit true TSR 1.7 and you have correct solidity, meaning maximum power extraction, it will take off into full lift mode. The problem is getting a correct sized blade to make the transition from TSR 1.3 to 1.4 into TSR 1.7. At Tsr 1.7 the AOA is high enough to generate strong lift in most blades. Once this happens it will spimup untill AOA goes beyond 15 - 20 degrees and the blades reach stall.
and wants to build it somewhere. That shape is pretty much similar to what I had in mind in the post below, except I'd do the whole balde that way and not just a segment.
I know what the problem is and it's what I've been trying to eliminate. The angle of attack is to low at slow speed to take the blade into full lift mode. Once spun-up the angle of attack goes up to 12 to 14 degrees and the blade reaches max lift. The vawt will spin but can not reach a high eanough TSR to spin-up. Lift Vawts run in the 4-6 TSR range. From everything I've read if the solidity is good and you reach TSR 1.7 or higher than it will take off. If you build with a blade that has high lift at low AOA then it stalls before spin-up. I'm shifting towards a Sav rotor instead of lift. At low wind it's the best bang for the buck. I have a modified sav foil that actually should reach a TSR of 1.6 due to lift designed into it.
The strange thing is it (the spin up problem) doesn't come out in my simulations, and I'm pretty sure the wings are stalling where they are supposed to. I found a web page that compared stall points for javafoil, xfoil and wind tunnel results at low Re on the NACA0012. I ran the same NACA 0012 foil and it looks like it's going to fall right on the wind tunnel numbers. When I get back home I'll superimpose the graphs and post the results. My Cd did come out too high though, almost a factor of 3 or 4 too big. I'd expect that to make the turbine look worse, not better.
So how can a blade have lift at the high AOA (low rotational speeds). Then have a band of speeds where it won't accelerate, then at a TSR of 2 or so take off again? Are there 2 different types of lift?
Here is the wing profile I have been using. Note the dimensions - they correspond to a three foot diameter and a two blade design. The dimensions are exact.
I am posting this because I know it self starts and it self starts to TSR +1.
Maybe it corresponds to a particular number airfoil.
I know what the problem is and it's what I've been trying to eliminate. The angle of attack is to low at slow speed to take the blade into full lift mode. Once spun-up the angle of attack goes up to 12 to 14 degrees and the blade reaches max lift. The vawt will spin but can not reach a high eanough TSR to spin-up. Lift Vawts run in the 4-6 TSR range. From everything I've read if the solidity is good and you reach TSR 1.7 or higher than it will take off. If you build with a blade that has high lift at low AOA then it stalls before spin-up. I'm shifting towards a Sav rotor instead of lift. At low wind it's the best bang for the buck. I have a modified sav foil that actually should reach a TSR of 1.6 due to lift designed into it.
This might be something to look into that would help with the low speed part of a Vawt starting. Is there any way to place a wire in you software?
Yes, I could put a wire in my software. But the problem is that right now in the simulation I don't see the startup problem. There is a positive power (even with the structure) all the way down to 10 RPM. Unless there is significant friction somewhere, I don't see why it hit some max (low) speed until spun past it.
Steve I don't know which blade you want the start speed for. If it's the S1223 the modified one I came up with should start in 3-5 MPH winds and produce some useble power in the 10-15MPH range. The drawing you show dosn't look like it would work because the air flow would delaminate at low speeds. The tricky part of the S1223 is that thin trailing edge needs to be very thin and very strong. If it flexes at all it won't perform very well.
That may be the problem. I did the same thing you did, because on my test cuts, the trailing edge was so thin that light passed through it. So I sepeareted the top and bottom side by .05, which thickened the whole blade a little. Still it's only foam and very thin at the end. I couldn't see it flexing, but it might have been.
Steve I don't know which blade you want the start speed for. If it's the S1223 the modified one I came up with should start in 3-5 MPH winds and produce some useble power in the 10-15MPH range. The drawing you show dosn't look like it would work because the air flow would delaminate at low speeds. The tricky part of the S1223 is that thin trailing edge needs to be very thin and very strong. If it flexes at all it won't perform very well. This was discussed in an RC Plane forum. The modifications I made were very slight thickening of the fattest part which shifted it down to the 3-5 MPH range. The drawing you show doesn't look very areodynamic to me. Electrondady posted a drawing that looks very similar to mine in an earlier thread. If you use an Naca0018 then you would use 0 Degrees AOA because of its symetrical design. -- Edited by Klyde on Monday 12th of July 2010 03:27:19 AM
-- Edited by Klyde on Monday 12th of July 2010 03:31:42 AM
Steve In your drwing below I would consider the orange line to be the chord line. The top of the drawing would be towards the center of rotation and you would in this case rotate the trailing edge down so the orange lines front point remains still and the new orange line trailing edge would be 9 degrees in reference to the original. You would also mount it about 34 percent back (2.72 inches for an 8 inch chord) from the leading edge.
-- Edited by Klyde on Sunday 11th of July 2010 06:53:20 PM
That's exactly what I did, including the mount point. It didn't work as well as expected. What do you think startup speed should be for that design?
Steve In your drwing below I would consider the orange line to be the chord line. The top of the drawing would be towards the center of rotation and you would in this case rotate the trailing edge down so the orange lines front point remains still and the new orange line trailing edge would be 9 degrees in reference to the original. You would also mount it about 34 percent back (2.72 inches for an 8 inch chord) from the leading edge.
-- Edited by Klyde on Sunday 11th of July 2010 06:53:20 PM
Steve. Checked his formula and is correct (at least its consistent with his prescriptions on solidity). I'm no geometry maths genius but I dont understand why you divide by pi - the swept area is a rectangle. Is this possibly a hawt formula? Stick close to your 8" (0.2m) as he warns below that, Re drops off significantly. Maybe higher solidity is just one of those trade-offs. Allan Steve. Just had another look. Kirke describes solidity of 0.2 - 0.6 as medium. If you can access his thesis Section 2.4.3 (pdf block 4) discusses solidity issues. There should be a graph somewhere which shows power curve relative to solidity for lift vawts.
The equation I use solidity is the ratio of wing area to the surface area of the cylinder swept out by the turbine. I guess yours is the ratio of wing area to the rectagle swept out by the turbine.
The .2 to .6 range and your equation puts my 8" wings in the right range (.4).
Thanks for the advice. When I get a chance I'll cut some new wings.
Steve. Checked his formula and is correct (at least its consistent with his prescriptions on solidity). I'm no geometry maths genius but I dont understand why you divide by pi - the swept area is a rectangle. Is this possibly a hawt formula? Stick close to your 8" (0.2m) as he warns below that, Re drops off significantly. Maybe higher solidity is just one of those trade-offs. Allan Steve. Just had another look. Kirke describes solidity of 0.2 - 0.6 as medium. If you can access his thesis Section 2.4.3 (pdf block 4) discusses solidity issues. There should be a graph somewhere which shows power curve relative to solidity for lift vawts.
-- Edited by Nangkita on Friday 9th of July 2010 05:54:18 AM
On solidity (= No of blades * chord length(in metres) divided by dia (metres))Kirke believes around 0.1 is the ideal for lift-type vawts. Your 8" on 60" would come out at 0.4 which may be a bit high. Kirke concludes:
I usually calculate solidity as blade chord * num blades / (dia * Pi). Are you sure your method is the one they use for the suggested 0.1 solidity? A 2 inch blade seems pretty small.
Using my method:
3 * 8 / (60 * PI) = .127
It looks like 6.2 inches would be a solidity of 0.1.
Hmmm... that diagram looks eerily like what I have in mind for the angled blade vawt, except for the big chunk notched outa the backside like Steve's foam wing thing.
Our wretched low zone-2 wind resource needs the hook to get it moving.
Steve. The chord line, which is the one to be toed in 9deg and curved to mill dia is the horizontal line in Electrondady's post of 23 June. The orange one in your drawing, although it looks a bit squashed-up for S1223! If you are modelling this you might want to compare it with S1223SRT and let me know how you go. On solidity (= No of blades * chord length(in metres) divided by dia (metres))Kirke believes around 0.1 is the ideal for lift-type vawts. Your 8" on 60" would come out at 0.4 which may be a bit high. Kirke concludes:
Turbine of 4m dia with 3 blades, chord 0.2m, should self start at 4m/s with Cpmax of ~0.35. Darrius of less than 4m dia unlikely to have acceptable performance because of need for low solidity and chord of not much less than 0.2 to avoid very low Re.
Tom. The Kirke work referred to below is written like a textbook. Although his objectives are for a variable pitch vawt suited to lower speed purposes like water pumping it is still useful for electricity generation. This site has quite a lot of data on different aerofoils http://www.ae.illinois.edu/m-selig/ads.html Remember "Google is your friend along, with Wikipedia". Allan
-- Edited by Nangkita on Thursday 8th of July 2010 01:27:59 AM
AOA. If you look down from the top the blade should be perpendicular to the center axis attached about 34% from the leading edge. If you rotate the leading edge in toward the center 9 degrees it gives the best result.
Sorry, I still don't understand. Which of these lines (if any) would you consider to be 0 degrees AOA for this blade?
