Wind speed power verses Generator Power out

[bvan1941]

"m12ax7"  (in another post) today, made a comment about the difference in generator torque / impedance matching to overcome part of the problem. He rightly pointed out there were trade-offs too. It started me thinking.
Using "Alton's wind Speed Table" as a reference, I've been trying to figure out adequate Rotor size for my modest W/T project.

First of all I'm talking about wind speed between 9-20 mph !
I have observed that accepted concept for Rotor design/speed is to go with higher TSR (3) bladed rotors (for many sound reasons). Part of the (higher TSR ) reason is that they do, is there's not much power in the wind at lower wind speed and higher TSR Rotors need RPM's to develop the torque required by the load and in return, the generator creates, in meeting load demands.
Some recent innovativeexperiments have been made by well known Forum contributors.

Example : Chris Olsen has developed the "chain-driven transmission" then coupled that together with a Clipper and the MPPT Controller, with outstanding results. but He also demonstrated all this with a smaller Rotor!     

Here's my proposal for reasonably more power in the 9-20mph wind band.

"Why not use a (4) bladed prop for more torque and use a "chain-driven transmission" similar to Chris's design for more Generator speed and power in the mid-range "normal" wind speed band."

I think the (4) bladed Rotor designed for good torque and medium speed would be have some inherent speed control as wind speed  increases above the 20 mph range. "The analogy is high speed aircraft use a thinner wing for speed thicker wings cannot get to the upper speeds because of aero dynamic drag, but on low speed (STOL- SHORT TAKE OFF AND LANDING ), Aircraft they use this high lift design to their advantage."
Just a thought,
Bill

[ChrisOlson]

"Why not use a (4) bladed prop for more torque and use a "chain-driven transmission" similar to Chris's design for more Generator speed and power in the mid-range "normal" wind speed band."

Bill, I think I would go with five blades instead of four.  I experimented with a four blade rotor on a geared turbine for several months.  It worked very will thru our typical lower wind speed summer.  But I could never get it dynamically balanced.  I fiddled with that thing every time I had a chance to try to get it so it wouldn't wag the tail on the turbine, but to no avail.

Going to five blades will make it a lot easier to balance.
--
Chris

[bvan1941]

Chris,
You are right I should have thought of that too!
It seems even numbered blades always seem to have a significant problem, where odd numbered blades seem to work out OK.   
Bill

[bvan1941]

Chris,
in view of your experiences with the S809 and GOE -222 airfoils, what would your preference be to a (5) bladed airfoil in the scenario of 9-20mph? or use another type? If so what do you recommend?

1. Would you give any thought for a much SMALLER (5) bladed GOE -222?  Being smaller a diameter my thought would be that its TSR
would enable it to excel under heavy loads at the middle windspeeds. Wouldn't it work out to provide maximum power.

2. Would the GOE-222 be able to be controlled there?

3. If I under stand your previous statement about the S-809 airfoil, it would not start to "fly" until well into the upper half of the wind band described. This would apparently lose out to the GOE-222 there. Missing making adequate power in the lower half of the band of wind described.

4. Would your "chain-driven transmission" be a good fit for this scenario?
Just interested in your thoughts with all your trials and experience with airfoils and control at different windspeeds.
Bill

[ChrisOlson]

in view of your experiences with the S809 and GOE -222 airfoils, what would your preference be to a (5) bladed airfoil in the scenario of 9-20mph? or use another type? If so what do you recommend?

If you want low wind, low speed, high torque power, definitely use the GOE222.  The S809 has to RUN (and I mean at high speed) to make power.

1. Would you give any thought for a much SMALLER (5) bladed GOE -222?  Being smaller a diameter my thought would be that its TSR

To get decent power from marginal wind speeds you need swept area.  It's like the old saying in tractor or truck pulling engines - "there's replacement for displacement".   If 575 cubic inches is good, 650 is better.

2. Would the GOE-222 be able to be controlled there?

Easily.  With five blades it would never hit very high speeds, and hence have no problems with furling.  But the torque would be tremendous in higher winds.

3. If I under stand your previous statement about the S-809 airfoil, it would not start to "fly" until well into the upper half of the wind band described.

No, the S809 works fine in lower wind speeds.  It just has to be running much faster.  It is a more slender, high speed, low drag, more efficient airfoil than the GOE222.

4. Would your "chain-driven transmission" be a good fit for this scenario?

Yes, it would work excellent.
--
Chris

[bvan1941]

Chris,
good info, will post if I'm going to incorporate any of these concepts. Those GOE-222'S are not cheap but it would a great experiment.
I would like to be able to demonstrate those
 blades with a (5) blade configuration along with your "chain-drive" to maximize power made good in that powerband. I don't know if anyone has done that with Royal's light weight poplar blades. I think the "combo" would definitely improve performance for many people in low-medium wind speed areas.
(If money were no object !!!)
Bill

[ChrisOlson]

I carved a set of GOE222's myself and it wasn't all that hard to do.  I made them from spruce, roughing them out with a hand power planer, then doing final shaping with a custom-made draw knife and sanding.  I think they're actually easier to make than twisted blades.

I've used both the poplar and ash blades from Royal Wind & Solar, and I prefer the poplar because they're lighter.

You could also use a conventional flat face airfoil like a NACA 4415.  The 4415 is pretty fat and those fat airfoils make good lift at slow speed.  But the GOE222 still makes more torque than the NACA 4415.  On a slow turning rotor like that those GOE222's would be awesome because you can't fully stall them.  The harder you load those down, the harder they pull.  You get a set of them GOE222's lit up and you can short a strong generator and can't stop them.  On a 12.3 foot three blade rotor I've seen torque from those blades that equals what a healthy small block Chevy can put out on the dyno.
--
Chris

[Wolvenar]

Can someone who knows what they are talking about please post references or links to what these GOE222 NACA 4415 are in a posting so everyone don't just go... huh? oh well next topic..
Yeah, can Google it but how many will.

[wolvtest]

Ok I'll do it 
GEO222
http://www.worldofkrauss.com/foils/435


NACA-4415
http://www.worldofkrauss.com/foils/1694

I was going to post on S809 but worldofkrauss.com stopped responding with

Application error
Rails application failed to start properly

[ChrisOlson]

Can someone who knows what they are talking about please post references or links to what these GOE222 NACA 4415 are in a posting so everyone don't just go... huh?

Sorry.  The NACA airfoils were developed by the National Advisory Committee for Aeronautics for aircraft wings.  They were never developed for wind turbines, but they work well at about 32% efficiency, and they're easy to carve.

All the NACA series airfoils are designated with the first digit describing maximum camber as percentage of the chord.  The second digit designates the distance of maximum camber from the airfoil leading edge in tens of percent's of the chord.  The last two digits designate maximum thickness of the airfoil as percent of the chord.

The GOE airfoils were developed by the Gottingen Aeronautics Research Center (now the German Aerospace Center) in Gottingen, Germany.  The GOE222 is a time tested airfoil that has been used on wind power systems since the early 1940's.
--
Chris

[bvan1941]

Does,
anyone have any personal experience they would like to share with (5) bladed wind turbines? Do they really make more power than the conventional 2/3 blade versions?
I know some have talked about high speed blade versions having worked for Ametec type conversions, but I was thinking more of the 8'-10' diameter rotors with homebrew or motor conversions in 700watts(+) category.
Bill

[ghurd]

If designed PROP-erly (    ), they should make 'the same' power regardless of the blade count.

It mostly comes down to matching the PMA.

More blades turn slower (in typical designs).
Less blades turn faster (in typical designs).

Here is a servo motor.
It did not need speed, it needed torque to keep out of stall. (or bigger blades, but I'm not exactly in an enviroment for bigger blades).
My quickie solution was some seriously short wide blades made to ZubWoofer angles.
It worked well, except the flimsey blades bent back and started to flutter, at about 14~16 MPH, IIRC.
Made 60~75W a few times when I was watching.
Seems like the dia is about 31.5", though I call it 'Ugly 30'.

G-

[ChrisOlson]

anyone have any personal experience they would like to share with (5) bladed wind turbines? Do they really make more power than the conventional 2/3 blade versions?

No, they don't.  Going from two blades to three, you can extract about 3% more power from the swept area.  Going from three to four you lose power.  The more blades you add, the more power you lose due to drag and aerodynamic efficiency problems.

There's a reason most of the commercially built very large turbines have three blades.  The reason involves both economics and efficiency.

The advantage to using 5 blades vs three would be very low wind startup, high torque available at low wind speeds, a slow turning, very pleasant, quiet running machine, and probably better power production on slow wind days when a conventional three blade rotor is trying to get up to speed but a five blade can extract power from what little wind is there.

The facts still are, that once you get a three blade rotor up to speed and making lift and power (usually 6 mph or so for most), you will not match it for efficiency with any other configuration of blade numbers.

"Low Wind Power" is a fallacy.  A 10 footer at 6 mph @ 30% efficiency will make 28 watts.  Assume a 10 foot turbine @ 28 watts 24 hours a day, 365 days a year.  You will generate 245 kWh.

Put that same turbine on a site that averages 12 mph and now you generate 2,303 kWh in a year - 9.4x  more power from an increase of 6 mph in wind speed.

A five blade turbine like you describe can make some useable power on a marginal site, and will probably do better overall than a conventional one because it will make power when the conventional one won't in the poor wind conditions.  But don't expect even a very large one to come close to what a conventional 10 footer can do on a good wind site that averages 12 mph.
--
Chris

[oztules]

Seems there are some misconceptions here.

The number of blades make no difference to the CP of the design.

The number of blades makes no difference to the tsr of the design. (can be the same for any number of blades)

There are no efficiency differences between blade numbers at the shaft.

If you go to a blade calculator (say altons) and plug your tsr, blade number and diameter in, the rpm and power at the shaft is the same for all wind speeds with any number of blades..... so thats the theory.

In PRACTICE this is not so easy to achieve. If you do do the above exercise, you will find the blades are impossible to actually build and have any strength when you get to high blade numbers.... they are so thin to achieve the same high TSR we expect with say 3 that supporting the force on them is no longer trivial.

Luckily, some folks (such as here: http://old.windmission.dk/workshop/bladenumber.html ) have actually built and operated 12 bladed designs, and achieved measured CP in the reigion of 0.47. Thats not too shabby at all.

If you only buy pre-made blades, then the more you add, the lower the TSR and the higher the torque, and all the things mentioned by Chris will come to pass...... but if you design for a TSR and build to those specifications (if possible) then blade number makes no difference.

Commercial mills didn't miss this. Two blades are cheaper to make for the same TSR, but wobble, and have their own problems. Three blades solve all those problems.... even though it is 50% dearer to make.... so they make these. Making three blades to go as fast as the 2 blade design is structurally significant, so they settle for a slower three blade with a bigger gearbox

5 blades for a given TSR offer no more power , no more ....or less speed, no better CP, TSR or any other advantage other than they will cost more to make, and be structurally weaker for the same TSR as a three blade version.

If we want more torque on a practical scale, we add more of the blades we have that are strong and available..... and we find lower speed operation, and higher torque.....but ONLY because we didn't change the cord and the pitch.

What we see and measure can lead us to the wrong conclusions if we dont fully appreciate what is really happening.

The most important factor is MATCHING THE LOAD to your blades, and blade count will make no difference..... loading will.

If you chose 5 blades of a three blade design, you will get more torque at a lower rpm, but you will need a much bigger alternator to match it physically (more magnet and copper and steel) for the lower rpms.



...............oztules

[ghurd]

That 5 blade idea came from ebay sellers?
ebay is not a good place to do blade research. You knew that.

It always amazed me they could claim 5 of those bent metal (slow) blades, or 6 or 8 of the Air-X knock-offs, would somehow make "more power" on an Ametek considering most peoples problems with Ameteks seems to be their 3 blades are not fast enough. Slower blades will not help if the PMA needs a higher TSR.

It all comes down to matching the blades to the PMA.
A slow 5-blade set of whatever 5 the guy happens to make for all his 2,3,4,5,6 and 8 blade sets may be fine on one PMA (like that Ugly 30),
but it won't make any power if it hardly ever reaches cut in RPM on another PMA (or treadmill motor).

Should be able to find out how to make a 2 blade, or 5 blade, of the same dia, that match a given PMA.
I just saw Oz posted, mentioned Alton's free calculator.
I like windstuffnow Ed's $5 download calculator.

A calculator lets you change things and see the impact of what is what.
That's when you can see a 5 blade setup, with 6" from the tip being only 1/128" thick, and getting thinner, is not a great idea on many PMAs.
3 blades is easier to build the blades. (2 or 4 can have balance issues, 5 is just more precise and need to make 5 instead of 3!)
G-