| Post Info | TOPIC: German VAWTS |
|---|
Bernd
Senior Member
Posts: 233
Date: May 8th
| German VAWTS |
|
|
Hello Windgen, it's not "my" design, it didn't invent this design.
The C-Rotor was patended in Germany on 25.06.1991 with patentnumber DP 41 20 908.
13 years later the patent ended and since this day it's free for everyone.
Bernd
-- Edited by Bernd on Saturday 8th of May 2010 08:57:10 PM
|
|
windgen
Senior Member
Posts: 209
Date: May 6th
| RE: German VAWTS |
|
|
Hi Bernd. This is windgen...I started this site a couple of years ago.
Could you let us know the patent number for your design, and is this a German patent?
|
|
wiboater
Senior Member
Posts: 242
Date: Jan 27, 2010
| RE: German VAWTS |
|
|
Thank's I had the account already but wasn't logged in.
|
|
sjh7132
Guru
Posts: 1252
Date: Jan 26, 2010
| RE: German VAWTS |
|
| wiboater wrote:
Vawtman , When I click your link all I get is a blank page on the otherpower site?
-- Edited by wiboater on Tuesday 26th of January 2010 01:23:18 PM
You have to make an account and log in before you can see his files.
Steve
|
|
wiboater
Senior Member
Posts: 242
Date: Jan 26, 2010
| German VAWTS |
|
|
Vawtman , When I click your link all I get is a blank page on the otherpower site?
-- Edited by wiboater on Tuesday 26th of January 2010 01:23:18 PM
|
|
keithturtle
Senior Member
Posts: 174
Date: Jan 26, 2010
| RE: German VAWTS |
|
|
Thanks, bernd
Neat pics, vawtman
I share technology any chance I get, if I think it'll work. Mebbe the airplane stucture will help the vawt to land safely should it take leave of its tower
<groan>
Turtle
__________________
Soli Deo Gloria |
|
sjh7132
Guru
Posts: 1252
Date: Jan 25, 2010
| RE: German VAWTS |
|
|
Lots of cool photos, Vawtman. In many cases I'm not really sure what I'm looking at.
In the photos of the stator winding jig, do you just use that to wind the coil and then break it off, or is that a permanent part of the turbine?
__________________
Steve
|
|
Bernd
Senior Member
Posts: 233
Date: Jan 25, 2010
| RE: German VAWTS |
|
|
"... What is you recommendation for the best c-rotor design? Straight or bent blade? ..."
In any case bent.
The leading edge or slash seems to be more efficient when the front is aerodynamic formed.
Also it seems to be better when the inner circle is fully round and not eliptical like the front.
The solidity should be around 35%, but we don't know exactly if this value is really the best.
I'm looking forward to your compare results !
Bernd
|
|
vawtman
Senior Member
Posts: 251
Date: Jan 25, 2010
| RE: German VAWTS |
|
| http://www.fieldlines.com/user/vawtman/files I had alot of fun designing this profile after many failed attemps. Not only does it selfstart but also could overcome the cogging of a 5hp motor conversion geared 3:1 i did for it early on. All done with common sense in mind.Has the wind hits the profile it turns. AIRPLANES DONT FLY IN LITTLE ROUND CIRCLES :) Lotsa fun over that time. Mark the tobacco farmer :) |
|
keithturtle
Senior Member
Posts: 174
Date: Jan 25, 2010
| RE: German VAWTS |
|
| link http://www.daswindrad.de/forum/viewtopic.php?f=2&t=21Yes, I had intended to build a c-rotor blade, but wanted to start with a lenz-type with curve to have a baseline for performance. The ribs are easy enough to make; this first one was proof of construction concept. Now I will build the true c-rotor in same dimensions and compare. What is you recommendation for the best c-rotor design? Straight or bent blade? Also, I saw the leading edge with two radii, a pointed front leading edge with a more open curve behind it. <( or c( More complex, but more efficient? I think so. Thank you for your input, Bernd! Turtle, still building
Soli Deo Gloria |
|
Bernd
Senior Member
Posts: 233
Date: Jan 25, 2010
| RE: German VAWTS |
|
|
hello Keithturtle, you saw a blade like this on my site ? Can you give me the link ?
What you build looks very nice, but it seems it's another lenz type with bended blade ?
Was your idea to build a c-rotor ?
Sorry but i can't follow what you want to say.
Bernd
|
|
keithturtle
Senior Member
Posts: 174
Date: Jan 25, 2010
| German VAWTS |
|
|
This is my understanding of a blade I saw at your other site, bernd.
8" radius, 40% chord, 24" long. Soaked balsa, basswood and lite-ply construction. I plan on using it for display at our local alt energy center; I plan on a smallish axialflux dynamo for it, should it spin fast enough.
Thank you for the inspriation
Turtle, never had an original thought
-- Edited by keithturtle on Monday 25th of January 2010 03:01:15 AM
-- Edited by keithturtle on Monday 25th of January 2010 03:02:47 AM
__________________
Soli Deo Gloria |
|
Bernd
Senior Member
Posts: 233
Date: Jan 19, 2010
| RE: German VAWTS |
|
|
"... if a VAWT has 3 blades the torque pattern repeats 3 times per revolution. ..."
Sorry, in my mind i saw only a single wing rotating. Of course you a right.
Bernd
|
|
sjh7132
Guru
Posts: 1252
Date: Jan 19, 2010
| German VAWTS |
|
| This is the torque graph for a 3 blade 280 RPM C-Rotor spin. As a rule I always ignore the first 0.02 seconds, although in this graph it looks like that wasn't enough. I guess I need to ignore at least 0.1 seconds. I may have to run some of these for a longer time. When I compare the power from this extended run to what I got from my first shorter run the difference is 2%. I'd be happy if any of this was accurate to 10%.  -- Edited by sjh7132 on Tuesday 19th of January 2010 06:36:01 PM
Steve
|
|
sjh7132
Guru
Posts: 1252
Date: Jan 19, 2010
| RE: German VAWTS |
|
| Bernd wrote:
"... The power is based on the average torque from the last x% of the rotation. For 2 blades x is 50%, for 3 blades it's 66% for 4 blades its 50%. ..."
Did i understand you correctly, that the power curves are formed from less than one turn ? Hmm... but the power do not create uniform during on rotation.
Yes, you understood correctly. I'm making the (big?) assumption that if a VAWT has 3 blades the torque pattern repeats 3 times per revolution. So I take either 1/3rd or 2/3rd of a revolution for the average. If a VAWT has 4 blades I work in 1/4th turns. In many cases this is a pretty good assumption. In some cases the pattern changes over multiple revolutions. It's a trade off between getting a reasonable estimate of power and using days of computer time to get really good numbers. If you are interested I will plot to torques from some of the tests I ran on the C-Rotor.
Steve
|
|
Bernd
Senior Member
Posts: 233
Date: Jan 19, 2010
| German VAWTS |
|
|
"... The power is based on the average torque from the last x% of the rotation. For 2 blades x is 50%, for 3 blades it's 66% for 4 blades its 50%. ..."
Did i understand you correctly, that the power curves are formed from less than one turn ?
Hmm... but the power do not create uniform during on rotation.
Bernd
-- Edited by Bernd on Tuesday 19th of January 2010 05:36:54 PM
|
|
Bernd
Senior Member
Posts: 233
Date: Jan 19, 2010
| RE: German VAWTS |
|
|
".. I built my Jelly2 turbine last night. .."
and where are pictures to which we all waiting for ? :)
Bernd
|
|
sjh7132
Guru
Posts: 1252
Date: Jan 19, 2010
| RE: German VAWTS |
|
|
It seems my simulation and your reality differ by quite a bit. Oh well, I'm still learning about simulation. Are you sure you aren't missing a factor of 2*pi in your TSR? :-) That solved my problems.
I built my Jelly2 turbine last night. Of course today there is no wind. :-(
I'm currently rerunning the torque test using a 1 RPM spin, and also doing a 120 RPM torque test. (single blade for both.)
__________________
Steve
|
|
Bernd
Senior Member
Posts: 233
Date: Jan 19, 2010
| German VAWTS |
|
| Hello steve and thanks for the new graph, i love it. :) I have added the curve for a 2 blade system which i measured here using my equipment. The curve i measured, based on the absolut values, was not as high like now into the graph, but comparing to the highest point of your 3 blade curve, its ok. So the green curve shows what i had measured and the blue what should be.  Bernd
-- Edited by Bernd on Tuesday 19th of January 2010 05:10:26 PM |
|
sjh7132
Guru
Posts: 1252
Date: Jan 18, 2010
| German VAWTS |
|
| Bernd, if you didn't like the last chart I put out, you are going to Hate this one. :-)  These numbers are based on a single rotation of the turbine. The power is based on the average torque from the last x% of the rotation. For 2 blades x is 50%, for 3 blades it's 66% for 4 blades its 50%. Normally I avoid using the first fractions of a second of a simulation because the air needs to get flowing. I looked for obvious mistakes in high power of the two blade but couldn't find any. Could it be real? -- Edited by sjh7132 on Tuesday 19th of January 2010 12:21:31 AM
Steve
|
|
turnymf
Veteran Member
Posts: 39
Date: Jan 18, 2010
| RE: German VAWTS |
|
| windstuffnow wrote:
It's really difficult to give a % between the two as the variables change throughout the rotation. This would also change exponentially by changing the wind speed. In order for drag to work it needs to be running at a speed lower than a TSR of 1. The optimum speed for a drag type turbine woulld be a TSR of .33 or 1/3 the wind speed, this would meet Betz law.
The intensity of the lift varies based on the angle of attack which in the case of turbines we have both positive and negative to deal with. Think of a plane flying an outside loop, although not a fair comparison because we have gravity to contend with. Wind direction would be similar as it traveled in a loop.
Since the Lenz2 design performs best at a TSR of .8 Lift plays the dominant role in winds from 0 to around 18mph. The fat wing design provides a very large lift force up to a certain wind speed at which point the excess drag on the upwind side only serves to burn energy. A STOL aircraft is extreemly efficient up to its designed speed at which point the airfoil must change in order to be more efficient at higher speeds, thus the use of slats and flaps. A jumbo jet can't land at 600 mph so inorder to get the speed down for the weight it has to change the airfoil shape to achieve a higher lift force at safer speeds.
Since the TSR of the Lenz2 is higher than optimum for the drag side it really only plays a small part in the extraction of energy - depending on the wind speed. As the wind speed increases the drag component grows on the upwind side making the downwind blade more dominant in the extraction process. Still becomming more and more inefficient as wind speed increases.
One way to look at it is the up wind wing at a TSR of 1 is moving into the wind at the same speed as the wind, so in a 10 mph wind the up wind wing sees 20 mph and extracts from that wind, the downwind side is moving away from the wind at the same speed the wind is comming in so there is no extraction.
Thanks Ed Still digesting the above Steve Wrote ------------------------------------------------------------------ Bable fish does a pretty good job at translating it. -------------------------------------------------------------------- Thanks steve I found the google translate button For those that don't know it's in the page drop down Hey Bernd Great site cheers |
|
Bernd
Senior Member
Posts: 233
Date: Jan 17, 2010
| German VAWTS |
|
|
"... Unlike your torque measurements, I believe a lot of force comes from the back side of the turbine, so I expect the power to go down if the solidity gets so large the airflow to the back is restricted.... "
The torque was measured at stand and with only one blade, where the wind can flow directly to the back side of the rotor.
Why the torque into my measurement was perhaps so different to yours, i wrote before.
I agree that there is surely a point where above more solidity gets infefficient.
Thanks for your support.
I'm looking forward to your experiments with the jellyfish design.
Its looking more like a tube, than a blade ?
Bernd
-- Edited by Bernd on Sunday 17th of January 2010 01:12:06 AM
|
|
sjh7132
Guru
Posts: 1252
Date: Jan 17, 2010
| RE: German VAWTS |
|
| Bernd wrote:
@ Steve
I don't know if you are still simulating the c-rotor.
But looking for the Betz laws ( the limit of 28%, like i wrote before, wasn't at TSR 1 but at TSR 0,5, which i determined as the best for loaded c-rotor)
i remembered that Betz says that at least 1/3 of the swept area should be free for the free flowing of the wind.
(i hope you understand my "english")
So i had the idea to use a higher solidity at the c-rotor because of now the free area is much greater.
Maybe you can position one or two more wings of the same size on the rotor, so that the solidity would grow up.
It would be nice for me to see if the cp would rise up too.
Bernd
-- Edited by Bernd on Sunday 17th of January 2010 12:17:13 AM
I'm currently simulating what I call the 'Jellyfish2'. In simulation a 1M diameter turbine has an efficiency in the 40+% range. I'm now simulating a small version of if that I can build. If that also has a high efficiency in simulation, I'll build it and do the measurements myself. When that simulation is done, I can try your c-rotor experiment. I will try 4 and 5 blades and see how that compares to 3 blades. Unlike your torque measurements, I believe a lot of force comes from the back side of the turbine, so I expect the power to go down if the solidity gets so large the airflow to the back is restricted.
Steve
|
|
Bernd
Senior Member
Posts: 233
Date: Jan 17, 2010
| German VAWTS |
|
|
@ Steve
I don't know if you are still simulating the c-rotor.
But looking for the Betz laws ( the limit of 28%, like i wrote before, wasn't at TSR 1 but at TSR 0,5, which i determined as the best for loaded c-rotor)
i remembered that Betz says that at least 1/3 of the swept area should be free for the free flowing of the wind.
(i hope you understand my "english")
So i had the idea to use a higher solidity at the c-rotor because of now the free area is much greater.
Maybe you can position one or two more wings of the same size on the rotor, so that the solidity would grow up.
It would be nice for me to see if the cp would rise up too.
Bernd
-- Edited by Bernd on Sunday 17th of January 2010 12:17:13 AM
|
|
Bernd
Senior Member
Posts: 233
Date: Jan 16, 2010
| German VAWTS |
|
|
I have posted that, what i could read here the last days, into my own discussion board.
I posted in my german board that the simulation showed that the c-rotor should have a cp of 35% (may be more at greater diameter)
I posted that the Lenz 2 should have a cp of 41% (tested in reallity bei Ed)
I posted that both turbines should be able to spin faster than the wind blows, at least undload, and
that both of them should be able to deliver power at TSR 1 .
Unfortunately until now there are not many usefull reactions.
http://www.daswindrad.de/forum/viewtopic.php?f=4&t=533
Before i registred at this board, i could never read anywhere (!) such extrem high values for such simple vawt turbines, especially for the value of CP.
Before i registred, i was of the opinion that turbines like that have a cp around 20%, as i could read everywhere in many various documents.
My own measurement with the c-rotor, on my teststand and into my garden, confirmed it.
Here now, i see total different values !!
So, what shall i believe ??? :)
Of course i would be happy if my Turbine would have a CP above 20 %.
Unfortunatly until now i could'nt measure a bigger c-rotor like my testrotor but my feeling is that it would'nt
be a great different in CP, using a bigger one.
Is there at you in the USA a better, different wind blowing than in germany ? :)
Was all, what i could read before, completly wrong ?
Are you genious and i'am stupid or vice versa ? (or a mixture of it ?)
I'm completly confused....
Such simple turbines, able to use drag, with big blades, with high CW resistance, much edges, low TSR and much vortex and
high solidity and and.... how could them be able to have a CP above, let me say 25% ??
Bernd
-- Edited by Bernd on Saturday 16th of January 2010 11:55:26 PM
-- Edited by Bernd on Sunday 17th of January 2010 12:15:21 AM
|
|
sjh7132
Guru
Posts: 1252
Date: Jan 15, 2010
| |
Caleb
Senior Member
Posts: 473
Date: Jan 15, 2010
| RE: German VAWTS |
|
| turnymf wrote:
. . . It's times like these that I wish I hadn't dropped
german at school
Don't feel too bad. I've had three years of German in high school and a semester in college, I've travelled in Germany a fair amount, and I had trouble with it. Technical language can be difficult.
- Bryan
Mechanical Engineer turned stay-at-home dad. |
|
sjh7132
Guru
Posts: 1252
Date: Jan 15, 2010
| RE: German VAWTS |
|
| Bernd wrote:
Also Betz himself has determined that the max. power coefficient at TSR 1 or lower could never been above 28%.
I have been looking for confirmation of that statement and have not found any. Can you point me to a source? I have trouble believing it's true for 2 reasons. 1) We seem to have real turbines that break that limit. 2) My simulation definitely lets me run a turbine with higher efficiency than that. While the simulation may allow me to put in unrealistic surface properties, etc. It does enforce the conservation of energy, momentum and mass. These are all that are needed to derive the Betz laws. I could believe a 28% limit for a pure drag machine.
Steve
|
|
windstuffnow
Senior Member
Posts: 204
Date: Jan 15, 2010
| RE: German VAWTS |
|
|
It's really difficult to give a % between the two as the variables change throughout the rotation. This would also change exponentially by changing the wind speed. In order for drag to work it needs to be running at a speed lower than a TSR of 1. The optimum speed for a drag type turbine woulld be a TSR of .33 or 1/3 the wind speed, this would meet Betz law.
The intensity of the lift varies based on the angle of attack which in the case of turbines we have both positive and negative to deal with. Think of a plane flying an outside loop, although not a fair comparison because we have gravity to contend with. Wind direction would be similar as it traveled in a loop.
Since the Lenz2 design performs best at a TSR of .8 Lift plays the dominant role in winds from 0 to around 18mph. The fat wing design provides a very large lift force up to a certain wind speed at which point the excess drag on the upwind side only serves to burn energy. A STOL aircraft is extreemly efficient up to its designed speed at which point the airfoil must change in order to be more efficient at higher speeds, thus the use of slats and flaps. A jumbo jet can't land at 600 mph so inorder to get the speed down for the weight it has to change the airfoil shape to achieve a higher lift force at safer speeds.
Since the TSR of the Lenz2 is higher than optimum for the drag side it really only plays a small part in the extraction of energy - depending on the wind speed. As the wind speed increases the drag component grows on the upwind side making the downwind blade more dominant in the extraction process. Still becomming more and more inefficient as wind speed increases.
One way to look at it is the up wind wing at a TSR of 1 is moving into the wind at the same speed as the wind, so in a 10 mph wind the up wind wing sees 20 mph and extracts from that wind, the downwind side is moving away from the wind at the same speed the wind is comming in so there is no extraction.
__________________
.
Windstuff Ed |
|
turnymf
Veteran Member
Posts: 39
Date: Jan 15, 2010
| |
windstuffnow
Senior Member
Posts: 204
Date: Jan 15, 2010
| RE: German VAWTS |
|
| sjh7132 wrote:
Bernd, I know we talked about the dimensions of your c-rotor through you-tube, but I don't think I understand them correctly.
I believe R is 25 cm.
What are D and L?
Is the shape correct?
Thanks
This is the same wing design I was working with just prior to going with the "Fat wing" on the Lenz2. It worked fairly well, but not quite as good as I was looking for at the time. This was posted on my site 6-8 years ago and there are still pdf files on the web showing this wing and it's origin.
Also was stolen by the builders of the Delta machine, PacWind
One note on building and testing small wind machines. They typically don't represent the actual efficiency of their scaled up brothers. Also, if your going to use fans to simulate the wind, its best to build a box that would accomodate the turbine with lots of clearance around it and use the fans to draw the air through it ( suck down ). The fan makes a nasty turbulance which can actually cause false readings of the output. Drawing the air through the tunnel allows the air to be smooth and simulates the actual environment much better.
A large portion of the original Lenz2 testing was done at WMU in a closed loop tunnel, this uint was a multimillion dollar machine and could monitor everything going on through it's computer system. One of 2 machines they had there. Their other was a nice suck down tunnel. The use of their lab was tedious and costly and I ended up building my own based on their suck down tunnel, much easier to make changes and record data as changes are made.
I have a background in aerodynamics and have scratch built over 30 planes and flown all but 1. I designed a few wings that would lift over 1000 lbs at 20 mph and climb like a home sick angel. The actual roll to take off was less than 20ft with maximum capacity at full power. The Lenz wing is actually a modified STOL wing and will produce lift in very low winds.
The wing is designed for lift only and is extreemly dirty in higher winds ( above 20mph) it runs the best power output at a TSR of .8 because of it's hybrid lift/drag design. It will run at a TSR of 1.6 completely unloaded.
I've also run the above wing in wind tunnel tests and although it runs well it's not as efficient as the "fat wing" design.
.
Windstuff Ed |
|
sjh7132
Guru
Posts: 1252
Date: Jan 14, 2010
| RE: German VAWTS |
|
| Bernd wrote:
To my opinion everything above 25%, coming form such a mostly drag systems, would be a wonder.
Also Betz himself has determined that the max. power coefficient at TSR 1 or lower could never been above 28%.
See this thread. This lenz was measured at 31% at the alternator output. Of course it could be a measurement error. But there are several cases of numbers like these being reported. Nobody has reported a true 50% lenz efficiency. My simulation said between 40% and 50% and I said that was too optimistic.
Steve
|
|
Bernd
Senior Member
Posts: 233
Date: Jan 14, 2010
| German VAWTS |
|
|
" However lets see if anyone can see a TSR > 1 because I do believe it's possible. "
I hope you are right. :)
Bernd
-- Edited by Bernd on Thursday 14th of January 2010 11:15:58 PM
|
|
Bernd
Senior Member
Posts: 233
Date: Jan 14, 2010
| German VAWTS |
|
|
"... But could that just be your turbine? I think a larger turbine might be a little more efficient. ..."
I belief more efficient could be, but not significant faster.
"... I don't think either the Lenz or the C-rotor mosty works with with drag. A pure drag machine would be half as efficient...."
half efficient of what ? Of a pure lift turbine, with less cw and high TSR ? I guess that could be happen.
I guess the efficient of the c-rotor, based on my realistic measurements, is around 20%.
Maybe a little bit higher using higher radius.
The efficient of a Savonius is, depending on how it is build, around 10 to 23%.
I guess everything about is probably only wishful thinking. :)
And i'm really really sure, that the lenz (and all other similar systems) could never have 40 - 50 % you write before.
To be honest i was shocked reading this !
I think such a high CP value is completly unrealistic.
That would be a wonder and Ed would have long been a millionair. :) i would grant him :)
To my opinion everything above 25%, coming form such a mostly drag systems, would be a wonder.
Also Betz himself has determined that the max. power coefficient at TSR 1 or lower could never been above 28%.
I do not build the c-rotor in the belief it has a better CP than other turbines.
Very well planed and optimized horizontal wind tubines are around 50%...... but only the newest versions and just under best wind conditions and and and...
Home build turbines, especially types like lenz or c-rotor or savonius, have naturally much less efficient. (But other advanteges)
"... Look at your torque measurement at 0 degrees. That's torque from pure lift and that won't decrease much with speed....!
I think completly different. At 0 degreee its pure drag (and around 20% recoil effect) generated by the the wind which is flowing
from the deflector blade into the slat. I think if wind stikes at degree of 90 on the blade,
it could never generate lift but drag in rotation direction.
"... I don't understand why its not nearly the same at 180 degrees ,like mine..."
This could be happen because of my bad wind conditions. The windspeed goes down from the nearest point of rotor to the fans, to the longest.
At front it might be 4m/s and back 2,5m/s, i don't no exactly.
"... Drag machines peak power happens at a low TSR (.4?) These peak at .6 - 0.8... "
I measured the best tsr around 0,5. It was about 60% less than at unload ( 0,82 )
Bernd
-- Edited by Bernd on Thursday 14th of January 2010 11:47:21 PM
|
|
sjh7132
Guru
Posts: 1252
Date: Jan 14, 2010
| RE: German VAWTS |
|
| Bernd wrote:
"... The chart agrees that there isn't much power above a TSR ..."
Hmm i see into the chart at tsr of 1 a power point around 8 to 11 Watt ( x 6,2 )
Depending on the max point of 10 to 15 Watt i think its much power.
The simulation is probably too optimistic at high TSRs due to the smooth blade assumption. However lets see if anyone can see a TSR > 1 because I do believe it's possible.
Steve
|
|
sjh7132
Guru
Posts: 1252
Date: Jan 14, 2010
| RE: German VAWTS |
|
|
Well I can't argue that your turbine doesn't go faster than a TSR of 1 because you have done the measurements. But could that just be your turbine? I think a larger turbine might be a little more efficient.
Bernd - "A turbine, which works mostly with drag function, could not turn above tsr 1, because the most part of propulsion power would not be present at higher tsr than under 1."
That could be a bad assumption. I don't think either the Lenz or the C-rotor mosty works with with drag. A pure drag machine would be half as efficient. Look at your torque measurement at 0 degrees. That's torque from pure lift and that won't decrease much with speed. I don't understand why its not nearly the same at 180 degrees ,like mine. Drag machines peak power happens at a low TSR (.4?) These peak at .6 - 0.8.
I've looked at the pressures at a TSR of 1.2 and you are correct, drag isn't doing anything at the speed. But the blade going with the wind isn't hurting much since it's moving with the wind. Two of the 3 leading edges have a negative pressure on them from air moving across them. Yes, this is all simulation, but I'm starting to have some faith in the results.
I'll run that case for a longer time to make sure it the results don't change.
We need some people to unload their alts and make some RPM measurements. Is anyone out there willing to provide some data?
__________________
Steve
|
|
Bernd
Senior Member
Posts: 233
Date: Jan 14, 2010
| German VAWTS |
|
|
"... The chart agrees that there isn't much power above a TSR ..."
Hmm i see into the chart at tsr of 1 a power point around 8 to 11 Watt ( x 6,2 )
Depending on the max point of 10 to 15 Watt i think its much power.
I wish a bigger diameter of the rotor may this be happen, but i dont think so because
a drag system couldn't work at this tip speed ratio.
In Summer i will test the unload tsr with a new bigger rotor.
@Ed
"... It's still on the net somewhere as a PDF file..."
Did you have the pdf of this (old) turbine present ?
I would be very interessting for me.
Grüsse
Bernd
-- Edited by Bernd on Thursday 14th of January 2010 09:58:40 PM
|
|
windstuffnow
Senior Member
Posts: 204
Date: Jan 14, 2010
| RE: German VAWTS |
|
|
This wing design was one I worked with quite a bit before I moved to the fat Lenz2 wing. It was posted on my site about 8 years ago. It works well but not as well as the fat wing. It's still on the net somewhere as a PDF file
__________________
.
Windstuff Ed |
|
sjh7132
Guru
Posts: 1252
Date: Jan 14, 2010
| RE: German VAWTS |
|
| BerndsHelper wrote:
wikipedia says its 76 to 96m over sea level...
i don't know how high Bernds testing-ground is...
Well 96 meters isn't enough to make much difference. I live at 1889m. That starts to make a difference.
Steve
|
|
BerndsHelper
Member
Posts: 9
Date: Jan 14, 2010
| RE: German VAWTS |
|
|
wikipedia says its 76 to 96m over sea level...
i don't know how high Bernds testing-ground is...
|
|
sjh7132
Guru
Posts: 1252
Date: Jan 14, 2010
| RE: German VAWTS |
|
| Bernd wrote:
"... So the Lenz is known to spin faster than a TSR of 1 when unloaded. This is because it uses lift and drag. I think the same is true for the C Rotor. ... "
No i dont think so.
And i think also the lenz will not turn above tsr 1, although it is described as... at least under load. Totally unload turning disregarded.
The chart agrees that there isn't much power above a TSR of one, so once you add in drag from the structure, I think unloaded is the only way you would see a TSR > 1. Feel free to post my graph on your board and ask if anyone has ever seen a Lenz or Crotor go that fast. I think the bigger turbines might see it. Also what is the altitude of where you live and test your turbines? My simulations are run for sea level.
Steve
|
|
Bernd
Senior Member
Posts: 233
Date: Jan 14, 2010
| German VAWTS |
|
| "... So the Lenz is known to spin faster than a TSR of 1 when unloaded. This is because it uses lift and drag. I think the same is true for the C Rotor. ... "
No i dont think so.
And i think also the lenz will not turn above tsr 1, although it is described as... at least under load. Totally unload turning disregarded.
I know i lean far out of the window if if i say this but i'm really sure.
I will test it on my teststand, but i'm pretty sure that the lenz will not turn so fast above tsr 1,
exactly like the c-rotor and all other simliar tubines too.
"... This is because it uses lift and drag ... "
I believe a rotor can use lift OR drag, not both at the same time, at least drag not about tsr 1.
I tested the tsr of my 50cm c-rotor (after testing on teststand with result of tsr 0,82) in real terms in my garden a long time
with a special Sytsem (see picture)
The result was nearly exact the same and differed just at the second digit after the comma.
So i know exactly that the 50cm test c-rotor never turns more than 0,82 tsr and this seems to me locical.
A turbine, wich works mostly with drag function, could not turn above tsr 1, because the most part of propulsion power would not be present at higher tsr than under 1.
Bernd
-- Edited by Bernd on Thursday 14th of January 2010 08:16:46 PM-- Edited by Bernd on Thursday 14th of January 2010 09:30:44 PM-- Edited by Bernd on Thursday 14th of January 2010 09:48:03 PM |
|
sjh7132
Guru
Posts: 1252
Date: Jan 14, 2010
| RE: German VAWTS |
|
| BerndsHelper wrote:
wich program are you using fore the simulations?
Openfoam-1.5-dev There is a later version out (1.6) but it took me so long to learn how to use 1.5 I'm afraid to switch. :-) Openfoam is public domain and free.
Steve
|
|
BerndsHelper
Member
Posts: 9
Date: Jan 14, 2010
| RE: German VAWTS |
|
|
wich program are you using fore the simulations?
|
|
sjh7132
Guru
Posts: 1252
Date: Jan 14, 2010
| German VAWTS |
|
| Bernd wrote:
Hello Steve
Thank you very much for your great work.
It is a pity that the simulations always take a long time and you have so much work.
I'm excited about the new results with coreccted radius.
But there is something i couldnt understand.
The C-Rotor, and i think the lenz too, are drag turbines.
I didn't ever measured a TSR at c-rotor above 0,85.
Without load it is turning with a tsr of 0,82.
At 0,82 (and above) there is no chance to get power from the rotor.
Why did your charts shows power output even above tsr of 1 ?
How could this be happen ?
I'm pretty shure there is no way for the rotor to speed so fast and certainly
not to deliver power.
Bernd
From the windstuffnow.com web page about the Lenz2... " The TSR ( tip speed ratio ) for this machine for peak power is 0.8. Because it is a hybrid lift/drag machine in order for it to extract energy from both the upwind and downwind wings it needs to run slightly slower that the wind. 0.8 seems to be optimum while loaded although it will run at 1.6 unloaded."
So the Lenz is known to spin faster than a TSR of 1 when unloaded. This is because it uses lift and drag. I think the same is true for the C Rotor.
I know you have real measurements, and it's hard to argue against those, but my C-rotor has no drag from a support structure. My blades are also perfectly smooth. I wonder if those factors would bring the unloaded TSR down below 1.
If we use Ed's statement and my Lenz chart we can guess that the drag of a support structure and a normal surface roughness subtracts about 6 watts (chart watts, not corrected) on a 1 meter tall turbine. Your turbine was smaller but probably had the same thickness support structure. That might put your unloaded TSR at below 1.
The simulations take long, and are a lot of work (for the computer.). For me it's between 10 minutes to an hour to set up the mesh. I do this once per design. Then it's about 2 minutes per TSR to edit a few numbers in a file and start the computer working on the problem. So in reality the C-rotor test was about 2 hours of work or less for me. I think you spent much more time building your prototype.
I have been considering setting up a server where people could set up their own meshes, and submit them, then see the results on a web page or get them in email a few days later. Would there be any interest in a system like that?
Even if I don't set that system up, if someone has a shape they want tested, if they could make a gmsh .geo file, I could easlily use that to start a simulation in a matter of minutes.
I'll post an example mesh in the CFD results thread.
-- Edited by sjh7132 on Thursday 14th of January 2010 05:05:41 PM
Steve
|
|
Bernd
Senior Member
Posts: 233
Date: Jan 14, 2010
| RE: German VAWTS |
|
|
Hello Steve
Thank you very much for your great work.
It is a pity that the simulations always take a long time and you have so much work.
I'm excited about the new results with coreccted radius.
But there is something i couldnt understand.
The C-Rotor, and i think the lenz too, are drag turbines.
I didn't ever measured a TSR at c-rotor above 0,85.
Without load it is turning with a tsr of 0,82.
At 0,82 (and above) there is no chance to get power from the rotor.
Why did your charts shows power output even above tsr of 1 ?
How could this be happen ?
I'm pretty shure there is no way for the rotor to speed so fast and certainly
not to deliver power.
Bernd
|
|
sjh7132
Guru
Posts: 1252
Date: Jan 14, 2010
| German VAWTS |
|
| The virtual power test of the C-Rotor is complete. Remember that my absolute values are not accurate. The simulations are mostly good for comparing two different designs. Due to a recently discovered bug, I now know that the power shown in these charts is low by a factor of 2*pi. So multiply the powers by 6.2 to get more realistic values.
 This is my chart for the Lenz2  C-Rotor people should not get discouraged about these results. Even when I normalize the power to swept area, there seems to be a slight advantage to testing a design on a larger turbine. The lenz2 was tested had a radius of 54 cm, and the CRotor had a radius of 28.25 cm. I'm doing another run of a 56 cm radius C-rotor at 90 RPM (TSR of 0.7). So far it's a little above the lenz, but the simulation is still running. Right now I'd say the CRotor and the Lenz2 are very much alike in their power outputs and power curves. I'm also running a designed based on the Jellyfish and so far it's coming out better than both the Lenz2 and C-Rotor (18.5 at a TSR of 0.8). This could be due to the large turbine advantage. I'll run better tests and publish that in a few days. Here is a sneak peak.  As always, take my simulations with some skepticism. They could be completely inaccurate. -- Edited by sjh7132 on Thursday 14th of January 2010 06:21:37 AM-- Edited by sjh7132 on Thursday 14th of January 2010 06:30:33 AM-- Edited by sjh7132 on Thursday 14th of January 2010 07:13:53 AM
Steve
|
|
Bernd
Senior Member
Posts: 233
Date: Jan 12, 2010
| German VAWTS |
|
|
hello turnymf,
"... Stand the magnets on their ends, flat sides facing each other attach them to the rotating plate ..."
Into my german board we talked about the same Idea (and some more to build the magnet ring)
I agree to you that there are advantages if you mount the magnet like this idea.
You can easily dissasamble the generator without needing to share the coilring.
You can wind the whole coilring from one piece of copper wire ! (This advantage i like especially)
There is just one gap direction wich can make problems, comparing on two directions in my ringgenerator.
But ... Stand the magnets on their ends, flat sides facing each other attach them to the rotating plate ... that wouldnt work i think.
If you try to stand magnets like a ring, the repulse is so high that there is the needing of a form or strong tool
which hold the magnets into there positions. But this thing makes it hard to fill the spaces between the magnets with fiberglass.
Futher i think only fiberglass bewteen the magnets would hold them safetly together.
Under the magnetring you can fix the ring on the plate on wich it lies.
On the top of the ring you must ensure that it wouldnt seperate.
The power of the magnets is really amazing.
The magnetring of my new generator would be blow up with a pressure of 1 tonn !
Maybe the ring could be secured with some windings of glass roving.
Bernd
-- Edited by Bernd on Tuesday 12th of January 2010 10:13:32 PM
|
|
Bernd
Senior Member
Posts: 233
Date: Jan 12, 2010
| German VAWTS |
|
|
"... My wind speed was almost twice yours at 6.7 m/s. ..."
Maybe that's the reason for the high peak.
Perhaps at higher windspeed the shape of the c-rotor blade works on some positions like a lift type.
" ... When I go to your board I have to use the translator for everything ... "
If you want you can of course write in my board in english. :) (like every time) :)
"... maybe this wouldn't require the coils to be on 3 sides of the magnets ... "
hello turnymf, yes maybe, but it means that the flux must then be 3 times higher to get the same result.
@ to all
btw. the flux into a normal (not extrem set) dual rotor is around 0,7 - 0,8 Tesla, depending on the thickness and
material of the magnets, the gap between the magnets and so on.
But... the flux of 0,8 Tesla is only between opposing magnets present.
Where are no magnets on the plate, there is no flux.
So the average flux on the hole plate is a lot less. Let us say around 0,5 Tesla.
The ringgenerator has a average flux (over all) of around 0,25 tesla.
But you have to notice that this lesser flux works on each of the 3 sides where the coppercoil is above the magnets !
So in total the ringgenerator has even a advantage !
It uses the magnetfield better, despite a larger distance through the air.
I tell this to show that there is no reason to think the ringgenerator is less efficient.
Bernd
-- Edited by Bernd on Tuesday 12th of January 2010 08:23:16 PM
-- Edited by Bernd on Tuesday 12th of January 2010 10:28:43 PM
|
|
sjh7132
Guru
Posts: 1252
Date: Jan 12, 2010
| RE: German VAWTS |
|
|
Yes, that's what I was thinking. I'll try it when I make mine. :-)
__________________
Steve
|
|
|
