Author Topic: Efficiency of Windmills (Read 3917 times)

Daniel Hugo · « **on:** June 03, 2006, 04:10:49 PM »

Dear Otherpower Board,

As windmill designer from Southern Argentina, I have come across some difficulties. I hope you might help me solve them. My question refers to windmill efficiency as a function of angle of axis of rotation with respect to wind direction. It's clear that power rating will reach its maximum when this angle is 0 (exact alignment) and 0 at 90º. Now, how does this function evolve from 0º to 90º. This is exactly what I would like to know. Can you help me? Thanking you in advance, I shall be looking forward to hearing from you soon,

Daniel Hugo

RP · « **Reply #1 on:** June 03, 2006, 10:26:25 AM »

Well neglecting any special aerodynamic issues, the apparent wind on the blades should be the cosine of the angle multiplied by the actual wind speed. The energy in the wind will be the cube of the result of that so it should drop off pretty fast after about thirty degrees or so.

wdyasq · « **Reply #2 on:** June 03, 2006, 04:03:05 PM »

There will be LOTS more numbers than RP advised. RP gave you a formula for "Area of blades exposed to the force of the wind". As the blades go through the "apparent wind" at an angle, with the twist, combined with the apparent angle of attack on each blade - retreating, advancing and such, combined with the lift/drag factors.... taking in account "tower shadow" - yes, even on an upwind machine - calculating stall points, drag at stall, disturbed wake, vortexes and probably a few factors forgotten, it will get involved.

I don't know anyone, who knows anyone, that has the knowledge and/or computer program to compute such things. There may be some folks who have taken data and have an "idea" what one machine, with a particular set of blades, will do in a particular set of conditions, on a particular tower at a set location. That may or may not fit your application.

Good Luck,

Ron

Daniel Hugo · « **Reply #3 on:** June 03, 2006, 05:29:02 PM »

Hi, Ron. I guessed it would be mathematically too difficult. I was thinking of someone or of some laboratory where this effect might have been measured. It would be very easy to carry out a full test for all angles in a wind tunnel (something I don't have, unluckily). We have been testing a new two-meter diameter turbine prototype at the University of La Plata. We mounted the turbine on a truck and measured torque at different speeds. The problem we had was a 10 km/h wind which hit the rotor at an angle of 40º; thus when we drove at 10 km/hr, the wind that went through the rotor did so at an angle of 20º. This angle became smaller at greater speeds but, I am convinced that the effect is large even at small angles. Can you suggest anything we might do to get this information? Thanks for your time. Regards,

Daniel

RP · « **Reply #4 on:** June 03, 2006, 05:47:17 PM »

Daniel,

Could you simply repeat the test with a tail on the windmill to let it "seek" the correct wind angle?

Daniel Hugo · « **Reply #5 on:** June 03, 2006, 06:25:52 PM »

Dear RP,

Your suggestion is great but can's do it now, mainly because in the last run the prototype broke down, and it will be two months before we can start a new series of tests. The post on which the rotor was mounted is in a fixed position as the wheel we use to measure torque by loading weights on the strip of steel that runs around it. At the end of a strip we hang calibr4atedf weights until the rotor is not able to maintain speed. It is abgit primitive, I agree, but this is all we have at the moment. This states of affairs made me think of asking for help. We have all the data but we have no fourmulas to eliminate the errors produced by lateral winds. I will try to imolement your suggestion, anyway, before the prototype is repaired. Thanks so much and bye for the time being,

Daniel

wdyasq · « **Reply #6 on:** June 03, 2006, 07:10:39 PM »

Daniel,

These folks: http://www.ae.uiuc.edu/m-selig/ are near the top in what you want to know.

Ron

Flux · « **Reply #7 on:** June 04, 2006, 01:19:09 AM »

I have looked at this for one machine and I am pretty sure that the type of blades , and how you are loading them will affect the answer, so don't take this as absolute.

In the machine I did the tests on the power curves followed very closely the cosine law and the power curve at 60 deg was very close to half the direct value.

I have seen the figure of cos squared mentioned and some machines may well follow nearer that.

I have a strong suspicion that it is closely related to the seeking force that keeps the rotor into the wind and will keep it up wind without a tail under the right conditions. This again depends drastically on the type of blades and loaded tsr.

Measuring power output is long and complicated and the machine I used was the only one up clear of obstructions that would affect the answer and it also had a mechanical furling that allowed me to set the tail at any desired angle.

For what it is worth I suspect that for most machines there is little loss up to angles of 30 deg to the wind but beyond that you will need to measure it on the specific machine.

Flux

Daniel Hugo · « **Reply #8 on:** June 04, 2006, 02:12:29 PM »

Dear Ron,

The preliminary results we conducted on our turbine have shown the following result: the power yielded by the rotor at a wind speed of 12 m/s was 3.000 w. Unluckily, due to an accident before the start of the tests, we were not able to go on to higher wind speeds, but at all speeds tested, the rotor's performance satisfied all our predictions. My question is:how does this yield compare to other current technologies. This information es important as we are discussing the project with many people who have little background knowledge about windmills. I consider you an authorized person to answer this question. Thanking you in advance, I'll be looking forward to hearing from you soon.

Daniel

Daniel Hugo · « **Reply #9 on:** June 04, 2006, 03:18:20 PM »

Ron,

While re-reading my post, I realized I had not specified the rotor diameter. It's 2.06 meters. Sorry,

Daniel

SamoaPower · « **Reply #10 on:** June 04, 2006, 05:18:38 PM »

For an area of 3.33 m^2 and a speed of 12 m/s, I calculate an available wind power of 4050 watts.

A rotor ouput of 3000 watts is 74% which exceeds the Betz limit of 59.3%.

A more reasonable results would be about half that. Vehicle testing is difficult.

Daniel Hugo · « **Reply #11 on:** June 04, 2006, 05:37:02 PM »

Dear Sir,

That's exactly the kind of comment I was waiting for. Let me tell y0u that the tests performed under the supervision of an Aeronautics Engineer from the Faculty of Aeronautical Engineering, National University of La Plata, Argentina. There were three other engineers in the testing team. There is no question about the test results. Wind speed was measured by means of very precise electronic devices and the brake used to measure torque at different wind speeds was calibrated at the University Workshop. I am talking about a New windmill. Its design will be the object of a research paper soon to be published by our University Press. I thank you very much for your comment. Regards,

Daniel

Flux · « **Reply #12 on:** June 05, 2006, 12:43:13 AM »

Why waste our time asking a question about the angle of the wind on a new type of windmill, which we have never seen or had experience of.

The Betz limit has been questioned many times and some have predicted that it can be exceeded, but as yet no one has equalled it so it has never been challenged.

It will be interesting to see how your device turns out, but I think your figure is too high to be credible. Good luck , if it is true it will be a break through, but I would rather trust power curves taken from real wind in the conventional way, rather than vehicle testing.

If you are so sure of your results you will not be inclined to check them.

Flux

Daniel Hugo · « **Reply #13 on:** June 05, 2006, 06:45:29 AM »

Dear Flux,

I'm very sorry you deem my question a waste of time. I know I've given only a fragmentary idea of our turbine prototype, but this is only because of prior confidentiality agreements that prevent me from disclosing more information than is absolutely necessary. I have been involved in this project since the very start and I wouldn't even dream of playing with something I'm so deeply committed to. I haven't said all about our turbine, but everything I have said is true. Anyway, I will add that the turbine has been patented in my country and we are initiating PCT filing procedures. Our turbine, with a diameter of 2.03 m) has 54 blades, and weighs only 15 kg. It is entirely made of ultralight materials. Again, I am really sorry you think answering my question is a waste of time.

Daniel

wind4Reg · « **Reply #14 on:** June 05, 2006, 07:09:24 AM »

Hi Daniel, I have a chicken here that runs 100mph that you might be interested in purchasing. I figured you could hook a cart to him and fix your windmill on it for some more testing. On second thought this might not be a good idea. Your windmill might start self propelling because of it's high efficiencies, and overrun the chicken.

:-)

Flux · « **Reply #15 on:** June 05, 2006, 07:16:25 AM »

Daniel.

My point was that even with tried and tested designs the way they react to change in direction is not always the same, so something that is possibly quite different may behave in a way that no one has experience of.

I am not trying to cast doubt on your work , it would be foolish to do so before knowing what it is. Just that no one here would be able to predict how it behaves at an angle to the wind without having some idea of what you were referring to.

Unless the facts are given , any answer can only be based on the assumption that it was a conventional machine.

Flux

paradigmdesign · « **Reply #16 on:** June 05, 2006, 08:35:39 AM »

Really, most turbine blades max out at about 35% eff. My question to you, is this one of thoes "vortex" turbines that have the "funnel" arround the prop? That could help explain your numbers.

P.S. Are we talking about a 3 blade prop, or more?

Daniel Hugo · « **Reply #17 on:** June 05, 2006, 09:37:16 AM »

Dear paradigmdesign,

There is no funnel whatsoever in our design; just the rotor. And the number of blades is 54. Thanks for your interest. My regards,

Daniel

TomW · « **Reply #18 on:** June 05, 2006, 10:12:05 AM »

Sir;

I know I've given only a fragmentary idea of our turbine prototype, but this is only because of prior confidentiality agreements that prevent me from disclosing more information than is absolutely necessary. I have been involved in this project since the very start and I wouldn't even dream of playing with something I'm so deeply committed to. I haven't said all about our turbine, but everything I have said is true. Anyway, I will add that the turbine has been patented in my country and we are initiating PCT filing procedures.

I find it rather disconcerting when people come in here seeking advice on their closed projects. Especially when they refuse to provide all the data needed.

If folks are patenting designs then they should pony up the cash for the development of that closed project. Seeking free advice for a patented project / device is very contrary to the point of this site.

I have signed NDA in the past but would never have sought free advice online to further that for profit project. I feel it is wrong but that is just me and probably will be argued by others.

Ok, here is where everyone tells me we should be happy to give away ideas to mercenaries seeking patents.

Nothing personal, Daniel, just one of my pet peeves [patents assume only one person / group could think something up].

T

dinges · « **Reply #19 on:** June 05, 2006, 10:28:02 AM »

Hear hear.

Couldn't agree more with you.

Daniel Hugo · « **Reply #20 on:** June 05, 2006, 10:35:34 AM »

Dear Tom W.,

I think that you missed something when you read my postings. In the first place, I am certainly not seeking advice to improve a turbine that was patented almost a year ago in Argentina. We ran a whole battery of tests and at 12 m/s wind speed, the rotor yielded consistent ratings of 3000w +/- 100w. I suspect that lateral winds at angles of 10-20 degrees might have affected our results by reducing output a fez percentage points. If my inkling proves correct, output power might be even higher than 3000 W. I don't really think this is, as you suggest, unethical, or wrong in any possible way. But, you think it is. Regards,

Daniel Hugo

wdyasq · « **Reply #21 on:** June 05, 2006, 12:12:37 PM »

Daniel,

Like Flux and SamoaPower I shall be waiting for "plans". I will also state just because a person has a pedigree consisting of several diplomas it seldom relates to knowledge. I am not saying the tests are not accurate, I am relating my experience correcting engineers "Plans and Specification" to make a working product. Seldom is the mechanic on one of these projects properly compensated even when he does all the actual work of taking the idea to fruition.

If, as you state, you machine has 54 blades, I doubt it will perform in any way similar to a conventional 2 or 3 blade device. From here on out, it appears you will be on your own.

If you are truly "Beating Betz" many of us will be leery of the numbers. I am sure there are stories in Spanish about knowing if the person telling the story is a farm hand or a salesman by noticing which side of the boots the manure is. The fact you will not show your device leads me to believe there is little manure on the outside of your boots.

Good luck, I hope your team is successful in beating theoretical and opening new avenues for wind power.

Ron

Tallwind82 · « **Reply #22 on:** June 05, 2006, 11:09:25 PM »

Hi Daniel

I hope you don't let some of the previous comments discourage you from using the board.

If my reasoning is correct, the easiest way to determine the effects of rotating the axis of the windmill out of the direction of the wind would be to first calculate the area of the mill the wind actually sees. Then experimentally find the difference at a couple different angles, and use that data to adjust the curve.

Here is what I come up with for the theoretical maximum percentage of the exact alignment output in 5 degree increments:

Degrees Percentage

99.6
98.5
96.6
94
90.7
86.7
82
76.7
70.8
64.4
57.6
50.3
42.6
34.5
26.5
17.7
8.8
0

Since your windmill is not in testable condition you will have to guestimate how much this curve will be modified by the actual flow across the blades as the angle is increased. I would think that because of adverse forces the 0% of exact alignment output would actually be reached at 80 degrees, + or -. With this assumption you would be getting about 92.4% of exact alignment output when the wind is coming in at 20 degrees. There are of course many other factors, as others have already mentioned, but I think this will get you close.

Hope this somehow helps, or at least stimulates thought.

Robert

dinges · « **Reply #23 on:** June 06, 2006, 11:26:26 AM »

Please read post #2 by WDYASQ where he explains all the other factors that should be accounted for apart from 'blade area exposed to wind'.

To the original poster:

As far as beating Betz goes; I'd say go for it. Maybe you could even go beyond the 100% limit too. Hope you succeed. Think you won't. And if you do, please patent it. This means that full plans, calculation details, design considerations, etc. will be fully documented and freely available to everyone in the world. Us amateurs on this board are allowed to build anything that is patented, provided we don't commercialize the product. So, everyone could be building your product as long it is for his own use. Sounds great to me.

The Chinese think a bit different about patents than the rest of the world, BTW.

And I agree with TomW; I find it very unethical to ask for our advice, input and ideas, without full disclosure of what it is you are asking advice on. Not only are you limiting the quality of the advice you will get, I consider it an insult to the people on this board. Basically you ask them to trust you and advice, but you won't trust them with the required technical details.

Carry on.

Peter.

hvirtane · « **Reply #24 on:** June 06, 2006, 05:32:53 PM »

I'm as many others thinking that it is

quite impossible to know the effect

of the wind angle in the relationship

with the wind rotor without knowing

anything about the shape of that rotor.

On the other hand I wouldn't be

much surprised, if somebody some day would

beat Betz limit with quite wide margin.

I think that the assumptions to calculate

Betz limit are not correct.

The wind doesn't go or doesn't need

to go straight through

the wind rotor as assumed to calculate

the Betz limit; there is no need to

reduce the speed of the air, which

is going through the swept area near

the blades only to 1/3 of

the original wind speed, when

with big rotors so much of the air

is not affected by the rotor at all;

the wind rotor could maybe be designed so that

the air going 'round the rotor' could

capture the air, which was totally stopped

by the wind rotor; .... etc.

I'm not thinking the way

the original poster is asking his

questions to be unethical. Rather I'm

thinking that the whole idea of patenting

things is somehow crazy. How can you 'own'

any kind of knowledge? 'The Chinese way'

to think about patents

might be much more clever

than 'the western way'.

If the original questioner

wants to keep his ideas secret,

it is more or less his own problem.

To get knowledge for the problem

without disclosing any information

about the shape of the

wind rotor is futile, I think.

- Hannu

Daniel Hugo · « **Reply #25 on:** October 30, 2006, 01:05:10 PM »

Dear Hannu,

I thank you for your comments and kind words and I entirely agree with you about patents but when you work within a large group of people, things get complicated. Anyway, it's time to show you my turbine so you may have a complete picture of what it is about. Please follow this link http://www.theinquirer.net/default.aspx?article=35394

It is an article with pics from The Inquirer, from London, whose correspondent visited the science fair INNOVAR 2006 (Buenos Aires, Argentina; Home page: www.innovar.gov.ar) where our wind turbine was on show. I hope you like it. Regards,

Daniel

ghurd · « **Reply #26 on:** October 30, 2006, 02:00:18 PM »

Hi Daniel,

Very nice!

That link should be posted as a new story, also.

G-

Daniel Hugo · « **Reply #27 on:** November 23, 2006, 07:18:24 PM »

Dear Dear Ron,

I really worked hard trying to find the formula for the said calculation. I haven't been able to find even an aproximation to it. I am building a small (0.5 m diameter) wind turbine to be tested in our wind tunnel. We will be able to test efficiency as a function of yaw angle and who knows may be we can write a formula based on what we find! I would like you to take a look at my turbine so you have a better understanding of the problem. Please follow this link http://www.theinquirer.net/default.aspx?article=35394

It is an article with pics from The Inquirer, from London, whose correspondent visited the science fair INNOVAR 2006 (Buenos Aires, Argentina; Home page: www.innovar.gov.ar) where our wind turbine was on show. I hope you like it. Regards,

Daniel

Daniel Hugo · « **Reply #28 on:** November 23, 2006, 07:29:17 PM »

Dear Ron,

I really worked hard trying to find the formula for the said calculation. I haven't been able to find even an aproximation to it. I am building a small (0.5 m diameter) wind turbine to be tested in our wind tunnel. We will be able to test efficiency as a function of yaw angle and who knows may be we can write a formula based on what we find! I would like you to take a look at my turbine so you have a better understanding of the problem. Please follow this link http://www.theinquirer.net/default.aspx?article=35394

It is an article with pics from The Inquirer, from London, whose correspondent visited the science fair INNOVAR 2006 (Buenos Aires, Argentina; Home page: www.innovar.gov.ar) where our wind turbine was on show. I hope you like it. Regards,

Daniel

News:

Author Topic: Efficiency of Windmills (Read 3917 times)