Hugh article on VAWTs

[Adriaan Kragten]

If you compare the aerodynamics of a HAWT with that of a H-Darrieus rotor you see the following differences.

A HAWT can be designed such that the angle of attack alfa is optimal for every radius r of the blade. One can use asymmetric airfoils which have very low drag/lift coefficients and so the Cd/Cl ratio is very low especially for big windmills for which the Reynold numbers are high. So big wind turbines can run at a maximum Cp of about 0.5. Small wind turbines can run at a maximum Cp of about 0.4 because of the lower Reynolds values. However, this is only true if the rotor is designed according to the aerodynamic theory. There are many small wind turbines which perform badly because of a bad rotor design or because of bad matching in between the rotor and the generator.

In my public report KD 601, I have tried to give an aerodynamic theory to design a H-Darrieus rotor. In figure 2 of this report I have calculated the angle of attack alfa for twelve positions of the blade. Table 1 gives the angles and the lift coefficient for these twelve postions. The angle is 9° when the blade is at the front side and -9° when the blade is at the back side and 0° when the blade is at the left and at the right side. This shows that one has to use a symmetrical airfoil for a H-Darrieus rotor. Symmetrical airfoils have lower minimum Cd/Cl ratios than asymmetrical airfoils at the same Reynolds number. Only during a part of a revolution, the angle of attack is lying close to the angle for which the Cd/Cl ratio is minimal. This means that the average Cd/Cl ratio during a full revolution is certainly higher than for a well designed HAWT. Another point is that the blades of a H-Darrieus rotor are connected to the hub by beams which have a certain drag. So a part of the power generated by the rotor is used to overcome this drag. So a H-Darrieus rotor must have a lower maximum Cp than a well designed HAWT for which the Reynolds numbers are about equal.

If people claim unrealistic high maximum Cp values for a VAWT and if they heave really measured a scale model in the wind tunnel or a real wind turbine in real wind, they must have made a mistake in measuring of the wind speed. If the wind speed is only 10 % higher than what the measuring device shows, this results in a Cp which is a factor 1.33 too high.   

[SparWeb]

Topspeed,
Do not let the lies told by others with a thing to sell make you go down in  frustration.
The figures printed by Anew are blatantly impossible.

This is not a matter of opinon.   I am not just disagreeing with you.   It is law set down by the ultimate authority in creation that decided that 59% is the limit.  For you to disagree with the laws of nature on our forum is against our rules of use.

Please edit your previous post to remove the offending attachment.

[topspeed]

Ok..

I am just wondering ..a company that has been running a business for about 30 years by now...wouldn't they have been sued by the customers by now for misleading info ?

[SparWeb]

Thank you for removing the erroneous performance claims.

[JW]

Just going to leave this here

https://www.symscape.com/blog/virtual-wind-turbine-breaks-betz-law

[topspeed]

Just going to leave this here

Betz was a very interesting caracter.

I would be interested to see a smoke test in a wind tunnel from a pitch articulating HD turbine.

[JW]

this topic has been unlocked

[Mary B]

He is no longer selling the wings and kits but this pic should give you ideas, it is a lift type vawt and can generate a little power IF you have a stiff wind... I have debated one because of zoning(My county bought into that national zoning crap, I can't put up a HAWT, even my solar panels are technically illegal!) to try and generate 50-100 watts to float the bats in winter when I can see a week of clouds... on top of very short days. Last version he was selling used a Fisher and Paykel motor as the generator and he ha d claimed wind curves showing 300 watts(note CLAIMED). I see pretty constant 18+mph winds in winter...

[topspeed]

Here is a design that I did a few years ago
(Attachment Link)

If anybody finds this interesting, they are welcome to use it.

Ed

Do you have 2 sets of magnets here Ed ? Rotating around 3-phase coils ?

[MagnetJuice]

Yes, there are 2 magnet rotors and the stator could have any number of phases depending on your application. But the most popular number of phases would be 3 because it is the most efficient.

Ed

[topspeed]

He is no longer selling the wings and kits but this pic should give you ideas, it is a lift type vawt and can generate a little power IF you have a stiff wind... I have debated one because of zoning(My county bought into that national zoning crap, I can't put up a HAWT, even my solar panels are technically illegal!) to try and generate 50-100 watts to float the bats in winter when I can see a week of clouds... on top of very short days. Last version he was selling used a Fisher and Paykel motor as the generator and he ha d claimed wind curves showing 300 watts(note CLAIMED). I see pretty constant 18+mph winds in winter...

Are the magnets and coils here in upright position ?

[MagnetJuice]

The above windmill uses a motor from a Fisher & Paykel washing machine. They use those a lot in Australia because they are tough and don't cost a lot. Also because the price of magnets over there are high.

You can read about it on their website at:

https://windgenkits.com

It is more fun and educational when you build your own, that way you can customize it to your own needs.

Ed

[topspeed]

He is no longer selling the wings and kits but this pic should give you ideas, it is a lift type vawt and can generate a little power IF you have a stiff wind... I have debated one because of zoning(My county bought into that national zoning crap, I can't put up a HAWT, even my solar panels are technically illegal!) to try and generate 50-100 watts to float the bats in winter when I can see a week of clouds... on top of very short days. Last version he was selling used a Fisher and Paykel motor as the generator and he ha d claimed wind curves showing 300 watts(note CLAIMED). I see pretty constant 18+mph winds in winter...

Mary B,

What are the dimensions here on this turbine ?

[Mary B]

60 inch tall wings, forget how wide it is... I am still tossing around ideas to get around the zoning crap in my town.

[topspeed]

60 inch tall wings, forget how wide it is... I am still tossing around ideas to get around the zoning crap in my town.

Ok I can measure it based on the info. Thanks a bunch !

[topspeed]

Is professor Tadeusz Koronowicz known to anyone ?

He seems to have re-evaluated the possibilities of the wind turbines.

[Adriaan Kragten]

In this article one is mixing Cp with the aerodynamic efficiency which are not the same. Betz has proven that the maximum Cp = 16/27 = 0.59. For the definition of the Cp, you compare the generated energy with the energy of the undisturbed wind flowing through an area identical to the swept area of the rotor. However, for the aerodynamic effciency you have to compare the generated energy with the area at the beginning of the expanding wake. This area is 2/3 of the swept area of the rotor. A Cp of 16/27 therefore corresponds to an aerodynamic efficiency of 3/2 * 16/27 = 8/9 (see more detailled information about this subject at page 15 of my public report KD 35).

[topspeed]

In this article one is mixing Cp with the aerodynamic efficiency which are not the same. Betz has proven that the maximum Cp = 16/27 = 0.59. For the definition of the Cp, you compare the generated energy with the energy of the undisturbed wind flowing through an area identical to the swept area of the rotor. However, for the aerodynamic effciency you have to compare the generated energy with the area at the beginning of the expanding wake. This area is 2/3 of the swept area of the rotor. A Cp of 16/27 therefore corresponds to an aerodynamic efficiency of 3/2 * 16/27 = 8/9 (see more detailled information about this subject at page 15 of my public report KD 35).

Okay,

I think someone here in Finland also claimed that this seems to have flaws.

Is it possible that some turbines accelerate the air mass flow into them or divert the air so that new fresh air enters the system so that it actually does not deny the Betz's law but sorta exceeds it aerodynamically and kinetically as the set up is not similar to propellers ( fluid break ) for instance ??

[Adriaan Kragten]

A way to get a higher Cp than the Betz coefficient is to surround the rotor by a venturi. However, an effective venturi must have large dimensions in relation to the rotor diameter. Especially the part behind the rotor must be very big to make that sufficient under pressure is created to suck a higher mass flow through the rotor. So an effective venturi is very expensive and one can better put that extra money into a bigger normal rotor. Some manufactures supply windturbines with a very small venturi and this might give a little increase of the Cp because the tip losses are reduced but one should not believe the claim that this venturi gives a strong increase of the Cpmax.

Long ago there was a project gouverened by Theo van Holten of the University of Delft which claimed to increase the mass flow by using special tip vanes at the blade tips. Wind tunnel research has demonstrated that indeed the mass flow was increased. However, the increase of the power due to the increased mass flow was completely consumed by the extra drag of the tip vanes and finally the Cp wasn't larger than for a normal rotor. So this project was cancelled.

The maximum Cp of a real rotor is much lower than 0.59 because of four reasons: wake rotation, tip losses, airfoil drag and an effective blade length k which is shorter than R. These effects are explained in chapter 4.3 of my public report KD 35. Airfoil drag is the most important effect for fast running rotors used for the generation of electricity as these rotors have a rather high optimum tip speed ratio.

Figure 4.7 of KD 35 gives the theoretical Cpth value as a function of the optimum tip speed ratio and the Cd/Cl ratio for a 3-bladed rotor. In this figure it can be seen that Cpth = 0.445 for a rotor with an optimum tip speed ratio of 6 and for an airfoil with a Cd/Çl ratio of 0.03. However, this Cd/Cl ratio can't be realised for the whole blade length R but only for a length k. Formula 6.3 gives the reduction of Cpth into Cpmax because of this effect. Depending on the ratio k/R, the final Cpmax will be in between 0.4 and 0.42 for a 3-bladed rotor with Cd/Cl = 0.03. In the same figure it can be seen that Cpth = 0.48 for Cd/Cl = 0.02 and 0.51 for Cd/Cl = 0.01. These very low Cd/Cl values can only be realised for big wind turbines which have large chords and run therefore at high Reynolds values. Very low Cd/Cl values are only possible for high Reynold values. So a real Cpmax of 0.5 is the absolute practical maximum.

[topspeed]

A way to get a higher Cp than the Betz coefficient is to surround the rotor by a venturi. However, an effective venturi must have large dimensions in relation to the rotor diameter. Especially the part behind the rotor must be very big to make that sufficient under pressure is created to suck a higher mass flow through the rotor. So an effective venturi is very expensive and one can better put that extra money into a bigger normal rotor. Some manufactures supply windturbines with a very small venturi and this might give a little increase of the Cp because the tip losses are reduced but one should not believe the claim that this venturi gives a strong increase of the Cpmax.

Long ago there was a project gouverened by Theo van Holten of the University of Delft which claimed to increase the mass flow by using special tip vanes at the blade tips. Wind tunnel research has demonstrated that indeed the mass flow was increased. However, the increase of the power due to the increased mass flow was completely consumed by the extra drag of the tip vanes and finally the Cp wasn't larger than for a normal rotor. So this project was cancelled.

The maximum Cp of a real rotor is much lower than 0.59 because of four reasons: wake rotation, tip losses, airfoil drag and an effective blade length k which is shorter than R. These effects are explained in chapter 4.3 of my public report KD 35. Airfoil drag is the most important effect for fast running rotors used for the generation of electricity as these rotors have a rather high optimum tip speed ratio.

Figure 4.7 of KD 35 gives the theoretical Cpth value as a function of the optimum tip speed ratio and the Cd/Cl ratio for a 3-bladed rotor. In this figure it can be seen that Cpth = 0.445 for a rotor with an optimum tip speed ratio of 6 and for an airfoil with a Cd/Çl ratio of 0.03. However, this Cd/Cl ratio can't be realised for the whole blade length R but only for a length k. Formula 6.3 gives the reduction of Cpth into Cpmax because of this effect. Depending on the ratio k/R, the final Cpmax will be in between 0.4 and 0.42 for a 3-bladed rotor with Cd/Cl = 0.03. In the same figure it can be seen that Cpth = 0.48 for Cd/Cl = 0.02 and 0.51 for Cd/Cl = 0.01. These very low Cd/Cl values can only be realised for big wind turbines which have large chords and run therefore at high Reynolds values. Very low Cd/Cl values are only possible for high Reynold values. So a real Cpmax of 0.5 is the absolute practical maximum.

So professor Tadeusz Koronowicz with Cp of 0.8 is way off the line then ?

[SparWeb]

Way off.
It is best to ignore what that individual claims.

[joestue]

So professor Tadeusz Koronowicz with Cp of 0.8 is way off the line then ?

is it possible he is referring to 80% of the maximum available (.59) so that would actually be .47?

[topspeed]

*Moderator edit (Sparweb): false claims from disreputable company have been removed*

Claims of wind turbine power generation greater than physical law allows is known as an "over-unity" claim.
Over-unity claims are not permitted on Fieldlines.  You agreed to these rules when you signed up.

You have been told this is impossible already, but persists in splattering fake information on this site.

You have no warnings left.  Your site membership will be revoked if you do it again.  A private message is also being sent to you, with this same text. 

[Bruce S]

OF all of these posts with plots and numbers.
I've yet to read any of them that aren't "theory".
Do you have any numbers from real "mills" being built that dis-prove Betz's limit? , if not then all this conjecture is still just "theory".
Once someone builds a "mill" that can be verified to actually dis-proving Betz's limit, then I'll pay closer attention.

Until then , remember, all these calculations are only conjecture and computer modeling, where number can be tweaked not real world examples.

Bruce S

[topspeed]

OF all of these posts with plots and numbers.
I've yet to read any of them that aren't "theory".
Do you have any numbers from real "mills" being built that dis-prove Betz's limit? , if not then all this conjecture is still just "theory".
Once someone builds a "mill" that can be verified to actually dis-proving Betz's limit, then I'll pay closer attention.

Until then , remember, all these calculations are only conjecture and computer modeling, where number can be tweaked not real world examples.

Bruce S

Here is an example of a US University built model.

Clearly showing the nature of the force typical when dealing with H-Darreus types.

*Moderator edit (Sparweb): false claims from disreputable company have been removed*

------------

Edit:

Data can be verified from LAVAL U...and Remi Gosselin is the author with Matt Boudreau.

[MagnetJuice]

You posted that example “clearly showing”. What I clearly see is just a dislocated image that doesn't tell anything by itself. We can't verify or refute any of it because there is nothing but an image.

It would be helpful if you tell us what it is that you are doing or want to do.

Do you want to prove that VAWT's are more efficient than HAWT's?

Are you on a quest to find out what is the state of the art and most efficient VAWT design?

It would be helpful, not only to you, but also to all of us if you could tell us what your intensions are.

On this Forum, most of us build things of fix things. And we collaborate and share knowledge and try to help each other to find solutions to problems.

Theory is good, but sometimes pursuing a theory can lead us into a rabbit hole where we spend a lot of precious time and never find what we are looking for.

It would be good if you post less images and use more text to express your beliefs and desires.

Ed

[DamonHD]

To be a bit clearer, we need you to make clear that you are not here to troll or otherwise waste our time; we have useful things to do with our time.

I have a Master's in Theoretical Comp Sci; theory is fine.  Hey, I even do government work!  But I have to back up claims, particularly extraordinary claims, with citations rather than handwaving and clip-art.  No one expects perfection or the right answers all the time, but a bit of respect for other members' time and effort and patience is important.

Rgds

Damon

[topspeed]

You posted that example “clearly showing”. What I clearly see is just a dislocated image that doesn't tell anything by itself. We can't verify or refute any of it because there is nothing but an image.

It would be helpful if you tell us what it is that you are doing or want to do.

Do you want to prove that VAWT's are more efficient than HAWT's?

Are you on a quest to find out what is the state of the art and most efficient VAWT design?

It would be helpful, not only to you, but also to all of us if you could tell us what your intensions are.

On this Forum, most of us build things of fix things. And we collaborate and share knowledge and try to help each other to find solutions to problems.

Theory is good, but sometimes pursuing a theory can lead us into a rabbit hole where we spend a lot of precious time and never find what we are looking for.

It would be good if you post less images and use more text to express your beliefs and desires.

Ed

Yes Ed !

I am very concerned, that Finland invested around 4 billion euros to erect 250 m tall wind turbines all over the best coastal sites and firms get money to run them even if  there wasn't any wind...or too much wind. At the same time all the funding for new innovations have been seized....especially in the field of wind energy as the previous 30 companies with own wind turbines all have failed to compete with the giants (one is barely alive).

*Moderator edit (Sparweb): false claims from disreputable company have been removed*

I constructed the chart enclosed yesterday to convince myself to keep fighting in this matter....alltough I have run outa funds long time ago.

rgds,

Juke

[topspeed]

I will keep testing my last year 1 x 1 m design. Here is the new mooring for the 1.8 m tall test tower.

[topspeed]

Testing it without mooring was interesting too as I discovered very interesting phenomena...the gyroforce.

System at high speed ( 14 m/s wind ) wind does not fall if you let go..it just starts shifting away from the wind.

[topspeed]

*Moderator edit (Sparweb): false claims from disreputable company have been removed*

Claims of wind turbine power generation greater than physical law allows is known as an "over-unity" claim.
Over-unity claims are not permitted on Fieldlines.  You agreed to these rules when you signed up.

You have been told this is impossible already, but persists in splattering fake information on this site.

You have no warnings left.  Your site membership will be revoked if you do it again.  A private message is also being sent to you, with this same text. 

How can I proof the data I send as I cannot post a link to verify the data ?

But I agree there is no way to proof the **** data for time being.

----

The second graph is from Laval University ...author is Remi Gosselin.

[electrondady1]

that looks like a sturdy base to use for experimentation Topspeed.
i am thinking the bent metal pipes will be driven into the ground to act as anchors.
 
 i live in a beach town so everywhere is sand.
i can attach a garden hose to a piece of steel pipe and using the force of the water simply push the pipe into the ground with out digging.
 it gives me a sturdy base that i can then attach windmills too .``````````





 

 
 

[MagnetJuice]

I'm glad to see you posting about your project, we love DIY experimenters.

I really sympathize with you about your concerns for the small wind producers in your Country. But I have seen many times that unless you have unlimited resources and a lot of power, fighting the government is a futile endeavor. It is like trying to break through a 100 meters thick brick wall.

Long ago I saw this written by Reinhold Niebuhr, an American theologian, and I memorized it:

“Grant me the serenity to accept the things I cannot change, the courage to change the things I can, and the wisdom to know the difference.”

That has served me well and given me peace of mind.

Ed