Designing, Building and Testing a Darivonius VAWT

[MattM]

Just be careful if one catches constantly as it goes down.  It may end up being a sand stake more than a dirt stake.

[MagnetJuice]

I have been busy working on other projects, but I have also been working on the speed control and a self-pitching system for the turbine.

I am still working on the speed control. If I get it done I will post images tomorrow.

Here is a preview of the self-pitching.

[Adriaan Kragten]

Here is a preview of the self-pitching.

(Attachment Link)

Why make it that complicated? If you chose the turning point of the blade at the airfoil nose, you can use the centrifugal force in the blade itself to push the blade outwards and you need only one spring and one stop per blade.

[MagnetJuice]

Do you mean like A, B or something else?



Could a setup like that make the blade flutter? If it flutters, that would decrease the Cp.

Ed

[Adriaan Kragten]

The stop must be at the inside of the blade otherwise the blade can't move to the outside. The blade is pulled against the stop by the spring. If the blade is made out of massive wood, the centre of gravity will lie at about 0.4 c from the nose. If the axis of rotation is laid at the aerodynamic centre, which lies at 0.25 c from the nose, the lift will give no moment but the centrifugal force will give a certain moment which turns the blade outwards. This centrifugal moment becomes larger if the axis of rotation is chosen closer to the airfoil nose. However, the lift force will give a moment in the opposite direction if the axis of rotation is lying in front of the aerodynamic centre. It depends on the density of the material of the blade, which of the two moments is increasing most if the axis of rotation is moved from the aerodynamic centre to the airfoil nose. You have to derive the moment equation if you want to predict the blade movement for rotational speeds above the rotational speed for which the resulting moment becomes equal to the moment of the spring.

Flutter is an effect which has to do with torsion and bending of the blade and occurs when the natural frequency for bending becomes the same as the natural frequency for torsion. For a HAWT, the natural frequency for bending increases strongly at increasing rotational speed. For a H-Darrieus rotor, this effect will be almost not valid so I think that there is no risk of flutter at high rotational speeds if there is no flutter at low rotational speeds. But it depends on how the blades are connected to the hub. If one blade is connected to the hub by two spars which are connected at 1/5 of the blade length from the blade tips, the torsion stiffness of the blade will certainly be high enough. But if only one spar is used in the centre of the blade, the free blade ends may be sensible for flutter if the chord is small with respect to the blade length.

[MagnetJuice]

Adriaan, I just want to make sure that we are talking about the same thing.

Blade pitching can be used to slow down the turbine and can also be used to help with self-start. I am interested in using it for self-start.


If it would be simple to build a mechanism for blade pitching to help start the turbine, we can eliminate the Savonius from the center. Without the Savonius at the center, the problem with the drag caused by the Savonius will be gone. Then I think it would be easier to work just with the H-Darrieus to attain a desired TSR.

Without the Savonius in the center, all we have to worry about would be getting the best solidity and Reynolds number to get the best efficiency at the right RPM.

As far as speed control for high winds, I have a mechanism that I think will be effective for that. It is similar to the self-pitching image that I posted on Reply # 199 but working in reverse. I am still working on that mechanism but I am confident that it will be effective to control the high speed.

Ed

[Adriaan Kragten]

I thought that you used the mechanism to limit the rotational speed at high wind speeds. A centrifugal force steered mechanism can't be used for starting as for starting the blade has to oscillate from positive blade angles at the front side to negative blade angles at the back side. If the centrifugal force works in the correct direction if the blade is at the front side, it will work in the wrong direction if the blade is at the back side.

In one of my earlier posts I have described a system which works as starting help but which also limits the maximum rotational speed. But this system needs an eccentric which can be moved by a small electric motor from behind the rotor axis to before the rotor axis and you need a vane to make that the path of the eccentric is always in line with the wind direction.

In my report KD 601, I describe a starting mechanism which is steered by the aerodynamic lift force acting on the blade. However, this system can't be used to limit the maximum rotational speed.

[MattM]

I thought he was going for Savonius to start it and centrifugal angle variance to limit top end speed.

[MagnetJuice]

I thought he was going for Savonius to start it and centrifugal angle variance to limit top end speed.

Yes, that has been my plan from the beginning. I was just exploring other possibilities to see if it would be possible to use some simple type of blade pitching to help start it. If that would have been possible, we could have eliminated the Savonius and the drag associated with it.

Because there is not a simple way to pitch the blade to help with self-start, we have to go with the Savonius in the center.

I would have to do a lot of experimenting with different blade configurations for the Savonius. The reason for that is that this is not going to be a normal Savonius. The only purpose of this drag device is to get the H-Darrieus rotor spinning. After that, I want the Savonius to ‘go to sleep' and create as little drag as possible while spinning fast. Only actual experiments will reveal the best configuration that will do that.

What I intent to do soon will be to build a testing platform so I can test different blades to get the best performance. Out of all the testing, a nice windmill will come out. That is the plan.

Ed

[Adriaan Kragten]

Because there is not a simple way to pitch the blade to help with self-start, we have to go with the Savonius in the center.

Ed

That isn't true. The lift steered system which is described in KD 601 isn't very complicated and it is certainly less complicated than the centrifugal force steered system which you proposed in your earlier post (and which won't work). Only a blade pitch system which helps starting and which also limits the maximum rotational speed becomes complicated. If you use a Savonious rotor for starting, you have not solved the problems which will happen at high rotational speeds.

Even if you use Savonious rotors, I doubt if the centre of the rotor is the best place from an aerodynamic standpoint. The Darrieus rotor has the best performance at the centre of the blades because there you have no tip losses. So if the Savonious rotors are placed in the centre, the wake of the Savonious rotors has the strongest negative effect on the power generation of the blade of the Darrieus rotor when it is at the backside. So I think you can better use one Savonious rotor at the top and one 90 degrees twisted Savonious rotor at the bottom to flatten the summerised torque of both Savonious rotors.

[topspeed]

I agree with Adrian.

---------

H-Darrieus can reach 2.5 Cp at one azimuth point !

http://www.lmfn.ulaval.ca/fileadmin/lmfn/documents/Articles/GosselinDumasBoudreau-CFD2013_reprint.pdf

[MagnetJuice]

H-Darrieus can reach 2.5 Cp at one azimuth point !

Please explain what you mean by that. Also tell me which H-Darrieus turbine was tested that produced that level of performance.

And I would appreciate it if you can explain in your own words without giving links to any documents.

Ed

[topspeed]

H-Darrieus can reach 2.5 Cp at one azimuth point !

Please explain what you mean by that. Also tell me which H-Darrieus turbine was tested that produced that level of performance.

And I would appreciate it if you can explain in your own words without giving links to any documents.

Ed

Remi Gosselin et al seem to test 3 blade straight bladed systems with an endplate.

They are able to get power coefficient up to 2.5 at the work phase end.

[MattM]

The simplest is probably something akin to a school bus bi-fold door lever.  When pulled in the door hinges in half.  When pushed out the door flattens to a closed position.  A dual-hinged pushrod made it all work.

[Adriaan Kragten]

H-Darrieus can reach 2.5 Cp at one azimuth point !

They are able to get power coefficient up to 2.5 at the work phase end.

Never believe these fairy tales! Betz has proven that the maximum theoretical Cp = 16 /27 = 0.59 if there are no losses. The best you may expect for a large H-Darrieus rotor (with no disturbing Savonious rotor in the centre) is Cp = 0.35. So Cp = 2.5 is more than a factor 7 too high!.

[topspeed]

H-Darrieus can reach 2.5 Cp at one azimuth point !

They are able to get power coefficient up to 2.5 at the work phase end.

Never believe these fairy tales! Betz has proven that the maximum theoretical Cp = 16 /27 = 0.59 if there are no losses. The best you may expect for a large H-Darrieus rotor (with no disturbing Savonious rotor in the centre) is Cp = 0.35. So Cp = 2.5 is more than a factor 7 too high!.

Cp 2.5 can only be reached on each round briefly....real Cp is lower of course.

[SparWeb]

Hello topspeed,

Please bear in mind that when you write extraordinary things, we expect to see some evidence of what you claim.  If you don't do this, then we cannot trust what you say.  Why would you want us to distrust you?

[JW]

Hi Steve,

Alot of us have the experience of posting here for years. As such we have been aware of all sorts of background as we have lived it.

Cheers

[topspeed]

Hello topspeed,

Please bear in mind that when you write extraordinary things, we expect to see some evidence of what you claim.  If you don't do this, then we cannot trust what you say.  Why would you want us to distrust you?

Why would you not trust Laval University researchers...I am not claiming a thing.

They average just over 0.5 Cp there...but peak 2.5 with a single blade CFD model....during a 360 degs rotation at 112 degs azimuth point.

[topspeed]

Hi Steve,

Alot of us have the experience of posting here for years. As such we have been aware of all sorts of background as we have lived it.

Cheers

I bet...I have tested now 2 models and reached 928 RPM and around 300 Gs...but not been able to measure the wattage. The third model will show that.

[Adriaan Kragten]

Hello topspeed,

Please bear in mind that when you write extraordinary things, we expect to see some evidence of what you claim.  If you don't do this, then we cannot trust what you say.  Why would you want us to distrust you?

Why would you not trust Laval University researchers...I am not claiming a thing.

They average just over 0.5 Cp there...but peak 2.5 with a single blade CFD model....during a 360 degs rotation at 112 degs azimuth point.

One should doubt any result which is against the laws of physics even if these results come from a University. Forgetting that closed wind tunnels give much too high Cp values because of tunnel blockage, is a mistake which has been made very often. A complete rotor gives wake expansion and the wind speed in the rotor plane is therefore much lower than the undisturbed wind speed. But if you test only one blade, you have no realistic wake. So an average Cp of over 0.5 must also be doubted if it results from wind tunnel tests which are not performed in an open wind tunnel.

When I worked at the University of Eindhoven we did wind tunnel tests to an 8-bladed wind servo and these tests gave unrealistic high Cp values because of tunnel blockage. The main results are given in my public report KD 671 in which I have corrected these measurements.

[topspeed]

Hello topspeed,

Please bear in mind that when you write extraordinary things, we expect to see some evidence of what you claim.  If you don't do this, then we cannot trust what you say.  Why would you want us to distrust you?

Why would you not trust Laval University researchers...I am not claiming a thing.

They average just over 0.5 Cp there...but peak 2.5 with a single blade CFD model....during a 360 degs rotation at 112 degs azimuth point.

One should doubt any result which is against the laws of physics even if these results come from a University. Forgetting that closed wind tunnels give much too high Cp values because of tunnel blockage, is a mistake which has been made very often. A complete rotor gives wake expansion and the wind speed in the rotor plane is therefore much lower than the undisturbed wind speed. But if you test only one blade, you have no realistic wake. So an average Cp of over 0.5 must also be doubted if it results from wind tunnel tests which are not performed in an open wind tunnel.

When I worked at the University of Eindhoven we did wind tunnel tests to an 8-bladed wind servo and these tests gave unrealistic high Cp values because of tunnel blockage. The main results are given in my public report KD 671 in which I have corrected these measurements.

Yes I wonder a lot about the extensive testing of H-Darreius types in CFD since several studies...at least 4-5  claim Betz limit exceeded. None of these research groups actually ever tested their models outdoors and measured the wattage output ...and the real life Cp.

[JW]

Yes I wonder a lot about the extensive testing of H-Darreius types in CFD since several studies...at least 4-5  claim Betz limit exceeded. None of these research groups actually ever tested their models outdoors and measured the wattage output ...and the real life Cp.

The Betz limit, is something that can not be exceeded, there have been many who have used empirical testing to prove this.

I went thru this sort of thing with steam tables. I did testing at a given pressure and it seem to defy the given data... Long story short, I was getting more pressure than I expected at a given temp.... My thermo couple data was flawed. the reason for this is that I should have used a non-contact IR thermometer. It took about 2 years to figure out. The whole time I believed that I was right, but later found out how the error was made.

Cheers

 

[SparWeb]

Sure, you can double-down on the BS.  Nobody's going to be happy if you do.

I read the document.  The things you are saying show that you didn't understand it, or choose to cherry-pick from it only the most provocative/annoying/wrong/extreme things.  I won't guess at your reason for doing so.  I suggest you examine your reasons for doing this yourself, again, as I already suggested to you yesterday.

The authors do not claim Cp greater than Betz limit can be achieved.  They are studying torque ripple and using a convenient metric.  They are printing their good data beside their garbage data because they are experimenting with a simulation software (called RANS) and seeking model parameters that most closely resemble "reality".  Their charts are pretty, they are speculative calculations made as they develop a simulation.  One that they admit is completely unvalidated.

[MagnetJuice]

Our Thanksgiving weekend is over for us Canadians. We have to celebrate that holiday before the U.S. because we are farther north and we have to catch the turkeys before they go into hibernation. 

Since nobody in my family especially likes roasted turkey, my wife makes her special Lasagna recipe. She uses ground turkey instead of ground beef. It is so good that it adds three pounds to my belly on a single weekend.

For me personally, Thanksgiving is every day. I am abundantly blessed daily, so thanksgiving is a daily privilege for me.

Now it is time to get back to work designing and building the turbine. Overcoming the problems with self-starting and speed control is challenging, but I am fully convinced that there are solutions. I will keep working on finding solutions to those two main problems.

Ed

[topspeed]

Sure, you can double-down on the BS.  Nobody's going to be happy if you do.

I read the document. The things you are saying show that you didn't understand it, or choose to cherry-pick from it only the most provocative/annoying/wrong/extreme things.  I won't guess at your reason for doing so.  I suggest you examine your reasons for doing this yourself, again, as I already suggested to you yesterday.

The authors do not claim Cp greater than Betz limit can be achieved.  They are studying torque ripple and using a convenient metric.  They are printing their good data beside their garbage data because they are experimenting with a simulation software (called RANS) and seeking model parameters that most closely resemble "reality".  Their charts are pretty, they are speculative calculations made as they develop a simulation.  One that they admit is completely unvalidated.

Can you enlighten us what I did not understand.

[Bruce S]

Sure, you can double-down on the BS.  Nobody's going to be happy if you do.

I read the document. The things you are saying show that you didn't understand it, or choose to cherry-pick from it only the most provocative/annoying/wrong/extreme things.  I won't guess at your reason for doing so.  I suggest you examine your reasons for doing this yourself, again, as I already suggested to you yesterday.

The authors do not claim Cp greater than Betz limit can be achieved.  They are studying torque ripple and using a convenient metric.  They are printing their good data beside their garbage data because they are experimenting with a simulation software (called RANS) and seeking model parameters that most closely resemble "reality".  Their charts are pretty, they are speculative calculations made as they develop a simulation.  One that they admit is completely unvalidated.

Can you enlighten us what I did not understand.

I could be wrong , but,,,
SparWeb is probably trying to say in a nice way is :
If you're going to post un- proven or incomplete information here ,,,, PLEASE do not. Otherwise post your references.
 
When you post incorrect or incomplete information , it's your reputation here that is at stake. There's more than enough people who have been posters and watchers that are knowledgeable enough to see right through incorrect or provocative information.

SparWeb ;
IF I'm incorrect on this assessment, please accept my apologies.

Bruce S

[JW]

Did somebody say turkey

Since my parents got divorced I cook the turkey at my house and we all go to my moms house to have diner

I make the stuffing and it needs sage The recipe is top secret

[topspeed]

Sure, you can double-down on the BS.  Nobody's going to be happy if you do.

I read the document. The things you are saying show that you didn't understand it, or choose to cherry-pick from it only the most provocative/annoying/wrong/extreme things.  I won't guess at your reason for doing so.  I suggest you examine your reasons for doing this yourself, again, as I already suggested to you yesterday.

The authors do not claim Cp greater than Betz limit can be achieved.  They are studying torque ripple and using a convenient metric.  They are printing their good data beside their garbage data because they are experimenting with a simulation software (called RANS) and seeking model parameters that most closely resemble "reality".  Their charts are pretty, they are speculative calculations made as they develop a simulation.  One that they admit is completely unvalidated.

Can you enlighten us what I did not understand.

I could be wrong , but,,,
SparWeb is probably trying to say in a nice way is :
If you're going to post un- proven or incomplete information here ,,,, PLEASE do not. Otherwise post your references.
 
When you post incorrect or incomplete information , it's your reputation here that is at stake. There's more than enough people who have been posters and watchers that are knowledgeable enough to see right through incorrect or provocative information.

SparWeb ;
IF I'm incorrect on this assessment, please accept my apologies.

Bruce S

I agree with the proof part....but I think Laval and Aachen universities are to blaim for their test results...I think.

[SparWeb]

Bruce,
Yes that's the intent.  Thanks for the added interpretation.

topspeed,
Continue exploring - you want to keep trying stuff and figuring it out.  I'm all in support of that.
The report from the Laval students is just a simulation.  No tests.  And goofy data because they are doing something not connected with real machinery but more related to comparing different computer algorithms.  They had no intent to publish data about the capabilities of any wind turbine, so don't use their results to say that.
It makes you look bad.

Perhaps an example from my own experience will help.  I use software a lot like what the Laval students have.  I've built simulations of structures, and managed a team of others developing air flow simulations.  When these simulation are not yet finished, but start to run for the first time, the mistakes haven't been cleaned out yet, and you can generate a lot of beautiful garbage.  When the first results come in, and we look over what they tell us, believe me, I do not get into a panic that airplanes will start falling out of the sky just because my broken simulation says it's wings generate 1/2 the lift they are supposed to.  I can look out the window and see one of them on final approach to the airport.  It's my sim that's pumping out crap.  Fix the simulation.

[topspeed]

Bruce,
Yes that's the intent.  Thanks for the added interpretation.

topspeed,
Continue exploring - you want to keep trying stuff and figuring it out.  I'm all in support of that.
The report from the Laval students is just a simulation.  No tests.  And goofy data because they are doing something not connected with real machinery but more related to comparing different computer algorithms.  They had no intent to publish data about the capabilities of any wind turbine, so don't use their results to say that.
It makes you look bad.

Perhaps an example from my own experience will help.  I use software a lot like what the Laval students have.  I've built simulations of structures, and managed a team of others developing air flow simulations.  When these simulation are not yet finished, but start to run for the first time, the mistakes haven't been cleaned out yet, and you can generate a lot of beautiful garbage.  When the first results come in, and we look over what they tell us, believe me, I do not get into a panic that airplanes will start falling out of the sky just because my broken simulation says it's wings generate 1/2 the lift they are supposed to.  I can look out the window and see one of them on final approach to the airport.  It's my sim that's pumping out crap.  Fix the simulation.

Yes I hear you.

[MagnetJuice]

Yesterday I ordered many of the parts that I need to build the turbine-testing platform. To attach the center shaft to the rest of the turbine, I will be using parts that are normally used for go-carts, like hubs and sprockets. Today I went to the U.S. and bought some of the metal that I will be using to attach the blades to the turbine. Also bought some electric metal conduit tubes to place in the center of the blades to give it strength. All that metal is a lot cheaper in the U.S. than in Canada. That is one of the advantages to living close to the border.

Next week I will start cutting the plywood pieces needed for the center of the turbine.

I am going to go ahead and build an alternator for testing the output of the turbine. The turbine dimensions will be 80 inches (2m) high by 52 inches (1.32m) in diameter. I have not been able to find a calculator that I can use to calculate the output of this type of H-Darrieus turbine. If any of you know of such a calculator, I would appreciate it if you can point me to it.

I am going to assume that the cut-in will be around 250 RPM. If I need to adjust the cut-in, I can do that by adjusting the air gap of the alternator. I will build an alternator that can output up to 800 watts, just in case that the turbine is capable of producing that much power.

Ed

[SparWeb]

The turbine dimensions will be 80 inches (2m) high by 52 inches (1.32m) in diameter. I have not been able to find a calculator that I can use to calculate the output of this type of H-Darrieus turbine. If any of you know of such a calculator, I would appreciate it if you can point me to it.

It is well worth the time to do the math yourself.  Use somebody's on-line calculator and you are stuck with their assumptions and their mistakes. 
You can download a copy of SMATH and write up the calc's yourself.  As you try different geometry you can vary the inputs to the calculations and they update immediately in that software.