Designing, Building and Testing a Darivonius VAWT

[Adriaan Kragten]

Up to now we have discussed VAWT's of the type Darrieus rotor, Savonious rotor and drag machine. There is a fourth type which I call the rotating blade turbine. I have built such a turbine almost 45 years ago when I knew almost nothing about aerodynamics. But in 2009 I have written public report KD 417 in which the system is described. I have met several people who came up with the same idea so I thought that it is usefull to investigate how it works. The optimum tip speed ratio is about 2/3 and for this tip speed ratio it works as a lift machine for about 5/6 of a revolution. Therefore it can have a rather high maximum Cp. However, the rather low optimum tip speed ratio makes that a lot of energy is lost into wake rotation (see figure 4.2 report KD 35) and therefore I think that the maximum Cp will not be higher than about 0.3. But this is better than for a Savonius rotor and much better than for a drag machine. The rotating blade turbine has a very high starting torque and so it can be used for loads with a high torque at n = 0 rpm like a positive displacement pump or grinding stones.

The rotor can turn in two directions depending on the position of the central shaft of the blade rotation mechanism. The rotor can also work as a brake so this can be used to limit the rotational speed at high wind speeds.

The main disadvantages of this turbine type is that you need a mechanisme to make that the blade spins with half the rotational speed of the rotor and that the central shaft of this mechanism has to be orientated to the wind direction. The total blade area is rather large with respect to the swept area of the rotor resulting in relatively high investment costs. Therefore I don't advice to develope this type of wind turbine but for VAWT's lovers it might be of interest to reed KD 417.

[MattM]

I would imagine you could consider that more of a axial turbine-hybrid than a vertical.

If you're looking for wild ideas, I have plenty.  Doesn't mean they are going to help anyone.  But I'm always trying to think outside the box.

Pic 1 is crazy idea based on squirrel cage being hung like a birdcage.

Pic 2 is crazy idea for hubless HAWT.

[JW]

All you guys should know is that I have 3000 posts.
I support Adriaan Kragten...

[MattM]

It's actually pretty exciting in the forum right now.  Many interesting ideas have been coming out of this place in the past couple of weeks.  Adriaan Kragtenis one of the more interesting posters here.  He communicates his ideas very well.

[electrondady1]

once you go squirrel cage you can never go back

[MagnetJuice]

WOW Matt, that is REALLY outside the box at it got me thinking.

We are searching for a device that can be placed at low altitude to generate about 200 watts to charge 12-volt batteries.

Why does it have to be a VAWT? It could be a HAWT of a MATT (Monumental Art To Try) 

I think that it would be worthwhile to consider the possibilities of a multi-blade (more than 3) HAWT. A HAWT with many blades doesn't spin out of control in high winds because the many blades create drag and limits the RPM. It would not need a furling mechanism. It could continue to spin and generate power in high winds. That power can be diverted to a heater to heat your home in those windy cold winter days. To keep it simple, the blades don't have to have any particular profile, they can be made flat, just angled properly. (By the way, I am not trying to re-invent the Western or American windmill)

By choosing the number of blades and the diameter of the rotor carefully, the RPM can be controlled and the maximum power can be predicted. The size of the rotor can be chosen to match the average wind in different locations.

One problem I see is finding a way for the blades to turn fast enough to face the wind. Would having a wheel bearing in the yawing mechanism help with that? What about the size of the tail?

Come on Fieldliners, keep thinking outside the box. No idea is too crazy.

Ed

[CraigM]

Come on Fieldliners, keep thinking outside the box. No idea is too crazy.

once you go squirrel cage you can never go back

How about using “real” squirrels?

I have a half dozen that will do darn near anything to rob a few sunflower seeds from the bird feeder. Couldn't be too difficult to rig a spinning wheel for them to traverse while they go the feeder. As long as they get thrown off now and then so they keep coming back.

That crazy enough? I think I could train these tree rats! 

[SparWeb]

It's been a long time since I saw this posted on Fieldlines, so I don't remember enough to find it with a search, but another fascinating WT idea we once saw used cloth sails to vary its geometry. 
In one VAWT sail turbine, the sails would blow open as they traversed the downwind side, and blow closed as they moved upwind.  It was a working unit but I don't remember any details about how efficient it was or how the power was extracted.  I think it was fairly large, allowing the arms to travel at wind speed without needing very high RPM.
There was also once posted a topic about a HAWT with sails that I believe could also vary their geometry.  Worth a try searching...  I'll try...

[MattM]

My plan was to use the pole that holds up the ring to more or less use the ring to self align to the wind.  The wheels support low would be mounted on a simple mast that is on one side of the pole.  The PMG would mount behind the pole.  Te planetary ring would straddle the pole between the wheel above the PMG and the wheels on the mast.  The PMG would need a robust shaft to support the weight.  Because the layout, though, extra bearings could support the shaft unlike a traditional axial that has to carry the load on the end of a lever so to speak.  If the planetary ring won't align properly, a tail can be mounted behind the PMG..

[SparWeb]

These are HAWTs:
Juris:
https://www.fieldlines.com/index.php/topic,140886

https://www.fieldlines.com/index.php/topic,144845

Sailwing & Hannu Virtane:
https://www.fieldlines.com/index.php/topic,139066

I was expecting to find some VAWT sails...  none yet...

[MagnetJuice]

Matt, that sounds interesting, I'll see if I can wrap my brain around it tomorrow.

SparWeb, I found this image on a patent. It could be noisy every time that the blade changes direction.



Craig

Nobody else can use that image, it is protected by Canadian copyright. 

Ed

[oneirondreamer]

WOW Matt, that is REALLY outside the box at it got me thinking.

We are searching for a device that can be placed at low altitude to generate about 200 watts to charge 12-volt batteries.

Why does it have to be a VAWT? It could be a HAWT of a MATT (Monumental Art To Try) 

I think that it would be worthwhile to consider the possibilities of a multi-blade (more than 3) HAWT. A HAWT with many blades doesn't spin out of control in high winds because the many blades create drag and limits the RPM. It would not need a furling mechanism. It could continue to spin and generate power in high winds. That power can be diverted to a heater to heat your home in those windy cold winter days. To keep it simple, the blades don't have to have any particular profile, they can be made flat, just angled properly. (By the way, I am not trying to re-invent the Western or American windmill)

By choosing the number of blades and the diameter of the rotor carefully, the RPM can be controlled and the maximum power can be predicted. The size of the rotor can be chosen to match the average wind in different locations.

One problem I see is finding a way for the blades to turn fast enough to face the wind. Would having a wheel bearing in the yawing mechanism help with that? What about the size of the tail?

Come on Fieldliners, keep thinking outside the box. No idea is too crazy.

Ed

Some idea's may be too crazy to try twice, best to look around and see if anyone else has tried a particular flavour of crazy before you jump.   

In terms of a HAWT with simple blades, wasn't that the premise of the “Proven” small HAWT?   I seem to recall some people with very high local winds finding them effective.    I'm not sure I've got the name right.    I think it was a 36” or less diameter 3 bladed black HAWT.

[MattM]

 :-[True.  I was looking at steam turbines for inspiration.  I made a 24-blade piece of yard art that was downright scary to try to fasten to a pole.  Not a planetary setup in that case, it was intended to eventually become a more conventional axial.  I had no second set of hands to help at the time and got ahead of myself.  Damn thing was super light and took off as soon as I let go.  It snapped the 1/2" shaft I mounted it on not realizing the torque in a 32" diameter rotor.  Its too bad it didn't survive the drop and it taught me a valuable lesson.  Make stuff repairable.

[Adriaan Kragten]

Matt, that sounds interesting, I'll see if I can wrap my brain around it tomorrow.

SparWeb, I found this image on a patent. It could be noisy every time that the blade changes direction.



Ed

This picture shows that even rotors which have already been invented by the Chinese before Christ can be patented and even when the postions of the blades are drawn incorrectly. These kind of turbines work in the same way as a sail boat which makes a 360 degrees turn. So there will alway be a position where the sail makes a big swing from one side to the other side. A much better system is the rotating blade turbine (see report KD 417).

[MagnetJuice]

Here are three images of H-Darrieus Rotors. How would the shape and positioning of the airfoils affect their behavior during operation?



I know it is a difficult question, if it was easy I would ask in another website. 

Thanks,

Ed

[electrondady1]

i don't build darius style but if i did "B' would be my first pic

[CraigM]

Here are three images of H-Darrieus Rotors. How would the shape and positioning of the airfoils affect their behavior during operation?

Good question, I've wondered about this myself. If you search VAWT on google and go to images you can sometimes zoom in and see the blade ends. I've seen all three configurations doing this. Can't say if any are better then others. Many of the Chinese made small VAWTs are like your bottom image. I've tried to view only commercial size VAWTs but it's difficult to see the ends of the blades.

[clockmanFRA]

As Adriaan says, The Chinese were using VAWT sails well before BC.

I have posted the below pics and my observations on this forum somewhere.?

I did build one, well I started one, Its very simple and easy to repair, its just Chinese Junk sails with each  tacking into the wind, gybe-ing running with wind then luffing into the wind and back to tacking. The Sheet, the rope that allows the sail boom to luff etc can be set for the wind speed.

I used a 25kg steel flywheel as a controlling load, and it pumped a hydraulic ram, or as the early Chinese used the design, it could pump water really nicely.

Pic one.     China late 1950's - 1960's pumping water, simple construction with local bamboo and Junk ship design sails.
Pic 2.  .......

I have a few more pics of other early Chinese differing designs, that's if they are any use?

I have wondered if using the latest sail boat technologies that form a variable aerofoil extremely efficiently and modern rapid sheet control, this early simple design could be seriously advanced. ?

[SparWeb]

Working out the resultant angles when combining the incoming wind speed, the incident wind from rotation, and considering the effect of taking kinetic energy in the form of power can be done.  It's a tough slog through geometry, but I've done it before.  Just not in a form that I can share online, because you'd need some expensive software.  It might be a good time now to make it easy for everyone to use.

I'd like to propose something:
Is there somebody good at coding HTML, scripts, and forms willing to make a calculator page?
I'd be willing to do the math.
Something like Alton Moore's page:  http://www.alton-moore.net/wind_calculations.html

We could set up a calculator page that would let you enter some inputs:

• wind speed
• RPM
• Diameter
• Height
• etc.

And when you click "submit" it could provide outputs such as:

• Swept Area
• TSR
• a plot of the relative combined flow angle to the blade
• etc.

Any takers?
If so I'll check with the Admin's to see how we could host it on Fieldlines.

[MagnetJuice]

Great idea SparWeb, here are two more examples of calculators:

http://users.xplornet.com/~rmanzer/windmill/rotor_calculator.html
https://rechneronline.de/wind-power

It would be good to have our own calculator(s) here because those links could disappear anytime. It could help to increase traffic too because a lot of people will come just to use the calculators.

About the A B C images that I posted above, since you know a thing or two about aerodynamics; could you give it a shot at explaining how they would behave when they are spinning?

Thanks,

Ed

[topspeed]

As Adriaan says, The Chinese were using VAWT sails well before BC.

I have posted the below pics and my observations on this forum somewhere.?

I did build one, well I started one, Its very simple and easy to repair, its just Chinese Junk sails with each  tacking into the wind, gybe-ing running with wind then luffing into the wind and back to tacking. The Sheet, the rope that allows the sail boom to luff etc can be set for the wind speed.

I used a 25kg steel flywheel as a controlling load, and it pumped a hydraulic ram, or as the early Chinese used the design, it could pump water really nicely.

Pic one.     China late 1950's - 1960's pumping water, simple construction with local bamboo and Junk ship design sails.
Pic 2.  .......

I have a few more pics of other early Chinese differing designs, that's if they are any use?

I have wondered if using the latest sail boat technologies that form a variable aerofoil extremely efficiently and modern rapid sheet control, this early simple design could be seriously advanced. ?

I am very interested in general.

[MagnetJuice]

As Adriaan says, The Chinese were using VAWT sails well before BC.

I have wondered if using the latest sail boat technologies that form a variable aerofoil extremely efficiently and modern rapid sheet control, this early simple design could be seriously advanced. ?

That is worth investigating. It would be nice if something like that could be easily built without using complicated and expensive materials and technology. It also has to be efficient and spin fast enough to generate electricity.

Thanks clockman, keep thinking outside the box.

Ed

[SparWeb]

Ed,
The two examples you found are the "actuator disk" model that doesn't provide detail inside.

I can work out the angle of attack of the blade when turning at X RPM in Y wind speed when it's at Z angle, if anyone wants it. 
Since there are lots of variables, there's no single answer, but there is a range of reasonable values and anyone wanting to know what they are would appreciate a way to work it out.

The thing that got me thinking of this web calculator was trying to come up with an answer to your question about A,B,C blades.
My gut feeling is that the angle of attack of the blade reverses every turn, and if the TSR is low, the flow on the blade reverses entirely.  So without checking with a lot of calculation, my answer would be A.

There is an aesthetic appeal to a camber in the blades that follows the circumference.  I don't think the advantage is there.  Camber changes the point of zero lift of the lift curve, but does not actually change the slope or peak of the lift curve.  By doing so it creates a pitching moment on the blade, forcing you to secure the blade against a force that would change its angle of attack.

[MattM]

Looks like a great application for forming foam blades with a hot wire to test the theory.

Soft blades could be created by stretching fabric between two unequal diameter pipes.  Light wind will deform the fabric minimally.  Strong wind will cause the fabric to cup, but because the unequal diameters of the pipe, it will impart proper push as if you had angle of attack on a blade, pushing the fat end forward.

[MagnetJuice]

You are thinking outside the box again Matt.

That lit up a bulb in my brain. I'm getting near the point of building an experimental mill in a way that I can switch blades easy, that way I can try different blade profiles. I have been thinking of different ways that blades can be built easy an inexpensively. If we can build the blade out of fabric and it works well, it can be finished using painted canvas, the construction techniques that Drew uses.

Ed

[clockmanFRA]

Hi topspeed,

Here is 3 more pics of early Chinese designs.

These 3 were first published in 1965 By Needham, Cambridge University, UK.

I have left the sub text on each.

[clockmanFRA]

In my spare time, when I get any, I am a yacht-ty, ie a yacht master.

 Most of my time is spent trying to hold a course bearing and watching the sails, and when tacking, constantly altering the sails to form that perfect aerofoil shape for the wind we have at that moment.

The latest tech and control computers have become hardy enough for the ocean conditions.

I have been watching the latest BIG racing yachts, and wow those modern sails and the modern control gear, are very quick to react to wind conditions and keep the vessel charging along at 50mph and using every drop of that wind energy.

If I was young enough I would have a go with at least 6 sails on a VAWT, the sails would be a Western Gaff Rig configuration so the sail can be individually tightened up or allowed to billow out depending on its relative position to the prevailing wind.  This could be controlled by simple servo motors or a simple cam arrangement. The controlling sheet/rope could be let out and tightened up individually by a central servo/cam arrangement.

As a VAWT is static and supported at its top central post then a double standard yacht sail could used with standard boom, but another sail could be added that is positioned upside down, so although you have 6 vanes/sails, there are now 2 sails on each vane. 

Have a look at those latest racing yachts. Fast acting tech has come on along way from my early sailing days of the 1970's with canvas sails to the latest variable thickness of KEVLAR variants.

[MattM]

https://eandt.theiet.org/content/articles/2013/05/wind-turbine-based-on-boating-technology-sets-sail/

[Adriaan Kragten]

Here are three images of H-Darrieus Rotors. How would the shape and positioning of the airfoils affect their behavior during operation?

(Attachment Link) (Attachment Link) (Attachment Link)

I know it is a difficult question, if it was easy I would ask in another website. 

Thanks,

Ed

In figure 2 of my public report KD 601, I give the speed diagramn for 12 positions of the blade and for a 3-bladed rotor with a NACA 0015 airfoil. In table 4, I give the angles of attack alpha for these positions if it is assumed that the tip speed ratio is 4.2 and that the wind speed in the rotor plane is 2/3 V. You can see that you have the maximum angle of attack alpha of + 9 degrees at position 1, the minimum alpha of - 9 degrees at postion 7 and that alpha is 0 degrees at positions 4 and 10. This means that you have to use a symmetrical airfoil and that the blade angle must be 0 degrees!

The Cl-alpha curves of the symmetrical airfoil NACA 0015 is given in figure 1 of KD 601 for different value of Reynolds. It can be seen that Cl = 0 for alpha is 0 degrees. The curves are only given for positive angles of alpha but the curves for negative angles of alpha can be found by 180 degrees rotation of the curves. So a symmetrical airfoil can be used for positive and for negative angles and generates the same absolute Cl value for the same absolute angle of attack and the same Reynolds value. The Cd/Cl values are rather low if the Reynolds value is high enough.

The Cl-alpha curves of the asymmetrical airfoil Gottingen 623 are given in figure 5.8 of my public report KD 35. In this figure it can be seen that Cl = 0.5 for alpha = 0 degrees and that Cl = 0 for alpha = - 5.3 degrees. The Cl/Cd curves are given in figure 5.9 of KD 35. The Cd/Cl value is only small for positive angles of alpha in between about 0 and 9 degrees. The Cd/Cl value becomes very large at large negative angles of attack.

Using an asymmetrical airfoil for a Darrieus rotor will always create strong negative angles of attack at a certain part of a revolution and the very strong drag at this part will consume almost all energy which is generated during the part of a revolution for which the Cd/Cl ratio is low and for which therefore a positive torque is generated.

A similar problem arises if the blade angle isn't chosen 0 degrees but for instance 5 degrees and if a symmetrical airfoil is used. At the front side now we will get a positive starting torque but at the back side we get a negative starting torque and the total starting torque is still about zero. But the effect of a postive blade angle at the front side is that the angle of attack at the optimum tip speed ratio is reduced resulting in a lower lift coeffcient. At the back side the angle of attack is increased resulting in stalling of the airfoil. This problem is only prevented if the blade angle is chosen 0 degrees.

[Adriaan Kragten]

I have sailed a lot and know that there is a dangerous move which should be prevented a high wind speeds if you are sailing in the direction of the wind. If you sail in the direction of the wind, the sail direction is almost perpendicular to the boat axis because then you have the highest force on the sail. So there is a long rope in between the bottom beam of the sail and the sailer. Suppose that the sail is at the left side of the boat. If the wind direction sudenly changes or if the boat is steared to the left, the wind can blow at the other side of the sail and then the sail makes a very big move to the right side. So the beam moves with a high speed and can hit you. This is called "gijpen" in Dutch but I don't know the English word. So normally you don't allow this and you make a 360 turn to the right if you want to go to the left.

But in a windmill using sails, you will allways have this position once every revolution and this will give very large shocks if the line in between the beam and a rotor spoke has a fixed length. 

[MagnetJuice]

After SparWeb and Adriaan explanations, it looks like the best blade profile for an H-Darrieus rotor would be a solid symmetrical one. The blade made of fabric that Matt proposed could probably be used for building flexible wings for a sail windmill.

Here are two images that help to visualize how the wind acts on a sail. I post this not to promote sailing (even though I think sailing is exciting) but to help someone who wants to use sails to build a windmill.


The images are courtesy of:
https://yeadonsailingclub.co.uk

Ed

[SparWeb]

I post this not to promote sailing

Agreed; an addictive and expensive habit.

If using sails for a VAWT, and relying on the sail to reverse in its cycle, then the reversal of the sail will be a "snap" made N times on every revolution.  I don't think the machine would be quiet.

[clockmanFRA]

Gybe with modern boats is controlled on the main booms.

Nowadays there are differing types of Vang, boom controllers, anti Chinese Gybe protectors etc etc.

Here is a vid of a ten year old racing job, with hydrofoils.  A very different set up to a normal yacht.

As the young lady says when the computer is set on auto pilot, the yacht sails better than a human being in charge, but she then remarks that the race authorities may ban auto pilots when racing.

Just look at that mainsail arrangement,  wow!!!!  scares an old buffer like me.

https://www.youtube.com/watch?v=BUihkBDAqEQ