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Dart

Active Member
Errr...you might be surprised but at least 4 universities have counted that 59,3 % is only valid on HAWT propellers..VAWTs can exceed the limit with a hefty margin.

https://iopscience.iop.org/article/10.1088/1742-6596/753/2/022056/pdf?fbclid=IwAR2KZbeLkfs1F01RTtNO7s-BqjsTWhuND4H2BLs8dde4uPe7QihjfcNkKtg
Thanks so much for this link! I've been saying that the Betz is not properly applied to VAWT's since about 2006.

I'm not really confident in their numeric simulation in this paper, which is the "proof" they have that VAWT's may have a higher limit. I've talked with experts in CFD flow simulation, at UVIC, and 2 years ago with one of the research heads at Canada's largest wind tunnel, they don't believe that CFD is capable of good modelling of a VAWT with 3D flows, yet. That's not really relevant to the question of should Betz be applied to VAWT's when the calculations are based on the conventional HAWT.

I'm not sure the limit is higher, or lower, just that Betz is a useful tool that doesn't fit in this application.

There's a paper by Gorlov which numerically "proves" a limit of 35% (by conicidence the exact number Gorlov claimed to reach with his helical darius). Since then Gorlov's work has been shown to be problematic. I worked with an independent group who licensed the Gorlov design and bought test turbines from Gorlov. The turbines did not survive testing, too fragile and never reached more than 20% (Cp 0.20). A straight blade Darius was tested in it's place which reached 25%, using the same blade profiles.

Dart

Active Member
Best source on this kinda turbine is the NREL data of the MCDonnell Aircraft Giromill tests in 1974-1978...during the oil crisis.

To me though the realization is that this is much more about reynolds numbers and scale. No one that I'm aware of, and I'd be happy to look at the polish version, has tested a small Darius type VAWT (helical, straight bladed, gyromil, or tropenskine) and got anything over 20% (Cp0.2). Small wings don't work like big wings.

bmcj

Well-Known Member
HBA Supporter
Thanks for the suggestion Hot Wings! I am going to start testing soon, and I will try this. I've heard of people using different paint and I think clay washes for this too. Any suggestions on where I can find recipes for mixes for this, or what you call the process? I'm also aiming to slap a gopro on the driven blade, and use a sheet laser to try to video smoke at different heights in the blade. However all that has to wait till I figure out what the power curve is and determine ideal rpm's at various wind speeds.
Stick with the oil. It offers easy flow and visibility. It might be best if you can apply the oil while it is spinning and look at it while it is still spinning (high speed camera or stroboscopic lighting), but if not, you can stop it and snap some photos immediately afterward.

Speedboat100

Well-Known Member

To me though the realization is that this is much more about reynolds numbers and scale. No one that I'm aware of, and I'd be happy to look at the polish version, has tested a small Darius type VAWT (helical, straight bladed, gyromil, or tropenskine) and got anything over 20% (Cp0.2). Small wings don't work like big wings.

Yes their system was heavily flawed, but their conclusions are very interesting. Also the solidity was very low...you can see the difference here in the ANEW company product which claims 70% efficiency in converting wind energy to electricity.

https://www.anew-institute.com/vertical-wind-turbine.html

Speedboat100

Well-Known Member
Thanks so much for this link! I've been saying that the Betz is not properly applied to VAWT's since about 2006.

I'm not really confident in their numeric simulation in this paper, which is the "proof" they have that VAWT's may have a higher limit. I've talked with experts in CFD flow simulation, at UVIC, and 2 years ago with one of the research heads at Canada's largest wind tunnel, they don't believe that CFD is capable of good modelling of a VAWT with 3D flows, yet. That's not really relevant to the question of should Betz be applied to VAWT's when the calculations are based on the conventional HAWT.

I'm not sure the limit is higher, or lower, just that Betz is a useful tool that doesn't fit in this application.

There's a paper by Gorlov which numerically "proves" a limit of 35% (by conicidence the exact number Gorlov claimed to reach with his helical darius). Since then Gorlov's work has been shown to be problematic. I worked with an independent group who licensed the Gorlov design and bought test turbines from Gorlov. The turbines did not survive testing, too fragile and never reached more than 20% (Cp 0.20). A straight blade Darius was tested in it's place which reached 25%, using the same blade profiles.
I think the H-Rotor ( cycloturbine/H-Darreius ) is not ready yet...I mean the design is still not 100% perfect. That is why so many investigate it.

Many have tried and failed, but Pinson and Buhler seemed to conquer something:

Roman Buhler broke a wing at 120 G:s.

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Dart

Active Member
Yes their system was heavily flawed, but their conclusions are very interesting. Also the solidity was very low...you can see the difference here in the ANEW company product which claims 70% efficiency in converting wind energy to electricity.

https://www.anew-institute.com/vertical-wind-turbine.html
Looking at the data it seems they are using a different set of measurements to create the 70% number, and it's interesting that they don't have any engineer signing off on their data. Instead of using the standard swept area section, they are using a cylinder. They seem to be selling 3 different units, and yet they haven't bothered to have any independent testing done. I've never sold a turbine and I only had to pay about 5,000$to get an engineer to inspect my setup, come along for a set of tests, and produce a report. That they haven't attempted any independent testing, or released it, speaks pretty loudly to me. It's sad, but the VAWT history is full of massaging of the metrics, to outright lying. Another issue is that historically, at least up to 2010, testing VAWT's in wind tunnels was most often done using standard blockage factors that produce incorrect results. This is true of the historical blackwell report from NREL, where they found a peak of 21%, when real world results find closer to 10%. Speedboat100 Well-Known Member Looking at the data it seems they are using a different set of measurements to create the 70% number, and it's interesting that they don't have any engineer signing off on their data. Instead of using the standard swept area section, they are using a cylinder. They seem to be selling 3 different units, and yet they haven't bothered to have any independent testing done. I've never sold a turbine and I only had to pay about 5,000$ to get an engineer to inspect my setup, come along for a set of tests, and produce a report. That they haven't attempted any independent testing, or released it, speaks pretty loudly to me.

It's sad, but the VAWT history is full of massaging of the metrics, to outright lying. Another issue is that historically, at least up to 2010, testing VAWT's in wind tunnels was most often done using standard blockage factors that produce incorrect results. This is true of the historical blackwell report from NREL, where they found a peak of 21%, when real world results find closer to 10%.
Polish company is 30 years old. It seems to me that their turbine stalls very early and actually cannot utilize the 70% efficiency for more than a brief period at wind speeds below 10 m/s...where there is very little energy in the first place.