Windpower Generators

[vagulus]

Why is it that the electricity generator windmills we see being erected all over the world, both on land and offshore, are always three-bladed? I would have thought that six blades would give the potential of twice the power output.

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Artificial Intelligence is no match for Natural Stupidity

 

[TugboatEng]

More blades equals more drag. It's a tradeoff.

 

[vagulus]

Drag doesn't stop three blades exporting excess energy. More blades, more excess energy.

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Artificial Intelligence is no match for Natural Stupidity

 

[LittleInch]

Did you not think of asking googly?

https://heathrowdropoff.apcoa.com/tripmanagement/result

Is one of many

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[vagulus]

O don't have an account with them and there is something wrong with their website so I can't create one. BTW: what does travel have to do with windpower generation of electricity?

And ... no, I did not ask Uncle Google. I went to an Engineering Forum and asked Engineers.

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Artificial Intelligence is no match for Natural Stupidity

 

[SWComposites]

More blades would add cost and drag, complicate the hub attachment, probably for little benefit.
Google found this in 10 micro-seconds:

https://interestingengineering.com/science/the-scientific-reason-why-wind-turbines-have-3-blades

 

[vagulus]

Thanks.

Complication of the hub seems to be the key.

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Artificial Intelligence is no match for Natural Stupidity

 

[JohnRBaker]

I've seen two bladed wind turbines, not many, but occasionally. Most of them are in older wind farms.

John R. Baker, P.E. (ret)
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

 

[vagulus]

I just have this idea that the efficacy of a windmill blade (one of the airfoil section type) would be governed by the ratio between lift and drag. That's true for all the other airfoils I have had anything to do with.

Increasing the number of windmill blades would have very little effect on the L/D ratio so, therefore, we have the idea that the more blades you have the more the power output. Of course there is a limit. You can have so many wings that there is interference between them which massively reduces the performances. Some of the early aeroplane designs went way beyond the biplane - I think I have seen photos of a seven-level wing - and these were hopeless. However, the modern generator windmill designs with three blades seem to me to have plenty of room for another three.

I can accept that this would require a more complex hub but doubling the power output looks like being an incentive to handle the complication. Since conventional engineering wisdom has settled on three blades there must be a consensus of opinion somewhere. I'd like to hear an engineer explain it.

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Artificial Intelligence is no match for Natural Stupidity

 

[hydtools]

I believe the odd number of blades has to do with vibration harmonics and balance.

Ted

 

[TugboatEng]

One blade is ideal. Two blades are difficult to balance. 3 blades are best. 4 blades are difficult to balance. 5 blades have too much drag.

Because Piper Cub pilots are the strangest breed:

 

[vagulus]

Here's an interesting discussion:

https://www.youtube.com/watch?v=vAW7sBSeYj0

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Artificial Intelligence is no match for Natural Stupidity

 

[TheTick]

It's not drag so much as each blade's wake causing interference with the next. There's are tradeoffs between speed, number of blades, and weight.

The ultimate boogeyman is the Betz limit. There is a theoretical maximum amount of energy that can be extracted from a given cross-section of wind. Wind turbine efficiency is measured against this ideal limit.

More or better blades or a cooler design are not going to get you beyond this limit.

No, it's not.

 

[Jboggs]

vagulus, This is a topic that has been extremely well researched and analyzed from every possible perspective for decades by some very smart engineers, even accountants, managers, builders, and politicians. Countless prototypes have been built and tested. Every option includes unanticipated benefits, costs, and risks. I don't have to go through the calculations myself to accept their results.

The same argument has existed, also for several decades, with propeller driven aircraft. Two blades? Three? Four? Even five or more? ALL those variations have been analyzed, built, flown, and maintained. Most fixed-pitch propellers will have two blades. Simple to build and very reliable. Variable pitch propellers nowadays will usually have three blades. You usually only see four bladed props on a few old very high-power models (think P-47 and B-29).

Several models have experimented with five blades. I think the Spitfire variant is the most widely known. Some pusher models like the now-defunct Beechcraft Starship also had five blades.

But after all things are considered, including actual performance and reliability, the three-blade design has come out on top.

 

[ctopher]

It seems to me the more blades, the bigger the center hub, the bigger the support post. More $$ and more maintenance. The bigger they are, more difficult to transport.

Chris, CSWP
SolidWorks
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