Wind turbine, 3 or 5 blades?

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darwenn
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Wind turbine, 3 or 5 blades?




by darwenn » 08/08/09, 07:42

Good morning all. After having successfully built my wind turbine (here is a photo below and thank you to those who helped me on this forum), this one works very well with a wind of 30 km / h. With a wind of 20 this is the minimum, but here is my concern. My wind turbine cannot rotate continuously. Let me explain: it will start to turn, sometimes very very quickly and produce well for 30 seconds and then slow down and stop. So the first thing I did was to review the profile of my blades according to indications given (pitch and shape) and to make a new propeller because before it was worse, it was going very badly. The result is current, it turns very well, but not long. At the moment we don't have a really strong wind in the north, so I can't really be sure it's not because of that. The wind does not exceed 20 to 30 km / h once or twice a week at this time.

After searching the internet, I came to this conclusion and ask for your opinion. My propeller with 5 blades, of 80cm each, that is to say a span of 1m60 (without the rotor + 15cm), in plywood 10mm profiled with line of flight (made with the plane). So far everything seems to be going well. But according to what I found, the 5-blade propellers by turning, eventually create deflection disturbances which cause the rotation to stop. A 5-blade propeller certainly provides more torque than a tri-blade, but in my case the torque requested by the multiplier and the generator is rather low so I wonder if to put a three-blade propeller as is the case on the majority of wind turbines, will not solve my problem. I have what it takes to make this three-bladed and I would like to know if, for the same wind, the three-bladed will rotate faster than the 5-bladed, with a lower torque but without causing this brake effect. I tell myself that if the majority of wind turbines have a three blade, there must be a reason, and therefore that the 5 blades in my case is not suitable. What do you think ? what is this famous difference between the 5 blades and three blades which makes that one finds in majority only three blades?. Thank you for your answers

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Cuicui
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by Cuicui » 08/08/09, 09:35

There are also single blade wind turbines (with counterweights) that work very well. Is it to avoid deviation disturbances? Should try.
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by Former Oceano » 08/08/09, 11:02

For elements of response between 5 and 3 blades here are propeller tests made for ULMs:

http://www.gilroy.fr/spip.php?article16

The 5 blades spring quieter and more torque.

However, each blade induces a drag so reducing the number of blades decreases the resistance

http://www.aero-hesbaye.be/dossiers/hlp ... elice.html

If you have what it takes to make a 3 blade propeller, why not build it with the same diameter and shape of blades as the 5 blade and then make comparisons of efficiency and noise because the rest of your wind turbine remains identical.

This would allow further reflection on self-built wind turbines.
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by darwenn » 08/08/09, 11:11

Yes, the simplest for me would have been to build the 3 blades and do a comparison test, but before doing it I said to myself as much to ask for some opinions before and be sure that it was worth it. So I think to build it indeed on the same dimensions of blades and compare as soon as the conditions are favorable, I hope that it will be able to solve my problem even if I may lose in rotation speed and torque, finally it will remain at see.
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by minguinhirigue » 08/08/09, 11:43

Bravo for your self-construction, great work.

Regarding blockages, I suppose you have already checked all the mechanics! Couldn't there be a problem with the alternator? Good luck...
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by darwenn » 08/08/09, 11:49

Hello Miguin, thank you, no worries on the mechanical side, no blocking everything is on bearings including the generator (which is a DC motor that I rewound and put on ball bearings), the propeller is perfectly free in terms of torque, so no effort or friction which would disturb the rotation, the propeller is well balanced, perfectly regular.

I also wonder if I should not add a cone on the rotor, a nose somehow in a warhead, like on other wind turbines, does it play a role on the sliding of the wind on the blades?
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by parfaitelumiere » 08/08/09, 12:51

I take the opportunity to ask a question, to be a suggestion, I don't know.
I saw planes with propeller motors, which turned in two directions, on two stages, why did they do like that?
could it be more interesting for your wind turbine project?
Last question, most of the propellers that I saw (plane among others) or insect wings, are very narrow at the level of the attachment in the center, then widen widen and taper towards the point, Why?
Wouldn't that be more effective?
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by elephant » 08/08/09, 14:30

I also think that maybe your wind turbine is not very clear. Every house and your roof cause turbulence. I think it is not by chance that wind turbines are placed at the bottom of gardens, in the middle of fields, etc ...
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by darwenn » 08/08/09, 15:12

Yes it is perhaps also badly located, I have the place to put it at the bottom of the garden where it is more clear indeed, but for the practical side (the shrouds) I preferred to place it where I thought to be the best compromise. There are perhaps several causes for my concern, it is not simple. If I could have avoided moving it it would have greatly helped me, especially since if it is not the main cause I would have done it for nothing. Okay, well, I'll think about the question.
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by Cuicui » 08/08/09, 15:30

parfaitelumiere wrote:I saw planes with propeller motors, which turned in two directions, on two stages, why did they do like that?

The counter-rotating propellers limit the size of the blades and cancel the anti-torque effect of the engine.
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