Wind turbines

[.... callchet ....]

Why do they only use 3 blades on the large wind turbines instead of 5, 7 or whatever ?

[NJmaverick]

1. The answer

The determination of the number of blades involves design considerations of aerodynamic efficiency, component costs, system reliability, and aesthetics. Noise emissions are affected by the location of the blades upwind or downwind of the tower and the speed of the rotor. Typically one bladed rotors will operate at higher tip speed ratios. Given that the noise emissions vary by the 7th power of blade speed, a small increase in speed can make a big difference.

Wind turbines developed over the last 50 years have almost universally used either two or three blades. Aerodynamic efficiency increases with number of blades but with diminishing return. Increasing the number of blades from one to two yields a six percent increase in aerodynamic efficiency, whereas increasing the blade count from two to three yields only an additional three percent in efficiency. Further increasing the blade count yields minimal improvements in aerodynamic efficiency and sacrifices too much in blade stiffness as the blades become thinner.

Component costs that are affected by blade count are primarily for materials and manufacturing of the turbine rotor and drive train. Generally, the fewer the number of blades, the lower the material and manufacturing costs will be. In addition, the fewer the number of blades, the higher the rotational speed will be. This is because blade stiffness requirements to avoid interference with the tower limit how thin the blades can be. Fewer blades with higher rotational speeds reduce peak torques in the drive train, resulting in lower gearbox and generator costs.


http://en.wikipedia.org/wiki/Wind_turbine_design

[Kindigger]

2. I don't know but

after having the experience of seeing one blade going down the highway on a triple-long flatbed truck, I would guess that any more than three would cause the 'base' to topple over, or the base would need a much more sophisticated construct to hold them up.

[OKIsItJustMe]

3. Try Google

Search for http://www.google.com/search?q="wind+turbines"+"three+blades"">"Wind Turbines" "Three Blades"

(You need a "none of the above" answer.)

[Berry Cool]

4. Why post a poll asking for an answer to a factual question?

Polls are for opinions, not facts. (And opinions by unknowledgeable people as to why only three blades are on large wind turbines are irrelevant when what you want to know is the REAL reason why--not just the majority belief of a handful of DU'ers who chose to respond to a poll as to why it is true.)

[OKIsItJustMe]

5. A: Because he's not looking for a factual answer

http://www.democraticunderground.com/discuss/duboard.php?az=show_mesg&forum=115&topic_id=181322&mesg_id=181398