How is the shape of the blades of an air fan determined? Trial and error, or is there a theory behind it? What are they trying to maximize, volume of air dislocated per rotation?
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2 Answers
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Mostly trial and error - but in a computer.
A combination of Computational Fluid Dynamics (modelling how the air flows over the blade) and Finite Element Modelling (how the stresses in the metal behave)
Both of these are complex areas - and when they come to together you need a lot of expensive computers and some even more expensive engineers.
answered May 10, 2011 at 15:33
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$\begingroup$ Maybe you also want to add en.wikipedia.org/wiki/Blade_element_theory , which is basically a subset of the computational methods you are referring to, but still often used. $\endgroup$– BernhardCommented Aug 27, 2012 at 8:01
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I would guess the Lift/Drag ratio of the blades is important. Lift = wind thrust (and speed), and Drag = friction and power loss.
Since the part of the blade moves slower the closer to the center, the angle of attack needs to increase to provide the same wind speed. Keeping an even velocity profile is probably important in order to minimize losses due to turbulence.
There is probably a lot to be done with the wing-tips that is not done due to aesthetic reasons. pffft.
answered May 10, 2011 at 2:12
Engineeringtag. Got to support my kind :-) $\endgroup$