Effect of Blade Angle on Power Output of wind turbine

[memoguy]

Homework Statement

Hi all! I am been working on an EEI. Basically I recorded the power output (P=VI) of a wind turbine with the blades at different angles. I went from 0 degrees (flat) to 180 degrees in 15 degree increments. Averaging the data I see a graph like this:

Also, just to clarify, when at 0 degrees the wind turbine looks like this (also not how the wings are not airofoils):
http://oi48.tinypic.com/9ab66e.jpg

I am trying to write the discussion but I can't find the science behind the phenomena which causes the wind turbine to be most effective at 15 degrees. I am assuming it is some kind of trade off between drag and something else but I am just not sure what to google. If anyone could point me in the right direction, or even just tell me what terms I should be googling that would be amazing! Don't get me wrong, I certainly do not want anyone to do this assignment for me. I simply want a nudge toward some relevant information.

Homework Equations

NA

The Attempt at a Solution

Much googling...

 

[AJ Bentley]

I would have though this had more to do with the blade shape than anything else.
It looks like an aerodynamics question - an angle of attack of 15 degrees sound like an efficient sort of climb just short of a stall.

 

[rcgldr]

So why didn't 165° output the same power as 15° (just reversed direction)? Are the blades assymetrical (is the "back" side different than the front)? Is there a direction sensitivity to the power generator or whatever is used to generate a load?

 

[CWatters]

Lots of reasons why the power at 15<>165..

The blades appear to be crude injection moulded flat plate sections with square/blunt edges so the stalling angle could easily be different.

The difference might be down to the way the pitch angle is measured.

How was the wind generated? It might have been generated by a desk fan and have a rotating component making the angle of attack different at 15 vs 165.

To answer the question I suggest you google for images showing lift vs Angle of attack for other wing sections. Most have a sudden loss of lift at around 15 degrees although it can vary...

https://www.google.co.uk/search?hl=...urce=og&sa=N&tab=wi&ei=9JCWUJWiNqPX0QWdvoCYCg

Someone (including me) has already used the magic word that explains the name given to this effect.