Aerodynamic data for wind turbine (curved plate)

Question

I am trying to find some aerodynamic data for curved plates, as I want to use them for wind turbine blades, similar to:

http://www.yourgreendream.com/diy_pvc_bl...

It's for a small (30cm diameter?) low power turbine to power a low voltage pump for my garden pond that is too far away from the house for mains power.

I have Hugh Piggott's "Windpower Workshop" book which gives the best lift/drag ratio at 3 deg angle of attack for a 10% curvature (i.e. thickness is 10% of chord). As the blade will taper further out from the centre, the curvature will be different, and I want to optimise the angle of attack for different curvatures. I know I could just make the whole thing a bit bigger to make up for inefficiencies or use a proper aerofoil section blade, but that's not the point. I want to make best use of theory, as I think my theoretical skills are better than my practical ones.

I haven't found anything specific for curved plates on the internet, only for NACA sections, etc.

Basically I want to know something like:

Curvature ...... AoA for Max Lift:Drag Ratio

5% .............. ???

6% .............. ???

7% .............. ???

8% .............. ???

9% .............. ???

10% ............. 3 deg

11% ............. ???

12% ............. ???

13% ............. ???

14% ............. ???

15% ............. ???

(Of course if it only varies from 2 deg to 4 deg over the range, then I'd just settle for 3 deg anyway.)

Links to the answers (or to the appropriate lift and drag curves so I can work out the optimum) would be great.

Answer 1

The CL x alpha for a curved plate is about the same as for flat plate, i.e., about 5.7

Alpha is in radians, I guess about 0.1 CL increase for each degree. There is another formula to find the angle (negative in the case) which gives zero lift.