Extrpolation-S809-Viterna model-NREL Phase VI Turbine

Wind & Water Airfoils
1

Dear members
I’m trying to use Viterna method for extrapolating S809 aerofoil characteristics to be used in BEM analysis.
I have a doubt in computation of Aspect Ratios
In literature I found two definitions,

AR= Bladespan^2/Planform area
AR=Bladespan/Chord at 80%

For that I need Aspect Ratio of NREL Phase VI turbine.
I found two AR, In work of Lindenburg " Investigation into Rotor Blade Aerodynamics". Aspect Ratio of NREL Phase VI is mentioned to 7. In the work of Tangler, “Wind Turbine Post-Stall Airfoil Performance Characteristics Guidelines for Blade Element Momentum Methods”. AR is mentioned to be 11 but increased to 14.

Can I know why there is difference in AR?
What is the correct formula for AR in VC method?

2

Dear IjazFazil.SyedAhmedKabir,

The Aspect Ratio (AR) is the ratio between the blade length (R) and a representative chord (c): AR = R/c. Both formulas you state are valid because the planform area = c*R. The “representative chord” can chosen based on a particular span, an average chord, etc. In the UAE Phase VI rotor, AR = 11 was commonly used, although I’ve seen variations. Regardless, the Viterna correction is not perfect and its application should be validated by measurements.

Best regards,

3

Dear Sir
Thank you