Extrpolation-S809-Viterna model-NREL Phase VI Turbine

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?

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,

Dear Sir
Thank you