BEM-S809_Aifoilcharacteristics-Extrapolation-Viterna doubt

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,

I’ve responded to your identical question in the following forum topic: http://forums.nrel.gov/t/extrpolation-s809-viterna-model-nrel-phase-vi-turbine/1237/1.

Best regards,