## Extrpolation-S809-Viterna model-NREL Phase VI Turbine

Discuss acquisition, use, and manipulation of airfoil data.

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IjazFazil.SyedAhmedKabir
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Organization: Nanyang Technological University
Location: Singapore
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### 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,

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?

Jason.Jonkman
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### Re: Extrpolation-S809-Viterna model-NREL Phase VI Turbine

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,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

IjazFazil.SyedAhmedKabir
Posts: 14
Joined: Fri Nov 15, 2013 10:28 am
Organization: Nanyang Technological University
Location: Singapore
Contact:

Dear Sir
Thank you