Aerodynamic Derivatives

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Adrian.Gambier
Posts: 8
Joined: Wed Dec 09, 2015 8:50 am
Organization: Fraunhofer IWES
Location: Germany

Aerodynamic Derivatives

Postby Adrian.Gambier » Tue Mar 05, 2019 7:10 am

Dear All,

we need the derivatives of aerodynamic power and thrust force with respect to the tip speed ratio. Is it possible to compute it by using the linearization capability of FAST? If not, do you have any suggestion how to do it?
We are using FAST 8 with AeroDyn 14. Is it possible to set FrozenWake = True here or we have to change to AeroDyn 15?

Thank you very much in advance for any help.

Best regards
Adrian

Jason.Jonkman
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Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
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Re: Aerodynamic Derivatives

Postby Jason.Jonkman » Tue Mar 05, 2019 9:06 am

Dear Adrian,

Yes, the linearization functionality of FAST v8 or OpenFAST can be used to calculate these derivatives. That said, FAST v8 and OpenFAST permit full-system linearization using AeroDyn v15, but not AeroDyn v14; so, I suggest upgrading your AeroDyn v14 model to v15.

The process we've used to calculate various aerodynamic derivatives is described in section 3.2 of our TORQUE 2016 paper: https://www.nrel.gov/docs/fy17osti/67015.pdf. To calculate derivatives of the aerodynamic power and thrust, you should use AeroDyn outputs RtAeroPwr and RtAeroFxh, respectively. The derivatives of these outputs will show up in the full-system linear state-space matrices C and D. While you can't calculate the derivatives with respect to tip-speed ratio (TSR) directly, you can calculate the derivatives with respect to rotor speed in the C matrix (assuming that the generator or drivetrain-torsion degree of freedom are enabled in ElastoDyn) and with respect to the uniform wind speed in the D matrix (assuming you've set LinInputs=1 in the FAST/OpenFAST primary input file), from which you can convert to TSR through appropriate algebra.

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

National Renewable Energy Laboratory (NREL)
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