Rotor interia once again!

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Rannam.Chaaban
Posts: 30
Joined: Wed Jul 20, 2011 9:25 am
Organization: Siegen University, Siegen, Germany
Location: Germany

Rotor interia once again!

Dear All,
I've a question about the rotor inertia (e.g. for the 5MW wind turbine), which is supposed to be variable depending on the blade pitch angle and the blade flapwise and edgewise motion.
However, when I do linearize a simple model where only the GenDOF, DrTrDOF are enabled at different operating points in region III (different blade pitch angles), I get a constant equivalent inertia J_eq = J_r + N^2 * J_g = 43780000 kg.m^2, which means constant rotor inertia of J_r = 38760000 kg.m^2.
My question is: Does FAST take into account the blades deformations and their pitch angles (collective or individual) and recalculates the inertia and the corresponding dynamic forces, or it consideres a constant inertia and calculates only the aerodynamic forces of the defomed sections of each blade.
MSc. Rannam Chaaban
Universität Siegen
Paul-Bonatz Strasse 9-11
57076 Siegen / Germany

Jason.Jonkman
Posts: 4952
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

Re: Rotor interia once again!

Dear Rannam,

Yes, FAST will take into account the deformations of the blade in the calculation of the rotor inertia. However, in the structural model of FAST v7 or the ElastoDyn module of FAST v8, the blade mass is distributed entirely along the pitch axis when the blade has no flapwise or edgewise deflection, so, changing the blade-pitch angle alone (without any flapwise or edgewise deflection) will not change the rotor inertia.

An MSC.ADAMS model would behave similarly unless you've specified mass offsets from the pitch axis or large sectional inertias (which are both assumed to be zero in the structural model of FAST v7 or the ElastoDyn module of FAST v8).

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

Rannam.Chaaban
Posts: 30
Joined: Wed Jul 20, 2011 9:25 am
Organization: Siegen University, Siegen, Germany
Location: Germany

Re: Rotor interia once again!

Thank you Jason
MSc. Rannam Chaaban
Universität Siegen
Paul-Bonatz Strasse 9-11
57076 Siegen / Germany