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Azimuth output

Posted: Tue May 14, 2019 3:10 am
by Matthias.Schmid
Dear all,

I have set up a simple OpenFAST simulation and got some strange output of the azimuthal angle.
I wanted to simulate a small wind turbine at a fixed rotational speed and I set:
- The total simulation time (TMax) equal to 10 rotor revolutions,
- The time step size (DT) equal to 0.1 degree,
- The output time step size (DT_Out) equal to 1.0 degree,
- And the starting time for the output (TStart) equal to 9 rotor revolutions.

Using this setup with a constant wind speed I get only zeros as azimuth values:

Code: Select all

Time         Wind1VelX    RotSpeed     RtTSR        B1Azimuth
(s)          (m/s)        (rpm)        (-)          (deg)     
    8.0304    5.000E+00    6.725E+01    5.007E+00   -0.000E+00
    8.0328    5.000E+00    6.725E+01    5.007E+00   -0.000E+00
    8.0352    5.000E+00    6.725E+01    5.007E+00   -0.000E+00
    8.0376    5.000E+00    6.725E+01    5.007E+00   -0.000E+00
    8.0400    5.000E+00    6.725E+01    5.007E+00   -0.000E+00
    8.0424    5.000E+00    6.725E+01    5.007E+00   -0.000E+00


With a turbulent inflow, generated by TurbSim, I get the following values:

Code: Select all

Time         Wind1VelX    RotSpeed     RtTSR        B1Azimuth
(s)          (m/s)        (rpm)        (-)          (deg)     
    8.0304    7.541E+00    6.725E+01    3.697E+00   -1.348E+02
    8.0328    7.552E+00    6.725E+01    3.692E+00   -1.381E+02
    8.0352    7.563E+00    6.725E+01    3.687E+00   -1.415E+02
    8.0376    7.574E+00    6.725E+01    3.681E+00   -1.422E+02
    8.0400    7.585E+00    6.725E+01    3.677E+00   -1.391E+02
    8.0424    7.596E+00    6.725E+01    3.673E+00   -1.332E+02
    8.0448    7.607E+00    6.725E+01    3.669E+00   -1.241E+02
    8.0472    7.618E+00    6.725E+01    3.664E+00   -1.102E+02


Both results are not what I expected. Does anybody has an idea what could be wrong with my setup or is there a bug in OpenFAST?

Thank you very much for your help.

Matthias

Re: Azimuth output

Posted: Tue May 14, 2019 7:45 am
by Jason.Jonkman
Dear Matthias,

The blade azimuth angle output from AeroDyn v15 is not the rigid-body rotation of the rotor, but defines the orientation of blade relative to skewed inflow--see the following forum topic for more information: viewtopic.php?f=4&t=1680&p=8567.

The Azimuth output from ElastoDyn is likely more in line with what you expect.

Best regards,

Re: Azimuth output

Posted: Wed May 15, 2019 7:46 am
by Matthias.Schmid
Dear Jason,

thank you very much, this is what I was looking for.

Best regards,

Matthias