Azimuth output

Wind & Water Computer-Aided Engineering Software Tools
1

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:

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:

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

2

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: Azimuth Angle of the Blade - #10 by Jason.Jonkman.

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

Best regards,

3

Dear Jason,

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

Best regards,

Matthias