How to prescribe a periodic change in rotation speed or blade pitch

Wind & Water Computer-Aided Engineering Software Tools
1

Good afternoon,
I am trying to simulate some changes in time of the rotor speed or in the blade pitch motion in addition to a surge motion of the platform. For that purpose, I am using external files with the aerodyn version obtained by cloning :
GitHub - ebranlard/openfast: Main repository for the NREL-supported OpenFAST whole-turbine simulation code. Documentation is avaiable at http://openfast.readthedocs.io -b f/driver
So I have generated the proper input files as described in the following link :
4.2.1.5. AeroDyn Driver — OpenFAST v3.3.0 documentation

First I am wondering if the labels azimuth_,rotspeed_, rotacc_,pitch_, pitch_rate_,pitch_acc_ are available in OpenFast and if it is the case under what denomination? I am asking because I would like to check that are correctly interpreted from my external file, because I don’t obtain the correct range of values for the thrust and the torque. Perhaps my data format is not adequate ? In the blade pitch variations case, the force is even not sinusoidal for a sinusoidal surge motion and a sinusoidal blade pitch signal. I checked that my results are ok when I removed the rotor speed variations and they are correct. This means that the model is ok itself. I guess the same holds for the blade pitch variations.
If you have any idea of the possible source of trouble ?
Many thanks in advance.
Best regards.
Florence Haudin.

2

Hi Florence,

At the moment the Echo option in AeroDyn does not write down the inputs provided by the user for the rotor or pitch motion files. One way to check that the rotor behaves as expected is by looking at the rotor rotational speed (“RtSpeed” sensor) and the azimuth angle (“Azimuth” sensor).

It’s important to note that when the user provides the rotor motion, it must provide the azimuth input as a non-wrapped angle (so, the user will not define the angle between 0 and 2pi radians). Below you can see an example of the three magnitudes for the rotor motion that I’m using in the OC6 phase III project (LC 2.16):

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In this case what I did was to define analytically the rotor speed (harmonic motion following a cosine function). Then I performed the time derivative to know the corresponding rotor acceleration. Finally, I integrated the rotor speed to know the azimuth position.

I hope that helps!

Roger

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Thanks a lot Roger for the explanations.
Best regards.
Florence.