I want to validate the aerodynamics in SIMPACK, which is a MBD software, and uses AeroDyn13 to calculate aerodynamic loads on wind turbine. I did a test with a rigid model. To simplify the test, the tilt angle, cone angle and aerotwist are set to zero; the rotor speed is 14.5 rpm; the wind speed is 6 m/s, with no error and inclination; the aerodynamic input for AeroDyn13 is as following: “StallMod=STEADY”,“InfModel=EQUILDB”,“IndModel=SWIRL”,“AToler=0.0001”,“TLModel=PRANDtl”,“HLModel=NONE”.

But the aerodynamic results from AeroDyn(.elm) seem questionable, the axial induction factor and angle of attack are oscillating, as below. However, my understanding is the axial induction factor and angle of attack should be constant or almost, as the blade is rigid and the ratio between wind velocity and body motion is constant. So could you tell me if the result is reasonable?

I see a once-per-revolution oscillation in your results. It sounds like you have disabled shaft tilt and tower deflection, but do you have a wind shear in your wind file?

Thanks for your answer! I set the inflow wind as the first attachment, which doesn’t contain shear. I also attach the aerodynamic input.
In fact, I have done a test before, in which the rotor cone angle and shaft tilt was included(the tower was still), and the results were oscillating, so I simplified the model as the last post, but the results were the same. This question has troubled me for a long time, so could you tell me if there are any other reasons? Thanks!

Well, I would guess something in your model is causing a skewed flow that is leading to a once-per-revolution oscillation in your results. If not shaft tilt or tower deflection, what about yaw error?

As you can see in the first post, the wind direction is zero. And there is only one shaft rotation degree of freedom in the model, that’s to say the model are without yaw degree of freedom, so I think the yaw error could be eliminated.
The question is such a tough problem that I even thought there is something wrong when aerodyn was integrated into simpack, because I have built a similar model in fast7, from which the axial induction factor is constant, which i think is reasonable.

I’m not sure. It sounds like you’ve built equivalent models in FAST v7 with AeroDyn v13 and SIMPACK with AeroDyn v13 and the oscillation shows up the latter, but not the former? Then, I would guess the problem is not in AeroDyn 13 or in your FAST model set up. I’m not too familiar with the interface between AeroDyn v13 and SIMPACK, but, perhaps there is a problem there? Sounds like a good question to ask SIMPACK.

In fact, I could not get the answer from SIMPACK, so i tried to find help from you. As the model I built, which kind of result would be reasonable for the axial induction factor from your experience? Oscillating or constant?

As I’ve said, I would expect something physical like shear, veer, yaw, tilt, or turbine deflection to be the cause of the oscillation you are seeing. But if you’ve eliminated all these in your SIMPACK with AeroDyn v13 model, and if FAST v7 with AeroDyn v13 give you the answer you expect (constant aerodynamic effects), then I would guess the problem is not with AeroDyn v13, but with your SIMPACK model or the SIMPACK-AeroDyn v13 interface.