## Different Behavior in Aerodyn v.14 and v.15

Discuss acquisition, use, and manipulation of airfoil data.

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### Different Behavior in Aerodyn v.14 and v.15

Dear all

This is my first post in the forum and I'm going to give a short summery of my work.

I am working on my PhD project on Maximum Power Point Tracking(MPPT) of wind turbines and I use FAST coupled with Simulink to simulate the dynamic behavior of the wind turbine and develop different control strategies to maximize the output power. The final prospect of the project is to develop an innovative predictive control strategy for small and medium size turbines.

So I used an almost linear model as my PMSG and I increase the generator torque to find the optimum TSR, to use for an simple TSR control strategy. However, I get different behavior when I use aerodyn v.14 and v.15.
The model used is TEST17 and the windSpeed is set to 12m/s steady and YawDOF to False.

1- By changing the pitch angle of the blade I get an optimum efficiency(Cp) in PitchAngle=2° in v.14 and PitchAngle=7° in v.15!! What is the optimum pitch angle for SWRT model? and why do I get different optimum pitch angles for different aerodyn versions?

2- The Cp curve reaches to almost Betz limit for V.14 but for V.15 is a value around 0.42!!

3- Another problem in v.14 is the really high fluctuation for the output RtrPwr (red line in pic below). The simulation time is around 10 mins and the generator torque slop is low enough. How may I find the reason behind this behavior ? The picture is attached below.

AeroDyn15.jpg (83.52 KiB) Viewed 6691 times

Thanks in advance for your help and sorry for the long post!!

Jason.Jonkman
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### Re: Different Behavior in Aerodyn v.14 and v.15

While the solution algorithm in AeroDyn v15 is quite different than AeroDyn v14, I would not expect larger differences in gross aerodynamic loads between the two models. (I would expect some differences if the tangential induction is large, if the inflow-skew angle is sizeable, or if the structural deflections are large.) From your results, I would guess that there is a problem in the simulation set-up of one or both models. If you are seeing very high power coefficients (in a time-averaged sense) out of AeroDyn v14, have you perhaps disabled the induced velocity calculation by setting IndModel to NONE instead of WAKE or SWIRL?

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

Posts: 6
Joined: Thu Apr 06, 2017 8:42 am
Organization: ghent university
Location: Ghent Belgium

### Re: Different Behavior in Aerodyn v.14 and v.15

Dear Jason

Thank you for your quick response. The IndModel is set to SWIRL. The behavior of Ayrodyn V.14 and V.15 are close for the pitch angles from 11° to 13°. However by changing it to values below 10° (e.g. 5° or 8°) the power coefficients goes unexpectedly high (in a time-averaged sense) and the fluctuations appear in the Rotorpower curve(red line in picture above), which makes me feel that Aerodyn V.14 fails to simulate some phenomenon in my simulation conditions.

I accidentally switched the InfModel from DYNIN to EQUIL and now, the simulation results are much closer to V.15 in my testing condition (for all pitch angles) especially for high generator torque and TSR values lower than optimum TSR. As DYNIN is a more recent algorithm comparing to EQUIL, would you recommend using EQUIL in my simulation?

I also receive these warnings using Aerodyn v.15.

Warning: block 'MiladTest/FAST Nonlinear Wind Turbine/S-Function':
FAST_Solution:CalcOutputs_And_SolveForInputs:SolveOption2:AD_CalcOutput:BEMT_CalcOutput(node 17, blade1): Compute_UA_AirfoilCoefs:UA_CalcOutput:Mach number exceeds 0.3. Theory is invalid. This warning will not be repeated though the condition may persist.

Would you please tell me the impact of these warnings on the validity of the results? Shall I be concerned and objective about them?

Kind Regards

Jason.Jonkman
Posts: 5771
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

### Re: Different Behavior in Aerodyn v.14 and v.15

The EQUIL option of AeroDyn v14 should match AeroDyn v15 better than DYNIN because dynamic wake is not yet included in AeroDyn v15. I would expect that the steady-state solution would be similar (but not identical) between EQUIL and DYNIN, with larger differences expected under transient dynamic conditions.

The warning regarding the disabling the unsteady airfoil aerodynamics routines at high angles of attack is not really a concern. See my post dated Mar 09, 2017 in the following forum topic for more information: viewtopic.php?f=30&t=1791&p=8793.

The warning regarding the Mach number exceeding 0.3 is potentially more serious. Are you expecting the Mach number to be so high?

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

Posts: 6
Joined: Thu Apr 06, 2017 8:42 am
Organization: ghent university
Location: Ghent Belgium

### Re: Different Behavior in Aerodyn v.14 and v.15

Dear Jason

Thank you very much for all your help. In high wind speed and low generator torque Mach number exceeds 0.3. I modified the model and don't get the warning anymore.

Kind Regards