Dear @Jason.Jonkman
I have some questions for you. I am currently doing load analysis based on TEST18. My analysis is divided into two parts. The first step is the analysis of steady wind and the second step is the analysis of turbulent wind. During the analysis, I found some problems that confused me. When doing steady-state wind analysis, I set RotSpeed=12.1 in ElastoDyn. After OpenFAST simulation, I finally found that RotSpeed is stable at a certain value, i.e. 6mps corresponds to 7.86 8mps corresponds to 8.96 11.4mps corresponds to 11.92 14mps corresponds to12.11, and the rotor speed changes with the change of wind speed. And lately when I was doing the simulation of turbulent wind conditions, I also set RotSpeed=12.1, the average wind speed of the hub height was 6 mps and the TI was 10%. After running the OpenFAST, I found that the speed of the rotor remained constant to 12.1. What was this? Was I wrong in that step? Thank you for your reading and answers, and I am sorry if my question is very simple.
Best regards,
Dear @Lin.Ding,
I would not expect the rotor speed to remain at 12.1 rpm for the NREL 5-MW baseline wind turbine operating at 6 m/s turbulent wind when the controller is enabled. Perhaps you disabled the generator degree of freedom in ElastoDyn, in which case the rotor speed will remain constant regardless of the loads applied?
FYI: As has been discussed many times on this forum, to avoid confusion by the controller, it is generally recommend to initialize the rotor speed and blade-pitch angle based on their expected (mean) value conditioned on the mean hub-height wind speed being simulated. Using incorrect initial conditions may mean the controller cannot recover.
Best regards,
Dear @Jason.Jonkman
Thank you for your answer. I noticed that I had turned off GenDOF and turned it on. The simulation results became more reasonable, and the operating conditions were set to turbulent wind with an average wind speed of 6mps, with its rotspeed fluctuating between 7.7 and 8.3. I will review more posts on the forum on how to initialize the rotor speed and blade pitch angle for answers.
In addition, I would like to consult you. What is the warning in the figure below? I am operating under turbulent wind and wind shear conditions. Should unsteady aerodynamics not be turned off? If it is turned off, will the data be inaccurate?
Best regards,
Dear @Lin.Ding,
This is a common warning message because the first 4 aerodynamic analysis nodes of the NREL 5-MW baseline wind turbine model are cylindrical cross sections, where the unsteady airfoil aerodynamics does not apply.
Best regards,
Dear @Jason.Jonkman
Thank you for your answer. I noticed that the blade root airfoil has a circular cross-section, but I did not associate it with unsteady aerodynamics.
Best regards,
Dear @Jason.Jonkman
I am currently encountering another problem. Based on test 18, I have set the operating conditions as wind speed of 14mps, wind shear of 0.18, and turbulence intensity of 30%. Before running this condition, I ran a uniform steady state wind of 14mps, set the wind shear to 0.18, and obtained the stable rotor speed and pitch angle (RotSpeed=12.1, BlPitch=7.69) under this condition, which was input as the initial condition into the condition. However, there were still some issues with the operation results, which showed that the unsteady aerodynamics were turned off at 235s. How can I solve this problem.I have attached a picture of the running process and a link to the input file.
Best regards,
Dear @Lin.Ding,
I would not say that this is really a problem to be solved. You are simulating with a very high turbulence intensity and moderate shear, so, the angle of attack is likely varying a lot, especially at inboard stations of the blade. AeroDyn will automatically disable the unsteady airfoil aerodynamics (UA) model when it is beyond its range of validity (at small angles of attack). You can change the threshold for when the UA model will be disabled by increasing UACutOut in the AeroDyn airfoil input file.
Best regards,
Dear @Jason.Jonkman
Do you mean that regardless of the warning information, the simulation results are still reliable. Will modifying the upper limit of UACutout make the simulation results not realistic. I am studying the impact of turbulence, so I set IECturbc=10%, 20%, and 30%. At 10% and 20%, the program runs normally. At high wind speeds and 30%, the program will give an warning message like this. Can you give me some suggestions? Thank you very much.
Best regards,
Dear @Lin.Ding,
Increasing UACutOut should eliminate the warning. We added the functionality to disable UA at high angles of attack to improve numerical robustness of the solution for cases involving transients with large yaw angles arise (before the ability to temporarily turn off UA was added, OpenFAST would abort when the angle of attack reached UACutOut). Iâm not sure how to test the validity of the UA model at higher angles of attack without other data to compare to (wind tunnel experiments or surface-resolved CFD of pitching airfoils for the airfoils of interest). I just know that the theory was developed for small to moderate angles of attack, and the 45-degree DEFAULT value of UACutOut is already quite high.
Best regards,
Dear @Jason.Jonkman
I encountered a problem while running turbsim. My settings are shown in Figure 1. If I set WrFMTFF=TRUE, I will encounter an error during runtime as shown in Figure 2. Is the. BTS file I obtained trustworthyďźHowever, if I set WrFMTFF=FALSE, there will be no error reported.
Best regards,
There appears to be an issue with writing the formatted grid files (WrFMTFF: *.u, *.v, *.w) when tower points (WrADTWR) are used. For now, you can just make sure that you donât have both WrFMTFF and WrADTWR set to true during the same simulation. We will work to fix that issue in a future pull request.
This error doesnât affect the .bts file at all, so I wouldnât be concerned with the files that are written.
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Thank you for your reply.
Dear @Jason.Jonkman
Based on test 18, I set the operating condition to a steady wind of 11.4m/s with no wind shear, and want to analyze the changes of âRotPwrâ, âRotThrustâ, and âRotTorqâ with âAzimuthâ. Based on the output results, I draw an image and attached the input file at the end.
I havenât figured out a few questions.
- Why does a minimum appear at positions 30 °, 150 °, and 270 ° in Figure 1.
- In Figure 1, due to the influence of the tower on the blades, the aerodynamic performance of the rotor is affected when the blades pass through the tower. The minimum value should appear at 60 °, 180 °, and 300 °, but it does not actually appear at this position and there is some phase lag.
- I think the variation pattern of Figure 2 and Figure 3 should be the same as Figure 1, but in reality, they are very different.
Best regards,
Dear @Lin.Ding,
Your model is quite complicated with dynamic inflow and unsteady airfoil aerodynamics enabled, many structural degrees of freedom (DOFs) enabled, and torque and pitch control enabled. I would think the results would be most easily interpretable if you have first reached a periodic steady state. Have you ensured that your solution is in a periodic steady state before post-processing the results? After that, I would recommend assessing the influence of various features of the model on the results, e.g., dynamic versus quasi-steady inflow, unsteady versus quasi-steady airfoil aerodynamics, structural DOFs, etc.
Best regards,
Dear @Jason.Jonkman
Thank you very much for your reply!
I ensure that the solution is in a cyclical and stable state.
Based on your reminder, I have identified the problem. By turning off all degrees of freedom, I have obtained images that match the results, as shown in the figure below. From this, I can clearly see the impact of the tower on the blades, as there are minima at 60 °, 180 °, and 300 °.
I recently read an article based on OpenFAST studying the aerodynamic elasticity of wind turbines, and its results are as follows. Does this mean that when studying aerodynamic elasticity, all degrees of freedom need to be turned off.
Best regards,
Dear @Lin.Ding,
Well, the term âaero-elasticsâ implies that you are considering aerodynamics and structural dynamics coupled together, so, disabling all structural degrees of freedom would not be an aero-elastic solution. Certainly, though, the aero-elastic solution is more complicated and can result in behavior that requires careful assessment relative to a pure aerodynamic solution.
Best regards,
Dear @Jason.Jonkman
I recently learned that DBEMT should be used instead of BEMT for variable pitch angle and high wind speeds, so I attempted to use DBEMT to run OpenFAST, but I encountered a warning during operation.
My working condition is based on test18, with a constant wind speed of 11.4m/s and WakeMod=2. All other settings are set by default.
Best regards,
Dear @Lin.Ding,
This is a standard warning issued by AeroDyn if you have a time-dependent tau1 time-constant (DBEMT_Mod = 2) and the induction is high; when this warning is issued, the rotor-averaged induction is limited to 0.5 in the calculation of tau1. You can avoid this warning by setting DBEMT_Mod = 1 with your own tau1_const or to avoid simulating in conditions with high induction.
Best regards,
Dear @Jason.Jonkman
I want to use OpenFAST and Mlife to study the fatigue analysis of wind turbine blades based on test18, mainly analyzing parameters such as RootMxb, RootMyb, RootFzb, etc. According to DLC1.2 of IEC 61400-1, I want to set different wind speeds of 3-25m/s (interval 2), different wind shear indices of 0.10-0.26 (interval 0.02), different turbulence levels of 10-20% (interval 2%), and different yaw angles of -30 °~30 ° (interval 5 °). There are a total of 8424 operating conditions, is this setting reasonable, Can you give me some suggestions.Thank you ever so much for your help.
I implemented the automatic operation of OpenFAST through MATLAB.
The OpenFAST input file is attached below, taking the wind speed of 3m/s, wind shear of 0.26, turbulence of 20%, and yaw angle of 30 ° as an example. In the input file, URef, PLExp, IECturbo in TurbSim, and NacYaw, RotSpeed, and BlPitch in ElastoDyn change with the operating conditions, while other settings do not change with the operating conditions.
Best regards,
