Dear all,
I have a small query regarding the RtAeroPwr variable, and maybe my understanding of Betz’s law.
I have a run the 5MW OC4 case, with a 12mps wind speed, with OF 3.2 and here are my results for the generator power and rotor aerodynamic power :
The mean for this values are 4.19 MW for the generator power and 4.50 MW for the rotor aero power. I don’t understand how the generator can get close to the total available power, as it means it would infringe Betz’law. Or is the rotor aerodynamic power already multiplied by the Betz coefficient ? I did not see a mention of this in the AeroDyn 15 documentation (which I only read briefly).
Best regards,
Maximilien
Dear @Maximilien.Andre,
AeroDyn output RtAeroPwr is the aerodynamic power extracted by the rotor, which already takes into account the Betz limit (and aerodynamic losses relative to the Betz limit such as drag and wake rotation) relative to the aerodynamic power that is available in the wind (0.5AirDensSweptArea*V^3). ServoDyn output GenPwr is the electrical power output of the generator, which accounts for other losses between the aerodynamic power and electrical power, e.g., mechanical friction and mechanical-to-electrical conversion efficiency.
Best regards,
1 Like
Dear Jason,
Thank you for the answer, I have computed the available power with
df['AvailablePower'] = df['RtArea']*(df["RtVAvgxh"]**2+df["RtVAvgyh"]**2+df["RtVAvgzh"]**2)**(3/2)*rho/2
It seems much better like this.
Best,
Maximilien
Dear @Maximilien.Andre,
I’m glad your results make more sense to you know.
Just FYI: For power available, I would look at the wind vector normal to disk rather than the magnitude of the total wind vector at the disk.
Best regards,
Dear Jason,
Sorry if my question is off-topic or not very smart — I’m still learning. I’m analyzing the IEA 15MW Reference Wind Turbine using AeroDyn v15 in standalone mode, without an active controller. I’m using compinflow=1 with turbulent wind input from TurbSim (IEC standard, .bts file, wind speeds 7–14 m/s).
Since there’s no controller, the blade pitch stays fixed, so I expected RotAeroPwr to fluctuate and not be optimized. Initially, I thought my results weren’t valid because the controller was missing. But then I saw results for the 5MW turbine (Maximilien’s case), where RotAeroPwr goes up to 8MW, while GenPwr stays below 5MW which would mean ~60% efficiency.
This made me wonder: is it normal for RotAeroPwr to exceed rated power like that, even in a valid setup? I thought losses between rotor and generator were small (1–3% gearbox, ~95% electrical efficiency).
What i get is RotAeroPwr even 30 MW and applying efficiency of 95% would mean getting 28.5 MW at Generator (using 0° Blade Pitch and 7rpm Rotor Speed). Am I leaving something behind? Did I miss something?
Should I consider my results valid, even without a controller, especially for comparing aerodynamic loads with/without control?
Thank you very much for your time and help!
Best regards,
Pic below (rotor setup according the “Figure 3-1” of 15MW IEA Reference Wind Turbine Technical Report):
- RotAeroPwr using 0° Blade Pitch and 7 rpm Rotor Speed
- RotAeroPwr using 6° Blade Pitch and 7.5 rpm Rotor Speed (i perfomed different Blade Pitch angle simulation)
- “Figure 3-1” of 15MW IEA Reference Wind Turbine Technical Report
Dear @Pierluigi.Pulzella,
You mention disabling the controller, but only mention blade pitch. What about torque control and what is happening with the generator/rotor speed?
Best regards,
Dear @Jason.Jonkman ,
Thank you for the quick answer and for your avaiability.
I didn’t have any type of active controller cause i’m using AeroDyn v15 in the standalone version. i know that in standalone version is not possible have a torque control, or this is what i understand from the examples input file at 4.2.11. Appendix — OpenFAST v4.1.1 documentation; is it right? or i missing somethings? there’s the possibility to set up a torque control in aerodyn standalone?
Below my aerodyn driver input file and my aerodyn primary input file.
Best Regards
AeroDyn Driver:
AeroDyn Primary:
Dear @Pierluigi.Pulzella,
Thanks for clarifying. Apparently I didn’t read that you were using the standalone version of AeroDyn, uncoupled from OpenFAST. I agree that in your case, the rotor will spin at a constant speed regardless of the forces applied and that there is no torque control.
I believe your results make sense. The wind speed is changing rapidly, many times exceeding rated wind speed, so without active control, RtAeroPwr is exceeding the rated capacity of the generator (15 MW) often.
Best regards,
Dear @Jason.Jonkman ,
again thank you for your availability.
I will improve my model introducing the active controller ROSCO, switching to the openFAST coupled analysis or switching to OrcaFLEX turbine module.
I wish you good work and nice weekend,
Best Regards.
