Dear all,
I hope this finds you well.
I have a question regarding the wake model in FAST.Farm. I am planning to run several simulations involving two wind turbines initially aligned with the global axial direction, where I vary the wind direction between -15 to 15 degrees by rotating the wind farm.
Specifically, I want to know if the wake effects are symmetrical around the zero-degree wind direction. If this symmetry exists, could I simplify my testing by only simulating wind directions from 0 to 15 degrees and assume that the results for -15 to 0 degrees would be the same?
I understand that some differences might occur due to the distribution of turbulent structures in the wind field. However, my main concern is whether the wake model in FAST.Farm inherently causes any asymmetry in wake behaviour that I need to consider in my simulations.
Kind regards
Dear @Abdulbaset.Alazhare,
FAST.Farm could include asymmetry in the wake, depending on the settings you are using. The polar wake model is always axisymmetric about the wake centerline, but the wake centerline could deflect more to one side if the horizontal wake deflection correction model. The curled wake model is not axisymmetric, and if you have Swirl enabled, the torque will shift the asymmetry (kidney shape of the wake resulting from skewed inflow) to one side depending on the skew axis and torque.
Best regards,
Dear @Jason.Jonkman, does the wake in FAST.Farm rotate as it travels through the wind farm?
Kind regards
Dear @Abdulbaset.Alazhare,
The axisymmetric polar wake model of FAST.Farm does not include wake rotation, but the curled wake model does include wake rotation when Swirl is enabled in FAST.Farm.
Best regards,
Dear @Jason.Jonkman, many thanks for the clarification.
May I kindly ask another question. Regarding wake-added turbulence (WAT) in FAST.Farm. While the manual refers to this as future work, the website MatthiasCK/OpenFAST: FAST.Farm with wake-added turbulence indicates that WAT was implemented in version 3.0.0 of the OpenFAST framework. Could you please confirm if this feature is included in FAST.Farm version 3.5.3 and if any specific parameter needs to be adjusted in the FAST.Farm input file to activate the model?
Thank you.
Dear @Abdulbaset.Alazhare,
Matthias Kretschmer of USTUTT added a form of WAT to FAST.Farm (released through the link you sent) as part of the following paper: WES - FAST.Farm load validation for single wake situations at alpha ventus. But this form of WAT was never incorporated into the FAST.Farm repository maintained by NREL.
Since then, an improved WAT formulation has been added to FAST.Farm as explained in our TORQUE 2024 paper: https://www.nrel.gov/docs/fy24osti/88164.pdf. This form of WAT was added through the following PR: Wake-added turbulence in FAST.Farm by andrew-platt · Pull Request #2202 · OpenFAST/openfast · GitHub, which is slated for the upcoming release of FAST.Farm within OpenFAST v4.0.
Best regards,
Dear @Jason Jonkman,
Thank you for your clarification. Do you have an estimated timeline for the release of OpenFAST v4.0?
Additionally, in reviewing the paper WES - FAST.Farm load validation for single wake situations at alpha ventus, I noticed that the implementation of the wake-added turbulence (WAT) model involved generating two wind fields, one using TurbSim and the other with the Mann turbulence generator. When the new version of FAST.Farm is released, will this same approach be required for implementing the WAT model?
Thank you for your time and insights.
Best regards,
Dear @Abdulbaset.Alazhare,
I’m expecting OpenFAST v4.0 to be released within the next two weeks.
Yes, the new WAT model of FAST.Farm will require two turbulence boxes, with the WAT box expected in Mann format. However, the new WAT model comes with a predefined WAT box which you only need to replace if you want to. See our TORQUE 2024 paper and PR (linked above) for more information.
Best regards,