Invalid Output channel - FAST.Farm

[ILDENIEL]

I'm trying to simulate the behaviour of 2 turbines with FAST.Farm, in particular the turbines are 2 identical turbines with the same characteristics of the NREL 5MW but for the tilt and the coming angle, which I both set to 0. I'm using one module of InflowWind with steady wind (@V rated), the downstream distance is 3D and they're both aligned with the wind direction.

The output related to the Axial wake velocity deficits for radial node 01 (and 2) and downstream distance 01 of turbine 01 is invalid.

the output section of FF is the following:

--- OUTPUT --- False SumPrint - Print summary data to .sum? (flag) 99999.9 ChkptTime - Amount of time between creating checkpoint files for potential restart (s) [>0.0] 0.0 TStart - Time to begin tabular output (s) [>=0.0] 1 OutFileFmt - Format for tabular (time-marching) output file (switch) {1: text file [.out], 2: binary file [.outb], 3: both} True TabDelim - Use tab delimiters in text tabular output file? (flag) {uses spaces if False} "ES13.3E2" OutFmt - Format used for text tabular output, excluding the time channel. Resulting field should be 10 characters. (quoted string) DEFAULT OutAllPlanes - Output all wake planes at all time steps. [DEFAULT=False] 5 NOutRadii - Number of radial nodes for wake output for an individual rotor (-) [0 to 20] 1, 2, 5, 11, 14 OutRadii - List of radial nodes for wake output for an individual rotor (-) [1 to NOutRadii] [unused for NOutRadii=0] 1 NOutDist - Number of downstream distances for wake output for an individual rotor (-) [0 to 9 ] 23.0 OutDist - List of downstream distances for wake output for an individual rotor (m) [1 to NOutDist ] [unused for NOutDist =0] 0 NWindVel - Number of points for wind output (-) [0 to 9] 0.0 WindVelX - List of coordinates in the X direction for wind output (m) [1 to NWindVel] [unused for NWindVel=0] 0.0 WindVelY - List of coordinates in the Y direction for wind output (m) [1 to NWindVel] [unused for NWindVel=0] 90.0 WindVelZ - List of coordinates in the Z direction for wind output (m) [1 to NWindVel] [unused for NWindVel=0] OutList - The next line(s) contains a list of output parameters. See OutListParameters.xlsx for a listing of available output channels (quoted string) "RtVAmbT1" "RtVAmbT2" "RtVRelT2" "YawErrT1" "YawErrT2" "CtT1N01" "CtT1N02" "CtT1N03" "CtT1N04" "CtT1N05" "WkAxsXT2D1, WkAxsYT2D1, WkAxsZT2D1" "WkDfVxT1N01D1, WkDfVxT1N02D1" END of input file (the word "END" must appear in the first 3 columns of this last OutList line)

but in the output file the channels related to the last line (WkDfVxT1N01D1 and WkDfVxT1N02D1) are invalid. What could it be wrong?

Thanks in advance

[ILDENIEL]

[jjonkman]

Dear @ILDENIEL,

The FAST.Farm outputs related to radial output nodes are only available for when using the polar wake formulation (Mod_Wake = 1). It appears that you are using curled wake model (Mod_Wake = 2), which is solved on a Cartesian grid. To output wake deficits with the curled wake model, you should use alternative outputs such as the flow visualization outputs or OutAllPlanes.

Best regards,

[ILDENIEL]

Dear @jjonkman, thanks a lot for your help. I would like to exploit your answer to ask you for a tip: if the main goal of the simulation is the assessment of the combined effect of yaw and distance of the turbines, would you use the polar or the curled wake model? Thanks in advance

[jjonkman]

Dear @ILDENIEL,

The curled wake model works better than the polar model when there is sizeable skew of the flow relative to the rotor, e.g., from yaw error associated with wake steering or rotor tilt associated with floater pitch (in floating offshore wind turbines).

Best regards,

[ILDENIEL]

Dear @jjonkman, thanks again for your help. Best regards Daniele

[ILDENIEL]

Dear @jjonkman, I'm sorry to bother you again, but I still have some issues regarding the simulation of 2 on-shore turbines with Y offset = 0.

The first one is that when I try to set the z-coordinate origin of the high-resolution grid equal to the one of the low-res grid: the Z0_low is set to 6 (6m above ground) and

• when I set Z0_high to the same value the simulation does not start
• when I set Z0_high to 0 (ground level) or 1m, the simulation starts without problems. Why is it so?

I'm still using the curled wake model and, as you suggested, I set the OutAllPlanes flag to true. Looking from above (in Paraview) everything seems correct, but the visualization of the wake planes does not seem to be correct. Is there something I could have wrongly set?

Thanks in advance

[ILDENIEL]

[jjonkman]

Dear @ILDENIEL,

Regarding Z0_High, can you clarify what error you receiving (or share the full message written to the command prompt) when executing with Z0_High = 6 m?

Regarding the visualization, I'm not sure what you are illustrating. Can you clarify what you are showing or share the VTK files directly?

Best regards,

[ILDENIEL]

Dear @jjonkman, These are the pictures of the .FSTF file and the message of the error, respectively. I solved the problem by setting the Z-coordinate of the high-res grid origins at 0.

[ILDENIEL]

Regarding the visualization, I've tried to plot on the same Pataview window all the files from:

• the vtk folder
• the vtk_ff folder resulting from the simulation. The second folder is generated when I set the following flag to "True" OutAllPlanes [-] Output all wake planes in VTK at all time steps. Note: this option requires intensive writing to disk and will drastically slow down the simulation. DEFAULT is False.

I don't understand why the wake planes have the center at ground level and distant from the turbines, so it is a little confusing: whether their origin were on the low-res domain reference system or in the global FoR, their location seems to be wrong, or (probably) I'm missing something.

Thanks in advance Best regards

[jjonkman]

Dear @ILDENIEL,

Regarding Z0_High, the error you are receiving is caused because an aerodynamic analysis node of the OpenFAST model is trying to access wind data outside of the high-resolution domain. I would guess that you have a tower aerodynamic analysis node in AeroDyn that is at or close to ground level. The solution is to ensure that all aerodynamic analysis nodes in each OpenFAST model stay within their high-resolution domain for all time steps, e.g., by lower Z0_High as you have done or raising the lowest tower aerodynamic analysis node.

Regarding OutAllPlanes, can you share an example VTK file of a plane both at time zero and well into the simulation? Also, which version of FAST.Farm/OpenFAST are you running?

Best regards,

[ILDENIEL]

Dear @jjonkman, I checked and it seems that the TwrAeroflag in the AeroDyn file is set to True, so this has to be the reason for the error regarding the high-res domain, thank you so much.

[ILDENIEL]

I'm using OpenFAST and FAST.Farm-v3.4.1. I think I cannot share the simulation with you, because when I try to select the planes from the Paraview pipeline window:

1. Paraview takes a lot of time to process all the files
2. I'm not managing to view the evolution of a single plane in time, since when I select the files from the folder (more than 100K elements...) they automatically appear on the visualization window.

Maybe it is just a matter of Paraview knowledge, so it is only my fault, but this is what I see when trying to select the files.

[jjonkman]

Can you share a couple of the VTK files from the _vtkff directory?

Best regards,

[ILDENIEL]

In this case there is a yawed turbine(tilt and cone = 0) upstream and one turbine with yaw, tilt and coning =0 after 3 diameters

[ILDENIEL]

in this case, without the vtk_ff_planes, the visualization works without problems

[ILDENIEL]

By adding, for example just one plane group from the vtk_ff_planes folder, the selected plane does not move/evolve even though the simulation keeps running

[jjonkman]

I mean can you attach a few of the VTK files from the _vtkff directory directly so that I can review the files rather than the Paraview plots?

Best regards,

[ILDENIEL]

only_yaw.zip sorry I didn't understand because it is not possible to directly attach the vtk files. Thanks again

[jjonkman]

Thanks for sharing. The issue is that the Z value of the ORIGIN is not being written properly in the VTK file. I don't see an issue in the latest version of source code, so, I would guess this bug was found and fixed since v3.4.1. I suggest upgrading to the newest version of FAST.Farm (currently within OpenFAST v3.5.2) to see if that solves the issue.

Best regards,

[ILDENIEL]

Thanks for your time and your disposability, I'll surely try the newest versions. Best regards.