4.2.15.5. Output Files

FAST.Farm produces five types of output files: an echo file, a summary file, visualization output files, a time-series results file, and OpenFAST-related files. The following sections detail the purpose and contents of these files.

4.2.15.5.1. Echo File

If Echo = TRUE in the FAST.Farm primary input file, the contents of the file will be echoed to a file with the naming convention <RootName.ech, where <RootName> is as defined in Section 4.2.15.4.3. The echo file is helpful for debugging the primary input file. The contents of an echo file will be truncated if FAST.Farm encounters an error while parsing the primary input file. The error usually corresponds to the line after the last successfully echoed line.

4.2.15.5.2. Summary File

If SumPrint = TRUE in the FAST.Farm primary input file, FAST.Farm will generate a summary file with the naming convention of <RootName.sum>. This file summarizes key information about the wind farm model, including the wind turbine locations and OpenFAST primary input files; wake dynamics finite-difference grid and parameters; time steps of the various model components; and the name units and order of the outputs that have been selected.

4.2.15.5.3. Visualization Output Files

If WrDisWind = TRUE in the FAST.Farm primary input file, FAST.Farm will generate full 3D low- and high-resolution disturbed wind data output files, i.e., the ambient wind and wake interactions across the wind farm for visualization. The VTK data format and spatial resolutions (number of grid points, origin, and spacing) of these output files matches those of the corresponding low- and high-resolution ambient wind data used by the FAST.Farm simulation. The VTK files are written to a directory named vtk_ff where the FAST.Farm primary file is stored. The naming conventions of these output files are <RootName>.Low.Dis.<n_low>.vtk and <RootName>.HighT<n_t>.Dis.<n_high>.vtk for the low- and high-resolution disturbed wind data files, respectively, where <n_t>, <n_low>, and <n_high are as defined in Section 4.2.15.4.3, but with leading zeros.

Likewise, if NOutDisWindXY, NOutDisWindYZ, or NOutDisWindXZ are set to be greater than zero in the FAST.Farm primary input file, FAST.Farm will generate low-resolution disturbed wind data (including wakes) output files that are 2D slices of the full low-resolution domain. The 2D slices are parallel to the X-Y, Y-Z, and/or X-Z planes of the global inertial-frame coordinate system, respectively. The VTK files are written to a directory named vtk_ff where the FAST.Farm primary file is stored. The naming conventions of these output files are <RootName>.Low.DisXY<n_Out>.<n_low>.vtk, <RootName>.Low.DisYZ<n_Out>.<n_low>.vtk, and
<RootName>.Low.DisXZ<n_Out>.<n_low>.vtk for the X-Y, Y-Z, and X-Z slices, respectively, where <n_Out> is as defined in Section 4.2.15.4.3, but with leading zeros.

The time step (inverse of the frame rate) of all disturbed wind data files is set by input parameter WrDisDT in the FAST.Farm primary input file. Note that the full high-resolution disturbed wind data output files are not output at a frame rate of \(1/\)DT_High, but are only output every WrDisDT seconds.

Each visualization output file follows the same VTK format used for the ambient wind data files for the high-fidelity precursor simulations. See Section 4.2.15.4.4 for details on the file format.

Visualizing the ambient wind and wake interactions can be useful for interpreting results and debugging problems. However, FAST.Farm will generate many files per output option when WrDisWind = TRUE and/or when NOutDisWindXY, NOutDisWindYZ, and/or NOutDisWindXZ are set greater than zero. This file generation will slow down FAST.Farm and take up a lot of disk space, especially when generating full low- and high-resolution disturbed wind data files. Therefore, disabling visualization is recommended when running many FAST.Farm simulations.

4.2.15.5.4. Wake dynamics Plane Files

Setting the option OutAllPlanes to true in the main FAST.Farm input file will result in the wake planes of the Wake Dynamics module to be written. This option requires intensive writing to disk and will drastically slow down the simulation. The wake planes are written in VTK format, in the folder vtk_ff_planes at the root of the simulation directory. A VTK file is written for each plane, time step and turbine. The number of planes written will increase with each DT_Low time step, until the full number of planes Num_Planes is reached. The coordinates of the planes are in the meandering frame of reference (not global coordinates) and using Cartesian coordinates. The following field are always written: x,y,z components of the wake deficit velocity (in the meandering frame), ambient, shear, and total eddy viscosity. When Mod_Wake=1` (polar wake), the fields are converted from polar to Cartesian. Additional velocity gradients are provided in the VTK file when Mod_Wake/=1`.

4.2.15.5.5. Time-Series Results File

The FAST.Farm time-series results are written to an ASCII text-based file with the naming convention <RootName.out. The results are in table format, where each column is a data channel with the first column always being the simulation time; each row corresponds to a simulation output time step. The data channels are specified in the OutList section of the OUTPUT section of the FAST.Farm primary input file. The column format of the FAST.Farm-generated file is specified using the OutFmt parameter of the FAST.Farm primary input file.

4.2.15.5.6. OpenFAST Output Files

In addition to the FAST.Farm-generated output files, the OpenFAST model of each wind turbine may also generate output files. The various output files that OpenFAST may generate (at both the driver/glue code and module levels, as specified within the OpenFAST input files) are described in the OpenFAST documentation and include summary (.sum) files, time-series results (ASCI .out or binary .outb) files, visualization (.vtk) files, etc. FAST.Farm simulations will generate these same files, but with the the path/rootname changed to <RootName of WT_FASTInFile>.T<n_t>.