SOWFA

All of these files compose the current version of the SOWFA (Simulator for Offshore Wind Farm Applications), created at the National Renewable Energy Laboratory (NREL). The files are based on the OpenFOAM software and are either new files or modifications of files in the OpenFOAM source code distribution. Please see the included OpenFOAM readme file ("README.OpenFOAM") and the GPL licence information ("COPYING"). Access to and use of SOWFA imposes obligations on the user, as set forth in the NWTC Design Codes DATA USE DISCLAIMER AGREEMENT that can be found at http://wind.nrel.gov/designcodes/disclaimer.html.

Solvers and Codes Included

Solvers

• ABLPisoSolver - A large-eddy simulation (LES) solver for computing atmospheric boundary layer turbulent flow with the ability to specify surface roughness, stability, and wind speed and direction. It must be used with hexahedral meshes (like those created by OpenFOAM's blockMesh utility).
• windPlantPisoSolver - A specialized version of ABLPisoSolver for performing LES of wind plant flow. It includes the ability to include actuator line turbine models with local grid refinement around the turbine.
• windPlantPisoSolverFAST - Like windPlantPisoSolver, but the actuator line turbine model is coupled to NREL's FAST aeroelastic and turbine system dynamics code.

NOTE: These solvers are meant to be used for flow over flat terrain. We hope to add the capability to handle non-flat terrain in the near future. Also, the way the sub-grid stresses are treated is different than the standard OpenFOAM practice. Therefore, the standard OpenFOAM turbulence models are unavailable in these solvers--only the standard Smagorinsky model is available. We wish to add more capability in the future. It is important to remember, though, that you may couple the actuator line models with any standard OpenFOAM solver, such as pisoFoam.

Utilities

• setFieldsABL - A utility to initialize the flow field for performing atmospheric boundary layer LES. With the utility, you can specify an initial mean profile and perturbations that accelerate the development of turbulence will be superimposed. You may also specify the initial temperature profile and location and strength of the capping inversion.

Libraries

• finiteVolume - Contains a custom boundary condition for pressure called buoyantPressureMod that is compatible with the above solvers but derived from OpenFOAM's standard bouyantPressure boundary condition.
• turbineModels - Contains the actuator line turbine model similar to that outlined by Sorensen and Shen (2002).
• openfast - A version of NREL's FAST code (see http://wind.nrel.gov/designcodes/simulators/fast/) meant for coupling with the windPlantPisoSolverFAST solver.
• fastturb - A version of the actuator line turbine model that is coupled with NREL's FAST aeroelastic and turbine system dynamics code.

Compiling/Installation

The included codes work only with the OpenFOAM CFD Toolbox. OpenFOAM has not been distributed with the SOWFA package. Please visit www.openfoam.com to download and install OpenFOAM. This release of SOWFA is known to work with OpenFOAM-2.0.x. It will probably need to be modified to run with earlier versions, but may run as is with OpenFOAM-2.1.x.

Once OpenFOAM is installed, please follow these steps:

1. Move the user-2.0.x to a desired location somewhere in your home directory and replace "user" with your username on your system.
2. When you installed OpenFOAM, you modified your login script (.bash_profile or similar). Make sure that the environment variable WM_PROJECT_USER_DIR points to where you put the renamed user-2.0.x directory.
3. Source your login script by entering source ~/.bash_profile or whatever is appropriate for your system.
4. Move the tutorialsSOWFA directory to any desired location.
5. Change directory to WM_PROJECT_USER_DIR by entering cd $WM_PROJECT_USER_DIR.
6. Run the Allwclean script to remove any dependencies by entering ./Allwclean.
7. Compile the SOWFA codes by running the Allwmake script by entering ./Allwmake.
8. Make sure that no error messages appeared and that all libraries and applications are listed as "up to date."

Running Tutorials

Tutorial example cases are provide for each solver. The tutorials are as follows

• precursorABL - An example case of how to perform an atmospheric boundary layer large-eddy simulation (without turbines). This will generate turbulent fields that can be used in wind plant simulations.

• windPlant - An example of how to use windPlantPisoSolver with a farm of NREL 5MW turbines.

• windPlantFAST - Like the windPlant example but for use of the FAST-coupled windPlantPisoSolverFAST.

To run a tutorial, change to that tutorial directory and run the Allrun script contained in the directory by entering ./Allrun. View the Allrun script to understand the basic use of the code. To return to the original state, run the Allclean script by entering ./Allclean.

These are very basic tutorials meant to familiarize the user with the general file structure of a case and the various input files. They are meant to run on a small amount of processors, but will not generate very meaningful results as the grid resolution is extremely coarse. The turbine models use a Gaussian projection (see the epsilon variable in the constant/turbineArrayProperties file) that should be set to at least twice the local grid cell width. For these examples, epsilon is set to a realistic value for performing true LES, but is much less than twice the local grid cell width of these very coarse grids. The precursorABL tutorial uses a periodic mesh, which is what we do in running a "real" precursor simulation. The wind plant tutorials also use a periodic mesh, but in actuality, we feed data saved from the precursor into the wind plant domain and have outflow boundaries elsewhere. We did not show this in these tutorials since the precursorABL simulation is too coarse to create meaningful inflow data for the windPlant simulations. We leave it to the user to experiment with this.