Overview

The files in this repository comprise the current version of 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 SOWPA imposes obligations on the user, as set forth in the NWTC Design Codes DATA USE DISCLAIMER AGREEMENT that can be found at https://nwtc.nrel.gov/disclaimer.

Solvers and Codes Included

Solvers

1. ABLSolver - A solver, primarily for performing large-eddy simulation (LES), 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) in order for it to perform the planar averaging it does.
2. ABLTerrainSolver - Basically the same as ABLSolver, but the planar averaging done in ABLSolver is replaced with time averaging since planar averaging does not make sense for terrain.
3. windPlantSolver. - A specialized version of ABLTerrainSolver for performing LES of wind plant flow. It includes the ability to include actuator line turbine models with local grid refinement around the turbine. The corresponds to the turbine type and is "ALM", "ADM", or "ALMAdvanced".
4. pisoFoamTurbine. - OpenFOAM's standard pisoFoam solver, but with the actuator turbine models included. This is useful for simple cases, or for cases where atmospheric effects are not important, like turbines in wind tunnels.
5. turbineTestHarness. - A simple code coupled to the actuator line model that allows you to quickly test a actuator line model setup. It mimics pisoFoam, but the governing equations are not actually solved, the velocity field is constant through the domain, but can change as a function of time. Therefore, no axial induction is computed. But, it lets one quickly test out a new actuator line model setup to see if things like pitch control gains are appropriate.

NOTE: These solvers have been primarily tested for flow over flat terrain. We have tested the non-flat terrain capabilities less, but will do so 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

1. 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

1. finiteVolume - Contains custom boundary conditions for:

• surface shear stress - Schumann model
• surface temperature flux / heating - Specify a surface cooling/heating rate and the appropriate temperature flux is calculated
• surface velocity - For use with surface shear stress model, which requires no wall-parallel velocity, but that velocity is required for specification of the gradient for the SGS model, and setting it to no-slip is not appropriate for rough walls
• inflow velocity - an inflow condition that applies a log-law with fluctuations and drives flow to a certain speed at a specified location
• inflow temperature - an inflow temperature condition that attempts to recreate a typical ABL potential temperature profile
• time varying mapped fixed value with organized random perturbations. Useful for taking inflow from a mesoscale weather model and applying temperature perturbations to create resolved-scale turbulence.

2. incompressible LES models:

• a modified version of OpenFOAM standard Smagorinsky model with Pr_t sensitization to atmospheric stability.
• Deardorff-Lilly one-equation model.
• Kosovic nonlinear backscatter anisotropy one-equation model.
• a modified version of OpenFOAM standard dynamic Lagrangian model of Meneveau et al. but that writes out the Cs field. Also, contains a modified version of that same model that clips the Cs field.

3. turbineModelsStandard - Contains the actuator line/disk turbine models similar to that outlined by Sorensen and Shen (2002).
4. turbineModelsFASTv8 - Actuator line model with coupling to FAST 8 (see http://wind.nrel.gov/designcodes/simulators/fast/) meant for coupling with the windPlantSolver.ALMAdvancedFASTv8 solver.
5. postProcessing - Function objects to simulate the sampling patterns of scanning lidar. Useful for simulating lidar to understand its capabilities and limitations.
6. fileFormats - Adds a structured VTK file format that cuts down on file size by greatly eliminating the write out of x,y,z points.
7. sampling - Adds a sampling set that defines an annulus. Useful for sampling annuli in rotor plane to see blade-local flow.

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 up to OpenFOAM-2.4.x. Making SOWFA work with versions 3.0 and higher may come in the near future.

Downloading and Compiling

1. Make sure that you have OpenFOAM version OpenFOAM-2.4.x downloaded and compiled on your system.
2. Use Git to clone SOWFA from the [https://github.com/NREL/SOWFA](SOWFA GitHub repository). We recommend that you clone the SOWFA repository into your OpenFOAM $WM_PROJECT_USER_DIR directory. For OpenFOAM version OpenFOAM-2.4.x this would be typically be ~/user-name/OpenFOAM/user-name-2.4.x. The Git command to clone SOWFA is:

   [/home/OpenFOAM/user-name-2.4.x]$ git clone https://github.com/NREL/SOWFA.git
   

3. Move into the SOWFA directory and execute Allwclean and Allwmake:

   [/home/OpenFOAM/user-name-2.4.x]$ cd SOWFA
   [/home/OpenFOAM/user-name-2.4.x/SOWFA]$ ./Allwclean
   [/home/OpenFOAM/user-name-2.4.x/SOWFA]$ ./Allwmake
   

4. Make sure that no error messages appeared and that all libraries and applications are listed as "up to date."

Tutorials

Tutorial example cases are provide for each solver in the SOWFA/exampleCases folder. The available tutorials are as follows:

1. Example cases for computing flat-terrain laterally periodic precursor atmospheric large-eddy simulations under the full range of stability.

• example.ABL.flatTerrain.neutral
• example.ABL.flatTerrain.unstable
• example.ABL.flatTerrain.stable
• Uses: ABLSolver

2. Example cases that use the actuator turbine models using the windPlantSolver. solvers. These cases assume that a precursor case has been run to generate inflow velocity and temperature data. Because the inflow data is large, we did not include it here.

• example.ALM
• example.ALMAdvanced
• example.ADM
• Uses:
  • windPlantSolver.ALM
  • windPlantSolver.ADM
  • windPlantSolver.ALMAdvanced

3. A case with the setup of the NREL Unsteady Aerodynamics Experiment Phase VI, in the NASA Ames 80'x120' wind tunnel.

• example.UAE_PhaseVI.ALMAdvanced
• Uses: pisoFoamTurbine.ALMAdvanced

5. An example of using mesoscale influence to drive the atmospheric boundary layer LES. This case is driven by WRF model output for the DOE/Sandia Scaled Wind Farm Technology (SWiFT) site in Lubbock, Texas. The terrain is flat with laterally periodic boundaries in this example. The case has enough WRF output contained in the "forcing" directory to simulate two diurnal cycles starting November 11, 2013 at 00:00:00 UTC.

• example.mesoscaleInfluence.SWiFTsiteLubbock.11Nov2013Diurnal

Running Tutorials

1. To run a tutorial, change to that tutorial directory and run the runscript.preprocess script to set up the mesh, etc. Then run the runscript.solve.1 script to run the solver.
2. These are basic tutorials meant to familiarize the user with the general file structure of a case and the various input files. They can be run on a small amount of processors with coarse meshes, but if that is done, they will generate poor results.