A Computational fluid dynamics (CFD) workbench for FreeCAD

CfdOF: A Computational fluid dynamics (CFD) workbench for FreeCAD

This workbench aims to help users set up and run CFD analyses within the FreeCAD modeller. It guides the user in selecting the relevant physics, specifying the material properties, generating a mesh, assigning boundary conditions and choosing the solver settings before running the simulation. Best practices are specified to maximise the stability of the solvers.

The workbench serves as a front-end to the popular OpenFOAM® CFD toolkit (www.openfoam.org, www.openfoam.com).

Disclaimer: This offering is not approved or endorsed by OpenCFD Limited, producer and distributor of the OpenFOAM software via www.openfoam.com, and owner of the OPENFOAM® and OpenCFD® trade marks

Features

Current:

• Incompressible, laminar flow (simpleFoam, pimpleFoam)
• Incompressible free-surface flow (interFoam, multiphaseInterFoam)
• High-speed compressible flow (HiSA)
• Basic material database
• Flow initialisation with a potential solver
• Cut-cell Cartesian meshing with boundary layers (cfMesh)
• Cut-cell Cartesian meshing with porous media (snappyHexMesh)
• Tetrahedral meshing using GMSH
• Postprocessing using paraview
• Porous regions and porous baffles
• Runs on Windows 7-10 and Linux
• Unit testing
• Extension to turbulent flow using RANS (k-w SST)
• New case builder using an extensible template structure
• Macro scripting

Platforms supported

Linux

Any system on which FreeCAD and the prerequisites listed below can be installed.

Windows

Windows 7-10; 64-bit version is required.

MacOSX

Not widely tested, but success has been reported.

Getting started

Prerequisites

The CfdOF workbench depends on the following external software, some of which can be automatically installed (see below for instructions).

Setting up the CfdOF workbench

Windows

The latest release or development FreeCAD build can be obtained (64 bit version) and installed by respectively running the installer or extracting the .7z archive to a directory . In the latter case, FreeCAD can be run in place (<FreeCAD-directory\bin\FreeCAD.exe).

Before installing CfdOF, the Plot workbench must first be installed into FreeCAD using the Addon manager:

• Run FreeCAD
• Select Tools | Addon manager ...
• Select Plot in the list of workbenches, and click "Install/update"
• Restart FreeCAD
• Repeat the above for the "CfdOF" workbench
• For installation of dependencies, see below

Note: The CFD workbench can be updated at any time through the Addon manager.

Dependency installation

Dependencies can be checked and installed conveniently from the CfdOF Preferences panel in FreeCAD. In the FreeCAD window, select Edit | Preferences ... and choose "CfdOF".

The OpenFOAM installation is via the OpenCFD docker package (version 1912). This can be installed manually using the above link, or by clicking the relevant button in the Preferences panel described above.

Set the OpenFOAM install directory in the preferences panel to the install directory ending in the 'vXXXX' subfolder (where XXXX is the version number installed). It will be automatically detected in the default install location.

Any version of ParaView can be installed, by following the above link or clicking the relevant button in the Preferences panel. Set the ParaView install path in the preferences panel to the 'paraview.exe' file in the 'bin' subfolder of the ParaView installation. Common defaults will be detected if it is left blank.

Likewise, cfMesh and HiSA can be installed from the Preferences panel. They are automatically built from source inside the OpenFOAM environment if installed from the Preferences panel. Note that this is a lengthy process. Do not close the Preferences panel until the 'Install completed' message is received.

Choosing the "Check dependencies" option will verify that all prerequisites have been successfully installed.

Linux

AppImages of the latest release or development versions of FreeCAD can be downloaded and run directly without installation. Note that you will have to enable execution permission on the downloaded file to run it. The Ubuntu PPA daily build packages are an alternative binary option. Otherwise, FreeCAD can be built from the source code at https://github.com/FreeCAD/FreeCAD .

Before installing CfdOF, the Plot workbench must first be installed into FreeCAD using the Addon manager:

• Run FreeCAD
• Select Tools | Addon manager ...
• Select Plot in the list of workbenches, and click "Install/update"
• Restart FreeCAD
• Repeat the above for the "CfdOF" workbench
• For installation of dependencies, see below

Dependency installation

Dependencies can be checked and some of them installed conveniently from the CFD Preferences panel in FreeCAD. In the FreeCAD window, select Edit | Preferences ... and choose "CFD".

However, in Linux, manual installation is required for OpenFOAM, Paraview and GMSH (optional). They should be installed using your distribution's package manager or the links above.

Set the OpenFOAM install directory in the preferences panel - examples of typical install locations are /opt/openfoam7 or /home/user/OpenFOAM/OpenFOAM-7.x (It will be automatically detected in common default install locations.)

cfMesh and HiSA can be installed using the Preferences panel described above, and can be downloaded and built from the source code inside your OpenFOAM installation if you have not already done so yourself. Note that this is a lengthy process.

Choosing the "Check dependencies" option will verify that all prerequisites have been successfully installed.

Feedback

Reporting Bugs

Please discuss issues on the CfdOF dedicated FreeCAD forum. Bugs can be reported on the github project site.

Please first read the guidelines for reporting bugs in order to provide sufficient information.

Development

It is asked that developers should only add functionality or code that is working and can be tested. Dead code, even portions included for possible future functionality, reduces function clarity and increases the maintenance overhead. Our philosophy is 'Do the basics well' and therefore robust operation takes precedence over extended functionality.

Testing

Unit testing is currently under development. Where possible, it is asked that all new functionality should be included in the unit test framework.

Style guide

For consistency please follow PEP8

1. Use 4 spaces per indentation level (spaces are preferred over tabs).

2. Limit all lines to a maximum of 120 characters.

3. Break lines before binary operators.

4. Blank lines

5. Imports should usually be on separate lines.

6. Comments

   • Docstrings always use """triple double-quotes"""

   • Block comment starts with a # and a single space and are indented to the same level as that code

   • Use inline comments sparingly. They are on the same line as a statement and should be separated by at least two spaces from the statement.

7. Avoid trailing whitespaces

8. Naming convention

   • ClassNames (Camel)
   • variable_names_without_capitals (Underscore)
   • CONSTANTS_USE_CAPITALS (Uppercase)
   • functions_without_capitals (underscore, preferred as it follows PEP8)
   • functionsWithoutCapitals (Camel instead of underscore is accepted as it is widely used within FreeCAD)
   • __class_attribute (Double leading underscore)

Acknowledgements

Funding

This development was made possible through funding from Eskom Holdings SOC Ltd and the Council for Scientific and Industrial Research (South Africa).

Lead developers

The code is maintained by

Contributors

We acknowledge significant contributions from

• Qingfeng Xia (2015) - Original framework
• Michael Hindley (2016) - Initial concept
• Klaus Sembritzki (2017) - Multiphase extension
• Thomas Schrader (2017-2018) info@schraderundschrader.de - Testing and user assistance

Dedication

CfdOF is dedicated to the memory of Michael Hindley, whose irrepressible enthusiasm for FreeCAD and open source software is the reason this workbench was created. Rest in peace.

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