Overview of OpenFOAM

• OpenFOAM stands for Open Source Field Operation and Manipulation.
• OpenFOAM is mainly a C++ library used to solve partial differential equations (PDEs), and ordinary differential equations (ODEs).
• OpenFOAM is under active development. It is originally developed by Henry Weller and Hvorje Jasak in Imperial College London and released as open source code in 2004.
• At the moment, the development of OpenFOAM have been forked into three main development¹⁾:
  • openfoam.com (OpenCFD Ltd, ESI Group)
  • openfoam.org (The OpenFOAM Foundation Ltd - Henry Weller)
  • foam-extend (Wikki Ltd - Prof Hvorje Jasak)
• OpenFOAM are packaged with ready-to-use solvers, pre-processing utilities, and post-processing utilities.
• OpenFOAM is licensed under the GNU General Public License (GPL). Therefore, it can be freely distributed with the source code, and run on massively parallel computers.
• Industries, academia and research labs makes up the large community of OpenFOAM users and contributors.

Fluid Dynamics/physical modelling features listed in CFD Direct (openfoam.org):

• Turbulence modelling: (Reynolds-Averaged Simulation (RAS), Large-Eddy Simulation (LES) and Detached-Eddy Simulation (DES, DDES, etc).
• Thermophysical modelling
• Transport/rheology
• Multiphase flows
• Rotating flows with multiple reference frames (MRF)
• Rotating flows with arbitrary mesh interface (AMI)
• Dynamic meshes
• Compressible/thermal flows
• Conjugate heat transfer
• Porous media
• Lagrangian particle tracking
• Reaction kinetics / chemistry

• Discretisation based on Finite Volume Method (FVM), with collocated polyhedral unstructured meshes.
• Second order accuracy in space and time. Various discretization schemes are available.
• Steady and transient solvers are available.
• Pressure-velocity coupling via segregated methods (SIMPLE and PISO). Coupled solvers are under active development.
• Massive parallelism through domain decomposition.
• All components are implemented in library structure to facilitate the development of customised solvers and applications.

Most capabilities offered by commercial CFD applications are available in OpenFOAM. However, the main differences are:

• There is no native GUI in official release.
  • The users have to execute each solvers and pre- and post-processing utilities via command line interface (CLI), particularly Linux bash shell.
  • The users have to directly edit case configurations in human-readable plain text format.
  • While being tedious and prone to errors, these allow:
    • automation of large number of runs using user-defined shell scripts.
    • development of 3rd party GUI and workflows tailored for a specific application.
• Official documentation may not be complete, but useful resources are available from various online sources contributed by users/developer community.
• Complete source code is accessible, allowing customisation of a solver for a specific need. Therefore OpenFOAM is suitable to be used for research and development.
• Most importantly, it is free. No restriction on the number of parallel computing processes makes OpenFOAM typically available in large HPC clusters.

• No official GUI
• But many 3rd party GUI available,
  • HELYX-OS
  • Desktop application suite from ESI
  • Web application suite at simscale.com
  • See more at https://openfoamwiki.net/index.php/GUI
• It is possible to develop own GUI tailored for a problem of interest, e.g a simple GUI can be quickly written in Python with PySimpleGUI GUI framework + PyFoam utilities

• Serious use of OpenFOAM can be a good reason to be exposed with linux-based OS and its CLI shell scripting for those uninitiated
• It is always recommended to follow official tutorials that will run through simple cases and demonstrate how OpenFOAM utilities can help including useful tips, e.g., https://www.openfoam.com/documentation/tutorial-guide
• More up-to-date and detailed description can be found in official user-guide, e.g., https://www.openfoam.com/documentation/user-guide
• There are also good learning materials from the community
  • OpenFOAMWiki
  • CFD Online
  • Wolf Dynamics .
    • While they offer paid training, most of their training slides and case files are available for free. Their 1000+ pages introductory training slides can be worth to follow, covering most important aspects of OpenFOAM comprehensively.
  • Other good resources can be found scattered in the internet. Users have to be careful in judging whether the materials are up-to-date or compatible with their version at hand, and to see if appropriate changes are required
• Ultimately, understanding the actual code is the only way to know the exact implementation and behaviour of the software. However, this is usually not required unless for a niche and advanced applications and for precise solution control.