====== 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 development((
More details [[oscae:software:openfoam:variants| here]])):
    * 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.


==== Features ======

Fluid Dynamics/physical modelling features listed in [[https://cfd.direct/openfoam/features/| 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


==== OpenFOAM in General CFD Workflow ======

{{ :public:software:openfoam_cfd_workflow_20220305_120819.png?800 |}}


==== Architecture and Numerics ======

  * 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.


==== OpenFOAM vs commercial CFD 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.


==== GUI for OpenFOAM ======

  * No official GUI
  * But many 3rd party GUI available,
    * [[https://engys.com/products/helyx-os | HELYX-OS ]]
    * [[https://www.esi-group.com/products/computational-fluid-dynamics/visual-environment-for-openfoam |  Desktop application suite from ESI ]]
    * Web application suite at [[https://www.simscale.com/product/cfd/ | 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 [[ https://pysimplegui.readthedocs.io/en/latest/ | PySimpleGUI ]] GUI framework + [[ https://openfoamwiki.net/index.php/Contrib/PyFoam | PyFoam ]] utilities


===== Learn ======

  * 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
    * [[ https://openfoamwiki.net/index.php/Main_Page | OpenFOAMWiki ]]
    * [[ https://www.cfd-online.com/ | CFD Online ]]
    * [[ http://www.wolfdynamics.com/tutorials.html | Wolf Dynamics ]].
      * While they offer paid training, most of their training slides and case files are available for free. Their [[ https://figshare.com/articles/media/OpenFOAM_Introductory_Training/16783657?file=31049242 | 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.