# OpenFOAM

Original author(s) OpenFOAM running in a terminal Henry Weller The OpenFOAM Team 10 December 2004 2.2.2 / 14 October 2013 Unix/Linux Computational fluid dynamics, Simulation software GNU General Public License www.openfoam.org

OpenFOAM (Open source Field Operation And Manipulation) is a C++ toolbox for the development of customized numerical solvers, and pre-/post-processing utilities for the solution of continuum mechanics problems, including computational fluid dynamics (CFD). The code is released as free and open source software under the GNU General Public License. It is maintained by The OpenFOAM Foundation,[1] which is sponsored by the ESI Group, the owner of the trademark to the name OpenFOAM.

## History

The original development of OpenFOAM started in the late 1980s at Imperial College, London, to develop a more powerful and flexible general simulation platform than the de facto standard at the time, FORTRAN. This led to the choice of C++ as programming language, due to its modularity and object oriented features. The predecessor, FOAM, was sold by UK company Nabla Ltd. before being released as open source in 2004.[2] On 15 August 2011, OpenCFD announced its acquisition by Silicon Graphics International (SGI).[3] On September 12, 2012, the ESI Group announced the acquisition of OpenFOAM Ltd from SGI.[4]

## Distinguishing features

### Syntax

One distinguishing feature of OpenFOAM is its syntax for tensor operations and partial differential equations that closely resembles the equations being solved. For example the equation[5]

$\frac{\partial \rho \mathbf{U}}{\partial t} + \nabla \cdot\phi\mathbf{U} - \nabla \cdot\mu\nabla\mathbf{U} = - \nabla p$

is represented by the code

solve
(
fvm::ddt(rho,U)
+ fvm::div(phi,U)
- fvm::laplacian(mu,U)
==
);


This syntax, achieved through the use of object oriented programming and operator overloading, enables users to create custom solvers with relative ease. However, code customization becomes more challenging with increasing depth into the OpenFOAM library, owing to a lack of documentation, and heavy use of template metaprogramming.

### Extensibility

Users can create custom objects, such as boundary conditions or turbulence models, that will work with existing solvers without having to modify or recompile the existing source code. OpenFOAM accomplishes this by combining virtual constructors with the use of simplified base classes as interfaces. As a result, this gives OpenFOAM good extensibility qualities. OpenFOAM refers to this capability as run-time selection[6]

## Structure of OpenFOAM

OpenFOAM is constituted by a large base library, which offers the core capabilities of the code:

• Tensor and field operations
• Discretization of partial differential equations using a human-readable syntax
• Solution of linear systems[7]
• Solution of ordinary differential equations[8]
• Automatic parallelization of high-level operations
• Dynamic mesh[9]
• General physical models
• Rheological models[10]
• Thermodynamic models and database[11]
• Turbulence models[12]
• Chemical reaction and kinetics models[13]
• Lagrangian particle tracking methods[14]
• Multi-reference frame and single-reference frame methodologies

The capabilities provided by the library are then used to develop applications. Applications are written using the high-level syntax introduced by OpenFOAM, which aims at reproducing the conventional mathematical notation. Two categories of applications exist:

• Solvers: they perform the actual calculation to solve a specific continuum mechanics problem
• Utilities: they are used to prepare the mesh, set-up the simulation case, process the results, and to perform operations other than solving the problem under examination

Each application provides specific capabilities: for example the application called blockMesh is used to generate meshes from an input file provided by the user, while another application called icoFoam solves the Navier-Stokes equations for an incompressible laminar flow.

Finally, a set of third-party packages are used to provide parallel functionality (i.e.OpenMPI) and graphical post-processing (ParaView).

## Capabilities

OpenFOAM solvers include:[15]

Simulation of burning Methane. The Graphical user interface is ParaView.
• Basic CFD solvers
• Incompressible flow with RANS and LES capabilities[16]
• Compressible flow solvers with RANS and LES capabilities[17]
• Buoyancy-driven flow solvers[18]
• DNS and LES
• Multiphase flow solvers[19]
• Particle-tracking solvers
• Solvers for combustion problems[20]
• Solvers for conjugate heat transfer[21]
• Molecular dynamics solvers[22]
• Direct Simulation Monte Carlo solvers[23]
• Electromagnetics solvers[24]
• Solid dynamics solvers[25]

In addition to the standard solvers, OpenFOAM's syntax lends itself to the easy creation of custom solvers.

OpenFOAM utilities are subdivided into:

• Mesh utilities
• Mesh generation: they generate computational grids starting either from an input file (blockMesh), or from a generic geometry specified as STL file, which is meshed automatically with hex-dominant grids (snappyHexMesh)
• Mesh conversion: they convert grids generated using other tools to the OpenFOAM format
• Mesh manipulation: they perform specific operations on the mesh such as localized refinement, definition of regions, and others
• Parallel processing utilities: they provide tools to decompose, reconstruct and re-distribute the computational case to perform parallel calculations
• Pre-processing utilities: tools to prepare the simulation cases
• Post-processing utilities: tools to process the results of simulation cases, including a plugin to interface OpenFOAM and ParaView.
• Surface utilities
• Thermophysical utilities

OpenFOAM is free and open source software, released under the GNU General Public License version 3.[26]

• Friendly syntax for partial differential equations
• Unstructured polyhedral grid capabilities
• Automatic parallelization of applications written using OpenFOAM high-level syntax
• Wide range of applications and models ready to use
• Commercial support and training provided by the developers

• Absence of an integrated graphical user interface (stand-alone Open Source and proprietary options are available)
• The Programmer's guide does not provide sufficient details, making the learning curve very gradual
• The lack of maintained documentation makes it difficult for the new users

### Free software

• blueCFD is a cross-compiled version of OpenFOAM that runs on Windows operating systems, and is derived from OpenFlow. The package also includes additional tools and functionality useful for OpenFOAM. It is produced by blueCAPE.[27]
• FreeFOAM[28] is geared towards freeing OpenFOAM from its system dependence, making it more portable and user-friendly for installation. The project closely tracks the official releases from OpenCFD and does not include additional functionality. CMake is used as a build system.
• HELYX-OS[29] is an Open Source preprocessing Graphical User Interface (GUI), for meshing and case setup, designed to work with the latest version of OpenFOAM® released by ESI Group. The GUI is maintained by Engys Ltd[30] using Java+VTK and delivered to the public under the GNU General Public License.
• OpenFlow is a source code patch developed by Symscape for a cross-compiled distribution of OpenFOAM that runs on Windows operating systems. The OpenFOAM components in blueCFD are derived from the OpenFlow source code.[31]
• OpenFOAM-extend[32] is maintained by Wikki Ltd.[33] This fork has a large repository of community-generated contributions, much of which can be installed into the official version of OpenFOAM with minimal effort.[34] It is developed in parallel to the official version of OpenFOAM, incorporating its latest versions, although these are released one or two years later.
• SwiftBlock[35] is an Open Source preprocessing Graphical User Interface for the OpenFOAM® meshing utility blockMesh. SwiftBlock was originally developed by Karl-Johan Nogenmyr[36] and is an add-on to Blender 3D.
• SwiftSnap[37] is an Open Source preprocessing Graphical User Interface for the OpenFOAM® meshing utility snappyHexMesh. SwiftSnap was originally developed by Karl-Johan Nogenmyr[36] and is an add-on to Blender 3D.

### Software available for purchase

• Caedium is a unified simulation environment produced by Symscape. The Caedium RANS Flow add-on[38] provides a graphical user interface for OpenFOAM case setup, solution steering, and post processing.
• Ciespace CFD is a web-based modeling and simulation environment produced by Ciespace Corporation.[39] The application includes a graphical user interface front-end for OpenFOAM, pre-processing mesh tools, and a collaborative workflow management system that runs from a web browser.
• CastNet is a proprietary modelling and simulation environment produced by DHCAE Tools.[40] The application includes a graphical user interface front-end for OpenFOAM.
• HELYX[41] is a fully integrated software suite with proprietary preprocessing Graphical User Interface (GUI), for meshing and case setup, designed to work with an enhanced version of OpenFOAM® that is fully documented, supported, and maintained by Engys Ltd.[30]
• iconCFD Process, a GUI sub-module of the iconCFD-3.x.x software suite is maintained by ICON Technology & Process Consulting Ltd.[42] It was originally developed around automotive applications through collaboration with the Volkswagen Group,[43] and Ford Motor Co.[44] This fork includes community-generated content as well as ICON-specific developments. It has since been developed to handle configuration of general multi-physics cases.