CFDDFC on Azure: Using OpenFOAM on the Virtual Machine

The OpenFOAM Configuration

OpenFOAM is a collection of 200+ applications that can be executed from the terminal prompt.  The applications include: “solvers” that solve equations to simulate fluid flow; and, “utilities” that perform other tasks needed in CFD, e.g. generation of the computational mesh, initialisation of fields, data manipulation, etc.  The applications can be executed from the terminal prompt, reading from and writing to data files of the problem case.  In OpenFOAM, the case files are stored within a directory, whose name reflects the problem being simulated, in which there are typically 3 further directories, named 0, system and constant containing the case files.  Users unfamiliar with Linux can consult our OpenFOAM Linux Guide.

In the OpenFOAM configuration, an environment variable named $FOAM_RUN is reserved to represent a default directory to put OpenFOAM case data. The default directory is $HOME/OpenFOAM/USER-VERSION/run, i.e. $HOME/OpenFOAM/ubuntu-8/run for USER=ubuntu and version number VERSION=8. There is also an alias named run that changes directory (cd) to the $FOAM_RUN directory.  The OpenFOAM installation can be found in the /opt directory and example cases are stored in a directory named tutorials within the installation. Another environment variable $FOAM_TUTORIALS is set to represent the tutorials directory.

Testing OpenFOAM

Users can test an example simulation of steady, incompressible, turbulent flow over a backward facing step, named the pitzDaily after authors of a report on experimental data to which the case relates. The test involves 5 steps:

1. changing to the $FOAM_RUN directory with the run alias;
2. copying the pitzDaily case files from the tutorials directory to the current directory (denoted in Linux as ‘.');
3. changing to the pitzDaily case directory;
4. generating a mesh for the backward step geometry with the blockMesh utility;
5. running the simpleFoam solver for steady, incompressible, turbulent flow

Execution these steps from the terminal prompt is as follows:

run
cp -r $FOAM_TUTORIALS/incompressible/simpleFoam/pitzDaily .
cd pitzDaily
blockMesh
simpleFoam

For more information about running cases, see:

• OpenFOAM User Guide: 2 Tutorials
• OpenFOAM User Guide: 3 Applications and libraries

Configuring OpenFOAM Applications

Solvers and utilities are configured through the data files in a case directory.  The configuration of a case can be modified by opening a file in a text editor, changing settings and saving the file.  3 popular editors which can work through a terminal are:

• nano: the easiest of the 3 editors for the purpose, see nano basics guide;
• emacs: powerful editor that uses a more complex set of key commands, emacs basics;
• vim: another editor with arguably a less familiar set of key commands, see vim quick guide.

It is worth knowing the command to exit the editor you use in case a problem arises:

• nano exits with C-x (C=Control key)
• emacs exits with C-x C-c (preceded by C-g, if needed)
• emacs exits with ESC :q!

The user may, for example, open the fvSolution file in the system directory in one of these editors, e.g. nano by

nano system/fvSolution

The user may edit the residualControls as follows, then exit with C-x, saving the file (Y)

residualControl
{
    p    1e-3;
    U    1e-4;
    "(k|epsilon|omega|f|v2)"    1e-4;
}

The user can then restart simpleFoam from the previous solution. For more information about configuration of case files, see:

• OpenFOAM User Guide: 2 Tutorials
• OpenFOAM User Guide: 4 OpenFOAM cases

Next Step → Data Transfer to a Virtual Machine