These are intented to provide a beginner C++ programmer with hands-on examples of how to develop code within the OpenFOAM® framework. These tutorials hope to be more approachable than most of the materials available on-line, which tend to assume that the user is proficient in the C++ programming language. Please see below for a brief summary of what each individual tutorial covers and how to use it.
The tutorials have been most recently tested on the official OpenFOAM 3.0.1 version.
It's advisable that you go through these basic C++ tutorials, having tried compiling and running most of the examples, before continuing: http://www.cplusplus.com/doc/tutorial/
Also, it's assumed you're familiar with running and setting up OpenFOAM® cases. If not, it's highly recommended you go through the official tutorials before you dive into the programming part: https://cfd.direct/openfoam/user-guide/tutorials/
Enjoy and please provide me with feedback to make these tutorials more useful! Contributions from the community are also more than welcome!
Copyright by Artur K. Lidtke, 2017.
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.
Presents a basic OpenFOAM executable which prints a simple, yet important, message.
To run:
wmake
cd testCase
./Allrun
Shows how to read information from dictionaries and output it into files.
To run:
wmake
cd testCase
./Allrun
Discusses how the OpenFOAM mesh description works and introduces the code interface used to interact with the grid.
To run:
wmake
cd testCase
./Allrun
Introduces the idea of a field object, reading values from OF-native files using built-in operators, as well as calculating field values by hand.
To run:
wmake
cd testCase
./Allrun
Gives a crash-course introduction to parallel computing with OpenFOAM and OpenMPI based on the example "solver" developed in Tutorial 2. The way OpenFOAM handles parallel domain decomposition is described, basic operators used for communication between parallel nodes are shown, and the basic solver is upgraded to work in parallel.
To run:
wmake
cd testCase
./Allrun
Shows how a new class may be added to expand OpenFOAM functionality, as well as gives an example implementation of a class derived from and OpenFOAM object. This is done by extending from the IOdictionary, with the aim of adding a custom method which lists the contents of the dict file, while keeping all of the baseline functionality.
To run:
wmake
cd testCase
./Allrun
Shows how an external library may be compiled and added to OpenFOAM. This is done by moving the key functionality of the "solver" from Tutorials 2 and 3 into an independent library, and then linking that against the rest of the solver code.
To run:
./Allwmake
cd testCase
./Allrun
Shows how a custom boundary condition may be implemented. It does not introduce a bespoke utility, but instead only implements a library. This defines an inlet condition that allows a boundary layer profile to be prescribed at the inlet of a pipe.
The BC is implemented as a class derived from the fixedValue boundary condition, adding several control parameters allowing the inlet profile to be customised. Key elements of the code are highlighted with the keyword NOTE:. Key methods to pay attention to are the two constructors, default and one constructing the BC from string, and .updateCoeffs().
The test case is a straight pipe, flow through which gets solved with the basic simpleFoam solver. Key things to note are the definition of the BC in 0.org/U and the incorporation of a custom library in system/controlDict. The simulation is 3D RANS on a coarse mesh so it takes a few minutes on a low-end machine. The effect of the boundary condition may be visualised by plotting the x-velocity through the pipe and noting the incident boundary layer profile at the inlet and how it affects the solution.
To run:
./Allwmake
cd testCase
./Allrun
Discusses the implementation of a a runtime post-processing utility which computes the flow rate through a face zone defined in the mesh using the topoSet utility.
The utility is implemented as a runtime postprocessing object derived from the built-in functionObjectFile class. It integrates the normal velocity through a specified face zone at each required time step and writes the result to a file, as well as prints in on the screen. The key methods to pay attention to are 1) the constructor 2) writeFileHeader(), as well as 3) write(), which implements the actual maths behind the functionality. Key elements of the code are highlighted with the keyword NOTE:. It is important to note that the utility gets compiled as a library, which then gets linked to the main solver, following the OpenFOAM runtime utility convention.
The test case is the same pipe as in Tutorial 6, except it uses a uniform inflow BC and is not run until full convergence. It is worth to note the definition of the faceZone of interest in system/topoSet. This may be visualised by selecting "Include zones" in paraview and applying the "Extract block" filter. As the simpleFoam solver is run, the output file gets created by the utility in the postProcessing directory.
To run:
wmake libso
cd testCase
./Allrun
Introduces the concepts behind solving a simple scalar transport equation.
The solver sets up the transport problem by importing a fixed velocity field from the last time step and solving the transport of a scalar, beta, in the presence of the velocity, beta being also subject to diffusion characterised by a fixed proportionality constant, gamma. The solver is conceptually similar to the built-in scalarTransportFoam, except it solves a steady-state problem. Key things to note are 1) the syntax behind the scalar transport equation 2) how OpenFOAM translates the syntax into specific operations and associates them with entries in system/fvSolution and system/fvSchemes dictionaries 3) inclusion of the boundary condition definitions in 0/beta into the equation 4) units of the equations being solved and how OpenFOAM handles them.
The test case is a simple 2D square domain with fixed scalar inlets at the bottom and the left-hand side. Transport takes place in the presence of a velocity field convecting away from the beta inlets. Once the case is run, it is best to visualise the initial conditions in the "beta" field and the solution to the transport equation saved as the "result" field.
To run:
wmake
cd testCase
./Allrun
Recommended reading:
- Wikipedia is always a good start:
https://en.wikipedia.org/wiki/Convection%E2%80%93diffusion_equation - Very brief description of the physical and mathematical concepts behind
the scalar transport equation by CFD-online:
https://www.cfd-online.com/Wiki/Generic_scalar_transport_equation - Chapters 3, 4 and especially 5 in "Numerical Methods in Heat, Mass,
and Momentum Transfer" by Murthy, J. Y. 2002:
https://engineering.purdue.edu/ME608/webpage/main.pdf