NS-EOF: Navier Stokes - Ernst-Otto-Fischer Teaching Code

General Information

This code has been tested under Ubuntu 20.04 or higher. Other Linux distributions will probably work. However, we do not recommend using Windows or MacOS. If you do not have Linux installed on your computer, please use WSL, Virtual Machine, or similar. Since NS-EOF uses CMake, it should work under Windows with MSVC or MacOS.

Dependencies

MPI (recommended OpenMPI)

• Under Ubuntu you can simply run apt install libopenmpi-dev to install OpenMPI.

PETSc

• Please install PETSc on your system.
• We recommend to use apt install petsc-dev to install.

CMake

• Run apt install cmake to install CMake on your system.

Docker

You can use the Dockerfile included in the repository. This will create an image where everything is set up and you can just begin with compiling the code. Of course, you can also just look at the Dockerfile as a recipe on how to set up your environment. For a short introduction on how to build and run a Docker container, refer to Docker.

Tutorial

Compilation

As build system configurator we use CMake. To compile the code execute the following commands in this directory:

• Create a build directory: mkdir build
• Switch to this directory: cd build
• (Optional): Choose the compiler being used (if you want to use a specific MPI compiler/version): export CXX=mpic++
• Run CMake: cmake .. (this configures a RelWithDebInfo build, which is default. For a Debug build, run cmake .. -DCMAKE_BUILD_TYPE=Debug) and for a Release build, cmake .. -DCMAKE_BUILD_TYPE=Release. This is especially recommended in production and benchmark runs.
• To enable PETSc, use cmake .. -DENABLE_PETSC=ON
• For developing, consider cmake .. -DENABLE_DEVELOPER_MODE=ON. For an overview of all available options, use ccmake ..
• Run Make: make (or make -j for compiling with multiple cores)
• (Optional): Run make test to validate your build (this will execute some unit tests and run some simulations).

Running a Simulation

• Run the code in serial via ./NS-EOF-Runner path/to/your/configuration
  • Example: ./NS-EOF-Runner ExampleCases/Cavity2D.xml
• Run the code in parallel via mpirun -np nproc ./NS-EOF-Runner path/to/your/configuration
  • Example: mpirun -np 4 ./NS-EOF-Runner ExampleCases/Cavity2DParallel.xml

Adding new source files

You can add new source files by just creating them somewhere within the Source folder. CMake automatically detects these files and adds them to the build.

Testing

Some basic unit tests have been implemented (make test). Feel free to add your own test cases inside the Tests folder.

Creating a Doxygen documentation

• Run the following CMake command: cmake .. -DENABLE_DEVELOPER_MODE=ON -DOPT_ENABLE_DOXYGEN=ON
• make doxygen-docs
• You should now see in your build directory a folder called html
• Open index.html to see the generated documentation.

Development Hints & FAQ

It does not compile and everything seems fine?

Make sure to use make clean before you use make. Sometimes there are build artifacts from previous build processes that spoil your current compilation process. make clean takes care of deleting everything that should not be there and allows the compiler to start from scratch.

Sometimes it is also helpful to delete the build folder and create a new one, following the steps from the compilation section above.

How can I see all the compiler flags the generated Makefile is using?

Instead of using make, run VERBOSE=1 make. You can also run make -n to invoke a dry run where you see what the Makefile would do in case of compilation.

How can I see the test output?

Instead of using make test, run ctest --verbose.