CoreFlows is an open source C++/Python library intended at solving PDE systems arising from the modeling of nuclear reactor cores which involves fluid dynamics, heat and neutron diffusion as well as solid elasticity. It is a simple environment meant at students and researchers to test new numerical methods on general geometries with unstructured meshes. It is developped by CEA Saclay since 2014 and proposes a few basic models as well as some basic finite volume and finite element numerical methods. The main objectives of CoreFlows are the study of

• Numerical schemes for compressible flows at low Mach numbers on general meshes
• Well balanced schemes for stiff source terms (heat source, phase change, pressure losses)
• Numerical handling of flow inversion, phase disappearance and counter-currents in two phase flows
• Numerical handling of stiff porosity or cross section functions
• Schemes that preserve the phasic volume fraction α ∈ [0, 1]
• Convergence of finite volume methods
• New preconditioners for implicit methods for two phase flows
• The coupling of fluid models or multiphysics coupling (eg thermal hydraulics and neutronics or thermal hydraulics and solid thermics)

CoreFlows relies on the numerical toolbox CDMATH-Toolbox of the project CDMATH for the handling of meshes and fields, and on the library PETSC for the handling of large sparse matrices. You will need the packages 'doxygen' if you want to generate de documentation and 'swig' if you want to use python scripts. The software is currently developed for linux distributions and is maintained on Ubuntu 16.04 LTS and 18.04 LTS, as well as on Fedora 24, 26, 29 and 30.

The user guide is organized as follows :

• The physical models
  • The linear scalar problems
    • The transport equation for pure advection phenomena
    • The diffusion equation for pure diffusion phenomena
  • The compressible Navier-Stokes equations
  • The two-phase flow models
    • The drift model with two partial masses, one momentum and one energy equation
    • The isothermal two-fluid model with two partial masses and two momentum equations (no energy equation)
    • The five equation two-fluid model with two partial masses, two momentum equations and one energy equation
• Software structure
• The numerical methods
• Summary of available functionalities
• CoreFlows example scripts

CDMATH-Toolbox can be downloaded and compiled together with PETSC in a single process, thanks to the cmake option -DCDMATH_WITH_PETSC=ON. We summarise the installation procedure that you can find in detailed form here

• https://github.com/ndjinga/CDMATH

In order to compile CDMATH-Toolbox you will need the packages 'cmake', 'gcc', 'gfortran', 'hdf5' plus 'numpy' and 'swig'. In a linux terminal, first create and access a working directory :

• mkdir -p ~/workspace/cdmath
• cd ~/workspace/cdmath

Then create build and install repositories:

• mkdir cdmath_build cdmath_install

In order to download the approriate branch of CDMATH-Toolbox either unzip the following file to a directory cdmath-master

• https://github.com/ndjinga/CDMATH/archive/master.zip or clone the git repository to a folder cdmath-master
• git clone https://github.com/ndjinga/CDMATH.git cdmath-master

This latter command results in the creation of a directory ~/workspace/cdmath/cdmath-master containing the source files of CDMATH-Toolbox.

Go to the build directory

• cd cdmath_build

Then run the commands

• cmake ../cdmath-master/ -DCMAKE_INSTALL_PREFIX=../cdmath_install -DCMAKE_BUILD_TYPE=Release -DCDMATH_WITH_PYTHON=ON -DCDMATH_WITH_PETSC=ON
• make
• make install

By default, CDMATH-Toolbox will compile a new sequential installation of PETSC. If an installation of PETSC (version 3.4 or later) is already available in the system, it is possible to save time by first setting the environment variables PETSC_DIR and PETSC_ARCH to the appropriate values as can be found in petscconf.h, and then running the above cmake command.

First create and access a working directory :

• mkdir -p ~/workspace/CoreFlows
• cd ~/workspace/CoreFlows Now create build and install repositories:
• mkdir CoreFlows_build CoreFlows_install

In order to download CoreFlows either unzip the following file to a directory CoreFlows-master

• https://github.com/ndjinga/CoreFlows/archive/master.zip or clone the git repository to a folder CoreFlows-master
• git clone https://github.com/ndjinga/CDMATH-CoreFlows.git CoreFlows-master Either of these latter commands results in the creation of a directory ~/workspace/CoreFlows/CoreFlows-master containing the source files.

In the following steps we assume that PETSC (version 3.4 or more recent) has been installed with CDMATH with the process described above. You need to set the following variables

• CDMATH_INSTALL, the path to your CDMATH installation, for example ~/workspace/cdmath/cdmath_install/share/petsc-3.13.5
• PETSC_DIR, the path to your PETSc installation. If PETSC was installed by CDMATH then CDMATH-Toolbox can be defined as ~/workspace/cdmath/cdmath_install
• PETSC_ARCH, the type of installation used (usually arch-linux-c-opt or arch-linux-c-debug)

In order to do so, it is sufficient to source the 'CDMATH' environment file. Type in you linux terminal

• source ~/workspace/cdmath/cdmath_install/env_CDMATH.sh

then create build and install repositories next to CoreFlows-master :

• mkdir CoreFlows_build CoreFlows_install

Go to the build directory

• cd CoreFlows_build

Then run the command

• ../CoreFlows-master/configure --prefix=../CoreFlows_install/ --with-petsc-dir=$PETSC_DIR --with-petsc-arch=$PETSC_ARCH --with-cdmath-dir=$CDMATH_INSTALL --with-python --with-doc
• make doc install

You can add the following optional commands

• --with-gui, if you want to use CoreFlows as a Salomé module (you will need to use a Salomé shell)
• --with-debug, if you want to use CoreFlows in debug mode instead of the default optimised mode

First load CoreFlows environment from the CoreFlows-master directory

• source ~/workspace/CoreFlows/CoreFlows_install/env_CoreFlows.sh

If you use C language: edit the file CoreFlows-master/CoreFlows_src/main.cxx then in a terminal type

• cd ~/workspace/CoreFlows/CoreFlows_build
• make
• make install Then you can run the simulation in any directory with the command line
• $CoreFlows

If you use python language: edit your own python file my_file.py following for example the pattern of the file CoreFlows-master/main.py. Then in a terminal type

• python my_file.py

If you use the graphic interface, you need to run a SALOME Unix shell

• ./salome shell and type the command line
• runSalome -mCOREFLOWS then click on new study to open CoreFlows interface

The complete documentation is available in the directory ~/workspace/CoreFlows/CoreFlows_install/share/doc/