Code_Saturne is open-source multi-purpose CFD software, primarily developed by EDF R&D and maintained by them. It relies on the Finite Volume method and a collocated arrangement of unknowns to solve the Navier-Stokes equations, for incompressible or compressible flows, laminar or turbulent flows and non-Newtonian and Newtonian fluids. A highly parallel coupling library (Parallel Locator Exchange - PLE) is also available in the distribution to account for other physics, such as conjugate heat transfer and structure mechanics. For the incompressible solver, the pressure is solved using an integrated Algebraic Multi-Grid algorithm and the scalars are computed by conjugate gradient methods or Gauss-Seidel/Jacobi.

The original version of the code is written in C for pre-postprocessing, IO handling, parallelisation handling, linear solvers and gradient computation, and Fortran 95 for most of the physics implementation. MPI is used on distributed memory machines and OpenMP pragmas have been added to the most costly parts of the code to handle potential shared memory. The version used in this work (also freely available) relies on CUDA to take advantage of potential GPU acceleration.

The equations are solved iteratively using time-marching algorithms, and most of the time spent during a time step is usually due to the computation of the velocity-pressure coupling, for simple physics. For this reason, the two test cases (CS_5.3_PRACE_UEABS_CAVITY_13M.tar.gz and CS_5.3_PRACE_UEABS_CAVITY_111M.tar.gz) chosen for the benchmark suite have been designed to assess the velocity-pressure coupling computation, and rely on the same configuration, with a mesh 8 times larger for CAVITY_111M than for CAVITY_13M, the time step being halved to ensure a correct Courant number.

## Building and running the code is described in the file Code_Saturne_Build_Run_5.3_UEABS.pdf