Enabling xnavis CFD Solver for Massively Parallel Simulations

In this paper, the work that has been performed to extend the capabilities of the navis software, a well tested and
validated parallel ow solver developed by the research group of CNR-INSEAN, is reported. The solver is based on the
nite volume discretization of the unsteady incompressible Navier-Stokes equations; main features include a level set
approach to handle free surface ows and a dynamical overlapping grids approach, which allows to deal with bodies in
relative motion. The baseline code features a hybrid MPI/OpenMP parallelization, proven to scale when running on
order of hundreds of cores (i.e. Tier-1 platforms). However, some issues arise when trying to use this code with the
current massively parallel HPC facilities provided in the Tier-0 PRACE context. First of all, it is mandatory to assess
an ecient speed-up up to thousands of processors. Other important aspects are related to the pre- and post- processing
phases which need to be optimized and, possibly, parallelized. The last one concerns the implementation of MPI-I/O
procedures in order to try to accelerate data access and to reduce the number of generated les.