Because of the evolution of the electricity market in Europe hydraulic machines are operated in non conventional conditions. This leads to the apparition of strong transient flow phenomena that are not well understood. Conventional numerical simulation tools are not well adapted to capture these transient phenomena. It is proposed to use a novel approach based on the mesh-free technique Smoothed Particle Hydrodynamics to simulate these flows. This numerical method has recently proved its ability to overcome some major shortcomings of conventional CFD techniques. The method can also remarkably simulate fast-transient phenomena. The novelty of the approach is firstly that the SiTHyM projects aims at using the SPH method to simulate internal flows, secondly that a coupling of the SPH and Finite Volumes approaches will be achieved. The idea is to take profit of the ability of the FV method to model boundary layers efficiently and with a reasonnable cost, while the main part of the flow where convective phenomena are predominant is solved by the SPH method. As a consequence the method does not need any rotor-stator interface. It is expected that this feature will bring a major improvement to the study of rotor-stator interactions in transient phases. In order to implement the coupled method in an industrial CFD process, an efficient parallel implementation of the tool is required. The project will tackle a GPU implementation, as it is a very promising technology that has recently emerged in the HPC community. The numerical tool will then be applied to transient free surface flows in Pelton turbines and to transient internal flows in reversible pump turbines.