Developing and Tailoring a CFD Code for Multiphase Multicomponent Flows

This paper focuses on the development and the tailoring of a open source multidimensional CFD code to the analysis of the internal flow-field in hydraulic components. A preliminary study of two basic geometries is carried out by simulating the efflux of an incompressible fluid through circular pipes and through an abrupt section change determined by a small sharp-edged cylindrical orifice. A qualitative description of the internal flow-field distribution, and a quantitative comparison of pressure and velocity profiles along the pipe axis are used to asses the multidimensional open-source code capabilities. For the circular pipe the results are compared with experiments and with theoretical trends coming from literature fundamentals (Hagen-Poiseuille theory and Nikuradse interpolation), while for the abrupt section change experimental measurements available in literature are taken as a reference for the numerical accuracy determination. Furthermore, the influence of grid resolution and of turbulence models on the vena contracta on the characteristics recirculating regions, on the reattachment point and on the pressure and velocity fields is addressed. Afterwards, to investigate the mixing of different fluids, a preliminary analysis of a reference test case is carried out. The modified VOF approach, used for modeling the fluid-fluid mixing process, is tailored in order to account for turbulence. Different grid resolutions and turbulence models are adopted and results are compared with experiments in order to asses their influence on the interface and on the fluids distribution inside the reference geometrical domain. In particular, two different turbulence models (k-e – SST) are implemented in the original code to address their effect on actual fluids mixing. Finally, the dynamic behavior of a low pressure fuel rail is investigated and the fuels distribution history within the rail is determined for different operating conditions to assess both the fuel mixture at injectors’ inlet, and to highlight the differences among the cylinders in terms of injected fuel blend.