We provide a scalable GPU code for droplet motion in biphasic streams. This code solves the NavierStokes incompressibility equation for two-fluid systems with a direct Poisson FFT solver based on the pressure equation. The interface between the two fluids is shown by the Volume Volume (VoF) method, which is suitable for complex flows due to its capacity to manage topological changes. The energy equation is explicitly solved and coupled with the momentum equation via the Bosinsk approximation. This code is modularly designed to be able to use different numerical methods independently, modify existing procedures, and combine new ones simply and consistently. FluTAS is written in Fortran and uses the MPI / OpenMP combination in the CPU-only version in parallel, accelerating GPU execution with OpenACC instructions. The two dominant forces affecting droplet fracture, drag force, and surface tensile force are confirmed using two benchmarks: pressure distribution on a cylindrical surface in uniform flow and oscillation of a square drop under surface tensile force. The results show that the failure process occurs in two steps. During the first stage, the droplets are stretched and thinned perpendicular to the direction of fluid flow. In the second stage, isolated points appear on the surface of the droplets which are attributed to the unstable growth of surface waves. The topology of the droplet after failure depends on the value of the Weber number: the larger the Weber number, the more isolated points on the surface of the droplets.

Keywords : Two-phase flows, Fluid volume method, Turbulence in multiphase flows, High-performance computing, OpenACC instructions