Presentation of the Multi-Phase CFD Solver NEPTUNE_CFD

The NEPTUNE project constitutes the thermal-hydraulic part of the long-term EDF-CEA-AREVA-IRSN joint research and development program for the next generation of nuclear reactor simulation tools. The project aims at developing high modeling capabilities for advanced two-phase flow thermal-hydraulics covering the whole range of modeling scales. The CFD scale for flow description is covered with NEPTUNE_CFD code. The multiphase approach, developed in the NEPTUNE_CFD code for nuclear engineering, is based on separate Eulerian transport equations for mass, momentum, energy, and turbulent quantities of the different fluids, which are coupled through inter-phase transfer terms. This model is primarily dedicated to the simulation of multiphase flows containing one continuous fluid always present, which carries dispersed fluids present in the form of bubbles, droplets, particles, whose dimensions are much smaller than the spatial resolution length of the model. The simulation of all range of multiphase flow situation, such as dispersed and liquid/gas stratified (separated) flows, which can be encountered in nuclear PWR circuits and pipes under nominal or incidental conditions, remain challenging cases for multiphase volume averaged flow models. The paper deals with a short presentation of NEPTUNE_CFD model, dedicated to incompressible, weakly compressible, unsteady, and turbulent 3D two-phase flow computations. Some modeling strategies will be detailed through the examples of two validations of semi-integral cases.