Modelling and simulation of steam-water transients using the two-fluid approach

This thesis deals with the modelling and the computation of steam-water two-phase flows. Liquid water flows are involved in many industrial facilities and a second phase may appear in some transients situations. Thus, pressure wave propagation and mass transfer are physical phenomena that need to be properly included in the modelling of such two-phase flows. A statistical two-fluid approach is used, leading to models similar to the Baer-Nunziato one. They include both convective and source terms without any assumption on the equilibrium between phases. Different closure laws for such models are compared on steam-water transient experiments including water-hammers and fast depressurization of liquid water. The computation of the different models is based on a fractional step method. A new convective scheme, able to deal with any Equation Of State, is used in the first step of the method. When compared with other schemes, it appears to be accurate, efficient and very robust. The second step of the method is dedicated to the treatment of source terms and requires several implicit schemes. Particular attention is paid to the verification of every scheme involved in the method. Convergence studies are carried out on test-cases with analytical solutions to that purpose. Based on existing work on fast depressurization of liquid water in an homogeneous approach, a new formulation of the mass transfer is proposed. Many comparisons between computational and experimental results are detailed in order to validate the models. (author)