Model for the simulation of the interface dispersion

Two models - basically different in their treatment of the two-phase flow - are coupled together to simulate transients with the dispersion of the interface. The Volume of Fluid (VOF) model, uses an interface-tracking algorithm for the simulation of the two-phase flow, can be used only as long as a local grid density allows surface tracking. Second model -'twofluid' model - is based on less accurate equations averaged in time and space and does not track the interface explicitly and is more suitable for simulations of dispersed flow. A Rayleigh-Taylor instability is used as a representative problem for the test of the coupled model, where long time development of the instability causes mixing of the fluids and dispersion of the interface. Grid refinement studies are made to examine the mechanism of the switch between models and to check the convergence of the physical characteristic. (author)