Simulations of a compressible two-layer mixed-flows model with a semi-implicit fractionnal step algorithm on staggered meshes

We present here a numerical scheme based on the classical SIMPLE algorithm for the time-stepping and on a MAC discretization on staggered meshes for the estimation of the spatial derivatives. This scheme is applied here to a two-layer two-fluid model that has been proposed in previous works of the literature in order to perform computations of gas-liquid flows in pipes with gravity effects. This model accounts for pressure relaxation and velocity relaxation between the two phases through source terms. Thanks to new forms of these source terms, their discretization can be easily introduced in the different steps of the SIMPLE algorithm. The whole algorithm then allows to couple convective terms and source terms without suffering from the CFL limitation of the explicit Godunov-type schemes. A detailed description of the scheme is proposed and some numerical tests have been performed in order to assess the behavior of the approximated solutions when pressure-velocity relaxation is taken into account.