MODELING OF 2-PHASE FLOW WITH 2ND-ORDER ACCURATE SCHEME

A second-order accurate scheme based on high-resolution shock-capturin g methods was used with a typical two-phase flow model which is used i n the computer codes for simulation of nuclear power plant accidents. The two-fluid model, which has been taken from the computer code RELAP 5, consists of six first-order partial differential equations that rep resent 1D mass, momentum, and energy balances for vapour and liquid. T he partial differential equations are ill-posed-nonhyperbolic. The hyp erbolicity required by the presented numerical scheme was obtained in the practical range of the physical parameters by minor modification o f the virtual mass term. No conservative form of the applied equations exists, therefore, instead of the Riemann solver, more basic averagin g was used for the evaluation of the Jacobian matrix. The equations we re solved using nonconservative and conservative basic variables. Sinc e the source terms are stiff, they were integrated with time steps whi ch were shorter than or equal to the convection time step. The sources were treated with Strang splitting to retain the second-order accurac y of the scheme. The numerical scheme has been used for the simulation s of the two-phase shock tube problem and the Edwards pipe experiment. Results show the importance of the closure laws which have a crucial impact on the accuracy of two-fluid models. Advantages of the second-o rder accurate schemes are evident especially in the area of fast trans ients dominated by acoustic phenomena. (C) 1997 Academic Press.