FIRST AND 2ND-ORDER ACCURATE SCHEMES FOR 2-FLUID MODELS

The six-equation two-fluid model of two-phase flow taken from the RELA P5/MOD3 computer code has been used to simulate three simple transient s: a two-phase shock tube problem, the Edwards Pipe experiment, and wa ter hammer due to rapid valve closure. These transients can be charact erized as fast transients, since their characteristic time-scales are determined by the sonic velocity. First and second-order accurate nume rical methods have been applied both based on the well-known, Godunov- type numerical schemes. Regarding the uncertainty of the two-fluid mod els in today's large computer codes for the nuclear thermal-hydraulics , use of second-order schemes is not always justified. While this pape r shows the obvious advantage of second-order schemes in the area of f ast transients, first-order accurate schemes may still be sufficient f or a wide range of two-phase flow transients where the convection term s play a minor role compared to the source terms.