First and Second-Order Accurate Schemes for Two-Fluid Models

The six-equation two-fluid model of two-phase flow taken from the RELAP5/MOD3 computer code has been used to simulate three simple transients: a two-phase shock tube problem, the Edwards Pipe experiment, and water hammer due to rapid valve closure. These transients can be characterized as fast transients, since their characteristic time-scales are determined by the sonic velocity. First and second-order accurate numerical methods have been applied both based on the well-known, Godunov-type numerical schemes. Regarding the uncertainty of the two-fluid models in today's large computer codes for the nuclear thermal-hydraulics, use of second-order schemes is not always justified. While this paper shows the obvious advantage of second-order schemes in the area of fast transients, first-order accurate schemes may still be sufficient for a wide range of two-phase flow transients where the convection terms play a minor role compared to the source terms

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