Applying Multiple Grids to a Multi-Field Model – The Resolution Requirements of Individual Fields in the Two-Fluid Model for 1D Pipe Flow

Abstract

Modeling two-phase pipe flow commonly involves gas and liquid fields which can differ greatly in density and compressibility. The physical scales governing the dynamics are divided amongst the phases in a way where the numerical grid requirements of one phase may be poorly suited for the other. Adopting a phase discriminating multigrid strategy is therefore an attractive approach, though little is known about how the phase coupled dynamics will respond to separate, non-equivalent numerical grids. The purpose of this article is to explore the resolution sensitivity of the two-fluid model for each phase individually, and examine how the dynamic coupling between phases is maintained across phase-individual grids of unequal coarseness. A dual-grid scheme is proposed and applied to S-riser terrain slugging and roll wave capturing simulations. Resolution sensitivity is checked. It is found that the resolution requirements in both cases are liquid dominated; we are able to reduce the spatial resolution of the gas phase far more than on the liquid phase while retaining physical predictions. The importance of reconstructing local pressure dynamics is demonstrated.

GRAPHICAL ABSTRACT

Keywords:

• Dual grid
• multiscale
• pipe flow
• roll wave
• terrain sluggig
• two-fluid model
• two-phase

ACKNOWLEDGMENTS

The author would also like to thank Tore Flåtten and Kontorbamse for helpful input.

Notes

¹The lowers gas–liquid scale ratio allowable without altering the DGS properties.