CFD analysis of a high pressure 2” pipe test loop with water-gas flow was undertaken using three different solvers. Multiphase flow induced forces were predicted on the bends at a range of operating pressures between 10 and 80 barg and compared with forces reconstructed from vibration measurements.
Overall the three different CFD solvers predicted consistent results. The fluid forces predicted on the bends of the double U-loop test rig have a good range of values compared to the test reconstructed forces. The forces predicted at low pressure were in line with the experimental reconstructed values, whilst at high pressure all three CFD solvers predicted higher forces. The trend of the forces reducing with increased operating pressure, evident in test, was matched by one of the CFD methods, but less well by the other two. At low operating pressure the forces are dominated by the momentum of the liquid in the multiphase flow, whilst at high pressure the pressure fluctuations and turbulent effects will be more important. All three CFD solvers use VOF methods and above about 40 barg it is possible that they struggle to fully resolve the flow behaviour, which will be more influenced by bubble and droplet entrainment and turbulence.
Multiphase flow can induce high amplitude vibrations in piping systems, potentially leading to fatigue failures. CFD modelling offers a potentially powerful tool to provide the flow induced forces required for assessing and diagnosing multiphase flow induced pipework vibration problems in hydrocarbon production systems.