A critical analysis of drag force modelling for disperse gas-liquid flow in a pipe with an obstacle

The accuracy of gas-liquid flow modelling strongly depends on an appropriate modelling of interfacial forces. Among those, the drag is dominating. Most drag models reported in the literature have been derived and validated for laminar or low-turbulence flow conditions only. In this study, we evaluated different drag models from the literature for a highly turbulent gas-liquid flow around an obstacle in a pipe that produces a pronounced vortex region. We compared void fraction, as well as gas and liquid velocity profiles with experimental data obtained by means of Ultrafast X-ray Computed Tomography. We found that all the models except Bakker and Feng, predict the void fraction well compared to experimental data upstream of the obstacle, that is, for a developed two-phase pipe flow with axial symmetry. However, the void fraction downstream is grossly overestimated by all of the models. Based on the results, a hybrid drag model is proposed, which improves void fraction predictions considerably.