Baseline model for bubbly flows: Simulation of monodisperse flow in pipes of different diameters

CFD simulations of the multiphase flow in technical equipment can provide a detailed insight into the local flow field and hence potentially be a valuable optimisation and design tool. Such simulations are feasible within the framework of interpenetrating continua, the so-called two-fluid modelling. Within this framework the interfacial transfer processes need to be modelled by suitable closure relations, many of which have been proposed in the literature. Predictions with multiphase CFD are only possible if a fixed set of closures is available that has been validated for a wide range of flow conditions and can therefore reliably be used also for unknown flow problems. To this end, a baseline model, which is applicable for adiabatic bubbly flow, has been specified recently (e.g. Rzehak and Krepper, 2013) and has been implemented into OpenFOAM (Rzehak and Kriebitzsch, 2015).
In this work we compare simulation results obtained using the baseline model with three different sets of experimental data for dispersed gas-liquid pipe flow given by Liu (1998), Shawkat et al. (2008), and Hosokawa and Tomiyama (2009). Air and water under similar flow conditions have been used in the different experiments, so that the main difference between the experiments is the variation of the pipe diameter from 25 mm to 200 mm. Overall all three experimental data sets are reasonably well reproduced by the simulation results, in particular in the bulk of the flow. The need for improved modelling of multiphase turbulence as well as wall effects manifests itself through larger differences with the experimental data in the near-wall region of the pipes.