Simulation of turbulent bubbly flow in pipes of different diameter

Many technical processes in industries such as chemical or electricity but also numerous natural phenomena involve multiphase flow. Due to the complex physics and the broad range of relevant length scales involved, it is a formidable task to achieve a better understanding of such flows. A detailed insight into the local flow field can be obtained from multiphase computational fluid dynamics, which therefore is a potentially valuable tool for the optimisation of existing and the design of new technical equipment. Such simulations are feasible within the Eulerian two-fluid framework of interpenetrating continua. 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. As a safe starting point a baseline model applicable for adiabatic bubbly flows has recently been defined by Rzehak and Krepper (2013).
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.