Computational fluid dynamics simulations of oil-water mixture flowing through a sudden expansion

Two-phase oil-water mixtures are frequently encountered in oil wells and pipelines of the chemical and petroleum industry. We present the results of computational fluid dynamics simulations of oil in water dispersed flow through a sudden expansion. The transient numerical simulations are performed using a 3-D numerical domain coupled to three different turbulence models concerning the water phase (k-ω SST, Realizable k-ε and Reynolds Stress Model) within the Eulerian multifluid framework. A sensitivity analysis is performed with respect to the correlations for the momentum exchange between the phases. Different drag coefficients are considered as well as the non-drag forces. The simulation results indicate that only the drag force should be considered to obtain physical results. Concerning the modelling of the dispersed phase a mono-dispersed approach is compared with a fixed poly-dispersed approach, where different droplet classes and velocity groups are implemented in the numerical model. The superficial velocity evaluated downstream of the singularity, ranges from 0.29 m/s to 0.44 m/s for the oil phase and form 0.56 m/s to 0.84 m/s for the water phase. All considered operating conditions result in a flow pattern of oil dispersion in continuous water. The numerical model is validated comparing the numerical results with the experimental data of Dehkordi et al. (2017) [1]. They performed experiments on an 11 m long pipe using optical methods, to obtain a detailed representation of the instantaneous velocity and in-situ phase fraction. Time-averaged oil velocity profiles at different axial positions after the sudden expansion (L⁄D=1; L⁄D=2.5; L⁄D=4; L⁄D=5.5 ), cross-sectional time-averaged oil holdup, and slip ratio are considered.