Simulation of liquid waves with flow reversal in stratified counter-current flow with a hybrid two-fluid model

Processes involving gas and liquid flows are important for reliable, efficient and safe operation of many industrial applications, such as electricity generation in nuclear power plants. Many different two-phase flow patterns can appear in these systems, with a wide range of scales considering both interfacial and turbulent structures. Stratified flow, i.e. phases being separated with a smooth or wavy interface, is one of the most important regimes for safety analyses.

The present paper presents simulations of an isothermal stratified counter-current flow of air and water in a rectangular channel of the WENKA experiment (Stäbler, T.D, 2007, PhD Thesis, Univ. Stuttgart). The partial flow reversal regime with liquid surface waves was considered. A hybrid two-fluid model, featuring consistent momentum interpolation numerical scheme, partial elimination algorithm to handle strong drag coupling between phases, and interface sharpening method, was used to resolve the air-water interface. The Unsteady Reynolds Averaged Navier-Stokes (URANS) approach with the k-ω SST (Shear Stress Transport) model and interface turbulence damping was used to model the turbulent stratified flow with wavy surface. Simulations were performed with the open source C++ library OpenFOAM. Results are validated with experimental data for the height of liquid surface, profiles of velocity and turbulent kinetic energy, and the amount of reversed liquid flow.