Euler-Euler-Modelling of Segregated Flows and Flows with Transitions between Different Flow Morphologies

Stratified two-phase flows are relevant in many industrial applications, e.g. pipelines, horizontal heat exchangers and storage tanks. Special flow characteristics as flow rate, pressure drop and flow regimes have always been of engineering interest. The numerical simulation of free surface flows can be performed using phase-averaged multi-fluid models, like the homogeneous and the two-fluid approaches, or non-phase-averaged variants. The approach shown in this paper within the two-fluid framework is the Algebraic Interfacial Area Density (AIAD) model. It allows the macroscopic blending between different models for the calculation of the interfacial area density and improved models for momentum transfer in dependence on local morphology. An approach for the drag force at the free surface was introduced. The model improves the physics of the existing two fluid approaches and is already applicable for a wide range of industrial two phase flows. A further step of improvement of modelling the turbulence was the consideration of sub-grid wave turbulence (SWT) that means waves created by Kelvin-Helmholtz instabilities that are smaller than the grid size. The new approach was verified and validated against horizontal two-phase slug flow data from the HAWAC channel and smooth stratified flow experiments of a different rectangular channel. The results approve the ability of the AIAD model to predict key flow features like liquid hold-up and free surface waviness. Furthermore an evaluation of the velocity and turbulence fields predicted by the AIAD model against experimental data was done. The results are promising and show potential for further model improvement.