Validation of AIAD Sub-Models for Advanced Numerical Modelling of Horizontal Two-Phase Flows

In this work, the modelling of horizontal two-phase flows within the two-fluid Euler-Euler approach is investigated. A modified formulation of the morphology detection functions within the Algebraic Interfacial Area Density (AIAD) model is presented in combination with different models for the drag force acting on a sheared gas-liquid interface. In the case of free surface flows, those closure laws are often based on experimental correlations whose applicability is limited to certain flow regimes. It is investigated here whether the implementation of the modified blending functions in ANSYS CFX avoids this limitation. The influence of the new functions on the prediction of turbulence parameters in free surface flows is also examined quantitatively for the k-omega and k-epsilon two-equation turbulence models. Transient simulations of the WENKA counter-current stratified two-phase flow experiment were performed for validation. A prediction of the correct flow pattern as observed in the experiment improved dramatically when a turbulence damping term was included in the standard two-equation models. Using the k-omega and a modified k-epsilon turbulence model with damping terms close to the interface, better agreement with the experimental data was achieved. The morphology detection mechanism of the unified blending functions within the AIAD is seen as an improvement with respect to the detection of sharp interfaces. Satisfactory quantitative agreement is achieved for the modified free surface drag. Furthermore, it is demonstrated that turbulence dampening has to be accounted for in both turbulence models to qualitatively reproduce the mean flow and turbulence quantities from the experiment.