Modelling of Free Surface Flow Within the Two-Fluid Euler-Euler Framework

Two-phase flows are regularly involved in the heat and mass transfer of industrial processes. To ensure the safety and efficiency of such processes, accurate predictions of the flow field and phase distribution by means of Computational Fluid Dynamics (CFD) are required. Direct Numerical Simulations (DNS) of large-scale two-phase flow problems are not feasible due to the computational costs involved. Therefore the Euler-Euler framework is often employed for large-scale simulations which involves macro-scale modelling of the turbulent shear stress and the interphase momentum transfer.
As a long term objective, the research activities at Helmholtz-Zentrum Dresden - Rossendorf (HZDR) pursue the development of general models for two-phase flows which are based on first principles and include less empiricism. Part of this effort is focused on the development of an algebraic interfacial area density model (AIAD) [1,2] which enables the simulation of two-phase flows with general morphologies including bubble, droplet and stratified flow regimes with the two-fluid approach.
In this work a short overview of the AIAD model is given and recent developments are presented.
The modelling of the interfacial drag in free surface flows is of particular interest and subject to ongoing research. Apart from empirical correlations which are limited to certain flow regimes, different models have been developed for the local computation of the interfacial drag coefficient [3,4]. In the AIAD model the drag model given by Höhne et al. [3] is used. It has recently been subject to modifications which are presented and validated as a part of this study.
Furthermore, special attention is paid to the turbulence treatment at the phase boundary of free surface flows. A model for the damping effect on the turbulent fluctuations in the near interface region as proposed in [1] is validated in this work.
Model validation is performed by means of simulations of horizontal stratified two-phase flow with the Euler-Euler two-fluid approach and the results are compared to experimental data given by Stäbler [5].