Validation of the AIAD model in ANSYS Fluent for horizontal two-phase flows

Computational fluid dynamics (CFD) simulations of flows involving free surfaces often use the homogeneous model approach, which focuses on solving a single set of balance equations. This approach assigns unique material properties to each phase but calculates only one shared velocity field. However, significant challenges arise when the phases are not distinctly spatially separated, such as during bubble entrainment in wavy or slug flows. In such scenarios, accurately modeling phase separation becomes difficult. To address this issue for industrial-scale multiphase flows, the Algebraic Interfacial Area Model (AIAD) was developed at the Helmholtz-Zentrum Dresden - Rossendorf (HZDR) in collaboration with ANSYS. The AIAD model adapts to local flow characteristics, such as phase distribution, by applying a transitional algorithm that selects appropriate correlations. This enables differentiation between regions with droplets or bubbles and those dominated by the free surface. In this study, the AIAD model—integrated into the ANSYS Fluent solver—is validated against experimental data from the HAWAC channel for horizontal slug flows. The k−ω−SST turbulence model with turbulence damping (TD) at the phase boundary is employed. Additionally, the AIAD model incorporates the subgrid wave turbulence (SWT) and droplet entrainment and absorption model (DEAM) submodels. The results demonstrate that the complete AIAD model, including these submodels, provides the most accurate predictions of slug flows compared to simplified AIAD models without submodels.