Comparative study of VoF and Euler–Euler models for aerated flow over spillway aerators under laminar flow conditions

Accurate prediction of aerated flow over spillway aerators is essential for mitigating cavitation risk in hydraulic structures, yet reliable numerical simulation remains challenging due to complex air–water interactions, turbulence-driven entrainment, and sensitivity to multiphase modelling approaches. This study presents a comparative analysis of two computational fluid dynamics (CFD) models: the Volume of Fluid (VoF) method and a two-phase Euler–Euler formulation. Simulations are conducted for a laboratory-scale spillway aerator using OpenFOAM, with the k–ω SST turbulence model applied to both solvers to account for shear-layer development and turbulence-driven air entrainment. The study focuses on cavity formation, air–water interaction, turbulent mixing, and pressure distribution along the chute bottom. A mesh sensitivity study is performed to evaluate the influence of spatial resolution on key flow characteristics. Both models reproduce the main flow features and general cavity development. The VoF approach captures a well-defined air–water interface and stable cavity geometry and shows improved prediction of dispersed aeration compared to laminar simulations. In contrast, the Euler–Euler model predicts stronger phase mixing and a more distributed air–water structure. The results highlight the combined influence of multiphase formulation and turbulence closure on aeration and pressure prediction, providing practical guidance for model selection in spillway applications.