Compressible two-phase VOF simulation of turbulent mold filling in high-pressure die casting and a quantitative evaluation approach

Air entrapment during mold filling critically affects porosity and overall casting quality in High-Pressure Die Casting (HPDC). This study assesses the feasibility of applying the Volume of Fluid (VOF) method within OpenFOAM to simulate compressible, turbulent mold filling in a thin-walled geometry. Three-dimensional simulations with the compressibleInterFoam solver were carried out under ambient initial cavity conditions, using both laminar flow and the k - ε turbulence model. The free surface dynamics were examined across a range of inlet velocities to evaluate their influence on interface morphology, cavity pressurization, and gas entrapment. To quantify these effects, three evaluation criteria were introduced: the Time-Integrated Free Surface Area (TIFSA) as a geometric exposure metric associated with oxidation potential, the Temporal Mean Volume Fraction (TMVF) as an indicator of filling continuity and air entrapment, and the Time-Integrated Volumetric Flow (TIVF) as a proxy for surface loading. Results show that turbulence modeling accelerates pressurization and limits the persistence of entrapped gas, with velocity governing the balance between smooth filling, turbulent breakup, and exposure duration. Comparison with experimental casting trials on a thin-walled HPDC plate in aluminum alloy AlSi10MnMg, including CT-based porosity analysis and photogrammetric surface evaluation, supported the interpretation that the water-based simulations capture key defect-relevant flow features in this geometry and provide a transferable methodological framework for process optimization.