Modeling two-phase air-water flow using the ISPH method: A case study of dam break flow

• Development of a unified ISPH framework for air-water flows, validated against experimental data. • Demonstration of the model’s capability to capture complex interactions, such as air-water mixing and energy dissipation. • Comparative analysis with single-phase models, underscoring the advantages of the proposed multi-phase approach. Accurate simulation of aerated (air–water) free-surface flows is critical for predicting energy dissipation, impact forces, and hydraulic performance in structures such as spillways, stilling basins, and dam-break systems. Despite extensive research, existing two-phase schemes often struggle with stability and computational cost when handling large air–water density contrasts. This study introduces a novel quasi-compressible two-phase formulation within the Incompressible Smoothed Particle Hydrodynamics (ISPH) framework that advances only the water particles while incorporating the dynamic influence of surrounding air through a modified local-density coupling. This innovation enables realistic air–water interaction without solving separate air-phase equations, improving both numerical stability and computational efficiency. The model is validated through dam-break simulations covering collapse, impact, splash-up, and run-down stages. The predicted free-surface profiles and front-position trajectories show excellent agreement with laboratory measurements, demonstrating high predictive fidelity. Quantitatively, the proposed two-phase ISPH achieved an average RMSE of approximately 0.007 for leading-edge position, with accuracy improving systematically as particle spacing decreased. The model also reproduces key hydrodynamic features—such as splash height variation, roller formation, and velocity gradients—consistent with observed aeration behavior. Sensitivity analyses confirm that it correctly reflects the effects of varying air density, maintaining numerical robustness across light- and heavy-air conditions. Overall, the developed two-phase ISPH with density coupling provides a physically consistent, efficient, and stable framework for simulating aerated free-surface flows. The method is directly applicable to dam-break risk evaluation, spillway aeration design, and energy-dissipation analysis, offering improved accuracy and practicality for advanced hydraulic engineering simulations.