The role of air modeling on the numerical investigation of coastal dynamics and wave-structure interactions

• A two-fluid model is implemented to numerically investigate coastal dynamics.
• The implemented F–RANS governing equations account for air compressibility.
• Simulations of dam-break and 1D water piston assess the model validity and accuracy.
• The role of air modeling is investigated during wave breaking and impact on wall.

The paper presents a numerical investigation on the role of air modeling in simulations related to coastal dynamics. The implemented code, named COBRAS2, solves the Favre–Reynolds Navier–Stokes equations for two-phase flows. The k–∊k–∊ model is adopted to define the Reynolds stress; the polytropic expression is chosen as the gas state equation to describe air compressibility; the Volume Of Fluid algorithm is implemented in order to track the interface. Simulations of dam-break wave and 1D water piston illustrate the model validity and accuracy, where air inertia and compressibility play a significant role in the reproduced dynamics. Wave breaking is analyzed in comparison with experimental data in order to focus on the influence of air flow in the wave propagation. Finally, air entrapment and compressibility are investigated during the wave impact on deck and on vertical wall and the opportunity to solve the implemented two-phase equations is discussed together with the aim to obtain accurate estimation of wave-induced loads.