A diffusive wetting model for water entry/exit based on the weakly-compressible SPH method

• A particle-based model for individual water entry/exit and the full process from entry to exit. • A coarse-grained model enables accurate simulation results. • Implicitly characterizes surface wettability without explicitly introducing complex physical characteristics. This paper proposes a diffusive wetting model for the weakly-compressible smoothed particle hydrodynamics (WCSPH) method to simulate not only individual water entry/exit but also the complete process from water entry to exit. The model is composed of a physically consistent diffusive wetting equation to describe the wetting evolution at the fluid-solid interface, a wetting-coupled identification approach to determine the type of fluid particles by taking into account the wetting degree of the contacted solid, and a numerical regularization on the fluid particles at the fully wetted fluid-solid interface. Compared to traditional models, the diffusive wetting model can effectively predict wetting-affected flow behaviors in water entry, and accurately capture flow separation and free-surface breaking in water exit. It can also reliably reproduce stage-specific hydrodynamic phenomena throughout the entire water entry/exit process. The accuracy and versatility of the present model are validated through qualitative and quantitative comparisons with experiments, including the 3-D water entry of a sphere, the 2-D water entry/exit of a cylinder, the complete process from water entry to exit of a 2-D cylinder, and the 2-D water entry of a wedge.