Complex fluid interface dynamics in water exit by improved diffuse interface-immersed boundary method

Accurate simulation of fluid–structure interaction problems involving multiphase flows remains a significant challenge in fluid mechanics, particularly in simulating water-exit phenomena where the interaction between a solid body and the free surface of water is highly dynamic and nonlinear. This study presents a three-dimensional numerical investigation of the water-exit process using the improved diffuse interface-immersed boundary method, which ensures mass conservation and enforces the no-slip boundary condition at the fluid–structure interface. Three scenarios are investigated: forced water exit of a fully submerged sphere and partially submerged sphere, free water exit under buoyancy forces, and forced water exit of a fully submerged cylinder. The simulation results provide detailed insights into the dynamic evolution of the free surface, including wave generation and air entrainment, and are validated against experimental results. The key phenomena, such as the large deformation of water surface, formation and breakup of water bridges, and splashing during the exit process, are successfully captured. Compared to experimental observations, the numerical model demonstrates high accuracy in predicting the shape and dynamics of the free surface, as well as the internal flow field characteristics.