Numerical Study on the Influence of Wettability on the Sphere Surface During Water Entry

The water entry of objects is a fundamental physics problem and has a wide range of engineering applications, such as ship slamming, spacecraft landing on water, and anti-submarine missiles. Due to large nonlinear deformation, and strong unsteady flow and cavity characteristics caused by large-scale motions at the free surface, it is very difficult to simulate the process of water entry using a numerical approach. In this study, based on the open-source computational fluid dynamics (CFD) code library OpenFOAM, the continuum surface force (CSF) model is introduced into the volume of fluid (VOF) multiphase flow model, and the object motion is realized by overlapping grid technology. A three-dimensional sphere water entry numerical calculation model considering the wettability of the object surface is established. The reliability and accuracy of the numerical method in this paper are verified by comparing with the results of the motion displacement and cavitation morphology evolution of the sphere in the experiment. On this basis, the vertical water entry of hydrophilic and hydrophobic spheres with different initial impact velocities was numerically simulated. The effects of surface wettability and initial impact velocity on cavity evolution and motion characteristics during water entry are analyzed in detail, and the formation mechanism of water entry cavity is revealed.