Water–air two-phase flow during entry of a sphere into water using particle image velocimetry and smoothed particle hydrodynamics

This paper uses experimental and numerical methods to present the hydrodynamic characteristics of water and air flows during vertical water entry of a sphere. In the experiment, a high-speed camera is equipped for multi-perspective recording of the cavity evolution process and particle image velocimetry is used to capture the velocity fields outside the cavity via different types of tracer particles applied to air and water. A theoretical solution for the velocity of a sphere as it enters water is developed. It provides a proper drag coefficient for a sphere with a water entry cavity and shows good agreement with the experimental results. A high-efficiency smoothed particle hydrodynamics method with adaptive particle refinement is employed for the numerical simulation due to its good performance in capturing cavity splash. The size of the water-entry cavity and the velocity field results are verified mutually using our experimental data. Moreover, the numerical results provide flow-field information regarding the volume inside the cavity, which is difficult to obtain via experimental means.