The effect of atmospheric density on splash of spheres during water entry

The dynamics of splash curtain by vertical water entry of a sphere under various atmospheric densities is investigated in the present study. To understand the mechanism of air density on the splash evolution, a simplified model is proposed to analyze the experimental results, revealing both the size of splash and surface seal time increase as the atmospheric density decreases. Considering the pressure drop caused by air flowing into the cavity and surface tension, the present model focuses on the rounded rim at the tip of splash, reducing the complex splash evolution to a ballistics problem. The results show that when pressure drop force is the dominant factor, the trajectory of the rounded rim is approximately a circular arc. As the atmospheric density decreases, the effect of pressure drop force is weakening and the surface tension gradually plays a role. This results in the increasing size of the splash curtain and longer surface seal time, transforming the trajectory into a spiral. Under the extreme conditions, the evolution of splash is such extended by surface tension that the surface seal may even disappear.