Velocity and Density Effect on Impact Force during Water Entry of Sphere

Abstract

A careful experimental investigation has been performed to quantify the impact forces on a sphere that passes from an air region to a water region. The experiments allowed changes to a wide range of parameters, including the impact velocity, the sphere density, and surface wettability. In addition to quantifying the impact force, results have allowed a qualitative discussion of the difference in fluid flow behaviour in the vicinity of the sphere. It was found that the parameters, particularly the sphere density, determined whether the adjoining air cavity would be quasi-static or deep-sealed. Non-dimensionalizing the input parameters reveals that there is a singular relationship which allows quantification of the average force coefficient up to the time of cavity pinch-off. Finally, it was found that the formation of quasi-static cavities resulted in larger impact forces compared to the deep-seal cases. The difference in these force coefficients did not depend on the dimensionless parameter.