Water entry of spheres with entry-axis channels

In this study, we modify the classical water entry sphere by including impact axis channels that permit flow passage through the impactor center. Perturbations to the classical impactor are critical for aligning fundamental investigations with real-world use. Impactors begin as slightly hydrophobic phenolic resin spheres, which are made superhydrophobic with surface coatings. Through-channels have various diameters and inlet/outlet tapers. Flow through the channels creates a trailing jet behind the impactor. Interactions of the trailing jet with the cavity wall result in a shallower pinch-off with a smaller cavity due to a hastened pinch-off. In comparison with solid, intact spheres, impactors with channels suppress the formation of air-entraining cavities. We propose a drag model for the channeled impactors and observe that channeled impactors experience more drag than their intact counterparts, a result of shear in the channel and a modified stagnation surface.