Jet amplification and cavity formation induced by penetrable fabrics in hydrophilic sphere entry

Abstract

Studies of solid impact with fluid surfaces have traditionally considered splashing in the context of impactor shape and surface texture. However, it is not always possible to tune impactor properties for desired splash characteristics. In this experimental study, smooth, hydrophilic, free-falling spheres are allowed to impact a quiescent liquid surface for Weber numbers in the range of 400–1580. The liquid surface is modified by the inclusion of a thin fabric upon which a falling sphere strikes and penetrates at water entry. With respect to clean water, inclusion of a single layer of fabric on the surface increases the Worthington jet height across all entry speeds tested. As the sphere penetrates, the fabric is drawn inward, providing a fabric funnel through which a Worthington jet subsequently passes. We show that the presence of fabric increases the drag at entry and enables air-entraining cavities otherwise unattainable by hydrophilic spheres for the impact speeds tested. Such cavity formation is made possible by alteration of the flow separation angle, analogous to greater values of the advancing contact angle.