On the impact of a concave nosed axisymmetric body on a free surface

TL;DR

This experimental study investigates how a concave nosed axisymmetric body impacts a free surface, revealing reduced splash and cavity size due to an air pocket, with lower pressure impacts compared to convex noses.

Contribution

The paper provides new insights into impact dynamics of concave nosed bodies, highlighting the role of an air pocket in reducing splash and pressure during impact.

Findings

Concave nosed bodies produce minimal splash and cavity.

Impact pressures are significantly lower than classical water hammer predictions.

Presence of an air pocket influences impact behavior and pressure.

Abstract

We report on an experimental study of the vertical impact of a concave nosed axisymmetric body on a free surface. Previous studies have shown that bodies with a convex nose, like a sphere, produce a well defined splash with a relatively large cavity behind the model. In contrast, we find that with a concave nose, there is hardly a splash and the cavity extent is greatly reduced. This may be explained by the fact that in the concave nosed case, the initial impact is between a confined air pocket and the free surface unlike in the convex nosed case. From measurements of the unsteady pressure in the concave nose portion, we show that in this case, the maximum pressures are significantly lower than the classically expected "water hammer" pressures and also lower than those generally measured on other geometries. Thus, the presence of an air pocket in the case of a concave nosed body adds an interesting dimension to the classical problem of impact of solid bodies on to a free surface.