Morphology Scaling of Drop Impact onto a Granular Layer

TL;DR

This study explores how water drops impact granular layers, revealing different crater shapes and a scaling law that relates impact parameters to crater morphology, emphasizing the importance of drop deformation.

Contribution

We introduce a phase diagram and a scaling law linking impact conditions to crater shapes, highlighting the role of drop deformation in granular impact phenomena.

Findings

Crater shape depends on impact speed and grain size.

A scaling law relates crater radius to impact parameters.

Drop deformation significantly influences crater morphology.

Abstract

We investigate the impact of a free-falling water drop onto a granular layer. First, we constructed a phase diagram of crater shapes with two control parameters, impact speed and grain size. A low-speed impact makes a deeper cylindrical crater in a fluffy granular target. After high-speed impacts, we observed a convex bump higher than the initial surface level instead of a crater. The inner ring can be also observed in medium impact speed regime. Quantitatively, we found a scaling law for crater radius with a dimensionless number consisting of impact speed and density ratio between the bulk granular layer and water drop. This scaling demonstrates that the water drop deformation is crucial to understand the crater morphology.