Published online by Cambridge University Press: 05 May 2015
We investigate drop impact dynamics near closed pits and open-ended pores experimentally. The resulting impact phenomena differ greatly in each case. For a pit, we observe three distinct phenomena, which we denote as a splash, a jet and an air bubble, whose appearance depends on the distance between impact location and pit. Furthermore, we found that splash velocities can reach up to seven times the impact velocity. Drop impact near a pore, however, results solely in splashing. Interestingly, two distinct and disconnected splashing regimes occur, with a region of planar spreading in between. For pores, splashes are less pronounced than in the pit case. We state that, for the pit case, the presence of air inside it plays the crucial role of promoting splashing and allowing for air bubbles to appear.
The impact of a drop near a closed pit. Videos are shown for an increasing amount of overlap between drop and pit, with Δ* = 0.89, 0.16, -0.14. It results in different phenomena, such as a splash created at the outer edge, a jet at the inner one and an air bubble that emerges from the pit. Both side view and bottom view images are shown.
Flow inside a pit after drop impact for an overlap Δ*= 0.22 where both a splash and a jet appear.
Various videos for the impact of a drop near an open-ended pore. Each video contains both a side and a bottom view for an increasing amount of overlap between drop and pore with Δ* = 1.14, 0.94, 0.74, 0.55, 0.14 respectively. Phenomena that are observed are a slow splash, a blob, a thin splash and planar spreading.