Nicole SharpWhen a raindrop hits a leaf, it spreads out into a rimmed sheet that breaks up into droplets. These tiny drops can carry dust, spores, and even pathogens as they fly off. But many leaves aren’t smooth-edged; instead they have serrations or teeth. How does that affect a splash? That’s the question at the heart of today’s study.
A water drop hits a star-shaped pillar and breaks up.To simplify from a leaf’s shape, the team studied water dropping onto star-shaped pillars. As seen above and below, the pillar’s edge shaped the splash sheet, with the sheet extending further in the edge’s troughs. This asymmetry extends into the rim also, concentrating the liquid — and the subsequent spray of droplets — along lines that extend from the edge’s troughs and peaks.
A viscous water-glycerol drop hits a star-shaped pillar, spreads, and breaks into droplets.The team found that, in addition to sending drops along a preferred direction, the shaped edge made the droplets larger and faster than a smooth edge did. (Image and research credit: T. Bauer and T. Gilet)
https://fyfluiddynamics.com/2024/09/shaped-splashes/
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Rim dynamics and droplet ejections upon drop impact on star-shaped poles
When a drop impacts next to the edge of a solid substrate, it spreads beyond the edge and forms a liquid sheet surrounded by a rim. As the rim decelerates, ligaments may form, then destabilize in droplets. This fragmentation scenario has been extensively investigated in the axisymmetric configuration of centered impacts on small circular targets. In this work, we investigate star-shaped targets. We show that the rim is shaped complementarily to the substrate: it goes farther and yields more droplet ejections in directions corresponding to troughs in the substrate edge profile.