Double Crown Formation During the Drop Impact onto Thin Film

The Edgerton crown is an iconic manifestation of drop impact splashing with a prominent cylindrical edge decorated with detaching droplets. Herein, we identify the formation of an intriguing double crown when a high-viscosity drop impacts a thin film of a lower-viscosity immiscible liquid. The first inner crown evolves in a regular manner, while the second outer crown forms near its base from the tip of the horizontally spreading drop when it approaches the outer free surface. The flow squeezed out between the drop and the solid surface generates counter-rotating vortex rings, which drive out the second crown. We mapped out the narrow parameter range in which this ephemeral structure emerges. Images were captured using a high-speed Phantom camera and long-distance microscope with adjustable magnification to visualize the impact dynamics. Direct numerical simulations were chosen to reproduce the impact using the Basilisk software, with multifluid setup comprising a drop, thin oil film, and surrounding gas, using dynamic adaptive grid refinement. This provided insight into the fine details, allowing us to identify the underlying dynamics of the double crown formation.