Thursday, May 5, 2016

Crown sealing and buckling instability during water entry of spheres

A sphere falling into water generates a spectacular crown splash at the surface. The object’s impact ejects a thin sheet of fluid that rises vertically. The air pulled down into the cavity by the sphere’s passage makes the air pressure inside the sheet lower than the ambient air pressure on the exterior of the sheet.

This pressure difference is part of what draws the crown inward to seal the cavity. As the splash collapses inward and seals, the liquid sheet starts to buckle and wrinkle, leaving periodic stripes around the closing neck. This so-called buckling instability occurs when the radius of the neck collapses faster than the vertical speed of the splash.


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