Why are drop-impact-crater jets so singular?

Fast microjets are known to emerge during the rebounding of drop-impact craters, or after a bubble bursts at a pool surface.    The thinnest jets are the fastest and generate the smallest secondary droplets of importance to aerosol formation and the aroma of champagne.   These jets are associated with the small dimple which forms at the bottom of the crater and rebounds without pinching off a bubble.  The radial collapse of this dimple has been shown to be purely inertial but is highly sensitive on initial and boundary conditions [1,2].  We perform high-resolution volume-of-fluid numerical simulations using Gerris to reveal a novel focusing mechanism, which reveals the mechanism behind the fastest jets.  This involves the entrainment of a conical air-sheet.   This jetting configuration explains the extreme sensitivity to the precise impact conditions which have been observed in the detailed experiments of the phenomenon.  It also shows why liquid viscosity does not strongly affect the jetting velocity.

[1] S. T. Thoroddsen et al. Singular jets during the collapse of drop-impact craters, J. Fluid Mech., 848, R3  (2018).

[2] Z. Q. Yang et al. Multitude of dimple shapes can produce singular jets during the collapse of immiscible drop-impact craters,  J. Fluid Mech., 904, A19 (2020).