The thinning of threads of low-viscosity fluids like water in air has been of interest for more than a century and is gaining new importance because of the emergence of applications involving the breakup of drops and jets of liquid metals which have viscosities comparable to but surface tensions and densities much larger than water. The dynamics of thinning and pinch-off is governed by the Ohnesorge number $\text{Oh}=\mu /\sqrt{\rho \gamma R}$, where $\mu , \rho , \gamma$, and $R$ stand for viscosity, density, surface tension, and nozzle or initial jet radius. When $\text{Oh}\ll 1$, the thread initially thins as if it were inviscid and its minimum radius ${\tilde{h}}_{\text{min}}$ obeys a universal scaling law ${\tilde{h}}_{\text{min}}=A{(\gamma /\rho )}^{1/3}{({\tilde{t}}_b-\tilde{t})}^{2/3}$, where ${\tilde{t}}_b$ is the time $\tilde{t}$ at which the thread breaks up and $A\doteq 0.717$. As the interface overturns prior to breakup when Oh is sufficiently small, it has proven challenging to observe in simulations and experiments the value of the prefactor $A$ predicted from theory and furthermore the transition of the dynamics as ${\tilde{h}}_{\text{min}}\to 0$ from the inviscid regime to a different scaling regime in which the effect of viscosity is no longer negligible. Here we employ high-accuracy simulation using a sharp-interface algorithm to show that for sufficiently small Oh, the value of $A$ predicted from computations agrees with the theoretical value to three decimal places and the inviscid power-law behavior can be observed over two to three decades in ${\tilde{h}}_{\text{min}}$ as ${\tilde{t}}_b-\tilde{t}\to 0$. Transition out of the inviscid regime and into a viscous one is also demonstrated from simulations.

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• Drop & bubble phenomena
• Drop breakup
• Flow instability
• Instability of free-surface flows
• Interfacial flows
• Liquid bridges