Abstract
We study the vertical impact of a droplet onto a cubic pillar of comparable size placed on a flat surface, by means of numerical simulations and experiments. Strikingly, during the impact a large volume of air is trapped around the pillar side faces. Impingement upon different positions of the pillar top surface strongly influences the size and the position of the entrapped air. By comparing the droplet morphological changes during the impact from both computations and experiments, we show that the direct numerical simulations, based on the Volume of Fluid method, provide additional and new insight into the droplet dynamics. We elucidate, with the computational results, the three-dimensional air entrapment process as well as the evolution of the entrapped air into bubbles.
Highlights
We study the vertical impact of a droplet onto a cubic pillar of comparable size placed on a flat surface, by means of numerical simulations and experiments
We investigate droplet impact onto a surface with a stand-alone cubic pillar, through both direct numerical simulations (DNS) and experiments
The numerical simulations further enable to understand the underlying air and bubble entrapment process for our cases, which is intrinsically different from the process occurring on smooth solid surfaces, where the droplet bottom gets deformed by the air that fails to escape, and the contraction of the air film eventually evolves into an air bubble[40,41,42,43,44,45]
Summary
We study the vertical impact of a droplet onto a cubic pillar of comparable size placed on a flat surface, by means of numerical simulations and experiments. By comparing the droplet morphological changes during the impact from both computations and experiments, we show that the direct numerical simulations, based on the Volume of Fluid method, provide additional and new insight into the droplet dynamics. For a wide range of applications, such as ink-jet printing, spray cooling, or prevention of soil erosion, droplet impact is of vital importance The research on this topic already started in 1876 with Worthington, who reported fascinating results observed during droplet impact onto solid and wetted s urfaces[1]. We investigate droplet impact onto a surface with a stand-alone cubic pillar, through both direct numerical simulations (DNS) and experiments. With both experiments and numerical simulations, during the impact process large air bubbles can be entrapped within the fluid flow around the cubic pillar.
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