Leidenfrost drop dynamics beyond frictionless levitation: jetting and interfacial oscillations*

Liquid-solid interactions are ubiquitous in numerous naturally occurring phenomena and industrial processes. Over the past few years, a particular interest has been given to understanding the characteristics and dynamics of liquid drop impact on heated substrates maintained above the Leidenfrost temperature, specifically in applications that require favourable conditions for efficient cooling. Upon impact, the drop exhibits a vigorous phase-change behaviour coupled with the inception of an intervening vapour layer leading to a drastic reduction in the heat transfer between the liquid and surface. Interestingly, the strong interfacial oscillations at the liquid-vapour interface give rise to rich dynamics and pattern formation, excited mainly by the incessant development and discharge of vapour pockets beneath the drop. Additionally, bubble entrapment and jetting are other unique manifestations of Leidenfrost drops attributed to the convergence of capillary waves at the liquid-vapour interface. This study employs an in-house solver for Direct Numerical Simulations (DNS) based on the Level Contour Reconstruction Method (LCRM) to accurately capture the highly deforming liquid-vapour interface. We determine the onset of the interfacial oscillations, demonstrate the singularities leading to vapour bubble entrapment, and validate the occurrence of upward and/or downward jetting.