Air-cushioning effect and Kelvin-Helmholtz instability before the slamming of a disk on water

Abstract

The macroscopic dynamics of a droplet impacting a solid is crucially determined by the intricate air dynamics occurring at the vanishingly small length scale between droplet and substrate prior to direct contact. Here we investigate the inverse problem, namely the role of air for the impact of a horizontal flat disk onto a liquid surface, and find an equally significant effect. Using an in-house experimental technique, we measure the free surface deflections just before impact, with a precision of a few micrometers. Whereas stagnation pressure pushes down the surface in the center, we observe a lift-up under the edge of the disk, which sets in at a later stage, and which we show to be consistent with a Kelvin-Helmholtz instability of the water-air interface.

arXiv commentSupplementary text: "KHshort_shallowlayer.pdf". Movies: "deformingpattern.mp4" shows the deforming pattern from TIR images. "50mmprofile.mp4" and "80mmprofile.mp4" are videos showing reconstructed water surface profiles under the approaching disk

References in corpus (6)

• Maximal air bubble entrainment at liquid drop impact
• Skating on a Film of Air: Drops Impacting on a Surface
• Real-time quantitative Schlieren imaging by fast Fourier demodulation of a checkered backdrop
• Universal mechanism for air entrainment during liquid impact
• Splash wave and crown breakup after disc impact on a liquid surface
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Cited by in corpus (5)

• Air Entrapment and its effect on Pressure Impulses in the slamming of a Flat Disc on Water
• On wedge-slamming pressures
• Linear stability analysis of a time-divergent slamming flow
• Total-internal-reflection deflectometry for measuring small deflections of a fluid surface
• Dynamic pressure enhancement upon disk impact on a boiling liquid