Double Contact During Drop Impact on a Solid Under Reduced Air Pressure

Er Qiang Li, Kenneth R. Langley, Yuansi Tian, Peter D Hicks, Sigurdur T. Thoroddsen

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Drops impacting on solid surfaces entrap small bubbles under their centers, owing to the lubrication pressure which builds up in the thin intervening air-layer. We use ultra-high-speed interference imaging, at 5 Mfps, to investigate how this air-layer changes when the ambient air-pressure is reduced below atmospheric. Both the radius and the thickness of the air-disc becomes smaller with reduced air pressure. Furthermore, wefind the radial extent of the air-disc bifurcates, when the compressibility parameter exceeds 25. This bifurcation is also imprinted onto some of the impacts, as a double contact. In addition to the central air-disc inside the first ring contact, this is immediately followed by a second ring contact, which entraps an outer toroidal strip of air, which contracts into a ring of bubbles. We find this occurs in a regime where Navier slip, due to rarefied gas effects, enhances the rate gas can escape from the path of the droplet.
Original languageEnglish
Article number214502
Number of pages5
JournalPhysical Review Letters
Issue number21
Early online date20 Nov 2017
Publication statusPublished - 24 Nov 2017

Bibliographical note

This study was supported by King Abdullah University of Science and Technology (KAUST) under URF/1/2621-01-01. Li acknowledges the Thousand Young Talents Program of the National Natural Science Foundation of China (Grant 11621202) and Fundamental Research Funds for the Central Universities (Grant WK2090050041).


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