Plastron induced drag reduction and increased slip on a superhydrophobic sphere

McHale, G., Flynn, M.R. and Newton, M.I., 2011. Plastron induced drag reduction and increased slip on a superhydrophobic sphere. Soft Matter, 7 (21), pp. 10100-10107.

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On low contact angle hysteresis superhydrophobic surfaces, droplets of water roll easily. It is intuitively appealing, but less obvious, that when such material is immersed in water, the liquid will flow more easily across its surface. In recent experiments it has been demonstrated that superhydrophobic surfaces with the same high contact angle and low contact angle hysteresis may not, in fact, have the same drag reducing properties. A key performance parameter is whether the surface is able to retain a layer of air (i.e. a plastron) when fully immersed. In this report, we consider an analytical model of Stokes flow (i.e. low Reynolds number, Re, creeping flow) across a surface retaining a continuous layer of air. The system is based on a compound droplet model consisting of a solid sphere encased in a sheathing layer of air and is the extreme limit of a solid sphere with a superhydrophobic surface. We demonstrate that an optimum thickness of air exists at which the drag on this compound object is minimized and that the level of drag reduction can approach 20 to 30%. Physically, drag reduction is caused by the ability of the external flow to transfer momentum across the water-air interface generating an internal circulation of air within the plastron.

Item Type: Journal article
Publication Title: Soft Matter
Creators: McHale, G., Flynn, M.R. and Newton, M.I.
Publisher: Royal Society of Chemistry
Date: 2011
Volume: 7
Number: 21
Rights: Copyright ©2011 Royal Society of Chemistry
Divisions: Schools > School of Science and Technology
Record created by: EPrints Services
Date Added: 09 Oct 2015 10:35
Last Modified: 23 Aug 2016 09:10

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