Investigation of the drag reducing effect of hydrophobized sand on cylinders

Brennan, JC, Fairhurst, DJ ORCID: https://orcid.org/0000-0001-5311-0762, Morris, RH ORCID: https://orcid.org/0000-0001-5511-3457, McHale, G and Newton, MI ORCID: https://orcid.org/0000-0003-4231-1002, 2014. Investigation of the drag reducing effect of hydrophobized sand on cylinders. Journal of Physics D: Applied Physics, 47 (20). ISSN 0022-3727

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Abstract

Superhydrophobic surfaces show strong potential for drag reducing applications. If such a surface supports a Cassie-Baxter state with low solid surface fraction and when immersed it retains a plastron air layer, large slip can occur across its surface and a consequent reduction in drag. In this work we report a facile method for creating hydrophobic cylinders an d hydrophobic flat surfaces with varying surface roughness able to support a Cassie-Baxter state . Cylinders of 12mm diameter were coated in hydrophobised sand with grain sizes in the ranges 50-100μm, 212-300μm 425-600μm and 600-710μm to produce the different roughness. A Laser Doppler Anemometer was used to measure the velocity profile of the water across their wake in a large water circulating flow chamber. The hydrophobic cylinders in the Cassie-Baxter state show drag reductions of up to 28% compared to the same sample in the Wenzel state for flows with Reynolds number s of 10,000 to 40,000. These drag reduction results , in combination with confocal microscopy images of the plastron air layer and feature height , show that the thickness of the plastron and the protrusion height of the features combine to give a drag reduction or drag increase depending on the ratio of the two.

Item Type:	Journal article
Publication Title:	Journal of Physics D: Applied Physics
Creators:	Brennan, J.C., Fairhurst, D.J., Morris, R.H., McHale, G. and Newton, M.I.
Publisher:	Institute of Physics Publishing Ltd.
Place of Publication:	Bristol
Date:	2014
Volume:	47
Number:	20
ISSN:	0022-3727
Identifiers:	Number Type 10.1088/0022-3727/47/20/205302 DOI
Divisions:	Schools > School of Science and Technology
Record created by:	EPrints Services
Date Added:	09 Oct 2015 11:17
Last Modified:	09 Jun 2017 13:55
URI:	https://irep.ntu.ac.uk/id/eprint/25592

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