title: Flexible conformable hydrophobized surfaces for turbulent flow drag reduction.
abstract: In recent years extensive work has been focused onto using superhydrophobic surfaces for drag reduction applications. Superhydrophobic surfaces retain a gas layer, called a plastron, when submerged underwater in the Cassie-Baxter state with water in contact with the tops of surface roughness features. In this state the plastron allows slip to occur across the surface which results in a drag reduction. In this work we report flexible and relatively large area superhydrophobic surfaces produced using two different methods: Large roughness features were created by electrodeposition on copper meshes; Small roughness features were created by embedding carbon nanoparticles (soot) into Polydimethylsiloxane (PDMS). Both samples were made into cylinders with a diameter under 12 mm. To characterize the samples, scanning electron microscope (SEM) images and confocal microscope images were taken. The confocal microscope images were taken with each sample submerged in water to show the extent of the plastron. The hydrophobized electrodeposited copper mesh cylinders showed drag reductions of up to 32% when comparing the superhydrophobic state with a wetted out state. The soot covered cylinders achieved a 30% drag reduction when comparing the superhydrophobic state to a plain cylinder. These results were obtained for turbulent flows with Reynolds numbers 10,000 to 32,500.
authors.affiliation: School of Science and Technology, Nottingham Trent University, Clifton Lane, Nottingham, NG11 8NS, UK.
authors.forename: Joseph C
authors.initials: JC
authors.lastname: Brennan
authors.affiliation: School of Science and Technology, Nottingham Trent University, Clifton Lane, Nottingham, NG11 8NS, UK.
authors.forename: Nicasio R
authors.initials: NR
authors.lastname: Geraldi
authors.affiliation: School of Science and Technology, Nottingham Trent University, Clifton Lane, Nottingham, NG11 8NS, UK.
authors.forename: Robert H
authors.initials: RH
authors.lastname: Morris
authors.affiliation: School of Science and Technology, Nottingham Trent University, Clifton Lane, Nottingham, NG11 8NS, UK.
authors.forename: David J
authors.initials: DJ
authors.lastname: Fairhurst
authors.affiliation: Faculty of Engineering &Environment, Northumbria University, Ellison Place, Newcastle upon Tyne, NE1 8ST, UK.
authors.forename: Glen
authors.initials: G
authors.lastname: McHale
authors.affiliation: School of Science and Technology, Nottingham Trent University, Clifton Lane, Nottingham, NG11 8NS, UK.
authors.forename: Michael I
authors.initials: MI
authors.lastname: Newton