Drag on superhydrophobic sharkskin inspired surface in a closed channel turbulent flow

Abstract

Salvinia leaf and sharkskin are prime examples of nature's marvel. Salvinia leaf‐inspired superhydrophobic surfaces keep themselves clean and reduce drag in fluid flow. Sharkskin also reduces drag in turbulent flow and inhibits biofouling. Therefore, the prospect of having a drag‐reducing surface with both salvinia leaf and sharkskin properties is attractive. However, fabricating such a surface is difficult, and the current fabrication methods require at least two separate steps. In addition, the mechanisms of drag reduction of salvinia leaf and sharkskin are different, and their combined effect on the flow field is not well understood. In this study, we produced a PTFE surface that mimics sharkskin in its surface pattern and copies the superhydrophobic nature of the salvinia leaf in its microstructure. This surface was fabricated by laser machining and tested in a closed channel under turbulent flow conditions. We measured the pressure drop at different Reynolds numbers on this surface both in pre‐wet and non‐pre‐wet conditions and compared the result with pressure drop data on four other PTFE samples: two types of non‐superhydrophobic sharkskin inspired surface (riblets), a superhydrophobic surface, and a non‐machined surface. Both the non‐superhydrophobic riblets and the superhydrophobic sample reduced drag compared to the non‐machined surface. However, we observed a lack of drag reduction by the superhydrophobic riblets sample. We presented a qualitative explanation for the lack of drag reduction and concluded that the modifications of the flow field by the two drag reduction mechanisms are not beneficial for overall drag reduction in our experiment.

Experimental methods in chemical engineering: Contact angles

“…In five of these papers, CA is only an inlet parameter in a model or a numerical simulation. The twelve remaining involve experimental measurements, all of which were performed with an optical goniometer or derived instruments . The latter enables analysis at a liquid/liquid/solid or a liquid/gas/solid interface instead of a gas/liquid/solid one (Figure ).…”

“…The latter enables analysis at a liquid/liquid/solid or a liquid/gas/solid interface instead of a gas/liquid/solid one (Figure ). Works performed with an optical goniometer mainly employed the static sessile drop method with only two employing dynamic methods . Three studies included qualitative surface analysis through scanning electron microscopy images to estimate the substrate roughness: Ahmmed et al published the only manuscript in which both advancing and receding contact angles are reported and in which an estimation of the hysteresis is provided.…”

“…Studies containing experimental work on contact angles were mostly interested in investigating the wettability of powders: nanoparticles and microparticles . Other surfaces of interest included polymeric films, rocks, and glass . Powders were usually either cast or pressed into films and pellets to perform CA measurement.…”

“…Other applications involve nanofluids: in one case, a nanopowder was used as an interfacial modifier to alter the wettability of a reservoir surfaces; in two others, nanoparticles were left in suspension to act as modifiers of the physical properties (viscosity, thermal conductivity, surface tensions) of water or bitumen . Probe liquids employed include water, salted water, toluene, denatured ethanol, n ‐dodecane, bitumen, and various oils …”

Preface of the 66th Canadian Chemical Engineering Conference: “Sustainability and Prosperity”

“…This special issue section would have not materialized without the efforts of the contributing authors and the reviewers to ensure, despite their busy schedules, that all accepted papers meet the quality standards of The Canadian Journal of Chemical Engineering . The guest editors are also sincerely thankful to the Editor‐in‐Chief of The Canadian Journal of Chemical Engineering , Prof. João Soares, for his support and guidance, and to his editorial staff for their efforts, in welcoming this series of papers on timely topics.…”