Engineering of surfaces for drag reduction in water with validation using computational and experimental methods

Lead Research Organisation: University of Southampton
Department Name: Faculty of Engineering & the Environment

Abstract

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Description The project has led to new understanding of the potential for drag reduction using surface treatments that produce an effective slip of fluid flow over a surface. The project contained both experimental and numerical simulation components. An experimental technique was developed to give excellent repeatability for towing tank experiments. A test plate holder was designed and manufactured, capable of testing sample surfaces with good control over transition to turbulence. Significant drag reductions were obtained comparing wetted to unwetted samples. For full details the reader is referred to the PhD thesis of Gruncell (2014). Simulation work considered models for the roughness necessary to retain the air layer in practice and the type of anisotropic surface slip that is most effective at giving drag reduction. Additional theoretical work showed the influence of different assumptions in the air layer, in particular a zero net mass flux, which may be a more realistic model for practical application. The reader is referred to the publications (Busse et al) that discuss the simulation and theoretical work in more detail.
Exploitation Route Surfaces with demonstrated drag reduction using superhydrophobic surfaces are of particular interest in the marine sector as surface coatings. The advantages of generating partial slip have been demonstrated in calculations of flows using a Navier-slip boundary condition (with non-isotropic surface characteristics) and with a full representation of the two-phase flow. Experiments have demonstrated drag reduction comparing superhydrophobic and wetted states and the important influence of roughness that protrudes through the surface air layer has been demonstrated. A test facility is now available for future work and commercial testing (contact the Wolfson Unit in Southampton).
Sectors Aerospace, Defence and Marine,Energy,Environment,Transport
URL http://www.southampton.ac.uk/engineering/about/staff/nds9.page
 
Description The potential for drag reduction with hydrophobic treatment for specific rough surfaces was demonstrated, although not an absolute drag reduction relative to smooth surfaces. This is guiding future research. We also alerted the research community to specific limits on the drag reduction that can be attained when fixed mass flow in the air layer is set.
First Year Of Impact 2013
Sector Aerospace, Defence and Marine,Energy