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Wall turbulence: from surface roughness to surface slip

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Partial slip offers a possible route to drag reduction. A promising technique is based on textured hydrophobic surfaces in water: if an air layer can be retained near the surface a significant drag reduction is theoretically possible. The present work includes a mix of simulation and experiment. Calculations in the laminar flow regime show delays in separation that offer significant drag reductions (10-20%) even when the surface texture (roughness) necessary to retain the air layer is included in the model. Fully turbulent simulations using the Navier-slip condition show the importance of slip anisotropy and roughness-resolving calculations quantify the drag penalty of the underlying surface. Finally a set of experiments are conducted using a treated test surface that is towed through water in the turbulent flow regime. Air layers are retained during the tests and drag reductions relative to wetted surfaces are measured.

This talk is part of the Fluid Mechanics (CUED) series.

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