Abstract

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.