A lubricant-infused slip surface for drag reduction

Abstract

Seaweed and fish have slippery outer surfaces because of the secretion of a layer of mucus. The hydrodynamics over a three-dimensional lubricant-infused slip surface that mimics the mucus layers of seaweed and fish was numerically explored. The morphological features of the lubricant-infused surface were designed to mimic such biological mucus storage systems. The lubricant was assumed to fill the cavity and to be supplemented without limit from the bottom surface of the cavity. The slip motion at the interface between the lubricant and water was simulated by using the volume of fluid method. Simulations were performed for two cavity open area fractions, 40% and 60%, and for three lid thicknesses, 0.01D, 0.03D, and 0.06D, where D is the width of the cavity (D = 400 μm). The simulation was conducted by employing realistic material properties. The contact angle of the lubricant in deionized water was directly measured (θeq = 25.9°). This slippery lubricant layer contributes to drag reduction by lessening the velocity gradient of the surrounding fluid. The hydrodynamics of the slip surface was examined by scrutinizing the effects of varying the open area and the lid thickness on the slip velocity and length, the dispersion area, and the lubricant consumption. The maximum slip velocity and length were obtained in the center of the contact interface, which forms a paraboloid. The effects of varying the cavity open area fraction on the maximum slip velocity and length are significant. The lid thickness affects both the lubricant dispersion pattern and the height to which the lubricant builds up. The lubricant consumption for a cavity open area fraction of 60% is larger than that for 40%. The cavity with an open area fraction of 60% and a lid thickness of 0.06D provides the best drag reduction of the cavities we simulated.