Meeting Abstract
The skin of sharks consists of numerous tooth-like scales (denticles) that form a rough surface covering the body. Imaging this surface has mostly been accomplished using (two dimensional) scanning electron microscopy. But in order to understand the hydrodynamic function of shark skin, it is critical to quantify surface roughness in three dimensions and measure fluid flow over the denticle surface on both engineered models and living animals. In this presentation we provide an overview of our recent work on three-dimensional skin surface imaging on a diversity of shark species and body locations using gel-based stereo profilometry, and summarize ongoing experiments that measure the effect of surface roughness on (1) denticle models mounted on airfoils to quantify their effect on lift and drag, (2) experiments on the propulsion of 3D-printed biomimetic shark skin flexible foils, and (3) flow over the denticle surface in living sharks. Surface roughness in smooth dogfish varied from 9 to 42 µm and particularly interesting transitions in denticle shape and roughness were observed on the skin over the gills and on the fins and tail. Denticles mounted on a NACA 0012 airfoil increased the lift-to-drag ratio by up to 323%, and corroborate biomimetic shark skin experiments demonstrating that denticle surfaces are capable of both reducing drag and enhancing thrust. Experiments on the propulsion of flexible shark skin membranes also show that denticle-containing surfaces are capable of both increasing self-propelled speed and reducing the cost of transport. Thrust enhancement by roughened denticle surfaces is an underappreciated aspect of shark skin, as almost all previous studies have focused on static drag reduction.
