58.1 Thursday, Jan. 5 Hydrodynamic function of shark skin and two biomimetic models LAUDER, G. V.*; OEFFNER, J.; Harvard University; Harvard University firstname.lastname@example.org
It has long been suspected that the denticles on shark skin reduce hydrodynamic drag during locomotion, and a number of man-made materials have been produced that purport to use shark skin-like surface roughness to reduce drag during swimming. But no studies to date have tested these claims of drag reduction under dynamic and controlled conditions in which the swimming speed and hydrodynamics of shark skin and skin-like materials can be quantitatively compared with that of controls lacking surface ornamentation or with surfaces in different orientations. We use a flapping foil robotic device which allows accurate determination of the self-propelled swimming speed of both rigid and flexible membrane-like foils made of shark skin and two biomimetic models of shark skin to measure locomotor performance. We studied the self-propelled swimming speed of real shark skin, a silicone riblet material with evenly spaced ridges, and Speedo “shark skin-like” swimsuit fabric attached to both rigid flat plate foils and made into flexible membrane-like foils. We found no consistent increase in swimming speed with Speedo fabric, a 7.2% increase with riblet material, and shark skin membranes (but not rigid shark skin plates) showed a mean 12.3% increase in swimming speed compared to the same skin foils after removing the denticles. Deformation of the shark skin membrane is thus critical to the drag reducing effect of surface denticles. Digital particle image velocimetry of the flow field surrounding moving shark skin foils shows that skin denticles promote enhanced leading edge suction which may have contributed to the observed increase in swimming speed.