Abstract: While sharkskin surface roughness in terms of denticle morphology has been hypothesized but remains yet controversial to be ca-pable of achieving turbulent flow control and drag reduction, sharkskin-inspired “riblets” have been reported to be an effective biomimetic design. Here we address an integrated study of biomimetic riblets inspired by sharkskin denticles by combining 3D digitizing and mod-eling of “fresh” denticles and computational fluid dynamic modeling of turbulent flows on a rough surface with staggered denticles and hound-tooth-patterned grooves. Realistic microstructures of denticles in five shark species of Galapagos, great white, whitetip reef, blacktip reef, and hammerhead sharks were first measured and digitized in three fold: (1) 2D imaging of lubricated sharkskin in a wet state by means of a “nano-suit” technique with a Field-Emission Scanning Electron Microscope (FE-SEM); (2) 3D structures of sharkskin denticles with a micro-focus X-ray CT; and (3) single denticles of the five shark species in a 3D manner with 3D-CAD. The denticles at mid-body location in the five species were observed to have a structure of five non-uniform-ridges (herein termed “non-uniform grooves”) with Angles Of Inclination (AOI) ranging over 20? – 32?. Hydrodynamics associated with the unique five-ridge denticles were then in-vestigated through modeling turbulent flow past a denticle-staggered skin surface. We further constructed a biomimetic riblet model inspired by the non-uniform grooves and investigated the hydrodynamic effects of height-to-spacing ratios of mid-ridge and side-ridges. Our results indicate that the morphological non-uniformity in sharkskin denticles likely plays a critical role in passively controlling local turbulent flow and point to the potential of denticle-inspired biomimetic riblets for turbulent-flow control in aquatic vehicles as well as other fluid machinery.

Key words: sharkskin, denticles, biommetic riblets;3D digitizing;computational fluid dynamics