Experimental Studies of Bioinspired Shark Denticles for Drag Reduction.

This article reviews recent research on shark skin-inspired surface structures, specifically dermal denticles and their riblet features, focusing on their drag-reducing properties and manufacturing techniques over the past 15 years. Shark denticles, composed of tooth-like scales with riblets, interact with turbulent boundary layers to reduce drag through mechanisms involving streamwise vortex lifting and suppression of crossflow interactions. Experimental studies show that sub-millimeter scale denticles and riblets consistently reduce drag across various flow speeds, while larger denticles (over 2 mm) tend to increase drag. Manufacturing methods such as molding, photolithography, and CNC machining enable replication of these structures, though 3D printing currently lacks the resolution to reproduce sub-mm features accurately. The review highlights additional functional aspects like denticle bristling, hydrophobicity, antifouling, and noise reduction, and suggests future research directions including diverse denticle morphologies, improved manufacturing resolution, and field testing for applications in energy-efficient underwater and aerial vehicles.