![]() Shark skin is one such example and is covered with rigid bony denticles (or scales) that exhibit a plate-like upper section with ridges, which narrows to a thin neck that anchors into the skin ( figure 1 a, b). Specifically, biological systems have evolved a wide range of drag reducing mechanisms that have inspired the design of synthetic surfaces. Nature, through the course of evolution, has arrived at structures and materials whose traits often offer inspiration for the design of synthetic systems with unique properties. By contrast, passive techniques are easy to implement and free from any kind of external energy requirements. Although active methods typically yield better results than the passive ones, they require the supply of external energy, and in fully automated systems rely on complex sensor technology and algorithm development. These include vortex generators, Gurney flaps and winglets, which reduce drag and increase lift by passively altering the flow to favourably affect the pressure gradients along the aerofoil. On the other hand, it has also been shown that passive flow control strategies based on geometric modifications are capable of altering lift and drag. On one hand, several active flow control methods, which involve the addition of auxiliary power into the system, have been demonstrated for both drag reduction and lift augmentation. Motivated by this need, two main strategies have been proposed to maximize the lift and minimize the drag. Systems that move suspended within a fluid, such as airplanes, wind turbines, drones and helicopters, all benefit from increased lift-to-drag ratios which results in lower energy consumption. Our findings not only open new avenues for improved aerodynamic design, but also provide new perspective on the role of the complex and potentially multifunctional morphology of shark denticles for increased swimming efficiency. Such behaviour is enabled by two concurrent mechanisms: (i) a separation bubble in the denticle's wake altering the flow pressure distribution of the aerofoil to enhance suction and (ii) streamwise vortices that replenish momentum loss in the boundary layer due to skin friction. Through parametric modelling to query a wide range of different designs, we discovered a set of denticle-inspired surface structures that achieve simultaneous drag reduction and lift generation on an aerofoil, resulting in lift-to-drag ratio improvements comparable to the best-reported for traditional low-profile vortex generators and even outperforming these existing designs at low angles of attack with improvements of up to 323%. Inspired by the drag-reducing properties of the tooth-like denticles that cover the skin of sharks, we describe here experimental and simulation-based investigations into the aerodynamic effects of novel denticle-inspired designs placed along the suction side of an aerofoil. There have been significant efforts recently aimed at improving the aerodynamic performance of aerofoils through the modification of their surfaces.
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