A shortfin mako, the fastest shark in the world. Image: Alessandro De Maddalena/Shutterstock
A shark’s natural ability to speed seamlessly through water could help us design next-generation aircraft and drones.
Nature has always inspired engineers to overcome the hurdles of the human body, such as replicating bird flight to create the first aircraft. Now though, we are looking to more subtle aspects of evolution to bring us even greater capabilities.
That is what a team of evolutionary biologists and engineers from Harvard University and the University of South Carolina has done through analysis of the scales of the fastest shark on Earth: the shortfin mako.
In a paper published to the Journal of the Royal Society Interface, the team revealed how it solved a decades-old mystery by looking beyond simply focusing on the drag-reducing properties of the denticles (scales) like many teams had done before.
Instead, the team asked whether the tooth-like scales could actually be more suited to creating lift.
In the case of the shortfin mako, its denticles have three raised ridges like a trident, so, using micro-CT scanning, the researchers imaged and modelled the denticles in three dimensions.
Next, the team 3D-printed the shapes on the surface of a wing with a curved aerodynamic cross-section, known as an airfoil.
“Airfoils are a primary component of all aerial devices,” said August Domel, co-first author of the paper.
“We wanted to test these structures on airfoils as a way of measuring their effect on lift and drag for applications in the design of various aerial devices such as drones, aeroplanes and wind turbines.”
Environmental scanning electron microscope image of denticles from the shortfin mako shark. Image: Harvard University
Bioinspired aerodynamic designs
By testing 20 different configurations of denticle sizes, rows and row positions on airfoils inside a water flow tank, the team found that, in addition to reducing drag, the denticle-shaped structures significantly increased lift, acting as high-powered, low-profile vortex generators.
These same vortex generators feature on most modern aerodynamic-dependent vehicles such as cars and aircraft, but are reliant on a simple blade-like design.
This new shark-inspired design, however, achieves a lift-to-drag ratio improvement of up to 323pc compared to an airfoil without vortex generators.
Speaking of this breakthrough’s potential, another co-author of the paper, Katia Bertoldi, said: “You can imagine these vortex generators being used on wind turbines or drones to increase the efficiency of the blades. The results open new avenues for improved, bioinspired aerodynamic designs.”
