Harvard scientists have developed a new structure inspired by shark skin that could improve the aerodynamic performance of planes, wind turbines, drones and cars.
The study published in the Journal of the Royal Society Interface sheds light on a decades-old mystery about sharkskin.
Sharks and airplanes are not actually all that different. Both are designed to efficiently move through fluid (water and air), using the shape of their bodies to generate lift and decrease drag, researchers said.
The difference is that sharks have about a 400 million- year head start on the design process, they said.
"The skin of sharks is covered by thousands and thousands of small scales, or denticles, which vary in shape and size around the body," said George Lauder, professor at Harvard University in the US.
"We know a lot about the structure of these denticles - which are very similar to human teeth - but the function has been debated," said Lauder.
Most research has focused on the drag reducing properties of denticles but Lauder and his team wondered if there was more to the story.
"We asked, what if instead of mainly reducing drag, these particular shapes were actually better suited for increasing lift," said Mehdi Saadat, a postdoctoral fellow at Harvard, who holds a joint appointment at the University of South Carolina.
For inspiration, they turned to the shortfin mako, the fastest shark in the world. The mako's denticles have three raised ridges, like a trident.
Using micro-CT scanning, the team imaged and modelled the denticles in three dimensions. Next, they 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, a PhD student at Harvard.
"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, airplanes, and wind turbines," said Domel.
The researchers tested 20 different configurations of denticle sizes, rows and row positions on airfoils inside a water flow tank.
They found that in addition to reducing drag, the denticle-shaped structures significantly increased lift, acting as high-powered, low-profile vortex generators.
Cars and planes are equipped with these small, passive devices designed to alter the air flow over the surface of a moving object to make it more aerodynamic.
Most vortex generators in the field today have a simple, blade-like design.
"These shark-inspired vortex generators achieve lift-to- drag ratio improvements of up to 323 per cent compared to an airfoil without vortex generators," said Domel.
"With these proof of concept designs, we have demonstrated that these bioinspired vortex generators have the potential to outperform traditional designs," Domel said.
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