Harvard Engineers Look to Sharkskin to Boost Aerodynamic Performance

What do you get when you pair together evolutionary biologists and aerospace engineers? A shark-inspired concept for how to make cars, drones, and wind turbines significantly faster and more efficient. 

Harvard researchers collaborated with a team from the University of South Carolina to see exactly how a shark's unique skin could boost the performance of aerospace technology. And the similarities between sharks and airplanes (on the surface level at least) are there; both have evolved over time to move efficiently through a fluid, and their body shape assists in generating lift and decreasing drag. 

"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, the Henry Bryant Bigelow Professor of Ichthyology and Professor of Biology in the Department of Organismic and Evolutionary Biology, and co-author of the research. "We know a lot about the structure of these denticles -- which are very similar to human teeth -- but the function has been debated."

However, one major theory around shark denticles is that they're a sort of drag-reducing adaptation. The Harvard team considered that theory and then looked at the accompanying force -- lift. Medi Saadat is a postdoctoral fellow at Harvard and a co-first author of the study. Saadat also has a joint appointment in Mechanical Engineering at the University of South Carolina. He was one of the first to suggest a non-drag-related explanation. 

"We asked, what if instead of mainly reducing drag, these particular shapes were actually better suited for increasing lift," he said. 

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In order to test the theory, the researchers looked for the fastest shark they could find -- the Mako. The shortfin mako can top out at speeds anywhere between 50 to 60 mph, earning it the name "the speed demon." The mako has three unique ridges on its denticles. The researchers analyzed those small scales through micro-CT scans. They then created a 3D rendering of the model and 3D printed the denticles on to an airfoil (surface of a wing with a curved aerodynamic cross-section). 

"Airfoils are a primary component of all aerial devices," said August Domel, a Ph.D. student at Harvard and 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, airplanes, and wind turbines."

The team tried out over 20 different styles of denticles and ultimately discovered that it increased lift while doubling as high-powered, low-profile vortex generators. 

Vortex generators are passive devices that change the airflow over the surface of a moving object like a car or a plane to make it more aerodynamic. The shark-inspired vortex generators managed to improve ratios of lift-to-drag by 323 percent compared to airfoils without the generators.  

"You can imagine these vortex generators being used on wind turbines or drones to increase the efficiency of the blades," said Katia Bertoldi, William and Ami Kuan Danoff Professor of Applied Mechanics at SEAS and co-author of the study. "The results open new avenues for improved, bioinspired aerodynamic designs."