Designing better drones, planes, and wind turbines using shark scales

Bioinspired vortex generators increase airfoil lift, decrease drag.

Designing better drones, planes, and wind turbines using shark scales
A team of evolutionary biologists and engineers at Harvard has demonstrated a new structure, inspired by sharkskin, that could improve the aerodynamic performance of planes, wind turbines, drones, and cars. Courtesy of James Weaver/Harvard University

A team of evolutionary biologists and engineers at Harvard University in collaboration with colleagues from the University of South Carolina has demonstrated a novel framework instigated by sharkskin, which could ameliorate the aerodynamic performance of planes, wind turbines, drones, and cars.

During this improbable study, researchers elucidate a decades-old mystery about sharkskin and discovered bioinspired framework. They investigated sharks and airplanes are not completely distinct. Both are framed to efficiently move through a fluid (water and air), utilizing the shapes of their bodies to produce lift and reduce drag. The difference is sharks have a 400-million-year head short on the design process.

George Lauder, the Henry Bryant Bigelow Professor of Ichthyology and professor of biology in the Department of Organismic and Evolutionary Biology, 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.”

“We know a lot about the structure of these denticles — which are very similar to human teeth — but the function has been debated.”

Utmost of the research has focused on the drag-reducing properties of denticles, but Lauder and his team wondered if there was more to the story.

Mehdi Saadat, a postdoctoral fellow at Harvard, said, “We asked, what if instead of mainly reducing drag, these particular shapes were actually better suited for increasing lift.”

Outbid to assist test that hypothesis, the researchers collaborated with a team of engineers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS). 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 modeled the denticles in three dimensions. Further, the 3-D printed the shapes on the surface of a wing with a curved aerodynamic cross-section, known as an airfoil.

August Domel, a Ph.D. student at Harvard’s Graduate School of Arts and Sciences said, “Airfoils are a primary component of all aerial devices.”

“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 group of investigators tested 20 distinct configurations of denticle sizes, rows, and row positions on airfoils under a water flow tank. They discovered that in addition to reducing drag, the denticle-shaped structures particularly raised lift, acting as high-powered, low-profile vortex generators.

Even if you are not aware what a vortex generator is, you have seen one in action. Cars and planes are equipped with these small, passive devices that alter how air flows 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.

Domel stated, “These shark-inspired vortex generators achieve lift-to-drag ratio improvements of up to 323 percent compared to an airfoil without vortex generators.”

“With these proof-of-concept designs, we’ve demonstrated that these bioinspired vortex generators have the potential to outperform traditional designs.”

Katia Bertoldi, William and Ami Kuan Danoff Professor of Applied Mechanics at SEAS 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.”

Lauder added, “This research not only outlines a novel shape for vortex generators but also provides insight into the role of complex and potentially multifunctional shark denticles.”

The research was co-authored by James Weaver of the Wyss Institute for Biologically Inspired Engineering at Harvard, and Hossein Haj-Hariri, dean of engineering and computing at the University of South Carolina. This research was supported by Office of Naval Research and the National Science Foundation.

The study is published in the Journal of the Royal Society Interface.