Sharks are typically considered to be aerodynamic creatures with specially designed skin that allows them to glide through the water with speed and precision, but a new study found that the denticles, or scales, on shark skin can actually increase drag.
A team led by Fotis Sotiropoulos, Ph.D., dean of the College of Engineering and Applied Sciences at Stony Brook University, in collaboration with the University of Minnesota used computer modeling to visualize how water flows around the sheets of denticles found on shark skin.
In order to do the computer modeling, Sotiropoulos and his team created different arrangements of shark skin by using data from a collaborator at Harvard on the three-dimensional geometry of the denticles on shortfin mako sharks.
They then applied simulations in order to more precisely study the flow of water through and over the beds of denticles.
Instead of allowing sharks to easily move through the water, the specific arrangement of denticles can increase drag by up to 50 percent, according to the simulation.
This effect could be due to the complex three-dimensional structure of denticles, which alters viscous stress and the flow patterns of water.
“Our work is also a great example of the power of computer simulations, which today have advanced to the point that they can be used as a tool of scientific discovery,” Sotiropoulos said.
On the other hand, riblets, engineered for commercial use to mimic the structure of denticles, reduced drag by 5 percent.
Companies have used riblets for drag-resistant swimsuits, aerodynamic airplane wings, and improved wind turbine blades to harness energy.
“This is a great example where a bio-inspired engineering solution, that of riblets, turned out to work much better than that of the natural shark skin which motivated its development,” Sotiropoulos said.
In the future, Sotiropoulos said the team plans to further “develop the computational model to account for the flexibility of the shark body.” He also said they intend to investigate how shark skin performs during swimming to better understand the drag and pressure forces that occur as sharks move through the water.
