Study Shows Sharkskin Increases Drag by 50 Percent
Surprise results of computational models by a Stony Brook Professor and colleagues stirs the academic debate about sharkskin and swimming speed
Computer simulations unveil flow around shark skin
Stony Brook, NY, March 15, 2016 – The nature of sharkskin with its riblets – the micro-grooved structures found in aircraft wings, wind turbine blades, and Olympic-class swimsuits – seems to suggest a design for speed and streamlined swimming. But a new study led by Stony Brook University using computational models demonstrates that the denticles that make up mako shark skin increase hydrodynamic drag by up to 50 percent. The study is published this week in the journal Physics of Fluids.
Sharskin’s ability to reduce hypodynamic drag has been academically contested for the past 30 years. Fotis Sotiropoulos, PhD, Dean of the College of Engineering and Applies Sciences at Stony Brook University and lead investigator of the project, teamed up with researchers at Stony Brook and the University of Minnesota to conduct simulations on the ability of the small, tooth-like denticles that make up sharkskin to modify hydrodynamic flow with an unprecedented level of resolution. From the results of the simulations they found that the denticles did not east the glide through the water but actually increased the drag significantly.
Sotiropoulos’ previous work focused on developing computational tools to study the evolutionary impact of hydrodynamic factors on fish body shapes and swimming styles. He and his PhD student, Aaron Boomsma, discuss their work exploring the hydrodynamics of sharkskin in the paper, titled “Direct numerical simulation of sharkskin denticles in turbulent channel flow.”
“The work on sharkskin was a natural progression, especially after observing the commonalities between sharkskin and riblet films,” said Sotiropoulos. “Our interest was piqued by the thought that sharkskin was capable of providing a hydrodynamic advantage to sharks.”
Sotiropoulos and his colleagues used experimental data about the three-dimensional geometry of shortfin mako shark denticles provided by George Lauder, a professor of organismic and evolutionary biology at Harvard University, to create computational beds of sharkskin denticles in aligned and staggered configurations. They then applied numerical simulations based on immersed boundary concepts to study the details of turbulent water flow through and over the stationary denticle beds.
“Our simulations show conclusively, that for the tested configurations, sharkskin actually increases drag—as high as fifty percent,” Sotiropoulos said.
The researchers also simulated the same flow over riblets, finding that they reduced drag by 5 percent.
This disparity arises due to differences between the objects’ geometries: riblets are able to confine viscous stress along their ridges because they’re essentially two-dimensional, whereas the complex three-dimensional features of denticles generate turbulence and swirling flow patterns that complicate the confinement of viscous stress.
“This is a great example of how our attempts to get inspired by nature have led to something truly beneficial, even though the functionality of the original natural construct may not be as simple to explain or understand,” said Sotiropoulos.
Future work for Sotiropoulos and his colleagues includes expanding their work to understand how sharkskin denticles perform under swimming conditions and its subsequent pressure forces. Sotiropoulos noted, however, that next-generation super computers are needed to gain a full understanding of this interplay.
About Stony Brook University
Part of the State University of New York system, Stony Brook University encompasses 200 buildings on 1,450 acres. Since welcoming its first incoming class in 1957, the University has grown tremendously, now with more than 25,000 students and 2,500 faculty. Its membership in the prestigious Association of American Universities (AAU) places Stony Brook among the top 62 research institutions in North America. U.S. News & World Report ranks Stony Brook among the top 100 universities in the nation and top 40 public universities, and Kiplinger names it one of the 35 best values in public colleges. One of four University Center campuses in the SUNY system, Stony Brook co-manages Brookhaven National Laboratory, putting it in an elite group of universities that run federal research and development laboratories. A global ranking by U.S. News & World Report places Stony Brook in the top 1 percent of institutions worldwide. It is one of only 10 universities nationwide recognized by the National Science Foundation for combining research with undergraduate education. As the largest single-site employer on Long Island, Stony Brook is a driving force of the regional economy, with an annual economic impact of $4.65 billion, generating nearly 60,000 jobs, and accounts for nearly 4 percent of all economic activity in Nassau and Suffolk counties, and roughly 7.5 percent of total jobs in Suffolk County.
Media Relations Manager
School of Medicine
Stony Brook University
Office of Communications and Marketing