Engineering mechanics found in nature
As we continue on the previous week’s blog which examined the biomimicry seen in shark skin, this week’s blog will look at a similar aquatic animal that can benefit many engineers that are working towards better aerodynamics technology, both in and out of the water. This week we look at the whale, or more specifically, a humpback whale fin and its characteristics that can be mimicked within the engineering fields. Even though whales can be 40-50 feet long and weigh in excess of 80,000 pounds they are some of the most agile and dexterous creatures in the ocean due in large part to their unconventional fin shape. By examining the properties of a whales fin, engineers are looking to redesign and improve many current technologies that deal with drag, lift and the entire field of aerodynamics.
Even with their immense size whales have amazing control over their movement due to their flippers. These flippers have large, irregular bumps called tubercles across their leading edge. A sheet of water that flows over a smooth surface will break into groups of turbulent vortices which increase drag and decrease lift. However, the bumps on a whale’s fin allow the water to form into fast-moving channels which allow the whale to maintain speed even as they bank at sharp angles while maintaining very low speed. A study at Duke University placed whale fin models in a wind tunnel and compared the bumpy flipper to a conventional smooth wing. The results showed that the flipper had nearly 8% better lift, 32% lower drag and could withstand stall at a 40% steeper angle
[i],. Stall is the dramatic and abrupt loss of lift due to angle of ascent.[ii] A whale fin works quite the opposite of a golf ball’s divots because as air passes over a golf ball, its flow becomes less and less attached to the ball whereas in the whale fin, it becomes more attached to the surface as it passes over.
Technological applications available
While the application possibilities are vast, the only current application in use for whale fin biomimicry is in wind turbines. Due to the fin’s ability to handle steep angles while avoiding stall, the turbine blades can be oriented at a higher angle to capture more of the wind without worrying about the severe damage that stalling causes.[iii] Capturing more of the wind creates more energy and leads to less turbines being needed as the efficiency continues to increase with current research. Using computational fluid dynamics simulations, many mechanical engineers are attempting to scale the size of the fin to smaller version to be used in commercialized industrial fans. By replacing conventional blades with whale fin shaped blades, the fans can move more are and ventilate a larger area with fewer blades, use 20% less power and only generate one fifth of the noise. Another obvious field to look into with whale fin technology is in airplanes: however major advancements have yet to be achieved. In theory it would allow the plane to operate at higher angles due to its stall capabilities. Some 3D-CAD models and simulations also show that by utilizing the characteristics found in the makeup of the whales fin, they could generate enough lift to allow the elimination of the heavy mechanical components that are needed to add lift to current airplane wings. Eliminating this extra weight, along with the increase in lift and decrease in drag, would make it much more economical for airplanes to fly and which would make it more cost-effective to fly or allow for more fuel storage and therefore increased flight range. In military applications, the ability to create lighter, faster and more maneuverable aircraft has always been the focal point when it comes to plane designs.
[i] Fish, F.E.; Battle, J.M. “Hydrodynamic Design of the Humpback Whale Flipper” 1995 J. Morphol 225 pg 51-60
[ii] MongaBay.com “Whale Biomimicry Inspires Better Wind Turbines” July 7, 2008
[iii] Marshall, Jessica Discovery News “Whales, Dolphins Inspire Wind Turbine Tech” July 11, 2008