The image above is of Associate Professor Dr. Laurens Howle, Duke University, WhalePower’s lead engineer. Dr. Howle has spent the last two decades exploring how and why tubercles make rotary devices more efficient. For a detailed explanation of why and how Tubercle Technology works, please read our white paper on the Operation of Tubercle Airfoils rev 5.4.
Major discoveries, like the importance of tubercles, always come with a story: Newton had his apple, Archimedes had his bath tub, and Dr. Frank E. Fish, while shopping for a gift, examined a sculpture of a humpback whale in a shop and issued a fatefully inaccurate observation: “Look at that. The sculptor put the bumps on the wrong side of the flipper.”
The shop manager quickly set him straight. She knew the sculptor’s work and that the sculptor knew humpbacks: That’s where the bumps should be. A quick check and Frank was convinced the artist got it right. But if the artist was right then at least part of the science of fluid dynamics was wrong. How could that be?
As it turns out, what the bumps on the humpback’s flipper are for is a deceptively difficult question and one that can only be answered with a combination of two of the most complex and difficult branches of science: fluid dynamics and biomechanics.
Fortunately, the question occurred to the right person: Frank Fish runs the Liquid Life Lab at West Chester University where he has carved out a reputation as one of the world’s leading experts on the biomechanics of how animals from tiny minnows to beavers and whales swim. His expertise has won him research awards and has even led to grants from the Office of Naval Research and DARPA, (the Defence Advanced Research Projects Agency).
Until Frank Fish asked his question, everyone studying airfoils and hydrofoils and the like “knew” that the leading edge of these devices had to be smooth and streamlined. They had proved that even insect debris stuck to the leading edges of wind turbine rotors, for example, could damage performance. What were the bumps doing on those flippers?
Working in his lab and with a variety of collaborators, Frank set out to find answers. He published a paper outlining his thoughts on the matter before he engaged Dr. Phil Watts to help with some of the fluid dynamics analysis, which they published. Along the way, Dr. Fish and Dr. Watts filed for a patent which was granted. (US Patent 6,431,498)
Then, Frank hooked up with his friend and fellow consultant to the Navy, Dr. Laurens E. Howle (above), who just happens to be one of the leading lights in fluid dynamics. Together they enlisted the help of two Navy engineers and the Naval Academy’s Wind Tunnel and with the support of the Academy’s research funds and the US National Research Council, they designed a remarkable experiment to test tubercle performance scientifically by comparing the performance of an unmodified airfoil to one with the same basic shape and surface area but with a tubercle leading edge. The surprising results, published in the leading scientific journal, The Physics of Fluids, made news in the scientific press around the world. Science and Scientific American ran news stories. Science News ran a feature. Even The Journal of Experimental Biology got into the act.
Tubercle Technology was on the map.
Since that time, more scientific research, much of it led by Fish and Howle, has yielded unprecedented discoveries.
- The 16 degree stall angle found in the first wind tunnel experiment has been enhanced to produce airfoils that don’t stall until they reach an astounding 31 degrees – far above anything previously known.
- Unlike virtually every other airfoil which can stall violently and even damage the machines they‘re employed on, tubercle airfoils always stall gradually. That changes the rules for turbines — forever.
CFD Analysis of Leading Edge Tubercle Effects on Wind Turbine Performance, Giada Abate and Dimitri N. Mavris., 15th International Energy Conversion Engineering Conference, AIAA Propulsion and Energy Forum, (AIAA 2017-4626), 2017.
CFD study on NACA 4415 airfoil implementing spherical and sinusoidal Tubercle Leading Edge, S.M.A. Aftab, K.A. Ahmad, PLOS 1 2017: 12 (8), 2017.
Hydrodynamic performance evaluation of a tidal turbine with leading-edge tubercles, Weichao Shi, Roslynna Rosli, Mehmet Atlar, Rosemary Norman, Dazheng Wang, Wenxian Yang, Ocean Engineering Vol 117, 2016.
Characterization and Design of Tubercle Leading-Edge Wings, Mark W. Lohry, David Clifton and Luigi Martinelli. Corresponding author: email@example.com. Department of Mechanical and Aerospace Engineering at Princeton University, Princeton, NJ 08544, USA, July 2012.
Performance Variations of Leading-Edge Tubercles for Distinct Airfoil Profiles, Kristy L. Hansen, Richard M. Kelso, and Bassam B. Dally. AIAA Journal, Vol. 49, No. 1 (2011), pp. 185-194, 2011.
Abstract: HC.00006 : Effect of Leading Edge Tubercles on Marine Tidal Turbine Blades , American Physical Society, November 23, 2010.
Abstract: ET.00004 : Explanation of the effects of leading-edge tubercles on the aerodynamics of airfoils and finite wings, American Physical Society. November 21, 2010.
Reduction of Flow Induced Tonal Noise through Leading Edge Tubercle Modifications, American Institute of Aeronautics and Astronautics, K.L. Hansen, R.M. Kelso, C.J. Doolan, School of Mechanical Engineering, The University of Adelaide, Adelaide, Australia, June 2010. (no link available)
The Effect of Leading Edge Tubercle Geometry on the Performance of Different Airfoils, American Institute of Aeronautics and Astronautics, K.L. Hansen, R.M. Kelso, C.J. Doolan, School of Mechanical Engineering, The University of Adelaide, Adelaide, Australia, June 2010. (no link available)
Humpback whales inspire new wind turbine technology: The unique design of their flippers enable a steeper operating angle of the blade—and a 40% performance increase, Tribology and Lubrication Technology, Dr. Neil Cantor (contributing editor), December 2008
Bumpy Whale Fins Outperform Smooth Turbines – Scientific American, July 8th, 2008
Whales and Dolphins Influence New Wind Turbine Design – ScienceDaily, July 8th, 2008
Going with (or Against) the Flow – Science, June 6th, 2008
Green Breeze – Material Handling Management, June, 2008
Whale-Inspired Wind Turbines – MIT Technology Review, March 6th, 2008
Lifting a whale – Nature, February 20th, 2008
How Bumps on Whale Flippers Delay Stall: An Aerodynamic Model– Physical Review Letters, February 8, 2008
Abstract: AB.00011 : Rationalizing the bumps on whale flippers using basic aerodynamic theory -American Physical Society, November 19, 2006
Abstract: EO.00003 : Spanwise visualization of the flow around a three-dimensional foil with leading edge protuberances -American Physical Society, November 19, 2006
Abstract: EO.00004 : Separation Control on a Hydrofoil Using Leading Edge Protuberances – American Physical Society, November 19, 2006
Passive and active flow control by swimming fishes and mammals – Annual Review of Fluid Mechanics, 2006
Stall delay by leading edge tubercles on humpback whale flipper at various sweep angles – Proceedings of the 14th International Symposium on Unmanned Untethered Submersible Technology, Autonomous Undersea Systems Institute, Murray , M. M., Fish, F. E., Howle, L. E. and Miklosovic, Durham New Hampshire .D. S. 2005.
Bumpy Flying – Scientific American, August 2004
Leading Edge Tubercles Delay Stall on Humpback Whale (Megaptera Novaeangliae) Flippers – Physics of Fluids, May 2004
General-purpose parallel unsteady RANS CFD code for ship hydrodynamics– IIHR Hydroscience and Engineering Report 531, The University of Iowa , Iowa City , Iowa, 2003
The influence of passive, leading edge tubercles on wing performance – Proceedings of the Twelfth International Symposium on Unmanned Untethered Submersible Technology, Autonomous Undersea Systems Institute, Durham, New Hampshire, 2001
Suppression of Karman Vortex Shedding – Phys. Fluids 12; n9: S9, 2000
Hydrodynamic design of the humpback whale flipper – J. Morph, 1995
Review of the physics of enhancing vortex lift by unsteady excitation – Prog. Aerospace Sci. 28, 1991
Drag reduction in Nature – Ann. Rev. Fluid Mech. 1991