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Body decreases swimming energy using vortices: bull trout

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Von Kármán Vortices over Aleutian Islands, Alaska / U.S. Geologi.. / LicensePD - Public Domain

Body of bull trout decreases energy required for swimming by using vortices in its liquid environment.

FUNCTION
Summary
To swim, many fish use an undulating motion that expends a great deal of energy. Some fish, such as trout, have adopted a special swimming motion that enables them to better conserve energy: using water vortices.
 
In a liquid environment, vortices are swirls of water often released from stationary objects and other living creatures, including other fish. Trout use these water vortices to their advantage by adjusting their bodies to produce a ‘slalom’ movement. To do this, they move the muscles closest to their head away from the center of a vortex force while moving the muscles nearest their tail toward it. In this way, they maneuver in between the vortices and push off of the swirling water. 

Check out these videos to see the trout's slalom movement in action.

This summary was contributed by Ashley Meyers.
Excerpt
"Researchers are studying how fish use surrounding vortices to provide an energy boost. Vortices can come from other fish or stationary objects. Conventional wind turbines need a steady wind, so use of eddies would require a new design. Vortices in water alternately spin clockwise and counter-clockwise. Similarly, a wind turbine that uses eddies caused by buildings would need to be able to adjust to varying angles. Dabiri has developed prototypes for both air and water. While they may produce less energy than a wind turbine, they can work over a longer period so the net energy produced per year should be similar." (Courtesy of the Biomimicry Guild)

"Aquatic animals swimming in isolation and in groups are known to extract energy from the vortices in environmental flows, significantly reducing muscle activity required for locomotion. A model for the vortex dynamics associated with this phenomenon is developed, showing that the energy extraction mechanism can be described by simple criteria governing the kinematics of the vortices relative to the body in the flow. In this way, we need not make direct appeal to the fluid dynamics, which can be more difficult to evaluate than the kinematics. Examples of these principles as exhibited in swimming fish and existing energy conversion devices are described. A benefit of the developed framework is that the potentially infinite-dimensional parameter space of the fluid–structure interaction is reduced to a maximum of eight combinations of three parameters. The model may potentially aid in the design and evaluation of unsteady aero- and hydrodynamic energy conversion systems that surpass the Betz efficiency limit of steady fluid dynamic energy conversion systems." (Dabiri 2007:L1)

"Fishes moving through turbulent flows or in formation are regularly exposed to vortices. Although animals living in fluid environments commonly capture energy from vortices, experimental data on the hydrodynamics and neural control of interactions between fish and vortices are lacking. We used quantitative flow visualization and electromyography to show that trout will adopt a novel mode of locomotion to slalom in between experimentally generated vortices by activating only their anterior axial muscles. Reduced muscle activity during vortex exploitation compared with the activity of fishes engaged in undulatory swimming suggests a decrease in the cost of locomotion and provides a mechanism to understand the patterns of fish distributions in schools and riverine environments." (Liao et al. 2003:1566)

"Simultaneous visualization of a two-dimensional, horizontal slice through the columnar vortices generated by the D-section cylinder (¡5) using digital particle image velocimetry (DPIV) (19) and the movements of trout with high-speed video revealed that trout slalom between vortices rather than through them…If the flow is decomposed into a downstream…and a lateral (z axis) component, slaloming between vortices occurs when trout move against the downstream flow but with the local lateral flow, Slaloming through oncoming vortices requires opposing the local lateral flow. Actuated foils generate more thrust if they slalom through rather than between Kármán vortices (20), but they require more power input to oppose the instantaneous local flow. Trout slalom between rather than through vortices and, thus, minimize power input rather than maximize thrust output. To quantify the movement of trout near vortices, we described the phase relation between the lateral motions of points along the body relative to the arrival of drifting vortices…When the center of a vortex drifted down to the center of mass (COM) of the fish, the COM was at its maximum lateral excursion away from the vortex, indicated by a phase relation of 180°. For all points anterior to the COM, the body moved away from an oncoming vortex (<1SO°), whereas body points posterior to the COM move toward the vortex (>I8O°). A phase relation of 0° or 360° would indicate that the fish had intercepted the center of a vortex." (Liao et al. 2003:1567)

“...an array of mechanosensory cells distributed along the body of most fish, potentially enables them to detect pressure discontinuities so as to select favourable hydrodynamic conditions in the flow” (Sutterlin & Waddy 1975; Braun & Coombs 2000).

Note: Studies were on trout, not specifically bull trout.
About the inspiring organism
Bull trout
Salvelinus confluentus (Suckley, 1859)
Common name: Bull trout

Learn more at EOL.org
Some organism data provided by: FishBase
Organism/taxonomy data provided by:
Species 2000 & ITIS Catalogue of Life: 2008 Annual Checklist


Bioinspired products and application ideas

Application Ideas: Wind turbines that work using eddies around large buildings or other large structures. Ocean energy devices that use eddies to generate energy.

Industrial Sector(s) interested in this strategy: Construction, energy, architecture, transportation



Experts
Dabiri Lab
John Dabiri
Stanford University
Lauder Laboratory
George V. Lauder
Harvard University
References
Dabiri, J. O. 2007. Renewable fluid dynamic energy derived from aquatic animal locomotion. BIOINSPIRATION AND BIOMIMETICS. 2(3): 1.
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Liao, J. C.; Beal, D. N.; Lauder, G. V.; Triantafyllou, M. S. 2003. Fish Exploiting Vortices Decrease Muscle Activity. Science. 302(5650): 1566.
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Whittlesey RW; Liska S; Dabiri JO. 2010. Fish schooling as a basis for vertical axis wind turbine farm design. BioInspiration and Biomimetics. 5(3):
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Beal, D.N.; Hover, F.S.; Triantafyllou, M.S.; Liao, J.C.; Lauder, G.V. 2006. Passive Propulsion in Vortex Wakes. Journal of Fluid Mechanics. 549: 385-402.
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