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full text from: http://www.sciencedaily.com/releases/2009/06/090626091127.htm
Dolphins Get A Lift From Delta Wing Technology
ScienceDaily (June 28, 2009) — We can only
marvel at the way that dolphins, whales and porpoises scythe through
water. Their finlike flippers seem perfectly adapted for maximum
aquatic agility. However, no one had ever analysed how the animals’
flippers interact with water; the hydrodynamic lift that they
generate, the drag that they experience or their hydrodynamic
efficiency. Laurens Howle and Paul Weber from Duke University teamed
up with Mark Murray from the United States Naval Academy and Frank
Fish from West Chester University, to find out more about the
hydrodynamics of whale and dolphin flippers.
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They publish their finding that some dolphins’ fins generate lift
in the same way as delta wing aircraft in The Journal of
Experimental Biology.
Using Computer tomography scanning of the fins of seven different
species ranging from the slow swimming Amazon River dolphin and
pygmy sperm whale to the super-fast striped dolphin, the team made
scaled models of the flippers of each species. Then they measured
the lift and drag experienced by the flipper at inclinations ranging
from -45deg. to +45deg. in a flow tunnel running at a speed that
would have been the equivalent of 2m/s for the full scale fin.
Comparing the lift and drag coefficients that the team calculated
for each flipper at different inclination angles, they found that
the flippers behave like modern engineered aerofoils. Defining the
flippers’ shapes as triangular, swept pointed or swept rounded, the
team used computer simulations of the fluid flows around the
flippers and found that sweptback flippers generate lift like modern
delta wing aircraft. Calculating the flippers’ efficiencies, the
team found that the bottle nose dolphin’s triangular flippers are
the most efficient while the harbour porpoise and Atlantic
white-sided dolphin’s fins were the least efficient.
Commenting that environmental and performance factors probably
play a significant role in the evolution of dolphin and whale
flipper shapes and their hydrodynamics, Howle and his colleagues are
keen to find out more about the link between the flippers’
performances and the environment that whales and dolphins negotiate
on a daily basis.
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Journal reference:
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Weber, P. W., Howle, L. E., Murray, M. M. and Fish, F. E. **Lift
and drag performance of odontocete cetacean flippers**. <em>J.
Exp. Biol.</em>, 212, 2149-2158
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