Dolphin Boundary layer on YouTube

James Gray, an English Zoologist discovered that dolphins managed to
attain speeds in the water that exceeded the power limit calculated for
their muscles by a factor of seven. This paradox led researchers to
investigate what phenomena accounted for this apparent discrepancy
between hydrodynamic theory and physical observation. While some have
questioned Gray’s calculations, others like Jim Rohr at the University
of California in San Diego have sought answers to this paradox by
studying the fluid dynamics. Using bioluminescent dinoflagellates as
visual signals and enhanced video recording equipment, he was able to
assess the boundary layer over the dolphins body surface at speeds of 2
m/s. These organisms give off light when the fluid layers around them
are subject to stresses τwall≈0.1Nm−2. He then studied the enhanced
recordings and proposed a solution to Gray’s paradox. Research revealed
that the dinoflagellates failed to light up in regions on the dolphin’s
body where the boundary layer is thinner. He concluded that their shape
creates an optimal boundary layer for greater speeds with less energy.

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