With their smooth, flexible fins, stingrays are extraordinarily efficient swimmers 鈥� but their eyes and mouth stick out, which intuitively seems like it would create drag and slow them down. It turns out that these bulging faces have the opposite effect, allowing stingrays to swim even faster and more efficiently.
at the Korea Advanced Institute of Science and Technology in South Korea and his colleagues investigated how the protruding eyes and mouths of stingrays affect how they move through the water using a series of hydrodynamic simulations. Some of the simulated rays had eyes and mouths, some only had one or the other, and some were completely smooth.
They found that the protrusions created a set of vortices as the water moved over them. One vortex pushed water towards the back of the ray, leaving an area of lower pressure in front of it. This low-pressure zone allowed the simulated rays to swim faster.
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Another vortex sloshed water to the sides, increasing the pressure below the ray and decreasing the pressure above it. This made each stroke of the fins generate more thrust, increasing the efficiency of swimming.
Sung says that he was 鈥渧ery surprised鈥� at these results, particularly at the magnitude of the effect 鈥� the analysis showed that stingrays鈥� eye protrusions increased their propulsion efficiency compared to rays without these features by about 20.5 per cent, and their mouth increased it by about 10.6 per cent.
These vortices only appear because the rays have bendy bodies with rigid eyes and mouths, says Sung. Similar effects may help other flexible, self-propelling animals move more quickly as well. He and his team are now trying to incorporate this knowledge into designs for efficient water vehicles that mimic the motions of sea creatures.
Physics of Fluids
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