Science

Shark's bristling scales make it faster, and may help make planes faster too

A shortfin mako shark in the North Atlantic, near the Azores
A shortfin mako shark in the North Atlantic, near the Azores
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A close-up view of a front row of the denticles, from a shortfin mako's flank behind its gills – they've been manually bristled for the photograph
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A close-up view of a front row of the denticles, from a shortfin mako's flank behind its gills – they've been manually bristled for the photograph
A shortfin mako shark in the North Atlantic, near the Azores
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A shortfin mako shark in the North Atlantic, near the Azores

Capable of swimming at speeds of up to 74 km/h (46 mph), the shortfin mako is the world's fastest species of shark. Scientists now have a new understanding of how it's able to reach such speeds, and they believe that their findings could be applied to improving human technology.

As is the case with other sharks, the skin of the shortfin mako is covered with tiny scales known as denticles. These are angled back from the front of the fish, so the skin feels smooth if you run your hand along it from nose to tail, but rough if you go "against the grain" in the other direction.

Led by astronautical engineer Amy Lang, a team from the University of Alabama discovered that on key parts of the shortfin mako, those 0.2-mm-long scales (pictured below) are capable of flexing up to an angle of 40 degrees out from the body. They do so in response to reverse water flow, which occurs due to a phenomenon known as flow separation.

A close-up view of a front row of the denticles, from a shortfin mako's flank behind its gills – they've been manually bristled for the photograph
A close-up view of a front row of the denticles, from a shortfin mako's flank behind its gills – they've been manually bristled for the photograph

In a nutshell, flow separation happens when fluid passes around the front of an object that's travelling through a liquid environment (or that's held in moving liquid), forming eddies alongside its back end. Those eddies create drag, slowing the object down – this effect can hamper both watercraft and aircraft, as it also occurs in the air.

Thanks to the mako's pop-out denticles, though, flow separation is greatly minimized along the length of its body. The protruding scales help prevent the formation of eddies, allowing the fish to move faster through the water. This beneficial effect was observed when the researchers placed samples of shortfin mako flank skin in a water-flow tunnel.

"We set up an experiment in the tunnel with a measured amount of flow separation induced on a smooth surface. Then we replaced the smooth surface with shark skin and requantified the flow separation," says Lang. "In all cases with the flank skin, we saw the size of the separated flow region reduced significantly by the presence of the skin."

It is now hoped that the research could lead to new materials for use on fixed-wing airplanes and the rotor blades of helicopters, making them more aerodynamic.

Source: American Physical Society via EurekAlert

4 comments
SimonClarke
The University of Alabama aught to check the records before conducting this research. This type of study resulted in a film that was applied to aircraft skin in the 80's/90's by Airbus. I think it has also been covered in New Atlas recently too.
Bionic88
I'm in the aviation community and this is the first I've heard of this..not saying it hasn't been in development. But I know something similar has been used in the automotive race industry..most recently I've seen it in video discussing a covering developed for a Salt Flats(pretty sure) motorcycle. As noted, golf ball dimples popped in my head when I first heard of it. "...astronautical engineer Amy Lang" aka rocket scientist.
Nobody
How does this compare to a dolphin which is also very fast and has skin as smooth as a wet inner tube? While diving I have had dolphin swim past me inches away and never felt the water move.
Martin Hone
Interesting but nothing new. Vortex generators do the same thing on aircraft now, mainly to re-attach airflow after separation, and lowering the stall speed. Not so much for speed.
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