Undulating Skin Results In 50% Less Drag

On Mon, 21 Apr 2008 14:31:15 -0500, Big John
wrote in :

Didn't one or more of the America's Cup sail boats have something like
this in one of the last sail off's?

Is this it?


http://www.newscientist.com/article/...fect-skin.html
Researchers have known for years that fast-swimming sharks are
covered with renewable scales, called dermal denticles, that have
microscopic ridges. Just what these ridges did was a mystery until
the 1980s when specialists in aerodynamics developed a way of
smoothing turbulent flow using microscopic surface grooves that
are aligned with the movement of fluid. These grooves are called
riblets. "There are very close connections between riblets and
shark skins," says Kwing-So Choi, a mechanical engineer at the
University of Nottingham specialising in drag reduction.

Riblets work by making turbulence more ordered near the surface.
"They are like tiny fences that prevent the lateral movement of
turbulence across the flow," says Choi. While any lateral movement
is hindered, any flow that is parallel with the riblets continues
unabated. "If you optimise the size and shape of the riblets, a
drag reduction of up to 10 per cent is possible."

Riblets have already been tested in real applications. Their
biggest claim to fame was as a putative contributor to the sailing
coup in 1987 when the US won the America's Cup, the prestigious
yachting trophy. The American boat had a riblet coating on its
hull, a development that was later banned by race officials. Other
mariners have been slow to follow suit because riblets are easily
clogged by microscopic marine debris. A more promising application
is in aircraft, where fouling is less of a problem. Such riblets
are already in use on some commercial airliners.


It sounds different from the active skin in the more recent article.

Larry Dighera wrote in
:

On Mon, 21 Apr 2008 14:31:15 -0500, Big John
wrote in :

Didn't one or more of the America's Cup sail boats have something like
this in one of the last sail off's?

Is this it?


http://www.newscientist.com/article/...-secrets-of-a-
perfect
-skin.html
Researchers have known for years that fast-swimming sharks are
covered with renewable scales, called dermal denticles, that have
microscopic ridges. Just what these ridges did was a mystery until
the 1980s when specialists in aerodynamics developed a way of
smoothing turbulent flow using microscopic surface grooves that
are aligned with the movement of fluid. These grooves are called
riblets. "There are very close connections between riblets and
shark skins," says Kwing-So Choi, a mechanical engineer at the
University of Nottingham specialising in drag reduction.

Riblets work by making turbulence more ordered near the surface.
"They are like tiny fences that prevent the lateral movement of
turbulence across the flow," says Choi. While any lateral movement
is hindered, any flow that is parallel with the riblets continues
unabated. "If you optimise the size and shape of the riblets, a
drag reduction of up to 10 per cent is possible."

Riblets have already been tested in real applications. Their
biggest claim to fame was as a putative contributor to the sailing
coup in 1987 when the US won the America's Cup, the prestigious
yachting trophy. The American boat had a riblet coating on its
hull, a development that was later banned by race officials. Other
mariners have been slow to follow suit because riblets are easily
clogged by microscopic marine debris. A more promising application
is in aircraft, where fouling is less of a problem. Such riblets
are already in use on some commercial airliners.


It sounds different from the active skin in the more recent article.


It is and it isn't. The riblets on shark skins are more closely related
to vortex generators.



Bertie