Undulating Skin Results In 50% Less Drag

On Mon, 21 Apr 2008 16:57:03 GMT, Larry Dighera
wrote:


If this technique can be adapted to gliders and other aircraft,
imagine the enabling effect it will produce:



http://technology.newscientist.com/c...-and-subs.html
Shape-shifting skin to reduce drag on planes and subs

* 13:30 16 April 2008
* NewScientist.com news service
* Colin Barras

Engineers have shown skin able to tune its wrinkles could cut
dramatically cut drag on submarines or planes (Image: IOP)
Engineers have shown skin able to tune its wrinkles could cut
dramatically cut drag on submarines or planes (Image: IOP)

Aircraft or submarines covered with an undulating skin able to
change at a flick of a button would experience 50% less drag than
conventional vehicles. This trick, which naturally occurs in
dolphins, is now being tested by human engineers.

Turbulence is the bane of engineers' lives. Chaotic air flow sets
up unstable vortices and patterns in gases and liquids, increasing
friction and drag.

Giving craft skin than can tweak its surface to impose order on
these currents could dramatically cut the effect of drag, says
Dimitris Lagoudas at Texas A&M University, US. Calming the chaotic
waves makes them interact less with the skin. "The particles in
the fluid stop "speaking" to the craft’s surface," he says.

Lagoudas and colleagues have worked out that wrinkling the surface
of a craft in the right way can cut problems. The surface must
assume the shape of the ideal ordered surface wave it is trying to
create, something that changes at different velocities.

Dolphin trick

It might seem counterintuitive to reduce drag by wrinkling the
surface of a craft, but nature provides a precedent. "Dolphins
induce their skin to wrinkle, so water won’t stick to them," says
Lagoudas.

After calculating that this approach would work, his team tested
designs for an "active skin" that shifts to ...

More...
http://technology.newscientist.com/c...-and-subs.html

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

Big John

"Big John" wrote in message
...
...

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

Big John



They have tried a textured surface (more than a couple races ago) but the
rules were changed again to outlaw this sort of thing (along with surface
tension modifiers that you drip into the water at the bow).

I don't believe that the "shape shifting" idea has been attempted in real
life - But you are right, it's not exactly a new idea.

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

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