Hi Eunometic and guys.

On Nov 7, 2:59 am, Eunometic wrote:
On Nov 7, 9:35 am, "Ken S. Tucker" wrote:



On Nov 6, 1:44 pm, wrote:

On Thu, 6 Nov 2008 01:54:20 -0800 (PST), in sci.engr.mech "Ken S. Tucker"

wrote:
On Nov 5, 2:40 pm, wrote:
On Wed, 5 Nov 2008 13:59:27 -0800 (PST), in sci.engr.mech "Ken S. Tucker"

Not quite. As far as riblets go, it is my understanding that the height
and spacing of the riblets is specified according to the boundary thickness
such as to prevent the growth of turbulent bursts which causes an exchange
of low momentum fluid near the surface with higher momentum fluid from
above. This momentum exchange being a loss/drag mechanism. The other point
of importance is the orientation of the riblets along streamlines.

Yes, that's seems clear...but NOT simple :-).

That's a lot different that your original point that it was not well
understood.

Well I think we're nit-picking sematics, my quote,

"My understanding is the theory is NOT _well_ understood,
but is evolving, along with applications, by experimental
feed-back, aka trial & error, (I'm using SM board). "

Note the word "theory"

Also after the original riblet research was performed
similarities to shark scales/skin were observed.
http://ntrs.larc.nasa.gov/search.jsp...de%20matchall&...

Yes! Thanks for those links.
Those papers are experimental results and testing,
AFAIK, there is NO generally accepted theory of the
"riblets effect", though it appears to be evolving.
(If you have a ref to a General Theory of Riblets, I'd
would appreciate a link).

I'm guessing: At a molecular level the riblets control
the turbulent interfacing between fluid and surface
and inhibit the integrated formation of macroscopic
turbulence, such as Eddy's. That micro control is
certainly a quantum relation between molecules in
the fluid and the interacting solid surface, whereby
the micro turbulences are quantized.

Setting aside sharks skin, we may want to have a
look at penguin swimming, that also has very low
resistance.
Regards
Ken

Riblets aren't the only way; hair and feathers have a similar effect.

"With Robert Brodkey, professor of chemical engineering, Koeltzsch has
now turned his attention away from sharks, to penguins and seals. He
hopes to determine whether hair makes these aquatic mammals more
hydrodynamic. Initial studies by other scientists have shown that
natural and artificial fibers can reduce drag by amounts that vary
from 1.5 to 50 percent.

Continued research could show whether hair would improve the design of
boat hulls and even airplanes, Koeltzsch said.

"Wouldn’t it be something if, in the future, airplanes had hairy
surfaces?" he asked. "

I did read the link you posted previously thanks.
I thought about tennis balls (hairy balls :-) too.
Regards
Ken