Modify laminar flow for increased performance?

[JonathanCole]

Below is an article I ran across on a UK engineering website which must have applications for sails, hydrofoils , some hulls and maybe even props. I believe it may directly relate to Grays Paradox mentioned in this MIT Robotuna article:
"The experimental results of tests clearly demonstrate that RoboTuna duplicates Gray's paradox (i.e. the drag of the swimming fish RoboTuna apperars to be less than the drag on the straight RoboTuna), but does so with unarguably "known" mechanical muscles. These experimental results, at least for the parameters tested, support Gray's claim that differences in marine/terrestrial muscle power are not the answer, but do not go so far as to explain what the solution to the paradox is. However, it does lend strong credence to the possiblity that some form of unconventional, highly beneficial hydrodynamic mechanism exists, which reduces drag in fish-like propulsion... Gray's paradox implies that a seven-fold reduction in drag be acheived."


Making wings sing

Published: 19 August 2005 01:06 PM
Industry Channel: Aerospace
Source: The Engineer Online


Using sound to control the flow of air over an aircraft's wing, greatly boosting its lift, has propelled UNSW aerospace engineering student Ian Salmon into the list of finalists for the Australian 2005 Fresh Science awards.

Salmon, who works at Qantas as an aircraft development engineer, is working on applying this idea to a new generation of light aircraft. He has developed a technique in which an aircraft's wing is covered with flexible plastic panels which vibrate when an electric current is passed through them, producing sound.

At a carefully selected frequency, the air passing over the wing can be made to remain more closely attached, increasing the wing's efficiency.

While the theory behind the technique is not new, the method of applying sound directly to the wing during flight is novel. Previous studies used large speakers pointing at a model in a wind tunnel with encouraging results but painful sound levels.

"This new method grew from the desire to carry a lightweight sound source on the aircraft, and to apply sound exactly where it was needed, rather than spraying it everywhere," Salmon said. "Obviously one thing we did not want to do was to make aircraft noisier."

It's unlikely that his method will be used on large commercial jets. "The beneficial effects are far more pronounced for small, slow aircraft which fly in conditions where the air's viscosity, or 'stickiness' has more influence on the air's behaviour."

Although the kind of sound which is most effective in manipulating airflow is a single-frequency tone, other forms, including music, have shown some effect.

Salmon is one of 13 Fresh Science finalists. His research was undertaken at UNSW as part of a BE thesis under the supervision of Associate Professor NA Ahmed.

For more information on the 2005 Fresh Science awards, visit the Fresh Science website.

[kach22i]

Cool story, I posted a link to here from a Martin Logan electrostaic speaker forum I visit.

[icetreader]

Jonathan,

As usual you're pointing to some refreshing subjects that are out of our daily scope.
In this context maybe it's worthwhile to mention the way the shark's skin works to reduce drag: http://www.bio.davidson.edu/Courses/...0Reduction.htm

...rather "counter-intuitive" isn't it?

Yoav

[JonathanCole]

Yoav,

Wow, don't you love succinct presentations. The guy that wrote that page should write internet encyclopedias for a living!

But the subject is fascinating and totally relevant to naval architecture and boat design. I think that it will be through a combination of understandings contained in physics, fluidics, wave theory, surface chemistry and nanotechnology, that we are likely to see major breakthroughs in this subject soon.

What Vlad was referring to in earlier threads comes down to a certain simple idea. There is something in nature that loves a wave. I have speculated previously and do so again here, that it relates to the way a traveling wave allows a flow that interferes less with the boundary layar (first laminar) which actually is an electrical/electronic/ionic layer identified and characterized by surface chemistry.

It has to do with resonance and the way that a resonant system can actually cause runaway effects, or ringing, like feedback in a public address system. If you remove the resistance to flow, then feedback effects actually create a kind of energy storage and release that allows for no-loss or low-loss systems. Such things are seen in electronic tank circuits (a capacitor and an inductor, if I recall properly). http://www.allaboutcircuits.com/vol_6/chpt_4/14.html
After you disconnect the power, it keeps on ringing.

When you think about it, if we can crack nature's code maybe a well designed 50 foot cat goes 24 knots with 5 HP. Now that's progress!

Here is something for technologists interested in this subject:
http://uwadmnweb.uwyo.edu/rpc/UWTechs/03-024.asp

Jon