Aerodynamics & Hydrodynamics from MotherNature

,.....consider these unusual findings from Mother Nature:

DURHAM, N.C. -- Wind tunnel tests of scale-model humpback whale flippers have revealed that the scalloped, bumpy flipper is a more efficient wing design than is currently used by the aeronautics industry on airplanes. The tests show that bump-ridged flippers do not stall as quickly and produce more lift and less drag than comparably sized sleek flippers.

The tests were reported by biomechanicist Frank Fish of West Chester University, Pa., fluid dynamics engineer Laurens Howle of the Pratt School of Engineering at Duke University and David Miklosovic and Mark Murray at the U.S. Naval Academy. They reported their findings in the May 2004 issue of Physics of Fluids, published in advance online on March 15, 2004.

In their study, the team first created two approximately 22-inch-tall scale models of humpback pectoral flippers -- one with the characteristic bumps, called tubercles, and one without. The models were machined from thick, clear polycarbonate at Duke University. Testing was conducted in a low speed closed-circuit wind tunnel at the U.S. Naval Academy in Annapolis, Md.

The sleek flipper performance was similar to a typical airplane wing. But the tubercle flipper exhibited nearly 8 percent better lift properties, and withstood stall at a 40 percent steeper wind angle. The team was particularly surprised to discover that the flipper with tubercles produced as much as 32 percent lower drag than the sleek flipper.

“The simultaneous achievement of increased lift and reduced drag results in an increase in aerodynamic efficiency,” Howle explains.

This new understanding of humpback whale flipper aerodynamics has implications for airplane wing and underwater vehicle design. Increased lift (the upward force on an airplane wing) at higher wind angles affects how easily airplanes take off, and helps pilots slow down during landing.

Improved resistance to stall would add a new margin of safety to aircraft flight and also make planes more maneuverable. Drag -- the rearward force on an airplane wing -- affects how much fuel the airplane must consume during flight. Stall occurs when the air no longer flows smoothly over the top of the wing but separates from the top of the wing before reaching the trailing edge. When an airplane wing stalls, it dramatically loses lift while incurring an increase in drag.

As whales move through the water, the tubercles disrupt the line of pressure against the leading edge of the flippers. The row of tubercles sheer the flow of water and redirect it into the scalloped valley between each tubercle, causing swirling vortices that roll up and over the flipper to actually enhance lift properties.

“The swirling vortices inject momentum into the flow,” said Howle. “This injection of momentum keeps the flow attached to the upper surface of the wing and delays stall to higher wind angles.”

“This discovery has potential applications not only to airplane wings but also on the tips of helicopter rotors, airplane propellers and ship rudders,” said Howle.

The purpose of the tubercles on the leading edge of humpback whale flippers has been the source of speculation for some time, said Fish. “The idea they improved flipper aerodynamics was so counter to our current doctrine of fluid dynamics, no one had ever analyzed them,” he said.

http://www.pratt.duke.edu/news/?id=101

There's a paragraph at Harvard professor Michael Brenner's pages at
http://www.seas.harvard.edu/brenner/Research%203.html

"We have been interested in understanding the aerodynamic mechanism for this stall-delay. Recent work with Ernst van Nierop and Silas Alben demonstrates the mechanism for the observed increase in stall angle. Although the bumps have been compared to vortex generators, we propose a different mechanism: we demonstrate that the bumps alter the pressure distribution on the wing such that separation of the boundary is delayed behind bumps; this ultimately leads to a gradualonset of stall and higher stall angle. Our mechanism predicts that as the amplitude of the bumps is increased, the lift curve flattens out leading to potentially desirable control properties. Model airplane builders have started experimenting with this type of wing shape."

Turbulence Discovery Could Lead to Better Planes (and Sailboats)

Turbulence Discovery Could Lead to Better Planes
With just a single measurement, a new model may deftly describe turbulent fluid flows near an airplane wing, ship hull or cloud, researchers report in the July 9 Science. If the long-sought model proves successful, it may lead to more efficient airplanes, better ways to curb pollution dispersal and more accurate weather forecasts.

Fluid dynamicist Alexander Smits of Princeton University calls the new model “a very significant advance” that opens up a new way of thinking about chaotic, energy-sapping turbulence.

Read More http://www.wired.com/wiredscience/2...&utm_content=Google+Feedfetcher#ixzz0tHwIh5el

The link to the WIRED article posted is based on Ivan Marusic's work at the University of Melbourne. My new company A1X Automation designed and built the electronics to control the Pitot Positioner for Melbourne's wind tunnel.

We have also just finished work on a one of kind wind tunnel for studying boundary layer physics for Portland State University. The tunnel has many unique systems, including electronically articulated pressure gradient adjustment(the ceiling can be re-configured for just about any pressure gradient), temperature controlled floor panels (for studying thermal effects on the boundary layer at different gradients) and an electronic pitot positioning system (less motion axis than Melbourne). The designer of the tunnel predicts the unique combination of features will allow for unprecedented visibility into what is going on in the boundary layer. Of particular interest, as mentioned in the article, is drag from turbulence.

Airliners use half their fuel to overcome turbulence 1 foot from the surface??? Incredible!!! Anyone know the numbers for a sail? I imagine the number is even higher for a sail on the water.

"John A1X" <jam@a1x.us>

Well how far away would you think this drag reduction is acting?? (attached photo of color enhanced tip vortice by NASA)

I think John was just using a double reference here, ...both a sail....and usually one on a water craft.

The point is that it took drag to produce them ...and that drag affected the craft while it was operating

I don't see where I am waffling, or back pedaling?

Are you calling these illustrations artifical?? These vortices are real...NASA simply utilized a special photo technic to make them visible. NASA did not create the stylized air flow. It is real.

Have a look HERE
"Wingtip vortices.
Bearing in mind the direction of rotation of these vortices, it can be seen that they induce an upward flow of air beyond the wingtip, and a downwash flow behind the wing’s trailing edge. This induced downwash has nothing in common with the downwash that is necessary to produce lift. It is, in fact, the source of induced drag. The greater the size and strength of the vortices and consequent downwash component on the net airflow over the wing, the greater the induced drag effect becomes. This downwash over the top of the wing at the tip has the same effect as bending the lift vector rearward; therefore, the lift is slightly aft of perpendicular to the relative wind, creating a rearward lift component. This is induced drag."

Likewise the boat created the wake. It took energy to create that wake, and the sole source of that energy was the boats passage thru the water. That energy to create the wake must be subtracted from the boat's energy....thats drag on the boat.