New model to help development of more efficient aircraft

WASHINGTON - A new model could deftly describe turbulent fluid flows near an airplane wing, ship hull or cloud. Its success may lead to the development of more efficient airplanes, help check pollution dispersal and improve the accuracy of weather forecasts.

According to fluid dynamicist Alexander Smits, of Princeton University, the new model is “a very significant advance” that throws up a new way of thinking about chaotic, energy-sapping turbulence.

The study appears in the journal Science.

The problem of turbulence extends far beyond a bumpy plane ride. Fluid flowing past a body - whether it’s air blowing by a fuselage or water streaming across a swimming suit - contorts and twists as it bounces off an edge and interferes with incoming flows, creating highly chaotic patterns. Airliners waste up to half of their fuel just overcoming the turbulence within a foot or so of the aircraft, and turbulent patterns in the bottom 100 meters of the atmosphere confound weather and climate predictions.

Scientists have a fairly good idea about the basic behaviours of fluids since the mid-1800s, but have been left baffled by the complexity of the tumultuous flows near a boundary.

“We don’t really have a handle on the physics. So even though the problem is over a hundred years old, we still really haven’t had a major breakthrough,” Wired News quoted study co-author Ivan Marusic of the University of Melbourne, Australia, as saying.

In their research Marusic and his colleagues measured forces in a giant wind tunnel, both near and away from a wall. Data collected by probes indicated a strong link between the small-scale turbulence near a wall and large, smoother patterns of air flow farther from the wall.

Newly identified flow patterns called superstructures, particularly, turn out to have a big effect on the turbulence near the wall. These smooth, predictable flow patterns away from the wall change the turbulence right next to the wall in predictable ways, a link that allowed Marusic and colleagues to write a mathematical formula relating the two.

Marusic said: “The fact is that we were sort of amazed because it’s such a simple formulation. Now with this model, all we need to do is measure the outer flow and we can predict what’s happening near the wall.”

If it is successful, the formula may find a use in models of climate, weather and pollution dispersal. And now that they have a better understanding of the near-wall turbulence, Marusic and his team are trying to reduce it by manipulating the smooth flow of fluids away from a wall.

Engineer Ronald Adrian of Arizona State University in Tempe, said: “This model is a breakthrough step, but we’re not ready to say that it’s going to solve all our problems. I don’t know if we have enough evidence yet to call it universal, but the hope is that it will be universal.” (ANI)