A New Method Helps Researchers Better Understand Turbulence

November 20, 2009

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Assistant professor of mechanical engineering, Nicholas Ouellette, combines two well-established approaches with an innovative technique to gain further understanding of what he characterizes as “the last great unsolved problem in classical physics” – turbulence.
 
With a three-year grant from the National Science Foundation’s Condensed Matter Physics program in the Division of Materials Research, Ouellette will take a close look at turbulent flow to determine how and if dynamic structures, such as the eddies that form in moving body of water, impact the fluid mechanics of the system or if they are merely a visually interesting effect of the flow.
 
“There are great sketches by DaVinci that look a lot like our current understanding of turbulence,” says Ouellette. But, with today’s ever-improving methods and technologies, Ouellette has confidence that this is a problem that can be solved.
 
Turbulence, a state of extremely chaotic flow, is a very relevant part of many macroscopic issues – from designing air flow in a building to predicting how contaminants will travel in the ocean. For years, researchers have studied turbulent flow using two methods of simplifying the dynamics: one that describes the system statistically, characterizing the average dynamics, and one that takes an in-depth look at the dynamic structures (i.e., vortices or eddies) themselves. Little work, however, has combined the two, which is what Ouellette has proposed.
 
Using small plastic particles that have the same density of water and high speed cameras, Ouellette is able to track particle movement in two-dimensional water flow contained in an ideal system he has set up in the lab. With measurements of up to 50,000 particles per frame at an imaging rate of 50 pictures per second, high computing power is necessary to extract meaningful data. “We’re not interested in the details of a single experiment. They are all different,” says Ouellette. Instead, they must identify what can be universally applied to any flow, which Ouellette describes as a data mining problem.
 
 
 
While little swirls of water appear interesting, there is no evidence that they are statistically relevant to the flow of the system. “Certainly something is making vortices form, but it’s not obvious that they should then couple back and influence the further evolution of the flow,” says Ouellette. He and postdoctoral associate Doug Kelley, use an innovative method for finding stagnation points, or points of zero velocity, as found at the center of a vortex, and other coherent structures. It is a new tool that should be very valuable as this 500 year plus study continues.
 
Ouellette is associated with the International Collaboration for Turbulence Research (ICTR), a multinational group of scientists dedicated to sharing their theoretical, numerical, and experimental expertise in order to further the understanding of the Lagrangian nature of turbulence.
 
For more information, contact Thea Reilkoff, SEAS Director of External Relations at (203) 432‐4244 or thea.reilkoff@yale.edu.
 
 
 

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