Andrew Bragg: Making Sense of Chaos in Environmental Systems

New faculty member Andrew Bragg studies how turbulent flows affect natural systems from coalescing raindrops to forming planets

By Ken Kingery

Andrew Bragg will join the faculty of the Department of Civil and Environmental Engineering at Duke University beginning September 1, 2016. Returning to academia after a stint at Los Alamos National Laboratory, Bragg plans to create a fluid dynamics research center to investigate how turbulence in fluid flows influences a variety of environmental systems.

The motion of fluids in the environment can be described as either laminar or turbulent. The former is a well-organized, well-understood flow with dynamics that can be precisely calculated and predicted. Most flows found in nature, however, are the latter.

Turbulent flows are a chaotic mess, often containing particles which move every which way at varying speeds. Thanks to their unpredictable nature, turbulent flows are difficult to understand, model and simulate. Bragg’s research focuses on addressing these difficulties.

“My research uses a mixture of advanced theoretical methods coupled with computational simulations,” said Bragg. “We use tools from applied mathematics and statistical physics to explore and understand the basic aspects of these systems, and then use that fundamental knowledge to develop simplified models that can be implemented in large-scale simulations.”

For example, different layers of ocean water vary greatly in temperature, salinity and density. These gradients cause water to flow and mix together chaotically, taking organisms living within along for the ride. Bragg is trying to better understand the dynamics of these systems and how they cause organisms to clump together and interact, which affects their population dynamics.

Another example is modeling how water droplets move relative to one another deep within storm clouds, where turbulent flows enhance collision rates and affect how droplets coalesce and form rain drops. Developing accurate large-scale models of these phenomena could help meteorologists better predict rainstorms.

On an even grander scale, turbulence plays an important role in the dynamics of interstellar nebulae, and is thought to be important for understanding the physical mechanisms responsible for the creation of planets and solar systems.

“The implications of my research are very diverse, going all the way from tiny organisms mixing in our oceans right up to astrophysical and cosmological questions,” said Bragg.

Of course, Bragg can’t do any of this alone. He has a network of experimentalist collaborators from all across the country, from the University of Buffalo to the University of Alabama and Cornell University—friends he made from several stops along the way to Duke.

After earning a PhD in theoretical fluid dynamics from Newcastle University in England, Bragg completed a postdoctoral position at Cornell University. He then decided to test the waters as a researcher at Los Alamos National Laboratory, but found that he missed working with students and the vibrancy of a university campus. Less than a year and a half later, he accepted his new position at Duke.

Bragg hopes to pull together a network of researchers studying fluid dynamics from all corners of campus, from faculty working on flutter in turbine engines and airplane wings to biomedical researchers focusing on the flow of blood through the vasculature system.

“There are some real stars in Duke engineering who work on related but different projects, so the ability to form collaborations and branch out into other areas is extremely exciting to me,” said Bragg. “And the superb reputation of the university attracts some of the brightest students in the country, so the position is very attractive in terms of the caliber of students that I’ll be able to work with.

“Both my wife and I are eager to return to the East Coast,” continued Bragg, who also has a two-and-a-half-year-old and a five-month-old daughter. “We vacationed at Morrow Mountain State Park a few years ago. It was very beautiful and made us fall in love with North Carolina. So while we both appreciate the beauty of the desert in the Southwest, we have really missed the greenery and water of the East Coast.”