Fluid Dynamics
Goes to the Movies

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The Great Lakes form the world's largest surface freshwater system but are coming under increasing risk from population, pollution and, according to some scientists, consumption. Although the level of the lakes remains fairly constant, climatologists warn that could change if temperatures rise and weather patterns change, as some expect.

To better understand lake hydrodynamics, currently and looking ahead, a professor at Purdue University, West Lafayette, IN, is working to develop a three-dimensional tool to illustrate movement of large volumes of water, how it affects plant and animal life, and how pollutants or other substances are dispersed. The visual program is seen as a tool to explain complex scientific data to the public, allowing politicians and communities to make better-informed decisions on how to use natural resources.

Cary Troy, an assistant professor of engineering at Purdue, has enhanced computer models of Lake Michigan with his own data and drawn on the expertise of the university's Envision Center for Data Perceptualization to produce animated
3-D images of the lake incorporating numerous layers of data. "It makes science more accessible to non-scientists," says Troy.

Image courtesy of Purdue University.

Troy's specialty is environmental fluid dynamics. Building on his doctoral dissertation on internal waves, Troy has been studying the layers of stratification in Lake Michigan and how the thermocline, a layer of separation between colder, deeper, and warmer water near the surface, affects circulation in warm-weather months. Understanding such physical systems will give scientists and engineers more information on how they affect development of native fish populations as well as recently introduced interlopers, such as zebra mussels. Among other things, Troy and his team are using computer modeling to predict how higher water temperatures in the cold-water upper Great Lakes would impact sport and commercial fisheries.

"We want to forecast in a variety of horizons," says Troy.

Image courtesy of Purdue University.

Using a Visual Model
Troy notes there are many computer models of Lake Michigan and the Great Lakes, but for his research he is using SUNTANS, a model developed at Stanford University, Palo Alto, CA, where Troy earned his Ph.D. The model uses an unstructured grid using triangular prisms for geometry that better fit irregularities within and around the lake, he says. It has been used in modeling of coastal systems but not for inland lakes.

For two years, Troy and his students gathered data in Lake Michigan using a wide range of instruments, including the Purdue engineering department's robotic underwater autonomous vehicle. The information is added to the model, which produces a huge volume of data. But sifting through all of that has proven difficult and tedious.

"The bottleneck now is not so much with computing," says Troy, pointing to the efficiencies of SUNTANS and other models. "You're generating terrabytes of data. You have to get to the point where you can look quickly at visualization results."

Professor Cary Troy examines his model of hydrodynamic flow in Lake Michigan on the Envision Center's wall-sized display.
Image courtesy of Purdue University.

To do that, Troy took his data to Purdue's visualization center, where computer scientists melded it with a powerful visualization program to produce an animated image. "I couldn't access that information before," he says. "That opened my eyes to the potential."

Using a program called Avizio, produced by Visualization Sciences Group Inc., Burlington, MA, Troy and his collaborators produced a 3-D version of his model. Avizio is a very high-end graphics program that can pull out numerous sets of data from the model for display, and animate it to show results over a period of time.

"What better way to illustrate fluid dynamics than to show a movie," he says. "It's the transferability of results."

Monitoring the Environment
On a more basic level, for a professional specializing in fluid dynamics, the visual model brings static and two-dimensional information to life. Troy points to its potential in communicating science to government agencies that fund research as well as federal, state, and local agencies that monitor and regulate the environment.

Troy believes the program has the potential to illustrate complex systems and problems throughout the Great Lakes region to a wide audience. For instance, pollution remains a problem throughout the region. The U.S. Environmental Protection Agency has identified "hot spots" of severe contamination throughout the lakes. Showing the public how contaminants actually disperse within a specific body of water may help people and municipalities change their behavior, he notes.

It could also be used to predict and illustrate how contaminants within rivers interact and disperse when entering a lake, or how hazardous substances move when released from a ship. The results could then be used by engineers in determining how to best remediate the problem.

"And it is just a good way to communicate science" in a manner more people can understand, Troy says.

What better way to illustrate fluid dynamics than to show a movie. It’s the transferability of results. Cary Troy, an assistant professor of engineering at Purdue in West Lafayette, IN.

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