Going with the Flow
How does a lobster find
what it’s looking for in turbulent water? Todd Cowen thinks the answer might
be the key to tracking the source of pollutants in the ocean.
By Leila Belkora
|
Outside, rocky terraces and deep plunge-pools shape the courses of Cascadilla, Fall, and Six Mile creeks, and wind-driven breakers pound Cayuga Lake’s south shore. Inside turbines and tilting water tanks reproduce some of nature’s hydrodynamic complexities in a variety of test conditions. Waves roll over a ripple bed. An artificial stream tumbles down the gentle slope of a flume. A turbulent, meandering current surges through a broad channel. Lasers flash as high-speed cameras record the scattered light from test particles in the tanks.
The facility is the DeFrees Hydraulics Laboratory, the focal point of experimental studies in the environmental fluid mechanics and hydrology program in the School of Civil and Environmental Engineering. (The lab is named after engineer and benefactor Joseph DeFrees ’29 CE.)
Edwin "Todd" Cowen, assistant professor, assumed the directorship of the laboratory when he joined the Cornell faculty in 1998. The term "hydraulics," he noted, is slipping as a descriptor of what he and his colleagues do; it doesn’t take into account the study of such problems as how pollutants disperse in the environment or how waves re-suspend sediments.
Hydraulics is, classically, man’s attempt to make water do what civilization needs it to do: open channel flow and delivering aqueducts with water, managing reservoirs, dissipating energy as water falls off a spillway," Cowen said. "Even lake source cooling, to a degree, is a hydraulics project," he continued, referring to a plan underway to use cold water from the depths of nearby Cayuga Lake in a heat exchange to cool campus buildings. "The Army Corps of Engineers comes to mind when you say hydraulics. Environmental fluid mechanics I think of as including that, but also extending to the natural environment’s flows. So one of the things I’m interested in is, for example, not only how do we take advantage of the lake to cool a body of buildings on campus, but what is the big transport picture, everything going on in the lake under its natural circulation, which maybe you wouldn’t normally consider to be part of hydraulics. That’s the direction I think environmental fluid mechanics is heading."
Cowen’s current research certainly stretches the traditional boundaries of fluid mechanics. One of his projects, sponsored by the Office of Naval Research, will add a potentially key lobster clause to the annals of research on chemical plume tracing.
The Navy’s problem is to find the sources of chemicals that are detected in turbulent waters in coastal zones. The chemicals might be explosives leaking from unexploded ordnance on the sea floor, for example, or pollutants escaping from lost 55-gallon drums. In any case, the challenge is to start at the downstream end of a plume of chemicals and follow it back to the source.
"If you look at a turbulent patch of a chemical in water, it’s not at all clear what direction is upstream," said Cowen. "Our goal is to understand the mechanisms, the physics by which local, naturally evolving turbulence will disperse a pollutant plume. Then we can look at those turbulent structures and try to understand what sort of algorithms would be effective at searching for a source."
As part of a multi-pronged effort to develop such algorithms, the government is funding studies of the lobster, which hunts very effectively for food or sources of sexual pheromones in choppy water. The Navy paired Cowen with biologists at the Marine Biological Laboratory in Woods Hole, Mass., whose expertise is in lobster behavior and olfactory capabilities. The biologists study how the lobster reacts to odorants it picks up through antennules, small antennae protruding from under the eyes.