Joseph H. DeFrees Hydraulics Laboratory
The RASJA is a computer-controlled array of water jets arranged on a grid. An algorithm turns each jet on and off randomly. Researchers can install the RASJA at the top of the turbulence tank, aiming the jets down at the water below, or submerge it so the jets shoot up toward the surface. Shaking a grid—the standard method of modeling turbulence—generates static eddies and risks creating secondary flows. The RASJA produces more accurate models. It can also recreate the behavior of sediment in the uprush of a swash zone, where 90 percent of erosion occurs.
Members of the Environmental Fluid Mechanics and Hydrology Group built the RASJA to study how quickly carbon dioxide enters the air-water interface, a project motivated by climate change. Researchers have since modified the turbulence tank to study sediment suspension, another project with important environmental implications.
With a giant paddle on a four-meter hydraulic piston—one of the longest in the world—the long stroke wave tank produces an impressive range of different wave patterns, including long, solitary, tsunami-like waves. At the other end of the 32-meter long tank, a sloping glass beach models surf and swash zones. A false bottom halfway down the tank enables researchers to place objects, sediments, or other materials in the tank to test, for example, how much uplift waves create on objects of different designs. Philip Liu, professor emeritus of Civil and Environmental Engineering, became a renowned tsunami expert using the long stroke wave tank to model complex solitary wave patterns.
Flumes create flowing bodies of water in laboratory conditions. A system of tanks, pumps, and pipes recirculates water to create a continuous flow through the 15-meter flume. The glass bottom and sides allow high precision imaging with cameras and lasers. As Cowen points out, “Nature is shallow.” Cayuga Lake, for example, is four kilometers wide but only 0.1 kilometers deep. The wide open channel flume’s wide, shallow aspect ratio enables the study of lateral meandering plumes and other phenomena that occur along coasts and in rivers and lakes.
DARPA funded construction of the wide open channel flume to develop techniques for tracing deep-water pollutants to their source. A Civil and Environmental Engineering graduate researcher is using the flume to find patterns of turbulence that maximize the direct air capture of carbon dioxide by water. This allows algae then to convert the carbon dioxide into biofuels. The project aims to produce low-cost means of mitigating greenhouse gasses.
The tilting wind-water tunnel, a 20-meter flume built of glass and plexiglass side walls and a steel bottom, rests on an adjustable tilting I-beam. Researchers use the tilting wind-water tunnel to study flowing water, air, or interaction between the two. A computer-controlled pump circulates water through the flume by means of an underground system of tanks and pipes. A 12-horsepower fan generates air movement strong enough to produce breaking wind waves. In a 7000-gallon tank below the floor of the lab, a gas-bubbling system can condition water in the flume for a variety of research purposes. It can strip away dissolved oxygen to study reaeration rates, or it can saturate it with carbon dioxide to study the dilution of a high-carbon dioxide jets into the environment.
Lance Collins, Silbert Dean of the College of Engineering, is part of a team that used the tilting wind-water tunnel, equipped with an active turbulence grid, to study the behavior of water vapor in a turbulent environment. The team solved a long-enduring quandary about the formation of rain from water vapor in clouds.
The Lagrangian sled accelerates a mounted camera up to 10 meters per second to match the speed of the mean flow in the tilting wind-water tunnel. Using high accuracy grayscale cameras, researchers can track the behavior of plumes, water vapor, sediments, or dissolved gasses with passive or dynamic particles or phosphorescent dyes.
Analyzing currents in the lab’s tanks and flumes relies on lasers. Lenses fan out beams into parallel sheets of light in the tanks or flumes. They create visible cross sections that are then captured by high accuracy grayscale cameras. Water vapor in air, or neutrally buoyant ceramic or nylon particles in water, pass through the laser light sheets and are illuminated like snow in headlights. In the laboratory, however, these particles pass successively through thin planes of light that enable tracking of individual particles. For the study of dilution or dissolved gasses, researchers add chemicals or dyes to the water. These chemicals emit light proportionate to the concentration of carbon dioxide, for example. This technique is called laser-induced florescence.
Cameras in the DeFrees lab can discretize over 60,000 shades of gray. Compare this to a standard phone camera that digitizes 256 shades of gray. The cameras’ high bit depth enables researchers to distinguish minute differences in concentrations when using laser-induced florescence.
The Joseph H. DeFrees Hydraulics Laboratory houses large-scale custom-designed tanks, flumes, and imaging equipment to study the flow of wind and water and the dissolved gases, particles, and sediments they carry. The lab’s unique facilities simulate swash zones, riverine sediment dispersal, cloud formation, and even tsunamis. Located in Hollister Hall, the lab supports major research on climate change, alternative energy technologies, and environmental sustainability. The original Cornell hydraulics lab below Beebe Lake Dam was one of the first in the United States. The DeFrees lab, constructed in 1984, represents a major expansion of the neighboring Environmental Hydraulics Teaching Laboratory.
Cornell Civil and Environmental Engineering shops built many of the tanks and flumes, and a talented cadre of technicians maintains the sensors, pumps, and specialized circuitry. AguaClara, Cornell’s Department of Natural Resources, Evolutionary Biology and Ecology, Sibley School of Mechanical Engineering, and a collaborative, multi-institution project funded by the Department of Defense are among the many groups who have used the facilities, in addition to Cornell’s Environmental Fluid Mechanics and Hydrology Group.
Director Edwin Todd Cowen considers the lab’s dual research and teaching functions complementary: “The DeFrees lab is a collisional space that brings undergraduates and graduate students together, so that undergraduates can see firsthand the kind of research taking place here.” Many undergraduates who work in the lab go to graduate school and then to faculty and research positions across the country.
“The scale of this space, the uniqueness of these facilities—Cornell is truly one of the few places in the world that has equipment like this,” Cowen says.