APS News

Hydrodynamics, Small-Scale Flows Highlight 2005 DFD Meeting

New research on the hydrodynamics of pectoral fins in fish and the dolphin kicks of Olympic-level swimmers were among the highlights of the 58th annual meeting of the APS Division of Fluid Dynamics (DFD), held November 20-22 in Chicago, Illinois. The meeting was jointly hosted by the Illinois Institute of Technology, Northwestern University, and the University of Illinois, Urbana-Champaign.

Last year marked the 100th anniversary of Einstein’s “miracle year” and was designated the World Year of Physics. One goal was to communicate the excitement of physics to the general public, thereby inspiring a new generation of scientists. In honor of the WYP, the meeting featured a special public lecture by Nobel laureate Leon Lederman on science education’s “quiet crisis.” His lecture was followed by a reception and an exhibit of the 2005 Gallery of Fluid Motion.

Hydrodynamics. The pectoral fins of fish are designed for a great degree of control over fluid forces: they are flexible and able to change their shape, enhancing their ability to maneuver in water. However, the kinetics do not lend themselves easily to the usual analysis based on pitching or paddling kinematics, or lift/drag-based propulsive mechanisms.

In order to glean new insights into the hydrodynamics of pectoral fins, researchers at Harvard University and at George Washington University used two-camera high-resolution digital video to measure 3-D fin conformation of fish during steady swimming and while maneuvering. They also performed high-fidelity numerical simulations of the hydrodynamics and thrust performance of the pectoral fin of a bluegill sunfish. The measurements and simulations showed that the fin produces a large amount of thrust at all phases in the fin motion, and produces a distinct system of connected vortices.

Similar numerical simulations are being used to study the fluid dynamics of the dolphin kick in competitive swimming: a stroke that is performed underwater after starts and turns, involving an undulatory motion of the body. A second team of GWU researchers–working in conjunction with scientists at IBM’s T.J. Watson Research Center–conducted highly detailed laser body scans of elite competitive swimmers, and recreated the kinematics of the dolphin kicks from videos of Olympic-level athletes. This work provided the scientists with the first glimpse of the fluid and vortex dynamics associated with the stroke.

Cover Your Mouth. Diseases ranging from the common cold to more lethal conditions like SARS are spread by cough-generated infectious aerosols, so understanding the range and behavior of such flows could help mitigate future outbreaks. To that end, researchers at the University of Colorado at Boulder used particle image velocimetry (PIV) to measure the velocity field of a human cough. They found that cough flow exhibits slow growth–maximum speeds ranged from 1.5 m/s to 28.8 m/s–indicating that a cough may penetrate farther into a room than a steady jet of similar volume.

Small-Scale Flows. As computers, electronic devices, microfluidic labs-on-a-chip, and other key technologies become smaller and smaller, scientists are seeking better understanding of the behavior of gaseous flows at the micro-and nano-size scales, where the traditional Navier-Stokes descriptions break down. MIT’s Nicolas Hadjiconstantinou suggests that gaseous hydrodynamics at these scales can be described by the Boltzmann equation. He described some basic results from an asymptotic analysis of that equation, which he has used to resolve a number of open questions in this area, including second-order slip, and a means of reconciling experimental measurements of slipping flows with theory.

The Fluid Mechanics of Fire. Howard Baum of the National Institute of Standards and Technologies illustrated his latest simulation work on fire dynamics in enclosures with the latest results from the NIST investigation of the collapse of the World Trade Center towers, as part of a broader discussion on the fluid mechanics of fires. His talk also covered the role of fire plumes in the transport of heat and mass. Specifically, the plume provides the feedback mechanisms that determine the strength of a fire, and also acts as a pump, mixing the fuel and oxidizer.

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Editor: Alan Chodos
Associate Editor: Jennifer Ouellette
Staff Writer: Ernie Tretkoff