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February 2002 (Volume 11, Number 2)
The latest research results in biofluid mechanics, hurricane physics and particle simulation flows were among the papers featured at the annual meeting of the APS Division of Fluid Dynamics, held November 18- 20, 2001, in San Diego, California. The technical program featured eight invited lectures and four mini-symposia on cutting-edge research topics in fluid dynamics, as well as more than 950 contributed abstracts and the annual Gallery of Fluid Motion.
Understanding the physics of the air/sea interface is a critical component of understanding hurricanes, which draw their energy from the thermodynamic disequilibrium that ordinarily exists between the tropical oceans and the atmosphere. The maximum wind velocity depends on maintaining a sensitive balance between the production of mechanical energy and frictional dissipation in the atmospheric boundary layer, which in turn depends on the fluxes of momentum and enthalpy through the sea surface. Yet little is know about such fluxes at extreme wind speeds. Kerry Emanuel of the Massachusetts Institute of Technology described recent laboratory experiments designed to better quantify flux wind speed relations and to explore possible control of the fluxes by application of molecular monolayers.
Dynamics in the structural hierarchies of living creatures are simplified by continuum mechanics and could be extended to support future research in biology and bioengineering, according to Y.C. Bert Fung of the University of California, San Diego, who spoke at a Tuesday morning session. And since fluid mechanics is the key determinant of stress and strain in cells, it can play an equally key role in those fields. He pointed out that every cell in the human body needs blood flow, and the dynamics of blood flow is coupled with DNA, cell function and tissue remodeling. "Significant problems of health and diseases always need a good systems analysis, and such analysis may use continuum mechanics," said Fung.
Martin Maxey of Brown University gave an overview of various simulation methods that could give scientists insights into the mechanisms of various types of particle- laden flows, which include turbulent combustion sprays, sedimentation of dilute suspensions, and bioparticle separation in micro-channels. Particles in such flows are dispersed by underlying turbulence, and depending on their size, their response to the turbulence can create local particle accumulations that are correlated to the flow structures. In dilute suspension flows, for example, interactions between particles via the fluid flow can have significant long-term effects, which would be masked in a more turbulent flow. Maxey illustrated the various processes with examples drawn from his experiments and simulation results.
Heating and ventilating buildings account for a significant fraction of the total energy budget of cities, and one of the most pressing challenges is the design of sustainable, low-energy buildings, according to Gary Hunt of the Imperial College of Science, Technology and Medicine in London, England, one of several speakers in a Sunday afternoon mini-symposium on the fluid dynamics of buildings. Hunt believes that natural ventilation provides such a low-energy solution. Modern naturally-ventilated buildings use such innovative design solutions has glazed atria and solar chimneys to enhance the ventilation, and demand for these and other designs has far outstripped current understanding of the fluid dynamics of such buildings. Particular challenges include improving our understanding of the thermal stratification and movement of air, which often involve complex geometries.
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