APS News

Insect Flight, Modeling Blood Flow Highlight 2005 DFD Meeting

Insect flight, granular mixing, and new models of blood flow that could lead to better understanding of the cause of aneurysms were among the featured highlights at the annual fall meeting of the APS Division of Fluid Dynamics, held November 21-23, 2004, in Seattle, Washington.

This year's technical program included three award lectures, seven invited lectures, five mini-symposia, and a special session in honor of physicist Bill Reynolds, who coined the term "large eddy simulations" 30 years ago and pioneered the proper mathematical field definition of the large scale field, as well as critical numerical simulation techniques to model turbulence physics.

A special conference reception was held at the world-famous Museum of Flight. In addition, the meeting featured the 22nd annual Gallery of Fluid Motion. The gallery features aesthetically pleasing, insightful displays of still pictures, computer graphics, and video clips submitted by meeting attendees.

A panel of referees selects the most outstanding entries, based on artistic content, originality and the ability to convey information. Winning entries will be displayed at the upcoming 2005 APS March Meeting in Los Angeles, California, and will be published in the September 2005 issue of Physics of Fluids.

Understanding Aneurysms. Our understanding of the factors that contribute to the development and rupture of aneurysms has developed rapidly over the last 15 years, accompanied by the development of new materials and devices for treatment.

For instance, scientists from the University of California, San Diego, described their recent clinical study of multiple Neuroform stents to regulate blood flow in the aneurismal sac. The team used a digital particle image velocimetry technique to measure how fast blood flowed at the entrance and inside the sac. They found that the use of stents can effectively reduce the strength of the vortex forming inside the sac, with a subsequent decrease in the magnitude of the shear stresses acting on the aneurismal wall.

Other speakers described new modeling and computer simulation techniques to study the dynamics of blood flow in aneurysms. The new knowledge could lead to improved interventional devices and an increase in patient survival rates.

Insects Flex Their Wings. The largest flying insects manage to stay airborne by relying on their ability to flex their wings, according to Thomas Daniel of the University of Washington. This ability to instantaneously reshape their wings has, in turn, a profound effect on the airflow forces they can generate. But to what extent is the surface shape of the wings controlled by structural mechanics versus fluid dynamic loading?

Daniel and his colleagues used a variety of methods to explore insect flight performance. They have demonstrated that for certain combinations of wing stiffness, wing motions, and fluid density, fluid pressure stresses play a relatively minor role in determining wing shape when the insect is moving in the air. Using this approach, they have demonstrated that even modest levels of passive elasticity can affect thrust for a given level of energy input. Insects appear to be able to tune their wing elasticity for optimal flight performance.

Granular Mixing. It is well known that granular mixtures segregate under flow, according to Julio M. Ottino of Northwestern University, who described his recent work modeling the dynamics of segregation, mixing, and coarsening of granular matter.

At a fundamental level, all such effects are due to particle-level interactions. But how does the entire ensemble behave? He is applying a wide range of modeling approaches to explore this question, including such discrete models as cellular automata and particle dynamics simulations that provide "realistic" details of the particle interaction processes.

Vortex Rings in Biological Propulsion. Caltech's Morteza Gharib is looking to squid and jellyfish-as well as cardiac blood transport-for insight into the dynamics of vortex formation and how it can be used as an underlying principle for biological propulsion.

Both species employ "pulsed-jet swimming" methods, which rely on the generation of vortices to maximize thrust and/or propulsive efficiency. Gharib plans to extend his studies to organisms, such as fish and birds, that generate more complex vortical structures

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Editor: Alan Chodos
Associate Editor: Jennifer Ouellette