Best Fluid Motion Pictures Named

Deformed Bubbles

Image courtesy Cavitation Lab, SPMS Nanyang Technological University, via APS

Bubbles "deformed" by bumping into their neighbors star in one of five pictures named the best fluid-motion images of 2009 by the American Physical Society.

The 25 bubbles, created simultaneously in liquid using a laser pulse, were photographed by a team at Nanyang Technological University in Singapore.

In such an array, the pressure of the air in the central bubbles is almost the same as that of the surrounding liquid. This allows the bubbles to grow larger before collapsing. But outer bubbles almost immediately burst due to the greater pressure of the surrounding liquid.

When this image was taken—six microseconds after the laser's impact—bubbles on the edges of the image were already collapsing, while bubbles at the center had almost reached their biggest sizes.

February 1, 2010

"Wine Glass" Droplet

Image courtesy R. R. La Foy, J. Belden, A. M. Shih, T. T. Truscott, & A. H. Techet via APS

A three-millimeter-wide oil droplet hits rubbing alcohol to form an upside-down "wine glass" in one of the American Physical Society's best fluid-motion pictures of 2009.

The image, created by a team at the Massachusetts Institute of Technology, was captured by projecting light onto the droplet from both sides. Oil and alcohol bend light differently, so the oil droplet's edges appear bright.

Because oil is denser than rubbing alcohol, the droplet fell through the alcohol to create the unusual shape. But oil is also soluble in alcohol, and the droplet dissolved as it fell.

February 1, 2010

Cylinder Wave

Image courtesy Jens Kasten Christoph Petz Ingrid Hotz Gilead Tadmor, Bernd R. Noack, Hans-Christian Hege via APS

Resembling a river valley seen from the air, this two-dimensional, computer-generated picture—one of the American Physical Society's best fluid-motion images of 2009—illustrates what's known as a von Kármán vortex street.

Named after Hungarian aerodynamicist Theodore von Kármán, a vortex street occurs when an airstream flows around a body—in the above image, a hollow cylinder—and breaks behind it into a series of wakes and eddies.

The purple-blue regions show where the resulting waves have met, and the red regions show where the airstream will split in the future, according to the winning team of scientists from the Zuse Institute in Berlin, Berlin Institute of Technology, and Northeastern University.

February 1, 2010

Wingtip Vortices

Image courtesy Harris, Miller & Williamson via APS

One of the hazards of modern flight takes shape in an award-winning picture from the American Physical Society's 2009 Gallery of Fluid Motion.

In flight, an airplane's wingtips create a counter-rotating pair of vortices—pockets of circulating air that get forced down underneath the plane's wings. These primary vortices can create secondary vortices when they interact with the ground. The vortices present a potential danger to other aircraft during flight.

Now, a Cornell University team has developed a new technique to visualize the vortices: Using a pair of flaps to simulate aircraft wings, the team pooled dye on the ground and used lasers to make the swirls of fluid glow.

In the above image, the primary vortices are seen as red circles, and the secondary vortices are the lime-green swirls. The mirror image in the lower half of the photo is a reflection on the ground.

February 1, 2010