Celebrating the physics of all that flows with Nicole Sharp, Ph.D.
- Profile
Transonic Flow
In the transonic speed regime the overall speed of an airplane is less than Mach 1 but some parts of the flow around the aircraft break the speed of sound. The photo above shows a schlieren photograph of flow over an airfoil at transonic speeds. The nearly vertical lines are shock waves on the upper…
Volcanic Vortex
This infrared image shows a kilometer-high volcanic vortex swirling over the Bardarbunga eruption. The bright red at the bottom is lava escaping the fissure, whereas the yellow and white regions show rising hot gases. Although the vortex looks similar to a tornado, it is actually more like a dust devil or a so-called fire tornado.…
Reconfigurable Liquid Metal
Terminator 2’s T-1000, a liquid metal robot capable of changing its shape at will, just became a little less far-fetched. Researchers at NC State have reported a new method for controlling the form of a liquid gallium alloy. Surface tension governs the shape a liquid assumes when it is not confined by a container, and, although…
Beading Fluids
Adding just a few polymers to a liquid can substantially change its behavior. The presence of polymers turns otherwise Newtonian fluids like water into viscoelastic fluids. When deformed, viscoelastic fluids have a response that is part viscous–like other fluids–and part elastic–like a rubber band that regains its initial shape. The collage above shows what happens…
Crow Instability
Behind airplanes in flight, water vapor from the engine exhaust will sometimes condense in the wingtip vortices, thereby forming visible contrails. The two initially parallel vortex lines are unstable and any small perturbation to them–a slight crosswind, for example–will cause an instability known as the Crow instability. The contrails become wavy, with the amplitude of…
Flames in Space
The jellyfish-like light show in the animations above shows the life and death of a flame in microgravity. The work is part of the Flame Extinguishment Experiment 2 (FLEX-2) currently flying aboard the International Space Station. When ignited, the fuel droplet creates a blue spherical shell of flame about 15 mm in diameter. The spherical…
The Archer Fish’s Arrow
Archer fish hunt by shooting jets of water at their prey to knock them into the water where the fish can eat them. Previous research showed that the archer fish’s projectile jet is pulsed such that the water released at a later time has a greater velocity. This makes the jet bunch up so that…
Antibubble Vortex Rings
Bubbles are familiar, but antibubbles are a bit more unusual. An antibubble typically has a liquid-air-liquid interface, with a thin shell of air separating a liquid droplet from the surrounding fluid. Although they look rather like bubbles, antibubbles behave differently. Antibubbles are, for example, very sensitive to pressure changes. A sinking antibubble like the one…
Lava Physics
Lava is rather fascinating as a fluid. Lava flow regimes range from extremely viscous creeping flows all the way to moderately turbulent channel flow. Lava itself also has a widely varying rheology, with its bulk properties like viscosity and its response to deformation changing strongly with temperature and composition. As lava cools, instabilities form in…
The Physics of Sneezing
Sneezing can be a major factor in the spread of some illnesses. Not only does sneezing spew out a cloud of tiny pathogen-bearing droplets, but it also releases a warm, moist jet of air. Flows like this that combine both liquid and gas phases are called multiphase flows, and they can be a challenge to study…