Celebrating the physics of all that flows with Nicole Sharp, Ph.D.
- Profile
Vortex Street
A flow visualization behind a cylinder shows the formation of a von Karman vortex street. The frequency of vortex shedding in the wake is directly related to the speed of the airflow–the higher the velocity, the faster vortices will shed from the cylinder. This relationship is expressed in the Strouhal number, which remains constant for…
Waves on Cornstarch
A thin layer of the non-Newtonian fluid oobleck on a vibrating surface (in this case, a speaker) is a great way to show off nonlinear standing waves known as Faraday waves. The waves form because, under these circumstances, the flat surface of the air/oobleck interface has actually become unstable.
Frosting on Superhydrophobic Surfaces
Icing on airplane wings can be disastrous for lift and control, and thus how ice initially forms on a wing is an active area of research. New work shows that superhydrophobic (water-fearing) surfaces may actually promote ice buildup. Superhydrophobic surfaces are prone to frosting–collecting ice that forms directly from a vaporous state–and that fine layer…
Droplet Impact in 3D
This stereo photo of a droplet by John Hart shows the formation of a crown and droplet breakup. It’s possible to see the picture in 3D by crossing one’s eyes. #
Thermal Convection
This video turbulent convection in a vertical channel. Buoyancy and the density variations caused by small differences in temperature are what drive the behavior.
The Roaming Rocks of Death Valley
The dry lake beds of Death Valley National Park in California are home to a perplexing phenomenon: roaming rocks. These rocks, some of which weigh hundreds of pounds, leave long furrows in the dirt but have no obvious means of propulsion. One theory posits that the rocks glide on collars of ice around their base.…
Steering Water Droplets
At the microscale, fluid behavior can be quite different than what we witness in everyday life. Mechanisms that have little effect on the macroscale suddenly become extremely important in a channel only a few hundred microns wide. Here, water droplets in oil are steered and controlled using lasers.
Starting a Rocket
This computational fluid dynamics (CFD) simulation shows the start-up of a two-dimensional, ideal rocket nozzle. Starting a rocket engine or supersonic wind tunnel is more complicated than its subsonic counterpart because it’s necessary for a shockwave to pass completely through the engine (or tunnel), leaving supersonic flow in its wake. Here the situation is further…
Viscous Fingers
This photo shows the Saffman-Taylor instability in a Hele-Shaw cell. Here a viscous fluid has been placed between two glass plates and a second less viscous fluid inserted, resulting in a finger-like instability as the less viscous fluid displaces the more viscous one. This is an effect that can be easily explored at home using…
Airplanes Creating Snow
Scientists now think that that airplanes may be responsible for increasing local snowfall by flash-freezing supercooled water vapor in clouds. Water droplets can persist in the atmosphere to temperatures of -42 degrees Celsius. But when an airplane’s wing passes through moist air, the acceleration of the air passing over the wing causes a pressure decrease…