Where warm and cold ocean currents collide, turbulent eddies form and pull up valuable nutrients from the ocean floor. Massive phytoplankton blooms ensue, effectively providing natural flow visualization for the process. #
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Marangoni Convection in Space
In this Saturday Morning Science video, astronaut Don Pettit demonstrates Marangoni convection in microgravity using a water film with tracer particles, a soldering iron, and a flashlight. This same effect occurs on earth but is masked behind the much stronger effect of buoyant convection.
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. #
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 that can drop the temperature by as much as 19 C, causing the water droplets to form ice crystals immediately. (The particulate matter in the aircraft exhaust probably also aids this process.) The same behavior can also create holes in clouds and cause ice to form on the wings. # (Related behavior: vapor cones)
Photo credit: lhoon
Leaping Ferrofluid
This video shows some of the dynamic behaviors of a ferrofluid near moving magnetic fields. Ferrofluids are formed from a suspension of ferrous particles in a liquid, usually oil.
Archimedes
Archimedes may be the world’s most famous fluid mechanician. The story of his discovery of the principles of buoyancy (and his subsequent running naked through the streets proclaiming “Eureka!”) is classic. His other famous fluid-related invention is the Archimedes screw, a type of pump still used today in applications from moving granular flows to maintaining blood flow in heart patients. Scientific American is currently featuring a book excerpt about Archimedes and his contributions to physics and math. It’s well-worth a read. #
Microgravity Water Films
In this video astronaut Don Pettit demonstrates some interesting laminar flow effects using a water film in microgravity. By using a film, fluid motion is essentially confined to two dimensions. This is important because it prohibits the development of turbulence, which is a purely three-dimensional phenomenon. Doing the experiment in microgravity allows Pettit to leave the experiment for a long period of time without buoyant effects or similar disturbances. When he first stirs the film, the tracer particles show some signs of what looks like turbulent mixing, but soon the film rotates uniformly with streaks of gray caused by different concentrations of tracer particles. Pettit notes that he allowed the film to rotate overnight and it eventually all turned milky white. This is the effect of molecular diffusion of the tracer particles; without turbulence, the only way for mixing to occur is through the random motion of molecules. See more of Pettit’s Saturday Morning Science videos for additional microgravity fluid mechanics.
The ABCs of Physics
b=buoyancy is part of Ashley JM’s photo set The ABCs of Physics. In her words:
Buoyancy is what causes less dense objects to float in a more dense fluid, such as a helium balloon in air. There is a buoyant force that pushes up on the object, equal to the weight of the displaced fluid.
That little diagram up there is called a force diagram, they can be even more daunting than equations at times. This one shows that the buoyant force up on the balloon is equal to the force of tension in the string, this keeps the balloon in equilibrium.
Be sure to look at the rest of her physics photos! # (via physicsphysics)
Vibrating Oobleck
[original media no longer available]
This video explores some of the non-Newtonian behaviors of oobleck when shaken. The pattern across the surface once the vibrations start is called Faraday waves, a type of nonlinear standing wave that forms once a critical vibrational frequency is passed and the flat surface of the fluid becomes unstable. Toward the end of the video, the frequency of the vibrations is increased until “finger-like protrusions” form. This is a behavior exhibited by shear-thickening non-Newtonian fluids.
Bristling Scales Give Sharks Speed
The shortfin mako shark is one of the ocean’s fastest and most agile hunters, thanks in part to flexible scales along its body. As water flows around the shark’s body, the scales bristle to angles in excess of 60 degrees. This causes turbulence in the boundary layer along the shark’s body and prevents boundary layer separation which would otherwise increase the shark’s drag. In this respect, the scales serve much the same purpose as dimples on a golf ball. (Abstract, National Geographic article) #