The Plateau-Rayleigh instability is one that just about everyone has witnessed. It describes how a liquid jet breaks up into droplets. Notice the waviness in the jet before breakdown. The tiniest curvature in the jet causes an imbalance in the liquid’s pressure due to surface tension. Because the system is unstable, any small changes will become larger, ultimately resulting in the jet breaking into droplets.
Tag: fluid dynamics
How to Grow Straight Icicles
New research suggests that icicles grow straighter when exposed to moving air while exposure to still air can cause icicles to sprout at their tips. To grow icicles, the researchers built a refrigerated box that dripped water from the top while the growing icicle rotated. Understanding ice growth is important for flight aerodynamics and icing on airplane wings. For videos and more on icicle growth, see the article at Wired Science. #
Happy Anniversary, Enterprise!
Wind tunnels are great, but there’s nothing like a flight test to learn about the aerodynamics of a new vehicle. Today in 1977, the space shuttle prototype Enterprise flew on its own for the first time. Enterprise was built purely to test the shuttle’s aerodynamic behavior during gliding and landing. Check out this video of one of Enterprise’s gliding and landing tests.
Un-mixing a Flow
Laminar flow (as opposed to turbulence) has the interesting property of reversibility. In this video, physicists demonstrate how flow between concentric cylinders can be reversed such that the initial fluid state is obtained (to within the limits of molecular diffusion, of course!)
For more examples, see the first half of this video.
Floating on an Invisible Sea
Many gases may be invisible to the human eye, but that doesn’t make them the same. Sulfur hexafluoride is more than 5 times as dense as air at standard conditions, which lends itself to some fun demonstrations.
The Weissenberg Effect
Non-Newtonian fluids exhibit all kinds of odd behaviors, even climbing up a spinning rod! This is known as the Weissenberg effect and is associated with polymers in the fluid.
Bouncing into a Pool
Here is another take on what happens when a drop of water falls into a larger pool.
Automotive Wind Tunnels
Wind tunnels have been a staple of aerodynamics since the Wright brothers built one to help them test wing shapes for their gliders and airplanes. The GM Aerodynamics Laboratory’s much larger wind tunnel, pictured above, tests full-sized vehicles’ aerodynamics. It is the largest automotive wind tunnel and has been in operation since August 1980. GM estimates that it has cut the coefficient of drag on vehicles by approximately 25% in that time. The tunnel can reach speeds near 125 mph, as one hapless reporter discovered firsthand. (Submitted by @Vinnchan)
Ferrofluid Art
Magnetism and fluid dynamics collide with ferrofluids! Ferrofluids are a suspension of ferrous material in oil or water, but their behavior around magnets can elevate them into a work of art (or a car commercial). Why leave it to professionals, though, when you can make your own ferrofluid?
Fizziness in Space
Removing gravity has interesting effects on fluids. Here an astronaut aboard the ISS demonstrates what happens when Alka-Seltzer is added to water in microgravity.
