Cooling helium down to 2 Kelvin creates a superfluid, a special type of fluid that exhibits some bizarre properties. Superfluids have zero viscosity, meaning that they are frictionless, and infinite thermal conductivity, which means that any temperature changes are immediate throughout the fluid.
Tag: fluid dynamics
Avalanche Disk
In the Science Storms section of the Chicago Museum of Science and Industry, you’ll find the mesmerizing sight of an avalanche disk. This 20ft disk spins at a variable rate and angle, and, from the video, you can see that the glass beads simulating an avalanche on the disk move very much like a fluid even though they are not. This is what’s called a granular flow and it’s driven by gravity and friction between particles.
Combustion in Microgravity
‘Hot air rises.’ It’s common knowledge. But we usually forget that this is only true thanks to Earth’s gravity. On Earth, a candle flame’s distinctive pointed shape is due to hot air rising. Without gravity, there is no buoyant convection; hot air has no reason to rise (and no definition of what up is either!). This makes flames in microgravity spherical, as in the video above from a drop tower on earth. See also: astronaut explains fire in microgravity.
Shock Waves in Space
Shock waves are not just an earthbound phenomenon. They can be found in space as well. In this photo, gas (colored yellow) ejected from a dying star hits clouds of gas and dust (colored blue), creating shock waves. #
Volcanic Vortex Rings
Plants and dolphins are not the only ones in nature creating vortex rings. Volcanoes are known to produce them as well. The vortex ring forms when gas is rapidly expelled from the volcano (much the same way as with a vortex cannon); the rings are visible in the video above because smoke has been entrained into the vortex.
Fire Tornado Formation
The phenomenon of a fire tornado caught our attention recently after the BBC published footage of one in Brazil. While it may look like the fiery wrath of a god, the fluid dynamics of a fire tornado are relatively simple (see figure above). Still, they make for some pretty wild video.
Tempus II
While not strictly fluid mechanical Philip Heron’s Tempus II features some great slow-motion action of fluids. (Submitted by @ftematt)
Vortex Shedding
Whenever a bluff (i.e. non-aerodynamic) body is placed in a flow of sufficient Reynolds number, it will shed periodic vortices, creating a pattern known as a von Karman vortex street. The animation above shows the phenomenon in the wake of a cylinder, but vortex streets form behind many other bodies as well, including islands. Each vortex shed causes forces on the body and alternating vortices can cause the body to vibrate. This is what causes suspended power lines to “sing” in the wind. #
Soap Bubbles in High-Speed
Everyone has played with soap bubbles. They’re an excellent demonstration of surface tension, even more so when filmed at 5,000 frames per second.
Whipping Instabilities
When jets of liquid are introduced into an electrified medium in a process known as electrospinning, they can exhibit behavior known as whipping instabilities.
