Another look at the science behind the roaming rocks of Death Valley.
Category: Phenomena
Rocket Launch Phenomena
The launch of the Solar Dynamics Observatory (SDO) last year provided a rarely seen glimpse of how shock waves affect the atmosphere during launch, but only recently have researchers explained the white column that seemed to follow SDO toward orbit. Simulations indicate that the shock waves from the rocket aligned the ice crystals in the atmosphere into an array of spinning tops. Individual crystals precess as a result of the rocket passing; the column is part of a larger oval that would have been visible had the ice crystals covered a larger range. See Wired for more. #
Hole-Punch Clouds
These hole-punch clouds seen over Myrtle Beach, SC were probably caused by three aircraft flying in military formation. When airplanes pass through supercooled water vapor, the acceleration of air over the wing causes a pressure drop that can flash-freeze the water vapor, resulting in a localized snow shower. See National Geographic for more. #
How Ferrofluids Work
Here’s a ferrofluid video with a little more explanation about how ferrofluids work. Surfactants prevent the tiny magnetic particles suspended in the fluid from separating out when exposed to a magnetic field.
High-Speed Leidenfrost Levitation
The Leidenfrost effect occurs when a liquid encounters a surface with a temperature much higher than its boiling point. Some of the liquid is instantly vaporized and then a droplet will skate across the surface on that vapor. This video shows the process at 3000 frames per second.
Volcanic Turbulence
One of the characteristics of turbulence is its large range of lengthscales. Consider the ash plume from this Japanese volcano. Some of the eddy structures are tens, if not hundreds, of meters in size, yet there is also coherence down to the scale of centimeters. In turbulence, energy cascades from these very large scales to scales small enough that viscosity can dissipate it. This is one of the great challenges in directly calculating or even simply modeling turbulence because no lengthscale can be ignore without affecting the accuracy of the results. #
The Pistol Shrimp’s Secret Weapon
The pistol shrimp (or pistol crab) is a finger-sized crustacean with a fluid dynamical superpower. When it snaps its claw, a jet of water shoots out so quickly (62 mph) that a low-pressure bubble forms in its wake. When the bubble collapses, it emits a bang and a flash of light in a process known as sonoluminescence. The whole event takes less than 300 microseconds. The light emitted suggests that temperatures inside the bubble reach 5,000 degrees Kelvin, around the temperature of the surface of the sun. #
Instability in a Jet
This photo shows the development of a flow instability in an axisymmetric jet. On the left, the jet is smooth and fully laminar, but, by the center of the photo, disturbances in the jet have grown large enough to distort the laminar profile. The jet is then in transition; by the right side of the frame, it has reached a turbulent state, as evidenced by the increased mixing (which causes the smoke to disperse more quickly) and intermittency of the flow. #
Reader Question: National Committee for Fluid Mechanics Films
lazenby asks: Have you seen these guys? http://web.mit.edu/hml/ncfmf.html
Yes, absolutely! Those videos, which date from the 1960s, are so useful that they’re still shown to undergraduates today. (Or at least they showed several of them to us when I was junior!) They can seem a bit slow by current standards, but the films are full of great demonstrations of basic fluid mechanics. If the links on that page don’t work (or, if like me, you can’t stream RealPlayer), a lot of the videos can also be found on YouTube by searching for individual titles. The Low Reynolds Number Flow video is one of my favorites because it’s hosted by G. I. Taylor, one of the the most prolific and influential fluid mechanicians of the 20th century.
Flow Visualization
[original media no longer available]
This video gives a neat introduction to some common and uncommon techniques used to visualize fluid flows.
