This video discusses a new quieter and more efficient CPU fan developed by engineers at Sandia National Labs. As the impeller spins, it draws ambient air down the center of the impeller while the shape of the fins forces air past the fins and out radially. As the air flows over the fins, it draws heat from the CPU away. In a sense, the design combines a heat sink with a fan. (Video credit: Sandia National Labs; submitted by Adam L)
Category: Research
Schlieren Montage
Dr. Gary Settles, a world-reknown expert in schlieren photography, shows here a montage of some of his lab’s results, including shockwaves from musical instruments, dogs sniffing, guns firing (both sub- and supersonic), and even snapping a wet towel going supersonic. As Settles jokes, schlieren is all mirrors and hot air. Mirrors are used to shine collimated light on the object to be imaged; then the light focused with a lens. By placing a knife-edge at the focal point, part of the light is blocked and the density variations in the final image become visible, thanks to their differing refractive indices. (Video credit: G. Settles et al.)
The Vibrating Network
We’ve seen the Faraday instability on vibrating fluids (and granular materials) before. Here researchers explore the effect on a a network of fluid-filled cells. Each square is filled with liquid and small holes near the bottom of each cell ensure the liquid levels are the same throughout the array. Then the entire container is vibrated. Above the threshold frequency, standing waves form but do not interact. When the wave amplitudes grow high enough for fluid to get exchanged from cell to cell, patterns begin to form. The waves in adjacent cells synchronize, eventually resulting in a regular pattern across the entire grid. Order out of chaos.(Video credit: G. Delon et al.)
Labyrinth
A labyrinthine pattern forms in this timelapse video of a multiphase flow in a Hele-Shaw cell. Initially glass beads are suspended in a glycerol-water solution between parallel glass plates with a central hole. Then the fluid is slowly drained over the course of 3 days at a rate so slow that viscous forces in the fluid are negligible. As the fluid drains, fingers of air invade the disk, pushing the beads together. The system is governed by competition between two main forces: surface tension and friction. Narrow fingers gather fewer grains and therefore encounter less friction, but the higher curvature at their tips produces larger capillary forces. The opposite is true of broader fingers. Also interesting to note is the similarity of the final pattern to those seen in confined ferrofluids. (Video credit and submission: B. Sandnes et al. For more, see B. Sandes et al.)
Antibubbles
Antibubbles–a liquid droplet surrounded by a thin film of gas and immersed in more liquid–are fragile things. This video explores how antibubbles behave when placed in proximity to a tornado-like whirl. When placed near the eye, where fluid motion is primarily vertical, the antibubble is stretched vertically. When placed in the rotating eyewall, the antibubble is distorted into a ring-like shape before it breaks down. (Video credit: D. Terwagne et al; APS Gallery of Fluid Motion 2009)
Fractal Fluids
These images from a numerical simulation of a mixing layer between fluids of different density show the development and breakdown to Kelvin-Helmholtz waves. The black fluid is 3 times denser than the white fluid, and, as the two layers shear past one another, billow-like waves form (Fig 1(a)). Inside those billows, secondary and even tertiary billows form (Fig 1(a) and (b)). Fig 1 (c)-(e) show successive closeups on these waves, showing their beautiful fractal-like structure. (Photo credit: J. Fontane et al, 2008 Gallery of Fluid Motion) #
How Mosquitoes Fly in the Rain
One might think that rainfall would keep the mosquitoes away, but it turns out that rain strikes don’t bother these little pests much. Because the insect is so small and light compared to a falling raindrop, the water bounces off instead of splashing. This results in a relatively small transfer of momentum, although the mosquito does get deflected quite strongly. Researchers estimate that the insects endure accelerations up to 300 times that of gravity, which is more than 10 times what a human can withstand. (Video credit: A. Dickerson et al; submitted by Phillipe M.)
Dancing Sands
Here a collection of dry grains are vertically vibrated, creating a series of standing waves on the surface of the sand. The shapes of these Faraday waves are dependent upon the frequency of the vibration. Despite the solid nature of sand particles, this behavior is much the same as the behavior of a vibrated fluid.
Splash Rebound
A ball dropped onto a puddle loses some of its rebound momentum to fluid motion. On impact, a splash curtain and radial jet form as the fluid is displaced by the ball. As the ball rebounds, the splash curtain is drawn inward into a column of fluid drawn up by the ball, reminiscent of the way cats and dogs drink. Eventually, when the gravity’s force on the fluid column overcomes the force of the ball’s inertia, the fluid column pinches off and falls back downwards, leaving the ball free to utilize its remaining kinetic energy as it flies upward. (Photo credit: T. Killian, K. Langley, and T. Truscott)
Rotating or Not-Rotating?
Rotating a fluid often produces different dynamical behavior than for a non-rotating fluid. Here this concept is demonstrated by dropping creamer into a tank of water. Both experiments produce a turbulent plume, but the way the plume spreads and diffuses is much different in the case of the rotating tank, thanks to the Coriolis effect. (Video credit: SPINLab UCLA)
