Wingtip vortices roll up in the wake of this U.S. Coast Guard C-130J. At the edge of a wing high-pressure, low velocity air is able to creep around the edge of the wingtip toward the low-pressure, high-velocity air atop the wing. This creates a swirling vortex that trails behind each wing, made visible here by the clouds entrained in the plane’s wake. Over time, these counter-rotating vortices will sink downward and break up due to viscosity and instabilities induced by their proximity. (via Aviationist)
Tag: science
The Chaos of a Bouncing Droplet
This video explores chaos in a bouncing droplet. A drop of silicon oil bounces on a vibrating bath of oil; the thin layer of air injected with each bounce between the droplet and bath keeps them from coalescing. Initially, the droplet behaves like a bouncing ball, jumping once per oscillation. As the vibration amplitude increases, the droplet begins making a small jump, then a large jump, then a small jump, and so on. This is called period doubling since the droplet now jumps in a pattern with twice the period of the original and is a hallmark of nonlinear dynamical systems. Further increase in the vibration amplitude leads to chaotic bouncing and occasional ejecta. (Video credit: D. Terwagne et al.)
Canyon Fire Timelapse
Wildfires continue to burn across Colorado and other parts of the United States. This timelapse video shows 5 days worth of the Waldo Canyon fire. Smoke billows through the night and day, with diurnal temperature changes and winds affecting whether the turbulent plumes rise high or hover on the horizon. It is hard to describe the eeriness of watching a fire burn uncontrollably on the horizon; we hope those fighting the fires stay safe and that those affected by the fires are able to return and recover soon. (Video credit: Steve Moraco; submitted by Chris P)
How the Sun Drives the Earth
This video describes how the sun’s energy drives wind and ocean currents on earth. As solar winds stream forth from the sun, our magnetosphere deflects the brunt of the impact (creating auroras at the poles) while the atmosphere, land masses, and oceans absorb thermal energy from the sun’s light. Because of our cycles of day and night and the differences in how land, water, and ice absorb heat, temperature differentials around the earth drive a massive heat engine, causing the circulation of water and wind all around our world. Numerical simulations like the ones underlying this video are vital for the prediction of climate and weather, as well as for developing models and techniques that can be applied to other problems in science and engineering. (Video credit: NASA; via Gizmodo)
Traffic Fluid Dynamics
What does traffic have to do with fluid dynamics? Rather a lot, actually! Many parallels exist between traffic and compressible fluid flow. One such example, the concept of a shock wave, is demonstrated in the video above. As the traffic jam develops, the cars experience sudden changes in their velocity and relative distance (in a fluid, this would be density). This change travels backward through the traffic in the form of a shockwave, just the same as discontinuous changes in a fluid.
Road construction provides another common example of compressible-flow-like behavior in cars. For an incompressible fluid like water, reducing the area of a pipe would increase the velocity, but just the opposite happens when a road is reduced from two lanes to one. Traffic slows down and clumps together. When the road opens back up from one lane to two, suddenly the speed and the distance between cars increases. This is exactly what happens in a rocket nozzle–it’s the expanding bell-like shape that causes air to accelerate supersonically. (Video credit: New Scientist)
Volcanic Vortices
The volcanoes of the South Sandwich Islands, located in the South Atlantic, have a notable effect on cloud formation in this satellite photo. Visokoi Island, on the right, sheds a wake of large vortices that distort the cloud layer above it. On the left, Zavodovski Island’s volcano does the same, with the added effect of low-level volcanic emissions, which include aerosols. These tiny particles provide a nucleus around which water droplets form, causing an marked increase in cloud formation visible in the bright tail streaming off the island. (Photo credit: NASA, via Earth Observatory)
New CPU Fan
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)
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.)
Inky Vortex
Ink released into water shows the swirling motion inside a vortex ring as well as its deformation and breakup upon stagnation against a wall. Although humans are known to make such vortex rings with smoke or bubbles, they are common in nature as well. Buoyant plumes often feature vortex rings at their head; dolphins and whales play with bubble rings; volcanoes blow smoke rings; and mosses use them to distribute spores.
