An artificial fire tornado makes for fascinating viewing. The box fans are positioned around a central firepit such that they impart the angular velocity needed to create a vortex. I’ve actually seen an even bigger live demonstration than this one at a fluid dynamics conference. Do not try this yourself. Fire tornadoes occur in nature, too: take a look at how they form. (submitted by acervant)
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Sea Surface Temperatures
This video shows sea surface temperature results and their seasonal variation from a numerical simulation modeling circulation in the atmosphere and oceans. Modeling such enormous problems requires the development of reasonable models of the turbulent physics, clever algorithms to quickly progress the solutions, relatively low-fidelity (a single grid node may cover tens of kilometers), and enormous computing power. (Video credit: NOAA; via Gizmodo)
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)
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)
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.)
“Cascades”
Ryan Teague’s “Cascades” music video features the enchanting process of ice growth. A chamber full of supercooled water vapor subject to a strong electric field is stimulated to grow crystals by providing a needle as the initial nucleation site. Because the vapor is supercooled, it will freeze upon contact with the nucleation site; the electric field keeps the water molecules aligned so that the crystal patterns formed are more even. The tree-like pattern seen here is called dendritic crystal growth; branches form at faults in the crystalline pattern. (Video credit: Ryan Teague, Village Green, Words are Pictures; via Gizmodo)
Viscous Dripping
Artist Skye Kelly’s “Creep (strain)” sculpture shown above is made from toffee. The viscous fluid deforms under the force of gravity, resulting in elongated drips and slow jets that buckle and coil upon reaching the floor. (Photo credits: Skye Kelly; via freshphotons)
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.
Honey Coiling
The liquid rope coiling effect occurs in viscous fluids like oil, honey, shampoo, or even lava when they fall from a height. The exact behavior of the coil depends on factors like the fluid viscosity, the height from which the fluid falls, the mass flow rate, and the radius of the falling jet. Here Destin of the Smarter Every Day series outlines the four regimes of liquid coiling behavior commonly observed. As with many problems in fluid dynamics the regimes are described in terms of limits, which can help simplify the mathematics. The viscous regime (2:34 in the video) exists in the limit of a small drop height, whereas the inertial regime (3:15) exists in the limit of large drop height. Many complicated physical problems, including those with nonlinear dynamics, are treated in this fashion. For more on the mathematics of the coiling effect, check out Ribe 2004 and Ribe et al. 2006. (Video credit: Destin/Smarter Every Day; submitted by inigox5)