Home to storms capable of lasting for a hundred years or more, Jupiter’s atmosphere is a highly turbulent place. Currently, no comprehensive theory exists to explain the symmetry of Jupiter’s bands of clouds and the persistence of vortices such as the Great Red Spot, however, the mixing and stratification visible on the planet remains a beautiful reminder of the power of fluid dynamics. (Photo credits:Cassini – 1, 2, Voyager 1, New Horizons – 1, 2)
High-speed video of a soap bubble being popped reveals the directionality of the process. Like a the rubber of a bursting balloon, the soap film rushes away from the point of rupture, disintegrating as the information about a sudden lack of surface tension is propagated across the remaining film surface. In this regard, it is much like what happens when you drop a slinky toy.
The scramjet–supersonic combustion ramjet–engine has been a holy grail of aerospace engineering for 50 years. It is an air-breathing engine with no moving parts capable of propelling crafts at hypersonic speeds beyond Mach 5. As indicated in the name, combustion in the scramjet occurs at supersonic speeds, where the heating due to air compression is sufficient to ignite fuel when injected into the engine. At present the record for the highest speed attained in scramjet flight is held by the NASA X-43A, which reached Mach 9.8 in 2004 after about 10 seconds of scramjet free-flight. The longest scramjet flight belongs to the Boeing X-51 Waverider with 140 seconds of burn time in a 2010 test flight. Few tests of these experimental hypersonic crafts have been completely successful; they represent the frontier of aerospace technology.
Atomization–breaking a liquid into a fine spay of droplets–is common in engines, printers, and in the shower. Here a droplet of water is placed on a thin metal diaphragm that is vibrated at 1 kHz with increasing vibrational amplitude. Capillary waves form on the droplet, and once a critical vibrational amplitude is achieved, tiny droplets are ejected. Full atomization of the original droplet is achieved in about 0.3 seconds real-time. #
Smoke issuing from a round jet undergoes transition from laminar to turbulent flow. As the smoke moves past the unmoving ambient air, the friction between these two layers creates shear and triggers a Kelvin-Helmholtz instability, recognizable by the formation and roll up of vortices along the edges of the jet. Those vortices then roll together in pairs, detach, and devolve into a generally turbulent flow. Because turbulence is far more efficient at mixing than a laminar flow is, the smoke seems to disappear.
An M-class solar flare with a towering prominence erupted from the Sun over the course of three hours in late September. Notice how the plasma does not fall straight back to the surface but flows back down following the Sun’s magnetic field lines. As an rarefied ionized gas, plasma follows coupled laws of electromagnetism and fluid dynamics. #
Swirls of blue in the Great Lakes mark locations of recent autumn storms whose winds have stirred up sediment in the lakes. The silt and quartz sand acts as a tracer particle, making visible the circulation patterns of the lakes. In contrast, the green streaks mark locations of calmer winds and warmer temperatures where algae blooms have grown. Note the fundamental dissimilarity in their structures. Blue eddies turn over and mix in a fashion reminiscent of convective instabilities while the green blooms are far more uniform in structure. #
When a droplet impacts a pool at low speed, a layer of air trapped beneath the droplet can often prevent it from immediately coalescing into the pool. As that air layer drains away, surface tension pulls some of the droplet’s mass into the pool while a smaller droplet is ejected. When it bounces off the surface of the water, the process is repeated and the droplet grows smaller and smaller until surface tension is able to completely absorb it into the pool. This process is called the coalescence cascade.
Schlieren imaging has applications even in public health. This video demonstrates the spread of contagion via coughing with and without a mask on. Although air from the cougher’s lungs escapes the sides of the mask, it mostly rises on a thermal plume rather than projecting 1 to 2 meters forward in a turbulent jet as in the maskless case. Flu season is just starting. Don’t forget to get your flu shot!
Tangentially fluids-related, but SpaceWeather has a fun video of a high-altitude helium balloon bursting. Although this balloon carried a space-related payload, it’s the same type of set-up used for weather balloons. With only a few basic assumptions, it’s possible to do some neat calculations on the buoyancy, loading capacity, and behavior of such balloons.