It may look like an oil slick, but the photo above actually shows the clouds of Saturn. The false-color composite image reveals the gas giant in infrared, at wavelengths longer than those visible to the human eye. NASA uses this infrared photography to identify different chemical compositions in Saturn’s atmosphere based on how they reflect sunlight. You can see an example of how they construct these images here. This detail shot appears to show cloud bands of different compositions mixing. You can see hints of shear instabilities forming along the edges where the light and dark bands meet. (Image credit: NASA; via Gizmodo)
Tag: flow visualization
Coarsening in a Soap Film
Flow in a soap film is driven by gravity’s efforts to thin the film and surface tension’s attempts to stabilize variations in thickness. Because evaporation guarantees that the soap film will eventually dry out, gravity typically wins the battle and causes a soap film to rupture. This video takes a close look at what happens in the film just before it ruptures. Black dots form in the thinnest region of the flow. These areas are not holes, but they appear black because they are thinner than any wavelength of visible light. Before rupture, the black dots begin coalescing with one another, first due to diffusion and later more rapidly due to convection in the soap film. Ultimately, the black dots are the harbingers of doom for the fragile bubble. (Video credit: L. Shen et al.)
Fluorescein Ghosts
Fluorescein is a popular chemical for flow visualization, and, as this video from Shanks FX demonstrates, it’s not hard to extract from highlighters if you’d like to experiment with it yourself. Fluorescein can also be purchased in powder form, but it’s typically rendered into a dye before use. When dripped into water, it can leave behind ghostly glowing wakes. Happy Halloween! (Video credit: Shanks FX)
In other news, I am back from my vacation! Thanks again to Claire from Brilliant Botany for looking out for everything while I was gone. – Nicole
Fluid Fingers
Fluid phenomena can show up in unexpected places. The collage above shows patterns formed when an aluminum block is lifted during wet sanding, a polishing technique. The dendritic fingers are formed from oil and the slurry of sanded particles being polished away. They are an example of the Saffman-Taylor instability, which forms when less viscous fluids (oil) protrude into a more viscous one (the slurry). Each image contains a different concentration of oil, resulting in very different fingering patterns. (Image credit: D. Lopez)
Vortex Wake in Quebec
These satellite images show Rupert Bay in northern Quebec. Sediment and tannins have stained the bay’s waters various shades of brown, which helps show the dynamic flows of the area. Rivers empty into the bay, but the tide appears to be coming in from the northwest as well. The flow is just right to create a wake of alternating vortices off a tiny island near the center of the bay. This pattern is known as a von Karman vortex street and often appears in the wake of spheres, cylinders, and, yes, islands. (Image credit: NASA Earth Observatory; submitted by Adam V.)
Giant Vortex Cannon
Playing with a vortex cannon is a ton of fun, and they are remarkably easy to make. You can knock over cups or card houses, create art, or just try your best Big Bad Wolf impression. Or you can supersize things like one group in the Czech Republic did and build a 3m vortex cannon capable of firing 100m! (Seriously, watch it in action here.) And if you’d like to learn more about how vortex rings form and why they’re useful in nature and engineering, check out my vortex ring video. (Image credit: Laborky Cz, source; via Gizmodo)
Fog Over Marin
Fog rolls over the hills of Marin County in this long-exposure photograph by Lorenzo Montezemolo. One of the most beautiful aspects of fluid dynamics is the way the same patterns and forms show up across situations. The slow flow of fog over hills in moonlight can echo the blurring speed of rivers pouring over a rocky streambed. Despite the differences in speed, lengthscale, and fluid, the physics remain the same. (Photo credit: L. Montezemolo; via Colossal)
Shear Across the Water
This photo series shows the development of a Kelvin-Helmholtz instability. It’s formed when two layers of fluid move past one another at different speeds. In this case, the two fluids meet off the back of a flat plate (seen at the left of the top image) when fast-moving flow from the top of the plate encounters slower fluid beneath. Friction and shear between the fluid layers causes billows to rise up and form waves very similar to those on the ocean (wind across the water works the same way!). Those waves turn over into vortex-like spirals and keep mixing until they break down into turbulence. This pattern crops up pretty frequently, especially in clouds. (Image credit: G. Lawrence)
“Catacomb of Veils”
Burning Man’s “Catacomb of Veils”, the largest sculpture burned in the 2016 event, produced a series of smoke tornadoes as it blazed. Like dust devils or fire tornadoes, these vortices are driven by hot, buoyant air rising – in this case, from the fire. As the surrounding air moves in toward the fire, any rotational motion, or vorticity, in the air is intensified due to conservation of angular momentum. That concentrates it into a vortex, which becomes visible when it picks up smoke. Simultaneously, the wind was blowing in a consistent direction, sending any new vortices generated marching downstream. You can watch even more vortices and some slow-motion footage of the burning in the full video by Mark Day. (Image credit: M. Day, source; submitted by Larry B)
Bioluminescent Shrimp
Trevor Williams and Jonathan Galione of Tdub Photo captured these beautiful images of bioluminescent shrimp along the Japanese coast. The duo collected the tiny shrimp and poured them over and near rocks to create the effect they wanted. With their blue light, the shrimp act like tracer particles in the water, and with long exposures, the photos track the movements of the shrimp and waves. Technically speaking, they trace out pathlines – the trajectory that a specific fluid (or shrimp) particle takes in a flow. It’s a lovely way of capturing the water’s dynamic motion in a still photo. (Image credit: Tdub Photo; via Colossal)
