Jupiter’s colorful cloud bands alternate between dark belts and light zones. The bands mark convection cells in Jupiter’s atmosphere, and, like on Earth, powerful jet streams form due to this atmospheric heating and the planet’s rotation. The jet winds can even move in opposite directions, creating strong shear forces between neighboring cloud bands. The shear helps drive Kelvin-Helmholtz instabilities in the clouds, resulting in the regularly spaced waves and vortices seen along the edges of some bands. (Image credit: NASA/ESA; via APOD)
Search results for: “art”
The Droplet Slide
One of the joys of science is the sense of discovery that can come even from looking at something seemingly simple. Take, for example, a water droplet sitting on a plate. If you slowly tilt the plate, the droplet’s shape will shift until a critical angle where it starts sliding down the plate. But what happens to two initially different droplets? As this video shows, tilting two droplets of initially different shapes and returning them to horizontal causes the droplets to assume the same shape. There’s a universal behavior at work here–like nature has a kind of reset button that makes gravity and surface tension work together such that a droplet will assume a preferred shape. For an experimentalist, it’s certainly a handy way to create repeatable experiments! (Video credit: M. Musterd et al.)
Viscous Fingers
Take a viscous fluid, like laundry detergent, and sandwich it between two plates of glass. Fluid dynamicists call this set-up a Hele-Shaw cell. If you then inject a less viscous fluid, like air, between the plates–or if you try to pry them apart–you’ll see a distinctive pattern of dendritic fingers form. This viscous fingering, also known as the Saffman-Taylor instability, occurs because the interface between the two fluids is unstable. Invert the problem, though–inject a more viscous fluid into a less viscous one–and no special shapes will form because the interface will remain stable. (Image credit: Random Walk Studios, source)
Deforming Soap Films
It’s the time of year when new Gallery of Fluid Motion videos start popping up online. We’ve already featured several and no doubt there will be more to come. Today’s post is a submission from Saad Bhamla, who gave this introduction to the work:
Soap bubbles occupy the rare position of delighting and fascinating both young children and scientific minds alike. Sir Isaac Newton, Joseph Plateau, Carlo Marangoni and Pierre-Gilles de Gennes, not to mention countless others, have discovered remarkable results in optics, molecular forces and fluid dynamics from investigating this seemingly simple system.
This video is a compilation of curiosity-driven experiments that systematically investigate the surface flows on a rising soap bubble. From childhood experience, we are familiar with the vibrant colors and mesmerizing display of chaotic flows on the surface of a soap bubble. These flows arise due to surface tension gradients, also known as Marangoni flows or instabilities. In this video, we show the surprising effect of layering multiple instabilities on top of each other, highlighting that unexpected new phenomena are still waiting to be discovered, even in the simple soap bubble.
As illustrated in the video, raising a bubble beneath the soap film moves surfactants in the film, which causes local differences in surface tension. Any time a difference in surface tension exists, fluid will flow from areas of low surface tension to ones with higher surface tension. This is called the Marangoni effect. On a soap bubble, this is visible in the chaotic swirling colors we see. In this system, Bhamla and his co-author found that by raising the bubble in steps, they could “freeze” the Marangoni-induced patterns created by the previous motion. (Video credit and submission: S. Bhamla et al.)
Glow-Stick Ferrofluids
Ferrofluids create all kinds of fascinating shapes when exposed to magnetic fields. In this video, Dianna from Physics Girl shows off what happens when you combine a ferrofluid with glowsticks and explains how ferrofluids get some of their unique properties. Ferrofluids consist of tiny nanoparticles of magnetic material that are surrounded by surfactants and suspended in a carrier fluid. This creates a fluid whose shape depends on gravity, surface tension, and the local magnetic field. By manipulating the relative strength of these forces, you can create everything from spikes to maze-like patterns to whatever this is. (Video credit and submission: Physics Girl)
Bullet-Time Inferno
Remember the bullet time effect from The Matrix? This spectacular video gives you a similar effect with the turbulent flames created by firebreathers. To capture this level of detail, Mitch Martinez uses an array of 50 cameras placed around the performers, allowing him to reconstruct the full, three-dimensional representation of the flames. Similarly, some scientists use arrays of high-speed video cameras to collect 3D, time-resolved data about phenomena like combustion. Because these flows are so complex in terms of their fluid dynamics and chemistry, capturing full 3D data is important to help understand and model the flow better. (Video credit: M. Martinez; via Rakesh R.)
Pollock-Style Physics
Here on FYFD, we like to show off the artistic side of fluid dynamics. But some researchers are actively studying how artists use fluid dynamics in their art. In this video, they examine one of Jackson Pollock’s painting techniques, in which filaments of paint were applied by flinging paint off a paintbrush. Getting the technique to work requires a fine balance of forces and effects. Firstly, the paint must be viscous enough to hold together in a filament when flung. Secondly, the centripetal acceleration of the rotation must be high to both form the catenary filament and throw it off the brush. And, finally, the Reynolds number needs to be high enough to add some waviness and instability to the filament so that it looks interesting once it hits the canvas. Also be sure to check out the group’s previous work exploring Siqueiros’s painting techniques. (Video credit: B. Palacios et al.)
Early Rocket Launch
Pre-dawn launches provide some of the most dramatic rocket footage. This video is from an October 2nd Atlas V launch, and the really fun stuff starts at about 0:34. As the rocket climbs to higher altitudes, the atmospheric pressure around it decreases. As a result of this low pressure, the rocket’s exhaust gases balloon outward in a giant plume many times larger than the rocket. This happens in every launch, but it’s visible here because the rocket is at such a high altitude that its exhaust is being lit by sunlight while the observers on the ground are still in the dark. The ice crystals in the exhaust–much of the rocket’s exhaust is water vapor–reflect sunlight down to the earth. Around 0:47, a cascade of shock waves ripples through the plume just before the first-stage’s main engine cuts off. Once the engine stops firing, there’s no more exhaust and the plume ends. (Video credit: Tampa Bay Fox 13 News; submitted by Kyle C)
Un-Mixing a Flow
This video demonstrates one of my favorite effects: the reversibility of laminar flow. Intuition tells us that un-mixing two fluids is impossible, and, under most circumstances, that is true. But for very low Reynolds numbers, viscosity dominates the flow, and fluid particles will move due to only two effects: molecular diffusion and momentum diffusion. Molecular diffusion is an entirely random process, but it is also very slow. Momentum diffusion is the motion caused by the spinning inner cylinder dragging fluid with it. That motion, unlike most fluid motion, is exactly reversible, meaning that spinning the cylinder in reverse returns the dye to its original location (plus or minus the fuzziness caused by molecular diffusion).
Aside from being a neat demo, this illustrates one of the challenges faced by microscopic swimmers. In order to move through a viscous fluid, they must swim asymmetrically because exactly reversing their stroke will only move the fluid around them back to is original position. (Video credit: Univ. of New Mexico Physic and Astronomy)
Flowing Water on Mars?
Scientists have known for years that Mars once had liquid water on its surface, and they have many contemporary examples of frozen water ice on the Red Planet. But this week NASA announced the strongest evidence yet that liquid water still flows on Mars. Researchers have observed from orbit dark line-like features called recurring slope lineae (RSL) that develop, darken, and grow seasonally in many locations on Mars. The appearance of these features coincides with warmer surface temperatures (above -23 degrees Celsius), and the lines fade again when temperatures cool. Although scientists suspected the dark lines might be related to flowing water, the evidence remained circumstantial until spectral observations of multiple sites indicated that the darker features contained hydrated salts. In other words, briny salt water is still flowing at or near the Martian surface. (Image credits: NASA)