FYFD

Videos

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    Simulating the Earth

    Computational fluid dynamics and supercomputing are increasingly powerful tools for tracking and understanding the complex dynamics of our planet. The videos above and below are NASA visualizations of carbon dioxide in Earth’s atmosphere over the course of a full year. They are constructed by taking real-world measurements of atmospheric conditions and carbon emissions and feeding them into a computational model that simulates the physics of our planet’s oceans and atmosphere. The result is a visualization of where and how carbon dioxide moves around our planet.

    There are distinctive patterns that emerge in a visualization like this. Because the Northern Hemisphere contains more landmass and more countries emitting carbon, it contains the highest concentrations of carbon dioxide, but winds move those emissions far from their source. As seasons change and plants begin photosynthesizing in the Northern Hemisphere, concentrations of carbon dioxide decrease as plants take it up. When the seasons change again, that carbon is re-released.

    These visualizations underscore the fact that these carbon emissions impact everyone on our planet–nature does not recognize political borders–and so we share a joint responsibility in whatever actions we take. (Video credit: NASA Goddard; h/t to Chris for the second vid)

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    Visualizing Flow with Snowfall

    One of the challenges in engineering and operating wind turbines is that full-scale turbines rarely behave as predicted in smaller-scale laboratory experiments and simulations. One way to reconcile these differences (and discover what our experiments and simulations are missing) is to take the experiments out into the field. One research group has done this by using snowfall to visualize the flow around wind turbines. In this video, they share some of their observations, which include interactions of tip vortices with one another and with the vortex from the tower. My favorite part starts around 1:50 where you can observe tip vortices leap-frogging one another behind the wind turbine! (Video credit: Y. Liu et al.)

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    Freezing Drops

    A water droplet deposited on a cold surface freezes from the bottom up. As anyone who has made ice cubes knows, water expands when it freezes. But watch the outline of the drop carefully. The drop isn’t expanding radially outward while it freezes. Instead the remaining liquid part of the drop forms what’s known as a spherical cap, a shape like the sliced-off top of a sphere. Surface tension creates that spherical shape, but the water still has to expand when it freezes. The result? The last bit of the drop freezes into a point! This means that surface tension maintains the drop’s spherical shape, for the most part, and all the expansion the water does takes place vertically. (Video credit: D. Lohse et al.)

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    Liquid Fragmentation

    From spilling coffee to driving through puddles, our daily lives are full of examples of liquids fragmenting into drops. A recently published study describes how this break-up occurs and predicts what the distribution of droplet sizes will be for a given fluid. Viscoelasticity is the property that governs this droplet size distribution. Viscoelasticity describes two aspects of a fluid–its viscosity, which acts like internal friction, resisting motion–and its elasticity, the fluid’s ability to return to its original shape after stretching. Most fluids have a little bit of each of these properties, which makes them somewhat sticky, both in the sense of not-flowing-easily and in the sense of sticking-to-itself. These same properties cause viscoelastic fluids to wind up with a broader droplet size distribution, ultimately creating both more small droplets and more large droplets than a Newtonian liquid like water. (Video credit: MIT News; research credit: B. Keshavarz et al.; submitted by mrvmt)

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    “Chemical Poetry”

    In “Chemical Poetry” artists Roman Hill and Paul Mignot use fluid dynamics to create incredible and engaging visuals. With a stunningly close eye to fluids mixing and chemicals reacting, their imagery feels like gazing on primordial acts of creation or destruction. There’s even a sequence that feels like you’re watching an explosion in slow-motion, but there’s no CGI in any of it. This is just the beauty of physics laid bare, revealing the dances driven by surface tension, the undulations of a fluid’s surface, and the dendritic spread of one fluid into another – all cleverly lit and filmed for maximum effect. It is well worth taking the time to watch the whole video and check out more of their work. (Image/video credit and submission: NANO; GIFs via freshphotons)

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    Buzzing Straws

    Many woodwind instruments owe their sound to the vibration caused when air moves past parts of them. As Nick Moore demonstrates in this video, you can create a simple version of this effect with a slit drinking straw. The buzzing the straw produces when air passes through is a sort of aeroelasticity – it’s a combination of aerodynamic and structural forces that drive the behavior. Low pressure created by the fast-moving flow tends to draw the straw together, but once flow is stopped, the elasticity of the straw makes it rebound open, allowing air to flow again. Even more elaborate vibrations are possible when the straw is elastic.  (Video credit: N. Moore)

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    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.)

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    APS DFD 2016

    It’s the time of year again for the American Physical Society Division of Fluid Dynamics meeting! Tomorrow I’ll fly to Portland, OR for three days of non-stop fluid dynamics. This year I’ll be giving two talks:

    – Sunday, November 20th, 3:23pm, Room B117: F*** Yeah Fluid Dynamics: Inisde the science communication process

    – Monday, November 21st, 6:01pm, Room E147-148: “In a sea of sticky molasses”: The physics of the Boston Molasses Flood

    The latter talk is part of an ongoing project exploring the fluid dynamics of the Boston Molasses Flood of 1919. Since you’ll be hearing more about the project in the coming weeks and months, I’m sharing a sneak peek video I originally made for my Patreon patrons. If you’re interested in following the project’s progress, you may want to become an FYFD patron – otherwise, rest assured that you will see the final results eventually 🙂

    I hope to see some of you in Portland, but if you can’t make it, I encourage you to follow the meeting on social media with !

    (Video credit: N. Sharp/FYFD)

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    The Blue Whirl

    We wrote earlier this year about the discovery of a new type of fire whirl – the blue whirl – but now the authors have published video of the blue whirl in action! The blue whirl was discovered while investigating the use of fire whirls to more efficiently burn off oil spilled atop water. A tightly spinning yellow fire whirl produces less soot than a non-vortex burn; the blue whirl is even more efficient, producing little to no soot at all. Much remains to be learned about this new type of fire vortex, but in the meantime, enjoy some high-speed video of the blue whirl, particularly from 1:50 onward. (Video credit: M. Gollner et al.)

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    Bouncing Droplets

    Droplets bouncing on a pool form a beautiful and fascinating system, as recently featured by Physics Girl, Veritasium, and Smarter Every Day. The Lutetium Project – a consortium of French physics, graphic design, and music students – have their own take on the subject with beautiful short videos constructed from experimental research footage. With simple text explanations and lovely original music, they combine science, art, and outreach brilliantly. Also check out their quantum walker video and be sure to subscribe to their channel (in English or French) for more!  (Video credit: The Lutetium Project; submitted by @g_durey)