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  • Sochi 2014: Why is Ice Slippery?

    Sochi 2014: Why is Ice Slippery?

    Ice is a key component of many Winter Olympic disciplines, including figure skating, hockey, speed skating, curling, and the sliding sports. The low friction and slippery nature of the ice are vital to the events, but oddly enough, scientists don’t yet fully understand why ice is slippery. A common explanation is that the narrow blades on which athletes compete cause extremely high pressures that locally melts the ice, creating a thin layer of water upon which the athlete glides. The trouble with this explanation is that it only accounts for ice being slippery within a few degrees of its melting point. Not only that, anyone who has fallen when walking on ice knows that it is slippery even without ice skates. In 1859 physicist Michael Faraday suggested that ice may be covered in a thin liquid-like layer even at temperatures well below freezing. Experiments since then suggest that this layer is tens or hundreds of nanometers thick, depending on the purity of the surface film. Robert Rosenberg has an excellent review of the subject in Physics Today. (Image credit: Reuters/D. Gray via The Big Picture)

    This post opens up our series on fluid dynamics in the Winter Olympics. Stay tuned for more over the next two weeks. Got a question in mind? Seen a great article? Feel free to ask questions or submit links on Tumblr, Twitter, or by email.

  • Sochi 2014 Incoming

    Sochi 2014 Incoming

    The Winter Olympics are underway in Sochi, Russia, and here at FYFD, I am busy preparing a special series of posts on fluid dynamics in the Winter Games. Look for the first of those starting on Monday.  In the meantime, you can check out some of FYFD’s previous themed series now compiled into a special archive. (Photo credit: B. Armangue)

  • Convective Impressionism

    Convective Impressionism

    Buoyant convection, driven by temperature-dependent changes in density, is a major force here on Earth. It’s responsible for mixing in the oceans, governs the shape of flames, and drives weather patterns. The images above show flow patterns caused by buoyant convection. The colors come from liquid crystal beads immersed in the fluid; red indicates cooler fluid and blue indicates warmer fluid. You can see plumes of warmer fluid rising in some of the photos. At the same time, though, the images are beautiful simply as art and are strongly reminiscent of works by Vincent van Gogh. (Image credit: J. Zhang et al.)

  • Wind and Waves Visualized

    Wind and Waves Visualized

    Much like the wind map we featured previously, designer Cameron Beccario’s visualizations of wind and ocean surface current data draw from near-real-time sources to create a stunning picture of fluid dynamics on a planetary scale. The number of options in terms of projections and data are really quite incredible, and you’ll want to play around to get a real sense for it. Want to see the wind and total precipitable water at 1000 hPa? Here you go. Maybe you prefer studying Pacific ocean currents. All the data are there to play with. People often wonder why weather forecasts aren’t always right, but, when you look at the scale and complexity of these flows, it’s almost a wonder that we can predict them at all. (Image credits:C. Beccario/earth; via skunkbear and io9)

  • Bubble Vortices

    Bubble Vortices

    Vortices appear in scales both large and small, from your shower and the flap of an insect’s wing to cyclones and massive storms on other planets. Especially with these large-scale vortices, it can be difficult to understand the factors that affect their trajectories and intensities over time. Here researchers have studied the vortices produced on a heated half bubble for clues as to their long-term behavior. Heating the base of the bubble creates large thermal plumes which rise and generate large vortices, like the one seen above, on the bubble’s surface. Researchers observed the behavior of the vortices with and without rotation of the bubble. They found that rotating bubbles favored vortices near the polar latitudes of the bubble, just as planets like the Earth and Saturn have long-lived polar vortices. They also found that the intensification of both bubble vortices and hurricanes was reasonably captured by a single time constant, which may lead to better predictions of storm behaviors. Their latest paper is freely available here. (Image credit: H. Kellay et al.; research credit: T. Meuel et al.; via io9)

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    Inksplosion

    Chemical Bouillon are a trio of artists who use the chemistry of surface reactions to create abstract videos full of exploding and imploding droplets and colors. As chemicals react, local concentrations at the interface vary, which changes the local surface tension. These gradients drive flow from areas of low surface tension to those of higher surface tension. This is called the Marangoni effect – the same behavior that drives tears in a glass of wine. Chemical Bouillon have a whole YouTube channel dedicated to these kinds of videos, with everything from inks to ferrofluids. Be sure to take a look at some of their other videos and, if you like them, subscribe. (Video credit: Chemical Bouillon)

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    Measuring Wind Turbines with Snowfall

    One of the challenges in large-scale wind energy is that operating wind turbines do not behave exactly as predicted by simulation or wind tunnel experiments. To determine where our models and small-scale experiments are lacking, it’s useful to make measurements using a full-scale working turbine, but making quantitative measurements in such a large-scale, uncontrolled environment is very difficult. Here researchers have used natural snowfall as seeding particles for flow visualization. The regular gaps in the flow are vortices shed from the tip of the passing turbine blades. With a searchlight illuminating a 36 m x 36 m slice of the flow behind a wind turbine, the engineers performed particle image velocimetry, obtaining velocity measurements in that region that could then be correlated to the wind turbine’s power output. Such in situ measurements will help researchers improve wind turbine performance. (Video credit: J. Hong et al.)

  • Tidal Bore

    Tidal Bore

    The daily ebb and flood of the tides results from the competing forces of the Earth’s rotation and the sun and moon’s gravitational pull on the oceans. In a few areas, the local topography funnels the incoming water into a tidal bore with a distinctive leading edge. The photo above comes from the Turnagain Arm of the Cook Inlet in Alaska, where bore tides can reach a height of 7 ft and move as quickly as 15 mph. For surfers, the bore can provide a long ride–40 minutes in this case–but they can be extremely dangerous as well. Bore tides are associated with intense turbulence capable of ripping out moorings and structures; the waves are often accompanied by a roar caused by air entrainment, impact on obstacles, and the erosion of underlying sediment.  (Photo credit: S. Dickerson/Red Bull Illume; via Jennifer Ouellette)

  • Hydrodynamic Quantum Analogs

    Hydrodynamic Quantum Analogs

    Over the past few years, researchers have been exploring the dynamics of droplets bouncing on a vibrating fluid. These systems display many behaviors associated with quantum mechanics, including wave-particle duality, single-slit and double-slit diffraction, and tunneling. A new paper examines the system mathematically, showing that the droplets obey many of the same mathematics as quantum systems. In fact, the droplet-wave system behaves as a macroscopic analog of 2D quantum behaviors. The implications are intriguing, especially for teaching. Now students of quantum mechanics can experiment with a simple apparatus to understand some of the non-intuitive aspects of quantum behavior. For more, see the paper on arxiv. (Image credit: D. Harris and J. Bush; research credit: R. Brady and R. Anderson)

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    Simulating Early Planetary Impacts

    Early in our geological history, Earth was a hellish landscape of molten oceans into which metallic impactors would sometimes collide. Geophysicists have been curious how the impactors behaved after collision: did they maintain their cohesion, or did they break up into a cloud of droplets? Here the UCLA Spinlab simulates this early planetary formation by dropping liquid gallium through a tank of viscous fluid. As the video shows, the impactor’s behavior varies strongly with size. Smaller impactors stick together as a single diapir, but, as the initial size increases, the diapir becomes unstable, eventually breaking down into a cascade of droplets – a metallic rain through an ocean of magma. (Video credit: J. Wacheul et al./UCLA Spinlab; submitted by J. Aurnou)

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