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  • Vortex Wake in Quebec

    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.)

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    Crushing Oobleck

    Oobleck is probably the Internet’s favorite non-Newtonian fluid. People vibrate it, run across it, shoot it, drop it, and even use it to fix potholes. But how does oobleck hold up to a hydraulic press? Fortunately, that’s been covered, too. Oobleck is a mixture of cornstarch and water, and it’s a bit unusual in that it is a shear-thickening material. That means that the faster you try to deform it, the more it will resist that deformation. Knowing this makes the above video’s results make more sense. When they try to crush the balloon full of oobleck, the deformation happens pretty slowly, so the fluid just flows away.

    The same thing happens initially with the pot full of oobleck; it overflows much like any other liquid. But as the press pushes deeper, the oobleck gets confined by the pot’s walls and things change. Research has shown that the shear-thickening of oobleck comes from cornstarch particles jamming up in the fluid. By confining the oobleck, the pot and hydraulic press magnify this jamming effect, causing a spurt of semi-solid cornstarch fingers and leaving the press tool thoroughly trapped by the jammed particles. (Video credit: Hydraulic Press Channel)

  • Inside a Supernova

    Inside a Supernova

    During a supernova, shock waves moving outward push denser material into less dense plasma and gas. This causes what is known as a Richtmyer–Meshkov instability, where the interface between the two fluids first becomes wavy and then develops finger-like intrusions. Those too break down, as seen in the simulation above, causing large-scale mixing between the different fluids.

    Here on Earth this instability shows up in the process of inertial confinement fusion. In that case, the outer shell material is denser than the fuel core and the instability is triggered during the implosion process. As the fusion material is suddenly compressed, waviness and mixing occurs along the interface between the shell and the fuel. That’s undesirable because it reduces the efficiency of the fusion reaction.  (Image credit: E. Evangelista et al.)

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    Ionic Sound

    So, as we learned previously, sound can actually travel through space. But the recordings our spacecraft send us from other planets or from the edge of the Solar System aren’t really that kind of sound. Acoustic waves require a medium; they travel when particles bump into one another, which, given the sparseness of space, means that only very low frequency sounds can travel. But space has a lot of ions and plasmas – charged particles like electrons and protons – and those particles can interact without physically contacting one another. Instead their motion causes a changing magnetic field that affects nearby particles, which in turn affect more particles (and so on). This transmits what’s called ionic sound. Check out the video above to hear some awesome examples of the ionic sounds of our solar system! (Video credit: The Point Studios)

  • Inside a Cello

    Inside a Cello

    At first glance, Adrian Borda’s photograph seems to show an old room. In reality, this is the interior of a cello with light shining through the f-holes. Dust particles in the air trace out pathlines that reveal the turbulent movements of air inside the instrument. Both the camera’s perspective and the visible flow try to trick our minds into seeing something larger than reality. It’s a reminder that the patterns and forms of fluid flow repeat across an enormous range of scales, from millimeters to light-years. (Image credit: A. Borda; via Joseph S./CU Boulder Flow Viz)

  • Giant Vortex Cannon

    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)

  • Making Droplets

    Making Droplets

    If you’ve ever wondered how fluid dynamicists create those tiny perpetually bouncing droplets they study, wonder no further. A typical method, shown here, is to use a simple toothpick. First, you take a shallow container of silicone oil and vibrate it vertically. Then you dip the tip of the toothpick into the oil and pull it out, stretching the oil into a long filament. When it detaches from the toothpick, a droplet will start to form at the tip of the filament as it falls back toward the pool. But the bouncing of the surface is enough to keep the new drop from coalescing back into the pool, leaving the little drop to bounce along on its liquid trampoline. (Image credit: S. Lapointe)

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    The Law of Urination

    Tonight is the 26th Ig Nobel Prize ceremony. As I’ve covered previously, the subject of fluid dynamics has been quite successful at winning these awards designed to “make people LAUGH, then THINK,” and last year’s ceremony was no exception. Georgia Tech researchers won the Physics Prize last year for explaining why mammals of very different sizes all urinate for roughly 21 seconds.

    Urination is a gravity-driven process, and larger animals have longer urethras, which means that gravity will have more time to accelerate fluid flowing from the the bladder to, well, the exit. Thus, larger animals will have higher flow rates. This allows them to empty their bigger bladders in essentially the same amount of time as a smaller animal. Recognizing this pattern can be helpful to both veterinarians diagnosing problems in animals and to engineers designing systems to move fluids efficiently.

    There’s no way to know whether fluid dynamics will win another Ig Nobel Prize tonight, but I can guarantee that subject will come up. I’ll be giving a 24/7 lecture on Fluid Dynamics during tonight’s Ig Nobel Prize ceremony.  You can see me – and find out this year’s winners – by watching the ceremony webcast here starting at 5:40pm EDT. (Video credit: DNews; research credit: P. Yang et al.)

  • Jovian Poles

    Jovian Poles

    We’re used to viewing Jupiter from its equator, where bands of light and dark clouds dominate the picture. From its poles, Jupiter looks very different, as these recent images from Juno show. Jupiter’s north pole is shown on the left and its south pole on the right. Both are awash in vortices. There’s another great black-and-white image of the south pole here, where the vortices really stand out. Jupiter’s atmosphere contains both cyclones, which rotate counterclockwise in the northern hemisphere and clockwise in the southern hemisphere, and anticyclones, which behave in the reverse. Unlike in Earth’s atmosphere, anticyclones dominate on Jupiter, especially among storms more than 2000 km across.  (Image credit: NASA/JPL/Juno Mission; via APOD)

    P.S. – Tomorrow night is the Ig Nobel Prize Ceremony, and I’ll be giving one of their 24/7 lectures. If you’d like to tune in and hear me describe fluid dynamics in 24 seconds + 7 words, there will be a webcast here.

  • Shark Tooth Instability

    Shark Tooth Instability

    Imagine that you partially fill a horizontal cylinder with a viscous fluid, like corn syrup or honey. If that cylinder is still, the fluid will simply pool along the bottom. On the opposite extreme, if you spin it very fast, that cylinder will become coated in an even layer of fluid that rotates along with the cylinder thanks to centrifugal force. Between those two extremes in rotational velocity, some interesting fluid behaviors occur. Start spinning the cylinder and some of the pooled fluid will be pulled up the sides, eventually forming a thicker film with a straight front along the bottom of the cylinder. Spin faster and that straight front starts to break down, forming sharper cusp-like waves known as shark teeth. (Image credit: S. Morris et al., source; research credit: S. Thoroddsen and L. Mahadevan)

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