FYFD

Tag: 2015gofm

  • Spin Cycle

    Spin Cycle

    Rotational motion is a great way to break up liquids, as anyone who’s watched a dog shake itself dry can attest. That same centrifugal force is what allows this rotary atomizer to break liquids into droplets. Relative to the photos above, the atomizer spins in a counter-clockwise direction. This motion stretches the fluid flowing off it into skinny, equally-spaced ligaments, which eventually break down into droplets.

    Just how and when that break-up occurs depends on the fluid, as well as the characteristics of the spin. For Newtonian fluids like silicone oil — shown in the first two pictures — the break-up is driven by surface tension and happens relatively quickly. But with a viscoelastic fluid — shown in the last image — the elasticity of polymers in the fluid allow it to resist break-up for much longer. Instead, the ligaments form the beads-on-a-string instability. See more flows in action in the video below. (Video, image, and research credit: B. Keshavarz et al., video)

  • Corrugating Water

    Corrugating Water

    The characteristics of a surface can have a major impact on the form a flow takes. The photo above shows a corrugated, almost pinecone-like water surface. It’s the result of a sheet of water flowing over a surface with alternating bands of hydrophobic (water-repelling) and hydrophilic (water-loving) properties. The water sheet narrows over hydrophobic sections and expands over hydrophilic ones. Gravity, inertia, and surface tension compete to create the overall braided appearance. You can see a top-down view of the flow in the original poster. (Image credit: M. Grivel et al., source)

  • Swirling Pollen

    Swirling Pollen

    This photo captures the chaotic mixing present in a simple puddle. Pine pollen strewn across the puddle’s surface acts as tracer particles, revealing some of the motion of the underlying water. As wind blows across the puddle, it moves the water through the formation of ripples and by shearing the surface. That deformation on the top of the puddle will cause further motion beneath the surface. With time and changing wind direction, the resulting pattern of flow can be very complex! (Photo credit: K. Jensen, original)

  • Inside a Humidifier

    Inside a Humidifier

    After this, you may never look at a humidifier the same way again. Ultrasonic humidifiers generate tiny droplets using piezoelectric transducers. When the humidifier is on, the ultrasonic vibrations of the piezoelectric transducer create a pressure wave that forces the water above into a hill with a string of liquid droplets extending upward. For a sense of the scale, the gray bars shown in each image above represent 1mm. The super-fine droplets the humidifier produces come from cavitation of these larger drops, as shown in image c). Image d) shows snapshots of the formation of the droplet string over a matter of milliseconds. (Image credit: S. J. Kim et al., original poster)

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    Quantum Droplets

    Over the past decade, fluid dynamicists have been investigating tiny droplets bouncing on a vibrating fluid. This seemingly simple experiment has remarkable depth, including the ability to recreate quantum behaviors in a classical system. In this video, some of the researchers demonstrate their experimental techniques, including how they vary the frame rate relative to the bouncing of the drops. At the right frame rate, this sampling makes the droplets appear to glide along with their ripples, giving us a look at a system that is simultaneously a particle (drop) and wave (ripple). (Video credit: D. Harris et al.)

  • Daily Fluids, Part 3

    Daily Fluids, Part 3

    A lot of the fluid dynamics in our daily lives centers around the preparation and consumption of food. (And in its digestion afterward, but that’s another story!) Here are a few examples of fluid dynamics you might not have realized you’re an expert on:

    Low Reynolds Number Flows
    This is a fancy way of discussing the motion of syrup, honey, and other thick and viscous fluids we interact with in our lives. These flows are typically slow moving and exhibit some neat properties like coiling or being possible to unstir.

    Immiscible Fluids
    Oil and water don’t mix, a fact anyone familiar with salad dressings or marinades is well aware of. The way around this is to shake them up! This disperses droplets of the oil within the water (or vinegar or whatever) to create an emulsion. While not truly mixed, it does make for more pleasant eating.

    Multiphase Flows
    Multiphase flows are ones containing both liquid and gaseous states. Boiling is an example we often see in our daily lives, though carbonated beverages, water sprayers, and sneezes are other common ones.

    Leidenfrost Effect
    The Leidenfrost effect occurs when liquid is introduced to a surface that is much, much hotter than its boiling point. Part of the liquid instantly vaporizes, leaving droplets to skitter around on a thin vapor layer. This is most often seen around the stove and in skillets. (And, yes, it does qualify as a multiphase flow!)

    Tune in all week for more examples of fluid dynamics in daily life. (Image credit: S. Reckinger et al., source)

    P.S. – I’m at VidCon (@vidconblr) this year! If you are, too, come say hi and get an FYFD sticker 😀

  • Daily Fluids, Part 1

    Daily Fluids, Part 1

    Just getting cleaned up and ready for the day involves a lot of fluid physics. Here are a few of the phenomena you may see daily without realizing:

    Plateau-Rayleigh Instability
    This behavior is responsible for the dripping of your faucet. More specifically, it’s the reason that a falling jet breaks up into droplets. It works on rain, too!

    Forced Convection
    Everyone is familiar with a winter wind making them colder or hot air from a dryer getting the moisture off their hands. These are examples of forced convection – heat transfer by driving a fluid past a solid. Another common example? The fans in your computer!

    Liquid Atomization
    This is the process of breaking a liquid into lots of tiny droplets. Aside from any aerosol can ever, this phenomenon is also key to your daily shower and internal combustion in your car.

    Archimedes Principle
    This might be one of my favorite bits of the whole video because it hearkens back to some of my own earliest fluid dynamics exposure. Archimedes Principle says that buoyancy is equal to the weight of the fluid a body displaces. My mom (a science teacher) taught me about this one in the bathtub! It’s key to everything that ever floated, including us!

    Tune in all week for more examples of fluid dynamics in daily life. (Image credit: S. Reckinger et al., source)

  • Featured Video Play Icon

    A Day in the Life of a Fluid Dynamicist

    Today I’m sharing one of my favorite videos from last year’s Gallery of Fluid Motion. It’s a short film entitled “A Day in the Life of a Fluid Dynamicist.” Although some parts of it probably only apply to fluid dynamicists (Navier-Stokes equations, anyone?) a lot of the activities depicted are common to everyone. The film does a nice job of highlighting some of the many examples of fluid dynamics that we come across in our daily lives. As a film by scientists made for scientists, though, you may find some of the terminology obscure. Never fear! This week on FYFD, I’ll be breaking down some of the film’s segments, explaining what they mean, and showing you just how much fluid dynamics you experience every day! (Video credit: S. Reckinger et al.)

  • Bubbles and Films Merging

    Bubbles and Films Merging

    As we’ve seen before, a water droplet can merge gradually with a pool through a coalescence cascade. It turns out that the coalescence of a soap bubble with a soap film can follow a similar process! Initially, the bubble and film are separated by a thin layer of air. Once that air drains away and the bubble contacts the fluid, it starts to coalesce. But the bubble pinches off before its entire volume merges, leaving behind a daughter bubble with about half the radius of the previous bubble. This process repeats until the bubble is small enough that it merges completely. To see more great high-speed footage of this bubble merger, check out the full video below.  (Image/video credit: D. Harris et al.)

  • Wrinkling Fluids

    Wrinkling Fluids

    What you see here is a viscous drop falling into a less viscous fluid. Shear forces between the drop and the surrounding fluid cause the drop to quickly deform into a shape like an upside-down mushroom as it descends. The cap forms a vortex ring that curls the viscous fluid back on itself. As it does, that motion compresses the viscous sheet, causing it to wrinkle, as seen in the close-up in the bottom animation. Check out the full video here. (Image credit: E. Q. Li et al., source)