FYFD

Tag: liquid sheet

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    Polymers and Fluid Sheets

    Even adding a small amount of polymers to a fluid can drastically change its behavior. Often polymer-doped fluids act more like soft solids, able to hold their shape like your toothpaste does when squeezed onto your toothpaste. Under a little stress, though, the fluids still flow; that’s why your toothpaste gets less viscous as you scrub.

    To study the changes polymers make, this research team collides two jets of fluid to create a liquid sheet. Depending on the flow rate and the added polymers, the break-up pattern of the sheet changes. By observing changes in the sheet thickness and the holes that form, they can draw conclusions about what the polymers are doing. (Video credit: C. Galvin et al.)

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    Flow Between Fibers

    Two vertical fibers, with a gap left between them, form a playground for flow in this Gallery of Fluid Motion video. If the fiber spacing is small enough, the flow will form a stable liquid sheet that runs the full length of the fibers. With a little more distance, though, the fluid forms intermittent bridges, whose spacing depends on flow rate. And when the fibers are not perfectly vertical, even more complex flows are possible. I love how a seemingly simple situation begets such complexity! (Image and video credit: C. Gabbard and J. Bostwick)

  • “Keeping Our Sheet Together”

    “Keeping Our Sheet Together”

    When two liquid jets collide, they form a falling liquid sheet. Here researchers explore how that sheet breaks up when the liquids involved contain polymers. The intact areas of the sheet show as dark red or almost black. The edges of the sheet appear in brighter red and yellow, outlining the holes that form and grow during breakup. The type of breakup observed depends on the concentration of polymer in the liquid. (Image credit: C. Galvin et al.)

  • The Shape of Splashes

    The Shape of Splashes

    When a wedge falls into a pool, it creates a distinctive, doubly-curved splash. Here’s how it works. When the front of the wedge first enters the water, it creates a thin sheet of fluid that gets ejected diagonally upward. As the wedge sinks further, the sheet thickens and ejects at a more vertical angle. That creates a low pressure zone in the air beside the splash, which causes outside air to flow inward, generating a sort of Venturi effect under the splash. Because the outer part of the splash sheet is thinner, it’s more strongly affected by the air flow beneath it, and it gets pulled downward, enhancing the splash’s curvature.

    This doubly-curved splash is particular to wedges of the right angle. To see what kind of splashes other shapes make, check out the video below. (Image and video credit: Z. Sakr et al.; for more, see L. Vincent et al.)

  • Rim Break-Up

    Rim Break-Up

    Splashing drops often expand into a liquid sheet and spray droplets from an unstable rim. Although this behavior is key to many natural and industrial processes, including disease transmission and printing, the physics of the rim formation and breakup has been difficult to unravel. But a new paper offers some exciting insight into this unsteady process. 

    The researchers found that if they carefully tracked the instantaneous, local acceleration and thickness of the rim, it always maintained a perfect balance between acceleration-induced forces and surface tension. That means that even though different points on the rim appear very different, there’s a universality to how they behave. They found that this rule held over a remarkably large range of situations, including across fluids of different viscosities and splashes on various surfaces. (Image and research credit: Y. Wang et al.; via MIT News; submitted by Kam-Yung Soh)

  • The Fishbone

    The Fishbone

    The simple collision of two liquid jets can form striking and beautiful patterns. Here the two jets strike one another diagonally near the top of the animation. One is slanted into the screen; the other slants outward. At their point of contact, the liquid spreads into a sheet and forms what’s known as a fishbone pattern. The water forms a thicker rim at the edge of the sheet, and this rim destabilizes when surface tension can no longer balance the momentum of the fluid. Fingers of liquid form along the edge, stretching outward until they break apart into droplets. Ultimately, this instability tears the liquid sheet apart. Under the right conditions, all kinds of beautiful shapes form in a system like this. (Image credit: V. Sanjay et al., source)

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    “Galaxy Gates”

    Viewing fluids through a macro lens makes for an incredible playground. In “Galaxy Gates”, Thomas Blanchard and the artists of Oilhack explore a colorful and dynamic landscape of paint, oil, and glitter. The nucleation of holes and the breakdown of sheets to filaments and droplets plays a major role in the visuals. The surface layer is constantly peeling away to reveal what’s going on underneath. In many cases this initial motion settles into a field of oil-rimmed droplets floating like planets against a colorful galactic backdrop. Watch carefully in the second half of the video, and you can even catch a few instances of a stretched ligament of fluid breaking into a string of satellite drops, like at 1:51. Check out some of Blanchard’s previous work here and here. (Video credit: Oilhack and T. Blanchard; GIFs and h/t to Colossal)

     
  • Breaking Up

    Breaking Up

    Liquid sheets break down in a process known as atomization. Above are top and side views of a liquid sheet created by two identical liquid jets impacting head-on. The jets themselves are off-screen to the left. Their collision generates a thin sheet of liquid that flows from left to right. In the center of the images, the sheet has begun to flap and undulate, shedding large droplets from its edges as it does. At the far end of the sheet, much finer droplets are sprayed out from the center as the sheet collapses completely. This is an example of an instability in a fluid. Initially, any disturbance in the liquid sheet is extremely tiny, but circumstances in the flow are such that those disturbances gather energy and grow larger, creating the large undulations. Those undulations are unstable as well and kick off a fresh set of disturbances that grow until the flow completely breaks down. (Image credit: N. Bremond et al., pdf)

  • A Particle-Filled Splash

    A Particle-Filled Splash

    A drop of water that impacts a flat post will form a liquid sheet that eventually breaks apart into droplets when surface tension can no longer hold the water together against the power of momentum flinging the water outward. But what happens if that initial drop of water is filled with particles? Initially, the particle-laden drop’s impact is similar to the water’s – it strikes the post and expands radially in a sheet that is uniformly filled with particles. But then the particles begin to cluster due to capillary attraction, which causes particles at a fluid interface to clump up. You’ve seen the same effect in a bowl of Cheerios, when the floating O’s start to group up in little rafts. The clumping creates holes in the sheet which rapidly expand until the liquid breaks apart into many particle-filled droplets. To see more great high-speed footage and comparisons, check out the full video.  (Image credit and submission: A. Sauret et al., source)

  • Piazza del Popolo

    Piazza del Popolo

    The lions of the fountain in Rome’s Piazza del Popolo eject a turbulent sheet of water. Random fluctuations in the water sheet cause holes to form. Driven by surface tension, these holes grow and merge, leaving behind ligaments of water which quickly break up into a spray of unevenly-sized drops. (Image credit: E. Villermaux)