The Kaye effect is particular to shear-thinning non-Newtonian fluids – that is, fluids with a viscosity that decreases under deformation. The video above includes high-speed footage of the phenomenon using shampoo. When drizzled, the viscous liquid forms a heap. The incoming jet causes a dimple in the heap, and the local viscosity in this dimple drops due to the shear caused by the incoming jet. Instead of merging with the heap, the jet slips off, creating a streamer that redirects the fluid. This streamer can rise as the dimple deepens, but, in this configuration, it is unstable. Eventually, it will strike the incoming jet and collapse. It’s possible to create a stable version of the Kaye effect by directing the streamer down an incline. (Video credit: S. Lee)
Search results for: “jet”
Ice in Engines
Ice build-up is a major hazard on airplane wings and control surfaces, but ice can accrete on internal engine components, too. When this happens, the turbofan jet engine can lose power. Such incidents have been observed in high-altitude flight even when pilots observed little to no inclement weather. Researchers think this ice accretion may occur when the plane flies through a cloud of tiny ice crystals. These ice crystals get ingested into the engine, where they hit the warmer internal surfaces and melt. Over the course of the flight, the engine components cool off due to this influx of ice and water. Eventually, ice begins to form and grow inside the engine, ultimately resulting in power loss. Researchers have recreated such ice cloud conditions in a facility at NASA Glenn Research Center and tested a full-scale jet engine for ice accretion. They aim to gather the data necessary to improve commercial engine capabilities under ice ingestion. (Video credit: NASA Glenn Research Center)
Spinning Polygons
Nature is full of surprising behaviors. If one imagines putting a bucket of water on a rotating plate and spinning it, one would expect the water’s free surface to take on a curved, axially symmetric shape. The photos above are from a similar experiment, but instead of the entire container rotating, only the bottom plate spins. Surprisingly, the water’s surface does not remain symmetric around the axis of rotation. Instead, the water forms stable polygon shapes that rotate slower than the spinning plate. As the plate’s rotation speed increases, the number of corners in the polygon increases. Shapes up to a hexagon were observed in the experiment. Photos of the set-up and more experimental results are available, as is the original research paper. Symmetry breaking and polygons can also be found in hydraulic jumps and bumps, liquid sheets, and planetary polar vortices. (Photo credit: T. Jansson et al.; research paper)
Hydraulic Jump in the Lab
When fast-moving liquids encounter regions of slow-moving liquids, they decelerate rapidly, trading their kinetic energy for potential energy and creating a hydraulic jump. Flow in the video above is from left to right. The depth difference between the incoming and outgoing water can be directly related to the velocity of the incoming fluid. Hydraulic jumps in rivers and spillways are often extremely turbulent, like the one in this video, but laminar examples exist as well. In fact, with the right height and flow rate, you can create stable hydraulic jumps right in your kitchen sink. The hydraulic jumps formed from a falling jet are typically circular, but with the right conditions, all sorts of wild shapes can be observed. (Video credit: H. Chanson)
Shooting a Bullet Through a Water Balloon
This high-speed video of a bullet fired into a water balloon shows how dramatically drag forces can affect an object. In general, drag is proportional to fluid density times an object’s velocity squared. This means that changes in velocity cause even larger changes in drag force. In this case, though, it’s not the bullet’s velocity that is its undoing. When the bullet penetrates the balloon, it transitions from moving through air to moving through water, which is 1000 times more dense. In an instant, the bullet’s drag increases by three orders of magnitude. The response is immediate: the bullet slows down so quickly that it lacks the energy to pierce the far side of the balloon. This is not the only neat fluid dynamics in the video, though. When the bullet enters the balloon, it drags air in its wake, creating an air-filled cavity in the balloon. The cavity seals near the entry point and quickly breaks up into smaller bubbles. Meanwhile, a unstable jet of water streams out of the balloon through the bullet hole, driven by hydrodynamic pressure and the constriction of the balloon. (Video credit: Keyence)
Hydrophobia
On a recent trip to G.E., the Slow Mo Guys used their high-speed camera to capture some great footage of dyed water on a superhydrophobic surface. Upon impact, the water streams spread outward, flat except for a crownlike rim around the edges. Then, because air trapped between the liquid and the superhydrophobic solid prevents the liquid from wetting the surface, surface tension pulls the water back together. If this were a droplet rather than a stream, it would rebound off the surface at this point. Instead, the jet breaks up into droplets that scatter and skitter across the surface. There’s footage of smaller droplets bouncing and rebounding, too. Superhydrophobic surfaces aren’t the only way to generate this behavior, though; the same rebounding is found for very hot substrates due to the Leidenfrost effect and very cold substrates due to sublimation. As a bonus, the video includes ferrofluids at high-speed, too. (Video credit: The Slow Mo Guys/G.E.)
Impacting a Viscous Pool
Whenever a hollow cavity forms at the surface of a liquid, the cavity’s collapse generates a jet–a rising, high-speed column of liquid. The composite images above show snapshots of the process, from the moment of the cavity’s greatest depth to the peak of the jet. The top row of images shows water, and the bottom row contains a fluid 800 times more viscous than water. The added viscosity both smooths the geometry of the process and slows the jet down, yet strong similarities clearly remain. Focusing on similarities in fluid flows across a range of variables, like viscosity, is key to building mathematical models of fluid behavior. Once developed, these models can help predict behaviors for a wide range of flows without requiring extensive calculation or experimentation. (Image credit: E. Ghabache et al.)
What Makes Squids Fast
Cephalopods like the octopus or squid are some of the fastest marine creatures, able to accelerate to many body lengths per second by jetting water behind them. Part of what makes its high speed achievable, though, is the way the animal changes its shape. In general, drag forces are proportional to the square of velocity, meaning that doubling the velocity increases the drag by a factor of four. The energy necessary to overcome such large drag increases generally prevents marine animals from going very fast (compared to those of us used to moving through air!) But drag is also proportional to frontal area. Like the bio-inspired rocket in the video above, jetting cephalopods begin their acceleration from a bulbous shape and then shrink their exposed area as they accelerate. Not only does this shape change help mitigate increases in drag due to velocity, it prevents flow from separating around the animal, shielding it from more drag. The result is incredible acceleration using only a simple jet for thrust. For example, the octopus-like rocket in the video above reaches velocities of more than ten body lengths per second in less than a second. (Video credit: G. Weymouth et al.)
Impacts on Sand
Granular materials like sand are sometimes very fluid-like in their behaviors. The high-speed video above shows a ball bearing being dropped into packed sand. Many features of the splash are fluid-like; the initial impact creates a spreading crownlike splash, followed by a strong upward jet that eventually collapses back into the medium. At the same time, many of the impact characteristics are decidedly non-fluidic. Sand has no surface tension, so both the crown and the jet readily break up into small particles. The granular jet is very narrow and energetic, reaching heights greater than the impacter’s drop height. Interestingly, the column begins collapsing on its lower end before the jet even reaches its highest peak. This may be due to the lower energy of the sand particles that were ejected later in the crater formation process. (Video credit: J. Verschuur, B. van Capelleveen, R. Lammerink and T. Nguyen)
Vibrating Paint
Paint is probably the Internet’s second favorite non-Newtonian fluid to vibrate on a speaker–after oobleck, of course. And the Slow Mo Guys’ take on it does not disappoint: it’s bursting (literally?) with great fluid dynamics. It all starts at 1:53 when the less dense green paint starts dimpling due to the Faraday instability. Notice how the dimples and jets of fluid are all roughly equally spaced. When the vibration surpasses the green paint’s critical amplitude, jets sprout all over, ejecting droplets as they bounce. At 3:15, watch as a tiny yellow jet collapses into a cavity before the cavity’s collapse and the vibration combine to propel a jet much further outward. The macro shots are brilliant as well; watch for ligaments of paint breaking into droplets due to the surface-tension-driven Plateau-Rayleigh instability. (Video credit: The Slow Mo Guys)