FYFD

Month: October 2019

  • Galileo’s Descent

    Galileo’s Descent

    In December 1995, the Galileo probe made its dramatic descent into Jupiter’s atmosphere at a velocity of more than 47 km/s. In 30 seconds, it decelerated from Mach 50 to Mach 1, undergoing incredible heating as it did so. Anytime an object moves through a fluid faster than the local speed of sound, it creates a leading shock wave that compresses the fluid, heats it, and redirects it around the object. The faster the speed, the hotter the fluid will be after passing through the shock wave. 

    Above about five times the speed of sound, the heating effect is so strong that it’s able to rip molecules apart, creating a chemically reactive mixture that will ablate away material from the object. For this reason, Galileo and other planetary entry vehicles carry heat shields made to sacrifice themselves while protecting the cargo and (in some cases) crew onboard. Data from Galileo showed that, although the heat shield survived the brunt of its descent, it experienced worse conditions than expected. Near the heat shield’s shoulder, almost all of its material ablated away. 

    Scientists continue to study Galileo’s descent even now, using it to test and inform their models of the flow and chemistry that occurs at these hypersonic speeds. The better we can understand and predict these flows, the better our designs will become. Mass that’s currently spent on overly-conservative heat shields can instead go toward additional instruments or supplies. (Image credit: Chop Shop Studio; research credit: L. Santos Fernandes et al.; via AIP)

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    Supercooling Thermodynamics

    In the latest Gastrofiscia episode, Tippe Top Physics takes on thermodynamics and the complicated truth behind certain phase changes. Although we’re accustomed to thinking of water freezing at 0 degrees Celsius and boiling at 100 degrees Celsius, reality is more complex, and temperature is only one of the factors that goes into a change of phase. Pressure and purity also play an important role. 

    This is why it’s possible, for instance, to supercool purified water to below 0 degrees Celsius without freezing it. Liquid water needs a nucleus to serve as a seed for its freezing. Without dust or other impurities, it takes a lot of energy for water to spontaneously generate its own nucleus. Check out the full video to see how and why that’s so. (Image and video credit: Tippe Top Physics)

  • Sliding Down a Pitcher Plant

    Sliding Down a Pitcher Plant

    Carnivorous pitcher plants supplement their nutrient-poor environments by capturing and consuming insects. The viscoelastic fluid inside them helps trap prey, but fluid dynamics plays a role elsewhere on the plant as well. The inner and outer surfaces of the pitcher are covered in macroscopic and microscopic grooves, seen above, oriented toward the interior of the plant. 

    Researchers found that these grooves trap droplets on the slippery plant through capillary action. Once adhered, the droplet cannot easily move across the grooves, but it can slip along them, carrying the droplet and any insect stuck to it, into the plant. By replicating pitcher-plant-inspired grooves on manmade surfaces, researchers found they were able to better control droplet motion on slippery, lubricant-infused surfaces than in previous work. (Image and research credit: F. Box et al.; via Royal Society; submitted by Kam-Yung Soh)

  • Bay of Fundy Tides

    Bay of Fundy Tides

    Canada’s Bay of Fundy has some of the wildest tidal flows in the world. Every six hours, the flow direction through the strait shifts and tidal currents rise to several meters per second. This creates distinct jets a couple kilometers long that pour from one side of the strait to the other. 

    What you see here is a numerical simulation of the flow using a technique called Large Eddy Simulation (or LES, for short). It’s one method used by fluid dynamicists to model turbulent flows without taking on the complexity of the full Navier-Stokes equations. At large lengthscales, like those of the jets and eddies we see above, LES uses the exact physics. But when it comes to the smaller scales – like the flow nearest the shores or the bottom of the strait – the simulation will approximate the physics in order to make calculations quicker and easier. Models like these make large-scale problems – including modeling our daily weather patterns – possible. (Image credit: A. Creech, source)

  • Reader Question: Exoplanetary Life

    Reader orbiculator asks:

    I’ve been having this thought regarding biological adaptations to viscous mediums. In a hypothetical exoplanet where the ocean is this thick, aqueous gel – could we assume that the native macroscopic species would have morphologies similar to Earth’s plankton despite their large sizes? That is, instead of being propelled by fins like our fish and whales, they’d go around using large ciliar or flagella?

    Propulsion-wise, that’s a reasonable theory. If the ambient environment were viscous enough that macroscopic creatures would still be limited to laminar flow, then, yes, you could expect them to use something like cilia or flagella to move. They’d be restricted by the same reversibility that microscopic species are here on Earth.

    But there are other factors that could come into play. Many microscopic species rely on diffusion for survival, whether that’s chemical diffusion across their exterior or diffusion within their body. As a species gets larger, the distance diffusion has to occur across grows, and diffusion becomes harder and harder to sustain. 

    So while hydrodynamic constraints might result in an exoplanet’s fauna having features similar to Earth’s microscopic life, it probably wouldn’t be as simple as merely enlarging the species we see here on Earth. Some of the key biophysics that goes on inside cellular life as we know it just doesn’t hold at larger scales.

  • Featured Video Play Icon

    A Broken Monitor’s Fingers

    In this short video, the artists of Chemical Bouillon explore a broken LCD monitor and its liquid crystals. By sandwiching the fluid between thin, transparent sheets, they create dendritic shapes as the liquid crystals and other fluids (air? ink?) push into one another. There’s a lot here that’s likely connected to the Saffman-Taylor instability, but without knowing more details on the ingredients and set-up, it’s hard to speculate beyond that. (Video and image credit: Chemical Bouillon)

  • Energy-Efficient Deicing

    Energy-Efficient Deicing

    Defrosting and deicing surfaces is an energy-intensive affair, with lots of heat lost to warming up system components rather than the ice itself. In a new study, researchers explore a faster and more efficient method that focuses on heating just the interface. They coated their working surface in a thin layer of iridium tin oxide, a conductive film used in defrosting. Then, once the surface was iced over, they applied a 100 ms pulse of heating to the film. That localized heat melted the interface, and gravity pulled away the detached ice. Compared to conventional defrosting methods, this technique requires only 1% of the energy and 0.01% of the time. If the method scales reliably to applications like airplane deicing, it would provide enormous savings in time and energy. (Image and research credit: S. Chavan et al.)

  • Boiling in Microgravity

    Boiling in Microgravity

    In the playground of microgravity, every day processes can behave much differently. This photo comes from the RUBI experiment, the Reference mUltiscale Boiling Investigation, aboard the International Space Station. Freshly installed and switched on, the apparatus is now generating bubbles like this one. On the left, you see temperature sensors used to measure bubble temperatures. High-speed and infrared cameras are also part of the experiment.

    The advantage of studying boiling in space is a lack of gravity that can mask or overwhelm subtler effects. It effectively slows down the process, making it easier to observe. And since boiling is such an important part of heat transfer in many manmade devices, it shows us how we have to adapt when operating in an environment where heat – and bubbles – don’t automatically rise. (Image credit: ESA; submitted by Kam-Yung Soh)

  • Champagne’s Shock Wave

    Champagne’s Shock Wave

    The distinctive pop of opening a champagne bottle is more than the cork coming free. The sudden release of high-pressure gas creates a freezing jet that’s initially supersonic. It even creates a Mach disk, like those seen in rocket exhaust. That supersonic flow can only be maintained, though, with a large enough pressure difference between the gas in the bottle and the atmosphere outside. Once the pressure drops below that critical point, the jet slows down and becomes subsonic. For more on champagne popping and its colorful plume, check out this previous post. (Image and research credit: G. Liger-Belair et al.; via Nature; submitted by Kam-Yung Soh)

  • Waves on a Supercell

    Waves on a Supercell

    This Colorado supercell thunderstorm features an unusual twist. Notice the sawtooth-like protrusions along the outer cloud wall. These are Kelvin-Helmholtz waves, like these fair-weather clouds we’ve seen before, but instead of occurring vertically, they project horizontally! That implies that the invisible layer of air just outside the cloud wall is moving faster than the wall itself. That creates shear along the outer edge of the cloud wall and causes these waves to form. This is the first time I’ve ever seen this sort of thing. What an awesome photo! (Image credit: M. Charnick; submitted by jpshoer)