FYFD

Tag: turbulence

  • Stunning Interstellar Turbulence

    Stunning Interstellar Turbulence

    The space between stars, known as the interstellar medium, may be sparse, but it is far from empty. Gas, dust, and plasma in this region forms compressible magnetized turbulence, with some pockets moving supersonically and others moving slower than sound. The flows here influence how stars form, how cosmic rays spread, and where metals and other planetary building blocks wind up. To better understand the physics of this region, researchers built a numerical simulation with over 1,000 billion grid points, creating an unprecedentedly detailed picture of this turbulence.

    The images above are two-dimensional slices from the full 3D simulation. The upper image shows the current density while the lower one shows mass density. On the right side of the images, magnetic field lines are superimposed in white. The results are gorgeous. Can you imagine a fly-through video? (Image and research credit: J. Beattie et al.; via Gizmodo)

  • Featured Video Play Icon

    “Monsoon 7”

    Storm-chasing photographer Mike Olbinski (previously) returns with another stunning timelapse of summer thunderstorms in the western U.S. I never tire of watching the turbulent convection, microbursts, billowing haboobs, and undulating clouds Olbinski captures. His work is always a reminder of the incredible power and energy contained in our atmosphere and unleashed in cycles of warming and cooling, evaporation and condensation. (Video and image credit: M. Olbinski)

  • Proving Superdiffusion

    Proving Superdiffusion

    Turbulence is very good at spreading things out. Drop dye into a turbulent flow and it will quickly disperse. Add in particles — like rubber ducks — and they can spread apart, often at speeds quicker than one would expect, based on the background flow. This is (roughly speaking) a phenomenon known as “superdiffusion,” where turbulence makes particles that start out as neighbors part ways.

    Physicists conjectured that turbulence — including simplified and idealized versions of it that are simpler to deal with — had this superdiffusion property, but no one was able to show that in a mathematically rigorous way. But now a group of mathematicians has done so, using a technique known as homogenization. There’s a lot more on the story over at Quanta, or you can check out the original papers on arXiv. (Image credit: J. Richard; research credit: S. Armstrong et al. and S. Armstrong and T. Kuusi; see also Quanta)

    Fediverse Reactions
  • Mapping the Mozambique Channel

    Mapping the Mozambique Channel

    The Mozambique Channel boasts some of the world’s most turbulent waters, driven by eddies hundreds of kilometers wide. Eddies of this size — known as mesoscale — determine regional flows that influence local biodiversity, sediment mixing, and how plastic pollution moves. To better understand the region, scientists measured a mesoscale dipole from a research vessel.

    Illustration of flows in the Mozambique Channel. The anticyclonic ring in dark blue rotates counterclockwise and consists of largely uniform water (labeled Ring R1). To the south, in green, a cyclonic eddy rotates in a clockwise sense (labeled Cyclone C1). This area is chlorophyll-rich and has varying salinity levels. Between the two is a filament of chlorophyll-rich water being drawn from the near-shore region (labeled Filament F1).
    Illustration of flows in the Mozambique Channel. The anticyclonic ring in dark blue rotates counterclockwise and consists of largely uniform water (labeled Ring: R1). To the south, in green, a cyclonic eddy rotates in a clockwise sense (labeled Cyclone: C1). This area is chlorophyll-rich and has varying salinity levels. Between the two is a filament of chlorophyll-rich water being drawn from the near-shore region (labeled Filament: F1).

    The dipole consisted of a large anticyclonic ring (shown in dark blue) that rotated counterclockwise and a smaller cyclonic eddy (shown in green) that rotated clockwise. Between these eddies lay a central jet moving up to 130 centimeters per second that drew material out from the shoreline. In the anticyclonic ring, researchers found largely uniform waters with little chlorophyll. The cyclonic eddy, in contrast, was high in chlorophyll and had large variations in salinity. Those smaller-scale variations, they found, helped to drive vertical motions of up to 40 meters per day.

    In situ measurements like these help scientists understand how energy flows through different scales in the ocean and how that energy helps transport nutrients, sediment, and pollution regionally. Such measurements also help us to refine ocean models that enable us to predict this transport and how regions will change as climate patterns shift. (Image credit: ship – A. Lamielle/Wikimedia Commons, eddies – P. Penven et al.; research credit: P. Penven et al.; via Eos)

    Fediverse Reactions
  • Escape From Yavin 4

    Escape From Yavin 4

    In an ongoing tradition, let’s take another look at some Star Wars-inspired aerodynamics. This year it’s the TIE fighter’s turn. Here, researchers simulate the spacecraft trying to escape Yavin 4’s atmosphere at Mach 1.15. The research poster’s blue contours show pressure contours, with darker colors connoting higher pressures. The bright low pressure region immediately behind the craft suggests a difficult, high-drag ascent and a turbulent, subsonic wake despite the craft’s supersonic velocity. (Image credit: A. Martinez-Sanchez et al.)

    Fediverse Reactions
  • Featured Video Play Icon

    “Legend”

    Filmmaker Roman De Giuli returns to his roots with this short fluid-filled film inspired by the color gold. He combines paint, ink, powders, and particles in a mix of micro- and macroscale photography. As always, the results are a mesmerizing plethora of fluid phenomena: Marangoni flows, turbulence, vorticity, viscous fingering and so much more. (Video and image credit: R. De Giuli)

  • Flying Without a Rudder

    Flying Without a Rudder

    Aircraft typically use a vertical tail to keep the craft from rolling or yawing. Birds, on the other hand, maneuver their wings and tail feathers to counter unwanted motions. Researchers found that the list of necessary adjustments is quite small: just 4 for the tail and 2 for the wings. Implementing those 6 controllable degrees of freedom on their bird-inspired PigeonBot II allowed the biorobot to fly steadily, even in turbulent conditions, without a rudder. Adapting such flight control to the less flexible surfaces of a typical aircraft will take time and creativity, but the savings in mass and drag could be worth it. (Image credit: E. Chang/Lentink Lab; research credit: E. Chang et al.; via Physics Today)

    Fediverse Reactions
  • Simulating a Sneeze

    Simulating a Sneeze

    Sneezing and coughing can spread pathogens both through large droplets and through tiny, airborne aerosols. Understanding how the nasal cavity shapes the aerosol cloud a sneeze produces is critical to understanding and predicting how viruses could spread. Toward that end, researchers built a “sneeze simulator” based on the upper respiratory system’s geometry. With their simulator, the team mimicked violent exhalations both with the nostrils open and closed — to see how that changed the shape of the aerosol cloud produced.

    The researchers found that closed nostrils produced a cloud that moved away along a 18 degree downward tilt, whereas an open-nostril cloud followed a 30-degree downward slope. That means having the nostrils open reduces the horizontal spread of a cloud while increasing its vertical spread. Depending on the background flow that will affect which parts of a cloud get spread to people nearby. (Image and research credit: N. Catalán et al.; via Physics World)

    Fediverse Reactions
  • Filtering by Sea Sponge

    Filtering by Sea Sponge

    Gathering oil after a spill is fiendishly difficult. Deploying booms to corral and soak up oil at the water surface only catches a fraction of the spill. A recent study instead turns to nature to inspire its oil filter. The team was inspired by the Venus’ flower basket, a type of deep-sea sponge with a multi-scale structure that excels at pulling nutrients out of complex flow fields. The outer surface of the sponge has helical ridges that break up the turbulence of any incoming flow, helping the sponge stay anchored by reducing the force needed to resist the flow. Beneath the ridges, the sponge’s skeleton has a smaller, checkered pattern that further breaks up the flow as it enters into the sponge’s hollow body. Within this cavity, the flow is slower and swirling, giving plenty of time for nutrients in the water to collide with the nutrient-gathering flagellum lining the sponge.

    By mimicking this three-level structure, the team built a capable oil-capturing device that can filter even emulsified oil from the water. They swapped the flagellum with a (replaceable) oil-adsorbing material and found that their filter captured more than 97% of oil across a range of flow conditions. (Image credit: NOAA; research credit: Y. Yu et al.; via Physics World)

    Fediverse Reactions
  • Featured Video Play Icon

    Salt Affects Particle Spreading

    Microplastics are proliferating in our oceans (and everywhere else). This video takes a look at how salt and salinity gradients could affect the way plastics move. The researchers begin with a liquid bath sandwiched between a bed of magnets and electrodes. Using Lorentz forcing, they create an essentially 2D flow field that is ordered or chaotic, depending on the magnets’ configuration. Although it’s driven very differently, the flow field resembles the way the upper layer of the ocean moves and mixes.

    The researchers then introduce colloids (particles that act as an analog for microplastics) and a bit of salt. Depending on the salinity gradient in the bath, the colloids can be attracted to one another or repelled. As the team shows, the resulting spread of colloids depends strongly on these salinity conditions, suggesting that microplastics, too, could see stronger dispersion or trapping depending on salinity changes. (Video and image credit: M. Alipour et al.)

    Fediverse Reactions