FYFD

Tag: turbulence

  • Seeding Clouds With Wildfire

    Seeding Clouds With Wildfire

    Raging wildfires send plumes of smoke up into the atmosphere; that smoke is made up of tiny particles that can serve as seeds — nucleation sites — where water vapor can freeze and form clouds. To understand wildfire’s effect on cloud growth, researchers sampled air from the troposphere (the atmosphere’s lowest layer) both in and around wildfire smoke.

    The team found that smoke increased the number of nucleating particles up to 100 times higher than the background air, but the exact make-up of the smoke varied significantly by fire. Smoke particles were mostly organic, though inorganic ones appeared as well. The temperature of a fire, as well as what materials it was burning, made a big difference; the fire where they measured the highest particle concentrations included lots of unburned plant material, thought to be carried aloft by turbulence around the fire. (Image credit: K. Barry; research credit: K. Barry et al.; via Eos)

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  • Bow Shock Instability

    Bow Shock Instability

    There are few flows more violent than planetary re-entry. Crossing a shock wave is always violent; it forces a sudden jump in density, temperature, and pressure. But at re-entry speeds this shock wave is so strong the density can jump by a factor of 13 or more, and the temperature increase is high enough that it literally rips air molecules apart into plasma.

    Here, researchers show a numerical simulation of flow around a space capsule moving at Mach 28. The transition through the capsule’s bow shock is so violent that within a few milliseconds, all of the flow behind the shock wave is turbulent. Because turbulence is so good at mixing, this carries hot plasma closer to the capsule’s surface, causing the high temperatures visible in reds and yellows in the image. Also shown — in shades of gray — is the vorticity magnitude of flow around the capsule. (Image credit: A. Álvarez and A. Lozano-Duran)

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  • 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)

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    “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)

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  • 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)

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  • 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.)

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    “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)

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  • 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)

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