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Search results for: “turbulence”

  • Studying Hydroelastic Turbulence

    Studying Hydroelastic Turbulence

    Can energy at the small-scales of a turbulent flow work its way up to larger scales? That’s a question at the heart of today’s study. Here, researchers are studying hydroelastic waves — created by stretching a thin elastic membrane over a water tank. The membrane gets vibrated up and down in just one location with an amplitude of about 1 millimeter. The resulting waves depend both on the movement of the water and the elasticity of the membrane, mimicking situations like ice-covered seas.

    Rather than simply dying away, the local fluctuations introduced at the membrane spread, coalescing into larger-scale hydroelastic waves. How energy flows between these scales could have implications for weather forecasting, climate modeling, and other turbulent systems. (Image and research credit: M. Vernet and E. Falcon; via APS)

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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)

  • Kolmogorov Turbulence

    Kolmogorov Turbulence

    Turbulent flows are ubiquitous, but they’re also mindbogglingly complex: ever-changing in both time and space across length scales both large and small. To try to unravel this complexity, scientists use simplified model problems. One such simplification is Kolmogorov flow: an imaginary flow where the fluid is forced back and forth sinusoidally. This large-scale forcing puts energy into the flow that cascades down to smaller length scales through the turbulent energy cascade. Here, researchers depict a numerical simulation of a turbulent Kolmogorov flow. The colors represent the flow’s vorticity field. Notice how your eye can pick out both tiny eddies and larger clusters in the flow; those patterns reflect the multi-scale nature of turbulence. (Image credit: C. Amores and M. Graham)

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  • Measuring Microfibers in Turbulence

    Measuring Microfibers in Turbulence

    Microplastic pollution is on the rise, especially in waterways. Microfibers — millimeters in length but only microns in diameter — are especially prevalent, as they get washed out of synthetic clothing. Collecting these pollutants first requires understanding how they move and cluster in turbulent flows. Researchers investigated that using a small water channel and high-resolution cameras.

    The team followed microfiber strands as they moved through turbulence, paying special attention to how the fibers tumbled (rotating about their short axis) and spin (rotating around their long axis). How much fibers tumbled depended on the turbulence level; with more intense turbulence, the fibers tumbled more. Rates of spinning, they found, were consistently even higher than those for tumbling. By better understanding how microfibers behave in turbulence, we’ll be able to, for example, predict how far plastics will travel before settling to the ocean floor. (Image credit: Adobe Stock Photos; research credit: V. Giurgiu et al.; via APS Physics)

  • Warming Temperatures Increase Turbulence

    Warming Temperatures Increase Turbulence

    After multiple high-profile injuries caused by atmospheric turbulence, you might be wondering whether airplane rides are getting rougher. Unfortunately, the answer is yes, at least for clear-air (i.e., non-storm-related) turbulence in the North Atlantic region. It seems that climate change, as predicted, is increasing the bumpiness of our atmosphere. There are a couple of mechanisms at play here.

    The first is that warming temperatures fuel thunderstorms. When ground-level temperatures and water temperatures are warmer, that provides more warm, moist air rising up and feeding atmospheric convection. Especially in the summertime, that translates into stronger, more frequent thunderstorms; even with flights avoiding the storms themselves, there’s greater turbulence surrounding them.

    The second mechanism relates to wind, specifically in the mid-latitudes. In general, a temperature difference between two regions causes stronger winds. (Think about the windy conditions that accompany an incoming cold front.) At the mid-latitudes, the difference between cold polar regions and warmer equatorial ones creates a strong wind, known as the jet stream. Now, as temperature gradients increase at cruising altitudes, the jet stream gets stronger, which means bigger changes in wind speed with altitude. And its those wind speed differences at different heights that drive turbulence.

    So, yes, we’re likely to see more turbulent flights now and in the future. But, fortunately, there’s a simple way to avoid injuries from that bumpiness: buckle up! If you keep your seat belt fastened while you’re seated, you can avoid getting tossed around by unexpected G-forces. (Image credit: G. Ruballo; see also Gizmodo)

  • Testing Turbulence’s Limits

    Testing Turbulence’s Limits

    Understanding chaotic, turbulent flows has long challenged scientists and engineers due to their sheer complexity. In turbulent flows, energy cascades from the largest scales — like the kilometer-size cross-section of a cloud — to the very smallest scales, less than a millimeter in size, where viscosity transforms the flow’s motion to heat. For nearly a century, our theoretical understanding of turbulence has posited that there are certain universal behaviors in the statistics of a turbulent flow — essentially that, due to this energy cascade, some aspects of every turbulent flow are the same from clouds to ocean currents to your coffee cup.

    Accordingly, experimentalists have tried for decades to measure this expected universality. Often, there are some signs of agreement, and any deviation was attributed to the finite difference between the large and small scales of the flow. (The theory assumes the difference in these scales’ size is effectively infinite.) But now researchers have achieved the largest range of scales yet — comparable to those found in the atmosphere — and the gaps between theory and experiment remain. The new study does show signs of universality but in a different way than existing theory predicts. As the authors point out, we’ll need new theories to explain these findings. (Image credit: D. Páscoa; research credit: C. Küchler et al.; via APS Physics)

  • Overcoming Turbulence

    Overcoming Turbulence

    Despite their microscopic size, many plankton undertake a daily migration that covers tens of meters in depth. As they journey, they must contend with currents, turbulence, and other flows that could knock them off-course. And, increasingly, research shows that a plankton’s shape makes a big difference in these flows.

    Spherical plankton tend to cluster in areas of flow moving opposite to their direction of travel. But more elongated plankton can resist — or even reverse — this tendency, helping them stay on track. In turbulence, elongated swimmers are also better at keeping their thrust oriented in the desired direction of travel. So both nature and engineers should favor elongated microswimmers when contending with turbulence and potential crossflows. (Image credit: Picturepest/Flickr; research credit: R. Bearon and W. Durham)

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    “Turbulence”

    In his recent short film, artist Roman De Giuli explores turbulence using metallic paints and inks in a fishtank. The effects are beautiful: sparkling pigments dispersing in clouds, mushroom- and umbrella-shaped Rayleigh-Taylor instabilities, and lots of swirling eddies. It’s exactly the kind of eyecandy to kick off your weekend with! (Image and video credit: R. De Giuli)

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    Turbulence From Vortex Rings

    When vortex rings collide, they reconnect into smaller, rings that eventually break down into chaos. Here, researchers experiment with colliding multiple vortex rings — focusing on an eight-ring collision. When they collide rings over and over, it creates a zone of isolated turbulence at the heart of the collisions.

    Many of the theories and predictions that exist around turbulence assume that the flow is homogeneous and isotropic; what this means is that the (statistical) characteristics of the flow are the same in every direction. In reality, this kind of flow isn’t always easily achieved, which makes testing theoretical predictions challenging.

    What’s neat about this set-up is that you get this desired turbulence in a very controlled way. It’s easy to tune the size and energy of your vortex rings, and those tweaks allow you to observe what — if any — changes occur in the resulting turbulence. (Image and video credit: T. Matsuzawa et al.)

  • “Turbulence”

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