“Architecture in Music”

Inside musical instruments gapes an emptiness that, to the eye of photographer Charles Brooks, resembles the vast architecture of music halls and cathedrals. In his series “Architecture in Music,” Brooks takes us into these empty spaces, revealing where the resonance at the heart of the instrument’s sound lies. In a stringed instrument like a violin, the vibration of the strings makes a relatively quiet sound on its own; it’s only in making the violin’s entire hollow body vibrate that resonance amplifies the strings. Similarly, wind instruments rely on air resonating within them to produce their sound. (Image credit: C. Brooks; via Colossal)

Manu Jumping, a.k.a. How to Make a Big Splash

The Māori people of Aotearoa New Zealand compete in manu jumping to create the biggest splash. Here’s a fun example. In this video, researchers break down the physics of the move and how it creates an enormous splash. There are two main components — the V-shaped tuck and the underwater motion. At impact, jumpers use a relatively tight V-shape; the researchers found that a 45-degree angle works well at high impact speeds. This initiates the jumper’s cavity. Then, as they descend, the jumper unfolds, using their upper body to tear open a larger underwater cavity, which increases the size of the rebounding jet that forms the splash. To really maximize the splash, jumpers can aim to have their cavity pinch-off (or close) as deep underwater as possible. (Video and image credit: P. Rohilla et al.)

Flamingo Fluid Dynamics, Part 2: The Game’s a Foot

Yesterday we saw how hunting flamingos use their heads and beaks to draw out and trap various prey. Today we take another look at the same study, which shows that flamingos use their footwork, too. If you watch flamingos on a beach, in muddy waters, or in a shallow pool, you’ll see them shifting back and forth as they lift and lower their feet. In humans, we might attribute this to nervous energy, but it turns out it’s another flamingo hunting habit.

As a flamingo raises its foot, it draws its toes together; when it stomps down, its foot spreads outward. This morphing shape, researchers discovered, creates a standing vortex just ahead of its feet — right where it lowers its head to sample whatever hapless creatures it has caught in this swirling vortex. And the vortex, as shown below, is strong enough to trap even active swimmers, making the flamingo a hard hunter to escape. (Image credit: top – L. Yukai, others – V. Ortega-Jimenez et al.; research credit: V. Ortega-Jimenez et al.; submitted by Soh KY)

Flamingo Fluid Dynamics, Part 1: A Head in the Game

Flamingos are unequivocally odd-looking birds with their long skinny legs, sinuous necks, and bent L-shaped beaks. They are filter-feeders, but a new study shows that they are far from passive wanderers looking for easy prey in shallow waters. Instead, flamingos are active hunters, using fluid dynamics to draw out and trap the quick-moving invertebrates they feed on. In today’s post, I’ll focus on how flamingos use their heads and beaks; next time, we’ll take a look at what they do with their feet.

Feeding flamingos often bob their heads out of the water. This, it turns out, is not indecision, but a strategy. Lifting its flat upper forebeak from near the bottom of a pool creates suction. That suction creates a tornado-like vortex that helps draw food particles and prey from the muddy sediment.

When feeding, flamingos will also open and close their mandibles about 12 times a second in a behavior known as chattering. This movement, as seen in the video above, creates a flow that draws particles — and even active swimmers! — toward its beak at about seven centimeters a second.

Staying near the surface won’t keep prey safe from flamingos, either. In slow-flowing water, the birds will set the upper surface of their forebeak on the water, tip pointed downstream. This seems counterintuitive, until you see flow visualization around the bird’s head, as above. Von Karman vortices stream off the flamingo’s head, which creates a slow-moving recirculation zone right by the tip of the bird’s beak. Brine shrimp eggs get caught in these zones, delivering themselves right to the flamingo’s mouth.

Clearly, the flamingo is a pretty sophisticated hunter! It’s actively drawing out and trapping prey with clever fluid dynamics. Tomorrow we’ll take a look at some of its other tricks. (Image credit: top – G. Cessati, others – V. Ortega-Jimenez et al.; research credit: V. Ortega-Jimenez et al.; submitted by Soh KY)

How Insects Fly in the Rain

Getting caught in the rain is annoying for us but has the potential to be deadly for smaller creatures like insects. So how do they survive a deluge? First, they don’t resist a raindrop, and second, they have the kinds of surfaces water likes to roll or bounce off. The key to this second ability is micro- and nanoscale roughness. Surfaces like butterfly wings, water strider feet, and leaf surfaces contain lots of tiny gaps where air gets caught. Water’s cohesion — its attraction to itself — is large enough that water drops won’t squeeze into these tiny spaces. Instead, like the ball it resembles, a water drop slides or bounces away. (Video and image credit: Be Smart)

Non-Newtonian Effects in Magma Flows

As magma approaches the surface, it forces its way through new and existing fractures in the crust, forming dikes. When a volcano finally erupts, the magma’s viscosity is a major factor in just how explosive and dangerous the eruption will be, but a new study shows that what we see from the surface is a poor predictor of how magma actually flows within the dike.

Researchers built their own artificial dike using a clear elastic gelatin, which they injected water and shear-thinning magma-mimics into. By tracking particles in the liquids, they could observe how each liquid followed on its way to the surface. All of the liquids formed similar-looking dikes at a similar speed, but within the dike, the liquids flowed very differently. Water cut a central jet through the gelatin, then showed areas of recirculation along the outer edges. In contrast, the shear-thinning liquids — which are likely more representative of actual magma — showed no recirculation. Instead, they flowed through the dike in a smooth, fan-like shape.

The team cautions that surface-level observations of developing magma dikes provide little information on the flow going on underneath. Instead, their results suggest that volcanologists modeling magma underground should take care to include the magma’s shear-thinning to properly capture the flow. (Image credit: T. Grypachevska; research credit: J. Kavanagh et al.; via Eos)

The Hidden Beauty in the Mundane

Physicist Sidney Nagel has spent his career on topics that are somewhat unexpected: how coffee stains form, how droplets splash — or don’t, and how fluid flows into viscous fingers. Often this means looking at the mechanics of everyday occurrences that we otherwise take for granted. Instead, Nagel probes carefully at things like a coffee stain, asking why it’s darker at the edges and what he could do to keep that from happening — all to ultimately uncover the forces and mechanisms at play. Quanta has a great little interview with him on this and other topics. Check it out here. (Image credit: S. Nagel and K. Norman; via Quanta)

Whale Migration Carries Nutrients

When it comes to the movement of nutrients in the ocean, we think of run-off from rivers, upwelling along coasts, and convective currents. We don’t typically think about animal migrations, but a new study of baleen whales (including species like humpbacks and right whales) suggests that these massive mammals provide a small but critical spreading service.

These whales feed in cold, nutrient-rich waters, like those in the Arctic, then travel thousands of kilometers to warm but nutrient-poor tropical waters to birth and raise calves. During that time, mothers do not hunt or eat; they live off their fat stores, which they also use to make milk for their offspring. Although they’re not eating during this time, they do still urinate, and it’s this activity that, according to researchers, adds some 3,000 tons of critical nitrogen to these areas. Since nitrogen is often a limited resource in these tropical waters, the whales’ urine may act like a fertilizer shipment for other species in their breeding grounds. (Image credit: C. Le Duc; research credit: J. Roman et al.; via Eos)

Bigger Particles Slide Farther

Mudslides and avalanches typically carry debris of many shapes and sizes. To understand how debris size affects flows like these, researchers use simplified, laboratory-scale experiments like this one. Here, researchers mix a slurry of silicone oil and glass particles of roughly two sizes. The red particles are larger; the blue ones smaller. Sitting in a cup, the mixture tends to separate, with red particles sinking faster to form the bottom layer and smaller blue particles collecting on top. And what happens when such a mixture flows down an incline? The smaller blue particles tend to settle out sooner, leaving the larger red particles in suspension as they flow downstream. (Video and image credit: S. Burnett et al.)

Great to host Dr. Anagha Madhusudanan (IISc Bangalore) INSPIRE faculty. She presented her work on Navier-Stokes-based linear models for intermittent & viscosity-stratified flows.
Wishing her all the best!
#FluidDynamics #Research #IITMadras #professor #Academia #Aerospace #IISc

“Now I See – The Collection Vol. 1”

On the heels of his behind-the-scenes introduction, here’s the first volume of artist Roman De Giuli’s “Now I See”. In it, we appear to soar above vast colorful landscapes. Rivers flow past islands. Glaciers creep along valleys. Canyons cut through deserts. It’s like a bird’s eye view of our planet’s terrestrial wonders. (Video and image credit: R. De Giuli)

Tracking Insects in Flight

Insects are masters of a challenging flight regime; their agility, stability, and control far outstrip anything we’ve built at their size. But to even understand how they accomplish this, researchers must manage to capture those maneuvers in the first place. Insects don’t stay in one small area, which is what the typical fixed camera motion capture set-up requires. Instead, one group of researchers has designed a system with a moveable mirror that tracks an insect’s motion in real-time, ensuring that the camera stays fixed on the insect even as it traverses a room or — for the drone-mounted version — a field.

Real-time motion tracking means that researchers can better capture detailed footage of the insect’s maneuvers in a lab environment, or they can head into the field to follow insects in the wild. Imagine tracking individual pollinators through a full day of gathering or watching how a bumblebee responds to getting hit by a raindrop mid-flight. (Video and image credit: Science; research credit: T. Vo-Doan et al.)

Fractal Fingers

As bizarre as the branching fractal fingers of the Saffman-Taylor instability look, they’re quite a common phenomenon. In his video, Steve Mould demonstrates how to make them by sandwiching a viscous liquid like school glue between two acrylic sheets and then pulling them apart. The more formal lab-version of this is the Hele-Shaw cell, which he also demonstrates. But you may have come across the effect when pealing up a screen protector or in dealing with a cracked phone screen. In all of these cases, a less viscous fluid — specifically air — is forcing its way into a more viscous fluid, something that it cannot manage without the fluid interface fracturing. (Video and image credit: S. Mould)

Pour-Over Physics

Fluids labs are filled with many a coffee drinker, and even those (like me) who don’t enjoy coffee, can find plenty of fascinating physics in their labmates’ mugs. Espresso has received the lion’s share of the research in recent years, but a new study looks at the unique characteristics of a pour-over coffee. In this technique, coffee grounds sit in a conical filter and a stream of hot water pours over the top of the grounds. Researchers found that the ideal pour creates a powerful mixing environment in a coffee-studded water layer that sits above a V-shaped bed of grains created by the falling water jet.

The best mixing, they find, requires a pour height no greater than 50 centimeters (to prevent the jet from breaking into drops) but with enough height that the falling jet stirs up the grounds. You also want to pour slowly enough to give plenty of time for mixing, without letting the jet stick to the kettle’s spout, which (again) causes the jet to break up.

That ideal pour extracts more coffee flavor from the grounds, allowing you to get the same strength of brew from fewer beans. As climate change makes coffee harder to grow, coffee drinkers will want every trick to stretch their supply. (Image credit: S. Satora; research credit: E. Park et al.; via Ars Technica)

Interstellar Jets

This JWST image shows a couple of Herbig-Hero objects, seen in infrared. These bright objects form when jets of fast-moving energetic particles are expelled from the poles of a newborn star. Those particles hit pockets of gas and dust, forming glowing, hot shock waves like those seen here in red. The star that birthed the object is out of view to the lower-right. The bright blue light surrounded by red spirals that sits near the tip of the shock waves is actually a distant spiral galaxy that happens to be aligned with our viewpoint. (Image credit: NASA/ESA/CSA/STScI/JWST; via APOD)

“Spines”

Water droplets cling to spine-covered plant life in this series from photographer Tom Leighton. The hairs are hydrophobic — notice how spherical the drops appear. Many plants make parts of their leaves and stems hydrophobic in order to redirect water toward their roots, where it can be taken in. Others use hair-like awns to collect and draw in dew that supplements their water capture. (Image credit: T. Leighton; via Colossal)

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.

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)

Kirigami in the Flow

Kirigami is a paper art that combines folding and cutting to create elaborate shapes. Here, researchers use cuts in thin sheets of plastic and explore how the sheets transform in a flow. Depending on the configuration of cuts, the sheets can stretch dramatically in the flow, creating complex, dynamic, and beautiful wakes. I feel like there must be some applications out there that would benefit from kirigami-induced mixing. (Video and image credit: A. Carleton and Y. Modarres-Sadeghi)

Inside Hail Formation

Conventional wisdom suggests that hailstones form over the course of repeated trips up and down through a storm, but a new study suggests that formation method is less common than assumed. Researchers studied the isotope signatures in the layers of 27 hailstones to work out each stone’s formation history. They found that most hailstones (N = 16) grew without any reversal in direction. Another 7 only saw a single period when upwinds lifted them, and only 1 of the hailstones had cycled down-and-up more than once. They did find, however, that hailstones larger than 25mm (1 inch) in diameter had at least one period of growth during lifting.

So smaller hailstones likely don’t cycle up and down in a storm, but the largest (and most destructive) hailstones will climb at least once before their final descent. (Image credit: D. Trinks; research credit: X. Lin et al.; via Gizmodo)

Dams Fill Reservoirs With Sediment

Dams are critical pieces of infrastructure, but, as Grady shows in this Practical Engineering video, they are destined to be temporary. The reason is that they naturally fill with sediment over time. Rivers carry a combination of water and sediment; the latter is critical to healthy shorelines and stable ecology. But while sediment gets carried along by a fast-flowing river, slower flow rates allow sediment to fall out of suspension, as demonstrated in Grady’s tabletop flume. As his river transitions to a deeper, slower-flowing reservoir, sand falls out of the flow, building up colorful strata. The sand and water even create dynamic feedback loops, as seen with the dunes that form in his timelapse and march toward the dam.

Any long-term plan for a dam has to deal with this inevitable build-up of sediment, and, unfortunately, it’s not a simple or cheap problem to address, as discussed in the video. (Video and image credit: Practical Engineering)