FYFD is dedicated to sharing the awesomeness that is fluid dynamics with the world—whether or not you care for calculus. It is a science and engineering outreach blog with a new post about the physics of liquids, gases, plasmas, or granular materials—anything that behaves like a fluid—five times a week. It features photos, videos, and research from scientists, engineers, and artists around the world along with a short explanation from FYFD’s author, Nicole Sharp.
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As manta rays swim, they’re constantly doing two important — but not necessarily compatible — things: getting oxygen to breathe and collecting plankton to eat. That requires some expert filtering Keep reading
As manta rays swim, they’re constantly doing two important — but not necessarily compatible — things: getting oxygen to breathe and collecting plankton to eat. That requires some expert filtering to send food particles toward their stomach and oxygen-rich water to their gills. Manta rays do this with a built-in filter that resembles an industrial crossflow filter. Researchers built a filter inspired by a manta ray’s geometry, and found that it has three different flow states, based on the flow speed. At low speeds, flow moves freely down the filter’s channels; in a manta, this would carry both water and particles toward the gills. At medium speeds, vortices start to form at the entrance to the filter channels. This sends large particles downstream (toward a manta’s digestive system) while water passes down the channels. At even greater speeds, each channel entrance develops a vortex. That allows water to pass down the filter channels but keeps particles out. (Image credit: mantaN. Weldingh, filterX. Mao et al.; research credit: X. Mao et al.; via Ars Technica)
Depending on the flow speed, a manta-inspired filter can allow both water and particles in or filter particles out of the water.
A cold region of Pacific waters stretches westward along the equator from the coast of Ecuador. Known as the equatorial cold tongue, this region exists because trade winds push surface Keep reading
A cold region of Pacific waters stretches westward along the equator from the coast of Ecuador. Known as the equatorial cold tongue, this region exists because trade winds push surface waters away from the equator and allow colder, deeper waters to surface. Previous climate models have predicted warming for this region, but instead we’ve observed cooling — or at least a resistance to warming. Now researchers using decades of data and new simulations report that the observed cooling trend is, in fact, a result of human-caused climate changes. Like the cold tongue itself, this new cooling comes from wind patterns that change ocean mixing.
As pleasant as a cooling streak sounds, this trend has unfortunate consequences elsewhere. Scientists have found that this cooling has a direct effect on drought in East Africa and southwestern North America. (Image credit: J. Shoer; via APS News)
Photographer Jonathan Knight likes capturing waterfalls about 45 minutes after sunset, creating ghostly images that emphasize the shape of the cascading water. The dim surroundings and misty shapes remind me Keep reading
Photographer Jonathan Knight likes capturing waterfalls about 45 minutes after sunset, creating ghostly images that emphasize the shape of the cascading water. The dim surroundings and misty shapes remind me of old daguerreotypes. See more of his images on his website and his Instagram. (Image credit: J. Knight; via Colossal)
In the Leidenfrost effect, room-temperature droplets bounce and skitter off a surface much hotter than the drop’s boiling point. With those droplets, a layer of vapor cushions them and insulates Keep reading
In the Leidenfrost effect, room-temperature droplets bounce and skitter off a surface much hotter than the drop’s boiling point. With those droplets, a layer of vapor cushions them and insulates them from the hot surface. In today’s study, researchers instead used hot or burning drops (above) and observed how they impact a room-temperature surface. While room-temperature droplets hit and stuck (below), hot and burning droplets bounced (above).
In this case, the cushioning air layer doesn’t come from vaporization. Instead, the bottom of the falling drop cools faster than the rest of it, increasing the local surface tension. That increase in surface tension creates a Marangoni flow that pulls fluid down along the edges of the drop. That flow drags nearby air with it, creating the cushioning layer that lets the drop bounce. In this case, the authors called the phenomenon “self-lubricating bouncing.” (Image and research credit: Y. Liu et al.; via Ars Technica)
Drops impacting a dry hydrophilic surface flatten into a film. Drops that impact a wet film throw up a crown-shaped splash. But what happens when a drop hits the edge Keep reading
Drops impacting a dry hydrophilic surface flatten into a film. Drops that impact a wet film throw up a crown-shaped splash. But what happens when a drop hits the edge of a wet surface? That’s the situation explored in this video, where blue-dyed drops interact with a red-dyed film. From every angle, the impact is complex — sending up partial crown splashes, generating capillary waves that shift the contact line, and chaotically mixing the drop and film’s liquids. (Video and image credit: A. Sauret et al.)
Your typical river has a single water basin and drains along a river or two on its way to the sea. But there are a handful of rivers and lakes Keep reading
Your typical river has a single water basin and drains along a river or two on its way to the sea. But there are a handful of rivers and lakes that don’t obey our usual expectations. Some rivers flow in two directions. Some lakes have multiple outlets, each to a separate water basin. That means that water from a single lake can wind up in two entirely different bodies of water.
The most famous example of these odd waterways is South America’s Casiquiare River, seen running north to south in the image above. This navigable river connects the Orinoco River (flowing east to west in this image) with the Rio Negro (not pictured). Since the Rio Negro eventually joins the Amazon, the Casiquiare River’s meandering, nearly-flat course connects the continent’s two largest basins: the Orinoco and the Amazon.
The Martian atmosphere lacks the density to support tornado storm systems, but vortices are nevertheless a frequent occurrence. As sun-warmed gases rise, neighboring air rushes in, bringing with it any Keep reading
The Martian atmosphere lacks the density to support tornado storm systems, but vortices are nevertheless a frequent occurrence. As sun-warmed gases rise, neighboring air rushes in, bringing with it any twisted shred of vorticity it carries. Just as an ice skater pulling her arms in spins faster, the gases spin up, forming a dust devil.
In “Dispersion,” particles spread under the influence of an unseen fluid. Like Roman de Giuli’s work, filmmaker Susi Sie creates macro images that look like ice floes, deserts, and river Keep reading
In “Dispersion,” particles spread under the influence of an unseen fluid. Like Roman de Giuli’s work, filmmaker Susi Sie creates macro images that look like ice floes, deserts, and river deltas viewed from above. This similarity of patterns at both large and small scales is a specialty of fluid physics. Just as artists use it to mimic larger flows, scientists use it to study planet-scale problems in the lab. (Video and image credit: S. Sie et al.)
Studying the physics of planetary atmospheres is challenging, not least because we only have a handful of examples to work from in our own solar system. So it’s exciting that Keep reading
Studying the physics of planetary atmospheres is challenging, not least because we only have a handful of examples to work from in our own solar system. So it’s exciting that researchers have unveiled our first look at the 3D structure of an exoplanet‘s atmosphere.
Using ground-based observations, researchers studied WASP-121b, also known as Tylos, an ultra-hot Jupiter that circles its star in only 30 Earth hours. One face of the planet always faces its star while the other faces into space. The team found that the exoplanet has a flow deep in the atmosphere that carries iron from the hot daytime side to the colder night side. Higher up, the atmosphere boasts a super-fast jet-stream that doubles in speed (from an estimated 13 kilometers per second to 26 kilometers per second) as it crosses from the morning terminator to the evening. As one researcher observed, the planet’s everyday winds make Earth’s worst hurricanes look tame. (Image credit: ESO/M. Kornmesser; research credit: J. Seidel et al.; via Gizmodo)
Coffee-making continues to be a rich source for physics insight. The roasting and brewing processes are fertile ground for chemistry, physics, and engineering. Recently, one research group has focused on Keep reading
Coffee-making continues to be a rich source for physics insight. The roasting and brewing processes are fertile ground for chemistry, physics, and engineering. Recently, one research group has focused on the phenomenon of channeling, where water follows a preferred path through the coffee grounds rather than seeping uniformly through the grounds. Channeling reduces the amount of coffee extracted in the brew, which is both wasteful and results in a less flavorful cup. By uncovering what mechanics go into channeling, the group hopes to help baristas mitigate the undesirable process, creating a repeatable, efficient, and tasty espresso every time. (Image credit: E. Yavuz; via Ars Technica)
