Fuck Yeah Fluid Dynamics

Celebrating the physics of all that flows. Ask a question, submit a post idea or send an email. You can also follow FYFD on Twitter and Google+. FYFD is written by Nicole Sharp, PhD.

Recent Tweets @
Posts tagged "bubbles"

Champagne is well-known for its effervescence, but its tiny bubbles do more than affect your sensation when sipping. Champagne bubbles form when carbon dioxide dissolved in the wine nucleates along imperfections in the glass. Buoyancy causes them to flow upwards, growing as they pull more carbon dioxide from the surrounding champagne. When the bubbles reach the surface, they pop, sending an almost imperceptible fountain of tiny droplets into the air, as seen in the photo above. You can sometimes feel the droplets if you hold a glass near your face. The droplets released from the bursting champagne bubbles spread the aroma of the wine, imparting additional flavor through our olfactory sense. (Photo credit: F. Beaumont et al.)

This high-speed video shows the cavitation that occurs when a bottle of water is struck. The impact accelerates the bottle downward, generating localized vacuums between the glass and the liquid. These are cavitation bubbles, which expand until the pressure of the water surrounding them is too great. This outside pressure triggers an implosion of the bubble, which collapses until the pressure within the bubble makes it expand again. These rapid oscillations in pressure can often shatter the glass bottle. Cavitation can also generate extremely high temperatures and even trigger luminescence. It’s used by both pistol shrimp and mantis shrimp to hunt their prey. (Video credit: P. Taylor)

Vortices appear in scales both large and small, from your shower and the flap of an insect’s wing to cyclones and massive storms on other planets. Especially with these large-scale vortices, it can be difficult to understand the factors that affect their trajectories and intensities over time. Here researchers have studied the vortices produced on a heated half bubble for clues as to their long-term behavior. Heating the base of the bubble creates large thermal plumes which rise and generate large vortices, like the one seen above, on the bubble’s surface. Researchers observed the behavior of the vortices with and without rotation of the bubble. They found that rotating bubbles favored vortices near the polar latitudes of the bubble, just as planets like the Earth and Saturn have long-lived polar vortices. They also found that the intensification of both bubble vortices and hurricanes was reasonably captured by a single time constant, which may lead to better predictions of storm behaviors. Their latest paper is freely available here. (Image credit: H. Kellay et al.; research credit: T. Meuel et al.; via io9)

Champagne owes much of its allure to its tiny bubbles. Unlike other wines, champagne undergoes a secondary fermentation in the bottle, during which the yeasts in the wine consume sugars and produce carbon dioxide, which dissolves into the wine. When opened, the carbon dioxide can begin to escape. Bubbles form in the glass around imperfections, either due to intentional etching of the glass or impurities left behind by cleaning. Once formed, trails of bubbles rise to the surface, swelling as more dissolved carbon dioxide is absorbed into each bubble. The bubbles then cluster near the surface of the champagne, occasionally popping and creating a flower-like distortion of the surrounding bubbles. The gases within the bubbles contains higher concentrations of aromatic chemicals than the surrounding wine, and the bursting of each bubble propels tiny droplets of these aromatics upwards, carrying the scent of the champagne to the drinker. For more beautiful champagne photos, I recommend this LuxeryCulture article; for more on the science of champagne, see Chemistry World’s coverage. Happy 2014! (Image credits: G. Liger-Belair et al.)

Surface tension usually constrains bubbles to the smallest area for a given volume - a sphere - but sometimes other forces generate more complicated geometries. The images above show bubbles flowing through microfluidic channels filled with a highly viscous carrier fluid. The bubble size and packing affects the shapes they assume, but so does the geometry of the channel. The narrow constrictions accelerate the flow, elongating the bubbles, whereas the wider channel regions slow the carrier fluid and squish the bubbles together. (Image credit: M. Sauzade and T. Cubaud (Stony Brook University))

A bubble initiated near a free surface—like the air-water interface here—can  generate some spectacular dynamics. Beginning at the far left, the expanding subsurface bubble causes a dome at the surface that sharpens into a spike. By Frame 3, the bubble is collapsing but overshoots and rebounds, which introduces the tiny instability in Frame 4 that grows in subsequent time steps to form the water skirt that surrounds the spike. Although generated entirely differently, the end result is reminiscent of the water sculptures made by artists like Marcus Reugels, Corrie White, Jack Long, and others. (Image credit: A. M. Zhang et al.)

Hitting a glass bottle full of a non-carbonated drink can shatter the bottle due to cavitation, but doing the same with a carbonated beverage can make the bottle overflow with foam. The video above breaks down the physics of this bar prank. It all begins with nucleation and the tiny bubbles of carbon dioxide that form in the liquid. Striking the top of the bottle generates a compression wave that travels through the liquid, shrinking bubbles as it passes. When it hits the bottom of the bottle, it gets reflected as an expansion wave that expands the bubbles. This reflection happens several times between the free surface of the liquid and the bottom of the bottle. The rapid collapse-and-expansion of the bubbles makes them implode into a cloud of tinier bubbles that expands until the local supply of carbon dioxide is used up. At this point, the buoyancy of the bubbles carries them upward in plumes, creating more bubbles with the dissolved carbon dioxide nearby. And, all of a sudden, you’ve got foam everywhere. Like all of this week’s videos, this video is an entry in the 2013 Gallery of Fluid Motion. (Video credit: J. Rodriguez-Rodriguez et al.)

In water and other Newtonian fluids, a rising bubble is typically spherical, but for non-Newtonian fluids things are a different story. In non-Newtonian fluids the viscosity—the fluid’s resistance to deformation—is dependent on the shear rate and history—how and how much deformation is being applied. For rising bubbles, this can mean a teardrop shape or even a long tail that breaks up into fishbone-like ligaments. The patterns shown here vary with the bubble’s volume, which affects the velocity at which it rises (due to buoyancy) and thus the shear force the bubble and surrounding non-Newtonian fluid experience. (Video credit: E. Soto, R. Zenit, and O. Manero)

A microgravity environment can cause some nonintuitive behaviors in fluids. Many of the effects that dominate fluid dynamics in space are masked by gravity’s effects here on Earth. As a result, it can be very difficult to predict how seemingly straightforward technologies like heat exchangers, refrigeration units, and fuel tanks will behave. The photos above show two bubble jets—created by injecting a liquid-gas mixture into a liquid—colliding in microgravity. This particular experiment was conducted in a drop tower rather than on-orbit, which produced some side effects like the large bubbles seen in the images. These were created by the coalescence of smaller bubbles that congregated near the top of the tank shortly before the experiment attained free-fall. (Photo credit: F. Sunol and R. Gonzalez-Cinca)

Vibrating a gas-liquid interface produces some exciting instability behaviors. The photo above shows air and silicone oil vibrated vertically within a prism. For the right frequencies and amplitudes, the vibrations produce liquid jets that shoot up and eject droplets as well as gas cavities and bubble transport below the interface. To see a similar experiment in action, check out this post. (Photo credit: T. J. O’Hern et al./Sandia National Laboratories)