Microfluidic channels are excellent at creating a steady supply of droplets. But depending on the characteristics of the two viscous fluids being used, as well as factors like flow rate and channel geometry, the results can be anything from well-defined and separated drops to steady jets to wild instabilities. The image above shows a series of different outcomes, including waves that break on the edges of drops and ligaments that stretch around the central fluid. (Image and research credit: X. Hu and T. Cubaud)
Search results for: “jet”
The World in a Droplet
Capturing refracted images in a droplet is a popular pastime among high-speed photographers, and in this solo Slow Mo Guy outing, we get to see that process in video. Physically, the subject is a simple drop of water, which on impact with a pool, rebounds into a Worthington jet and ejects one or more droplets from its tip. Despite hundreds of years of study, it’s still a joy to watch, especially at 12,000 frames per second.
It’s also not the easiest image to capture, and one thing I rather enjoy about this video is how it gives you a sense of the trial and error involved in capturing just the right view. Even without having to worry about the timing issues, there is a lot of fiddling with lenses, focus, lights, and positioning — something familiar not just to photographers and videographers but to many researchers as well! (Image and video credit: The Slow Mo Guys)
Flowery Splashes
Plunge a disk into water and you’ll get a dome-like splash that closes back on itself. But what happens when that disk has a patterned surface? In this video, researchers added a wedge-like surface pattern to the disk, creating a splash with petals like a flower. Just as the surface of disk is about to submerge completely, a jet of the remaining air spurts out the trough of each wedge. This air jet breaks up the tip of the triangular splashes focused by the wedge. (Image, research, and video credit: H. Kim et al.)
Recreating Volcanic Lightning
Some natural phenomena, like volcanic eruptions or tornado formation, don’t lend themselves to fieldwork — at least not at the height of the action. The danger, unpredictability, and destructiveness of these environments is more than our equipment can survive. And so researchers find clever ways to recreate these phenomena in controllable ways. The latest example comes from a lab in Germany, where researchers are recreating volcanic lightning.
To do so, they heat and pressurize actual volcanic ash in an argon environment and let the mixture decompress into a jet, like a miniature eruption. The lightning that accompanies the jet is thought to depend on friction between ash particles, which build up electric charges when rubbed, just like a balloon rubbed against one’s hair. When the charges get large enough, lightning discharges the build-up.
Small-scale experiments like this one allow researchers to vary the temperature and water content of the ash and observe how this changes the lightning. Drier ash generates more lightning, but it’s hard to distinguish whether this is inherent to the ash or the result of the denser jets that form without the added eruptive force of steam. (Image credit: eruption – M. Szeglat, lab lightning – Sönke Stern/Ludwig-Maximilians-Universität München/Gizmodo; research credit: S. Stern et al.; via Gizmodo)
Waltzing Defects
Liquid crystals are a peculiar state of matter with both liquid and crystalline properties. In this video, a microfluidic device breaks water into droplets surrounded by a shell of liquid crystal. Because the molecular structure of the liquid crystals is helical and cannot pack neatly in a spherical shell, there are visible defects in the liquid crystal shells. Given time, those defects can merge as the liquid crystal shell thickens. (Image and video credit: The Lutetium Project)
Events
If you’re interested in scheduling an event, please contact [email protected].
Upcoming Events
Check the links below for specific event details.
- 27 March 2020 – Online – Science Talk ’20
Selected Past Events
Slides from past events and talks are typically archived here. Past FYFD webcasts are available to FYFD patrons on Patreon.
- Mar. 2016 – Online, The Internet – FYFD Webcast with Prof. Tadd Truscott and Ph.D. student Randy Hurd – Watch the webcast here
- Apr. 2016 – Norton, MA – Wheaton College, APS New England Section Meeting, Banquet Keynote Address, “The Extremes of Fluid Dynamics”, slides here
- Apr. 2016 – Online, The Internet – FYFD Webcast with Prof. Geoffrey Collins and NASA JPL mission operations engineer Keri Bean
- Sep. 2016 – Cambridge, MA – 2016 Ig Nobel Prize Ceremony – Airplane Deluge Announcer and 24/7 Lecturer
- Mar. 2017 – Pasadena, CA – “Celebrating the Beauty and Diversity of the Flow,” NASA’s Jet Propulsion Laboratory
- Nov. 2017 – Denver, CO – APS DFD Talk, “Getting Into Science Communication,“ slides here
- Oct. 2018 – Delft, The Netherlands – Workshop, “Communicating Your Science: Reaching Beyond Your Peers”
- Nov. 2018 – Atlanta, GA – APS DFD Talk, “Tips for Connecting with Broader Audiences,” slides and video
- Feb. 2019 – Denver, CO – Keynote speaker, ASME Students in Industry Day
- Mar. 2019 – Washington, DC – “Communicating Science in the 21st Century,” United States National Committee on Theoretical and Applied Mechanics.
- Nov. 2019 – Seattle, WA – APS DFD 2019; including a panel, a regular talk, and an invited talk
- Jan. 2020 – Boston, MA – Northeastern
- Jan. 2020 – Chicago, IL – ORDCamp
Bay of Fundy Tides
Canada’s Bay of Fundy has some of the wildest tidal flows in the world. Every six hours, the flow direction through the strait shifts and tidal currents rise to several meters per second. This creates distinct jets a couple kilometers long that pour from one side of the strait to the other.
What you see here is a numerical simulation of the flow using a technique called Large Eddy Simulation (or LES, for short). It’s one method used by fluid dynamicists to model turbulent flows without taking on the complexity of the full Navier-Stokes equations. At large lengthscales, like those of the jets and eddies we see above, LES uses the exact physics. But when it comes to the smaller scales – like the flow nearest the shores or the bottom of the strait – the simulation will approximate the physics in order to make calculations quicker and easier. Models like these make large-scale problems – including modeling our daily weather patterns – possible. (Image credit: A. Creech, source)
Champagne’s Shock Wave
The distinctive pop of opening a champagne bottle is more than the cork coming free. The sudden release of high-pressure gas creates a freezing jet that’s initially supersonic. It even creates a Mach disk, like those seen in rocket exhaust. That supersonic flow can only be maintained, though, with a large enough pressure difference between the gas in the bottle and the atmosphere outside. Once the pressure drops below that critical point, the jet slows down and becomes subsonic. For more on champagne popping and its colorful plume, check out this previous post. (Image and research credit: G. Liger-Belair et al.; via Nature; submitted by Kam-Yung Soh)
The Impressive Take-Off of Pigeons
One reason that peregrine falcons are such amazing fliers is that their prey, pigeons, are no slouches in flight, either. Able to take off vertically and accelerate to 100 kph in two seconds, pigeons are pint-sized powerhouses. With this high-speed video, BBC Earth highlights the mechanics of this vertical take-off. Pigeons begin by bending their legs and jumping high enough that their first downstroke can extend fully and still clear the ground. That gives them a headstart on generating the force they need to propel themselves upward.
Note the way the pigeon’s wings move, sweeping from directly behind the bird’s back to a full extension in front of it. With the bird moving vertically, this motion tells us that it’s thrust – not aerodynamic lift – from the wingstroke that’s powering this take-off. In that sense, the pigeon is something like a Harrier jet, using the thrust of air downward to take off vertically. (Image and video credit: BBC Earth)
Cavitation Collapse
The collapse of a bubble underwater doesn’t seem like a very important matter, but when it happens near a solid surface, like part of a ship, it can be incredibly destructive. This video, featuring numerical simulations of the bubble’s collapse, shows why.
When near a surface, the bubble’s collapse is asymmetric, and this asymmetry creates a powerful jet that pushes through the bubble and impacts the opposite side. That impact generates a shock wave that travels out toward the wall. As the bubble hits its minimum volume, a second shock front is generated. Both shock waves travel toward the wall and reflect off it, generating high pressure all along the surface. (Image and video credit: S. Beig and E. Johnson)