Undoubtedly one of the most mind-boggling instances of fluid dynamics I’ve learned about in writing FYFD is that of sonoluminescence – an effect in which light is produced from imploding cavitation bubbles. In a laboratory, the effect is usually initiated with acoustic waves. A bubble can be forced to oscillate and collapse periodically when forced by the sound. During the collapse, the vapor inside the bubble reaches temperatures of the order of thousands of Kelvin, and light is produced. What is far more wild, though, is that the effect occurs in nature as well. Both the pistol shrimp and the mantis shrimp produce the effect. As shown in the video above, the mantis shrimp swings its club-like arm with such speed that the local pressure drops below the vapor pressure, causing a cavitation bubble to form and sonoluminescence to occur. Some real Mortal Kombat finishing move s&#% there, indeed. (Video credit: Z. Frank)
Tag: fyfd4thbday
4th Birthday: Rogue Waves
Rogue waves—individual, isolated waves far larger than the surrounding waves—were reported for centuries by sailors. But their stories of massive walls of water appearing in the open ocean were not corroborated until 1995 when a rogue wave struck an offshore platform. How these giant waves form is still under active research, but one leading theory is that nonlinear interactions between waves allow one wave to sap energy from surrounding waves and focus it into one much larger, short-lived wave. I first learned of rogue waves during a seminar in graduate school. At the time, this idea of nonlinear focusing had only been explored in simulation, but a few years later a research group was able to demonstrate the effect in a wave tank, as shown in the video above. Wait for the end, and you’ll notice how the rogue wave that takes down the ship is much larger than its predecessors. For more on rogue waves and their mind-boggling behavior, be sure to check my previous post on the subject. (Video credit: A. Chabchoub, N. Hoffmann, and N. Akhmediev)
4th Birthday: The Kaye Effect
Today’s post continues my retrospective on mind-boggling fluid dynamics in honor of FYFD’s birthday. This video on the Kaye effect was one of the earliest submissions I ever received–if you’re reading this, thanks, Belisle!–and it completely amazed me. Judging from the frequency with which it appears in my inbox, it’s delighted a lot of you guys as well. The Kaye effect is observed in shear-thinning, non-Newtonian fluids, like shampoo or dish soap, where viscosity decreases as the fluid is deformed. Like many viscous liquids, a falling stream of these fluids creates a heap. But, when a dimple forms on the heap, a drop in the local viscosity can cause the incoming fluid jet to slip off the heap and rebound upward. As demonstrated in the video, it’s even possible to create a stable Kaye effect cascade down an incline. (Video credit: D. Lohse et al.)
4th Birthday: Wingtip Vortices
Wingtip vortices are a result of the finite length of a wing. Airplanes generate lift by having low-pressure air travelling over the top of the wing and higher pressure air along the bottom. If the wing were infinite, the two flows would remain separate. Instead, the high-pressure air from under the wing sneaks around the wingtip to reach the lower pressure region. This creates the vorticity that trails behind the aircraft. I was first introduced to the concept of wingtip vortices in my junior year during introductory fluid dynamics. As I recall, the concept was utterly bizarre and so difficult to wrap our heads around that everyone, including the TA, had trouble figuring out which way the vortices were supposed to spin. A few good photos and videos would have helped, I’m sure. (Photo credits: U.S. Coast Guard, S. Morris, Nat. Geo/BBC2)
4th Birthday: Intro
Next week marks FYFD’s 4th birthday! It’s hard to believe that it’s been so long, or that the blog and I have come so far. I set out with the intention of explaining fluid dynamics to a broad audience because it’s a subject we all experience daily and yet one that few learn formally. (I also, as you may have guessed from the blog’s name, didn’t take things too seriously.) Many things have surprised me these past four years, but one of my favorites is how much I’ve learned. In researching and writing FYFD, I am constantly learning new and fascinating physics. I love it every time something new stuns me with its beauty, its cleverness, or its jaw-dropping, mind-blowing awesomeness. In celebration of that feeling, next week’s posts will revisit some of my favorite subjects, especially those that did and do amaze me. In the meantime, try not to let the ice cream melt. Unless you’re into that. (Video credit: I. Yang; submitted by Stuart B.)