This high-speed video shows a soap bubble being blown via didgeridoo, a wind instrument developed by the Indigenous Australians. The oscillations of the capillary waves on the surface of the bubble vary with the frequency of note being played. High frequency notes excite small wavelengths, whereas lower notes create large wavelength oscillations. For more fun, check out what you can do with didgeridoos in space. (submitted by Christopher B)
Tag: fluid dynamics
Using Flow Viz for Optimization
Flow visualization is a powerful design tool for engineers. When Google was interested in determining optimal configurations for their heliostat array, they turned to NASA Ames’ water tunnel facility to test upstream barriers to deflect flow off the heliostats. In each photo, flow is from left to right and fluorescent dye is used to mark streamlines and reveal qualitative flow detail. Upstream of the obstacles, the streamlines are coherent and laminar, but after deflection, the flow breaks down into turbulence. In this case, such turbulence is desirable because it lowers the local fluid velocity and thus the aerodynamic loads experienced by each heliostat, potentially allowing for a savings in fabrication. For more, see Google’s report on the project. (Photo credits: google.org)
When Fluids Behave Like Solids
Many common fluids–like air and water–are Newtonian fluids, meaning that stress in the fluid is linearly proportional to the rate at which the fluid is deformed. Viscosity is the constant that relates the stress and rate of strain, or deformation. The term non-Newtonian is used to describe any fluid whose properties do not follow this relationship; instead their viscosity is dependent on the rate of strain, viscoelasticity, or even changes with time. A neat common example of a non-Newtonian fluid is oobleck, a mixture of cornstarch and water that is shear-thickening, meaning that it is resistant to fast deformations. Like the cornstarch-based custard in the video above, these fluids react similarly to a solid when struck, resisting changing their shape, but if deformed slowly, they will flow in the manner of any liquid.
Falling Oil
A drop of silicone oil falling through a liquid with lower surface tension distorts into multiple vortex rings connected by thin films. This behavior is caused by the interaction between viscous and capillary forces and is observable for only a narrow range of oil viscosities. (Photo credit: A. Felce and T. Cubaud)
The Sinking of the Lusitania
In 1915, the early days of submarine warfare, the RMS Lusitania was sunk off the coast of Ireland by a torpedo. Eyewitnesses reported a second, more powerful explosion just after the torpedo strike–possibly a boiler or powder explosion–that contributed to the ship sinking in only 18 minutes, resulting in nearly 1200 lives lost. Researchers at Lawrence Livermore National Laboratory have tackled the historic mystery, combining computational efforts with experimentation and historical research to reconstruct the physics of what happened. The full documentary airs tonight on the National Geographic Channel as “Dark Secrets of the Lusitania”. (submitted by Stephanie N)
Viscoelastic Fingers
This series of photos shows two plates with a thin layer of polymer-laced, viscoelastic liquid. As the two plates are separated, complex instabilities form. The lower section of each photograph shows the fluid on the plate, with finger-like Saffman-Taylor instabilities forming as air rushes in between the gap in the plates. As the separation increases, the polymers in the liquid stretch under the increased strain, inducing elastic stresses in the fluid that cause the formation of secondary structures. (Photo credit: R. Welsh, J. Bico, and G. McKinley)
Creating Lava
In Syracuse, NY, artists and scientists work together to study volcanic flows by melting crushed basalt in a special furnace before releasing the lava into the parking lot. This particular flow is very prone to boiling behavior, likely because of the cold air and ground temperatures (less than 0 C). The outer layers of rock cool quickly, leaving bubble-shaped chambers which hotter lava can fill before melting out. (via It’s Okay To Be Smart; submitted by @jpshoer)
Homemade Astronomy
Artist Julia Cuddy uses liquids, soaps, and glitter to create photographs that replicate the look of deep space astronomy. By adding soap to the dyes, she uses Marangoni effects to drive surface tension instabilities that cause swirling colors and motions reminiscent of galaxies and nebulae. Although I’ve seen fluid dynamics used in art before, this may be one of the cleverest usages I’ve seen! (Photo credits: Julia Cuddy)
Fireball in Slow Motion
The high-speed video above shows an atomized spray of flammable liquid being ignited using a lighter. It was filmed at 10,000 fps and is replayed at 30 fps. Although uncontained, this demonstration is similar to the combustion observed inside of many types of engines. Automobiles, jet engines, and rockets all break their liquid fuel into a spray of droplets to increase the efficiency of combustion. The turbulence of the flames dances and swirls, with small-scale motions close to the sprayed droplets and larger-scale motions around the vaporized fuel. This variation in size of the scales of motion is a hallmark feature of turbulence and can be used to characterize a flow.
Bubbles and Jets
In the photo sequence above, a bubble is created at the interface between two immiscible liquids–water on top and denser hydrofluroether (HFE) below. Initially, the bubble expands explosively due to the vaporization of water generated by a short laser pulse. As the bubble collapses, a jet forms and accelerates into the HFE. After collapse, the bubble remnants injected in the HFE cause the formation of a jet that shoots back into the water above. Surface instabilities make the jet assume a mushroom or crown-like structure that detaches from the jet. Eventually gravity will return the system to its initial undisturbed fluid-fluid interface. (Photo credit: S. Avila et al. 1,2)
