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)
Tag: thin film
Soap Film Flow Viz
Flowing soap films provide an educational and beautiful method for visualizing the wakes of objects in two-dimensional flows. High-speed photography highlights the interference patterns on the soap film, providing detail without the necessity for the particulate tracking of other flow visualization methods. Highlights here include wakes behind bluff bodies, interacting cylinders, and flapping flags. (pdf) #
Drafting Flags
Wired Science has published a gallery of fluid dynamics photos and videos, several of which have been featured here previously. There’s some neat stuff there, well worth checking out. #
This image shows two flags oriented in line with a film flowing top to bottom. The second flag interrupts the wake of the first one, which reduces the drag experienced by the first flag and increases that on the second. This is called inverted drafting and occurs because the flags are passive objects that bend to every change in the flow. #
Butterfly Soap Spiral
A stationary soap film disturbed by a flapping foil (seen in the top center) creates a butterfly-like double spiral roll. Two vortices form at the tip of the foil each time it changes direction; look carefully and you can see those tiny vortices all the way through the spirals. (From the 2010 Gallery of Fluid Motion; pdf)
Marangoni Convection in Space
In this Saturday Morning Science video, astronaut Don Pettit demonstrates Marangoni convection in microgravity using a water film with tracer particles, a soldering iron, and a flashlight. This same effect occurs on earth but is masked behind the much stronger effect of buoyant convection.
Microgravity Water Films
In this video astronaut Don Pettit demonstrates some interesting laminar flow effects using a water film in microgravity. By using a film, fluid motion is essentially confined to two dimensions. This is important because it prohibits the development of turbulence, which is a purely three-dimensional phenomenon. Doing the experiment in microgravity allows Pettit to leave the experiment for a long period of time without buoyant effects or similar disturbances. When he first stirs the film, the tracer particles show some signs of what looks like turbulent mixing, but soon the film rotates uniformly with streaks of gray caused by different concentrations of tracer particles. Pettit notes that he allowed the film to rotate overnight and it eventually all turned milky white. This is the effect of molecular diffusion of the tracer particles; without turbulence, the only way for mixing to occur is through the random motion of molecules. See more of Pettit’s Saturday Morning Science videos for additional microgravity fluid mechanics.
