In honor of astronaut Don Pettit’s launch to the International Space Station (and in the hope that he’ll do more neat microgravity fluids demonstrations while in space!), here’s a look a the behavior of viscoelastic fluids in microgravity. The elasticity of these fluids means that, when strained, the fluid deforms instantaneously and then returns to its initial shape when the strain is removed. Pettit demonstrates both Plateau-Rayleigh instability behavior, where a column of fluid breaks apart due to surface tension variations, and die swell, where a fluid jet expands beyond the diameter of nozzle from which it was extruded. Such swelling is commonly caused by the stretching and relaxation of polymers in the fluid as they react to forces caused by the nozzle opening.
Tag: astronaut
Mixing in Space
Living here on earth, we are so accustomed to gravity’s effects on fluid behaviors that it’s not always obvious how microgravity will affect them. Here astronaut Richard Garriott demonstrates mixing and separating immiscible liquids in space.
Microgravity Water Spheres
Here astronaut Don Pettit demonstrates the effects of rotation on a sphere of water in microgravity. Bubbles, being less dense than water, congregate in the middle of the sphere along its axis of rotation. Tea leaves, which are denser than the water, are thrown to the outside; this is the same concept used in a centrifuge for separating samples.
Happy Anniversary
ESA astronaut Pedro Duque shown refracted through a water droplet in microgravity. Today marks the 50th anniversary of human space flight. #
Godspeed, Discovery!
The space shuttle, despite three decades of service, remains a triumph of engineering. Although it is nominally a space vehicle, fluid dynamics are vital throughout its operation. From the combustion in the engine to the overexpansion of the exhaust gases; from the turbulent plume of the shuttle’s wake to the life support and waste management systems on orbit, fluid mechanics cannot be escaped. Countless simulations and experiments have helped determine the forces, temperatures, and flight profiles for the vehicle during ascent and re-entry. Experiments have flown as payloads and hundreds of astronauts have “performed experiments in fluid mechanics” in microgravity. Since STS-114, flow transition experiments have even been mounted on the orbiter wing. The effort and love put into making these machines fly is staggering, but all things end. Godspeed to Discovery and her crew on this, her final mission!
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 Marangoni
Astronauts are preparing an experiment on the Marangoni effect, in which a variation in surface tension can cause mass flow, for flight aboard the International Space Station. The effect, also responsible for causing tears of wine, will benefit from study in microgravity because competing effects like gravity-induced sedimentation and buoyant convection will be negligible. Astronaut Ron Garan reports more on the upcoming experiment on the Fragile Oasis blog.
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.
Zero-G Water Bubbles
Astronaut Don Pettit narrates some of his experiments with air and water droplets in microgravity in this video. The lack of body forces and buoyancy in microgravity means that surface tension effects frequently dominate. Pettit’s demonstrations also involve some fun basic physics with bubble behaviors inside of water droplets. See more of Pettit’s Saturday Morning Science videos for additional microgravity fluid mechanics.
Combustion in Microgravity
‘Hot air rises.’ It’s common knowledge. But we usually forget that this is only true thanks to Earth’s gravity. On Earth, a candle flame’s distinctive pointed shape is due to hot air rising. Without gravity, there is no buoyant convection; hot air has no reason to rise (and no definition of what up is either!). This makes flames in microgravity spherical, as in the video above from a drop tower on earth. See also: astronaut explains fire in microgravity.
