Tag: astronaut

Typhoon Neoguri
Astronaut Reid Wiseman has been posting photos of Typhoon Neoguri in his Twitter feed this week. From our perspective on the ground, it’s easy to forget how three-dimensional the typhoons and hurricanes in our atmosphere are. But Wiseman’s photos capture the depth in the storm, especially the depression of the eye. From the top, the typhoon looks much like a vortex in a bathtub, or what’s more formally known as a free surface vortex. To understand why a vortex dips in the middle, imagine a container of water on a rotating plate. As the water is spun, its interface with the air takes on a paraboloid shape. Two external forces are acting on the fluid: gravity in the downward direction and a centrifugal force in the radial direction. The free surface of the fluid adopts a shape that is always perpendicular to the combination of these two forces. This ensures that the pressure along the free surface is a constant. (Photo credits: R. Wiseman 1,2,3)
July 11, 2014
Glacier Flows
These astronaut photos show Patagonian glaciers as seen from space. Glaciers form over many years when snow accumulates in larger amounts than it melts or sublimates. Over time the snow collects and is compacted into a dense ice which slowly flows downslope due to gravity. Many of the dark streaks in the photos are moraines, sediment formations deposited by the movement of the ice. Lateral moraines often line the edges of a glacier, and when two or more glaciers flow together, like in the lower left corner of both photos, the lateral moraines of each of the glaciers combine to form a medial moraine running through the combined glacial flow. (Photo credits: M. Hopkins and K. Wakata)
March 11, 2014
Washing Your Face in Space
What happens to a wet washcloth when wrung out in space? Astronaut Chris Hadfield answers this question from students with a demonstration. Without gravity to pull the water downward, surface tension effects dominate and the wrung cloth forms a tube of water around it. Surface tension and capillary action draw the fluid up and onto Hadfield’s hands as long as he holds the cloth. After he lets go, we see that the water remaining around the cloth soaks back in (again due to capillary action) and the wet, twisted washcloth simply floats without releasing water or relaxing its shape. While pretty much what I would have expected, this was a very cool result to see! (Video credit: C. Hadfield/CSA; submitted by Bobby E)
April 19, 2013
Spitting Droplets
Any phenomenon in fluid dynamics typically involves the interaction and competition of many different forces. Sometimes these forces are of very different magnitudes, and it can be difficult to determine their effects. This video focuses on capillary force, which is responsible for a liquid’s ability to climb up the walls of its container, creating a meniscus and allowing plants and trees to passively draw water up from their roots. Being intermolecular in nature, capillary forces can be quite slight in comparison to gravitational forces, and thus it’s beneficial to study them in the absence of gravity.
In the 1950s, drop tower experiments simulating microgravity studied the capillary-driven motion of fluids up a glass tube that was partially submerged in a pool of fluid. Without gravity acting against it, capillary action would draw the fluid up to the top of the glass tube, but no droplets would be ejected. In the current research, a nozzle has been added to the tubes, which accelerates the capillary flow. In this case, both in terrestrial labs and aboard the International Space Station, the momentum of the flow is sufficient to invert the meniscus from concave to convex, allowing a jet of fluid out of the tube. At this point, surface tension instabilities take over, breaking the fluid into droplets. (Video credit: A. Wollman et al.)
January 31, 2013
Liquid Lenses
Here astronaut Andre Kuipers demonstrates fluid dynamics in microgravity. A roughly spherical droplet of water acts as a lens, refracting the image of his face so that it appears upside down. The air bubble inside the droplet refracts the image back to our normal perspective again. (Photo credit: Andre Kuipers, ESA; via Bad Astronomy)
September 28, 2012
Sally Ride
Today FYFD takes a brief aside from fluid dynamics to mark the passing of Sally Ride, the first U.S. woman to travel to space. A physicist by training, Ride served as a mission specialist on STS-7 and STS-41G, shuttle missions that included deploying satellites as well as conducting scientific experiments. After her career with NASA, Ride returned to physics as a faculty member at the University of California, San Diego and dedicated herself to motivating children and young adults–most especially women–to pursue careers in science, math, and engineering. She was an inspiration and role model to more than a generation; her courage and her passion for science touched many lives, including my own. Godspeed, Dr. Ride.
July 24, 2012
Microgravity Cornstarch
We’ve seen the effects of vibration on shear-thickening non-Newtonian fluids here on Earth before in the form of “oobleck fingers” and “cornstarch monsters”, but, to my knowledge, this is the first such video looking at the behavior in space. The vibrations of the speaker cause shear forces on the cornstarch mixture, which causes the viscosity of the fluid to increase. This is what makes it react like a solid to sudden impacts while still flowing like a liquid when left unperturbed. In microgravity there is one less force working against the rise of the cornstarch fingers, so the formations we see in this video are subtly different from those on Earth.
May 23, 2012
Breaking Water with Sound
Previously we saw how vibration could atomize a water droplet, breaking it into a spray of finer droplets. Here astronaut Don Pettit shows us what the process looks like in microgravity using some speakers and large water droplets. At low frequencies the water displays large wavelength capillary waves and vertical vibrations. Higher frequencies–like the earthbound experiment on much smaller droplets–cause fine droplets to eject from the main drop when surface tension can no longer overcome their kinetic energy. (submitted by aggieastronaut, jshoer and Jason C)
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May 7, 2012
Science Off the Sphere: Liquid Lenses
Astronaut Don Pettit delivers more “Science Off The Sphere” in his latest video. Here he demonstrates diffusion and convection in a two-dimensional water film in microgravity. He notes that the viscous damping in the water is relatively low and that, left undisturbed, mixing in the film will continue for 5-10 minutes before coming to rest, which tells us that the Reynolds numbers of the flow are reasonably large. The structures formed are also intriguing; he notes that drops mix with mushroom-like shapes that are reminiscent of Rayleigh-Taylor instabilities and cross-sectional views of vortex rings. It would be interesting to compare experiments from the International Space Station with earthbound simulations of two-dimensional mixing and turbulence, given that the latter behaves so differently in 2D.
March 23, 2012
Science off the Sphere: Thin Films
Stuck here on Earth, it’s hard to know sometimes how greatly gravity affects the behavior of fluids. Fortunately, astronaut Don Pettit enjoys spending his free time on the International Space Station playing with physics. In his latest video, he shows some awesome examples of what is possible with a thin film of water–not a soap film like we make here on Earth–in microgravity. He demonstrates vibrational modes, droplet collision and coalescence, and some fascinating examples of Marangoni convection.
March 12, 2012