Category: Phenomena

F-18 Flow Viz
Water tunnels are useful tools for determining aerodynamic characteristics of aircraft, such as this F-18 model placed in the NASA Dryden Flow Visualization Facility. By matching the Reynolds number of the model in the water tunnel to that of the full-scale aircraft in air, engineers can observe flow around the aircraft inside the laboratory. This similarity of flows is a powerful design tool. Here dye introduced along the nose, wings, and fuselage traces streamlines around the F-18, revealing areas of turbulence at different flight conditions.
April 19, 2012
Vibrating Oil
This high-speed video shows the behavior of oil on a vibrating surface. As the amplitude of the vibration is altered various behaviors can be observed. Initially small waves appear on the surface of the oil, then the surface erupts into a mass of jets and ejected droplets, reminiscent of a vibrated interfaces within a prism or vibration-induced atomization. When the amplitude is reduced after about half a minute, we see Faraday waves across the surface, as well as tiny droplets that bounce and skitter across the surface. They are kept from coalescing by a thin layer of air trapped between the droplet and the oil pool below. Because of the vibration, the air layer is continuously refreshed, keeping the droplet aloft until its kinetic energy is large enough that it impacts the surface of the oil and gets swallowed up.
April 13, 2012
Dancing Plasma
Two dark areas of plasma, cooler than the surrounding fluid, dance and intertwine above the sun’s surface. Plasma, a rarefied gas made up of ions, is an electrically conductive fluid, shaped here by the magnetic field of the sun. Note how the strands pass material back and forth along the magnetic field lines. This timelapse video, captured by NASA’s Solar Dynamics Observatory, takes place over the course of a day and is captured in the extreme ultraviolet range.
April 10, 2012
Volcanic Clouds
The volcano Tungurahua erupts in a cloud of ash while molten lava flows down the mountain’s sides. Overhead a wispy lenticular cloud has formed where moist air flowing over the volcano dropped below its dew point. Volcanic eruptions have been known to produce shock waves and vortex rings as well as their distinctive turbulent plumes. (submitted by A. Jones III)
April 6, 2012
Squeezing Bubbles
An air bubble trapped inside a viscoelastic fluid is squeezed between two plates in this video, revealing a Saffman-Taylor-like fingering instability stemming from local stress concentrations. (Video credit: Baudouin Saintyves)
March 30, 2012
Winds Across the US
A collaborative project on data visualization brings to life the wind velocity data across the United States. The Wind Map is an interactive, nearly real-time indicator of wind conditions across the country, compiled on an hourly basis from the National Digital Forecast Database. Be sure to click through to see the data in motion. Observing the variety in wind patterns over the scale of days brings to light the swirling motion of surface winds much the way Perpetual Ocean does for surface currents. Fluid dynamics are all around us. (via Gizmodo)
March 29, 2012
Micro Air Vehicle Flow Viz
A smoke wire shows the deformation of streamlines around a swept-winged micro air vehicle (MAV). These crafts typically feature wingspans smaller than one foot and, thus, never develop the type of flow fields associated with larger fixed-wing airplanes. This complicates theoretical predictions of lift and drag for MAVs as well as making them difficult to control. MAVs have numerous commercial and military applications, including search and rescue operations. (Photo credit: Tom Omer)
March 28, 2012
Vortex Cannon
Building a vortex cannon is a great way to demonstrate the power and longevity of vortex rings. As demonstrated here, it’s possible to create one with just a box with a round hole in it. Adding some smoke or stage fog helps visualize the rings. Vortex rings are found frequently in nature: volcanoes make them, some plants use them to distribute spores, and dolphins and whales use them to play. (submitted by @aggieastronaut)
March 26, 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
Supersonic Flow
This video shows a sphere in a small supersonic wind tunnel at Mach 2.7. Once the tunnel starts, a curved bow shock forms in front of the sphere, close to but not touching the model’s surface. Areas of low pressure are visible behind the sphere, as is a weak shock wave caused by overexpansion in those low pressure areas. Contrast this with a sharp cone in the same tunnel at the same Mach number. In the case of the cone, the shock wave is attached at the nose of the model. The attached shock follows the body more closely, resulting in a shock that impacts the walls of the tunnel further downstream than in the sphere’s case.
March 20, 2012