Turbulent plumes stream out behind airplanes in an airshow. #
Tag: fluid dynamics
Computational Shock Compression
[original media no longer available]
Computational modeling can help verify and visualize experimental results, as in this video of supersonic flow. Oak Ridge National Laboratory produced the work as part of a project using shock compression and turbines to capture carbon dioxide gas. Shock waves and velocity profiles are shown throughout the computational field, and velocity isosurfaces paint a telling portrait of the complicated flow pattern. Wired Science features other award-winning simulation videos, many of which also feature fluid dynamics. #
To Splash or Not to Splash?
Hydrophobic surfaces tend to repel water while hydrophilic ones attract it. This video explores the effects that hydrophobic and hydrophilic surface coatings can have on spheres when dropped in water. There are noticeable differences in splash formation and wake shape. For more, see this research paper.
Vortex Ring Collisions
Gorgeous color schlieren photography reveals the development and interaction of ring vortices. (Photo credit: Rebecca Ing)
It’s Schlier-tastic!!
These are my invisible wonders! Gas flows and fluid interactions. Nothing but hot air, metho and acetone, yup, humble old nail polish remover.
The images were captured using a colour indicating z-system schlieren optical array, an open shutter and a flash duration of 125 microseconds.
Molecular Diffusion
This video explains molecular diffusion with demonstrations in gases and liquids. Molecular diffusion is an important process in all fluids and will occur in laminar, turbulent, or quiescent fluids. Diffusion occurs more quickly in heated fluids because molecules move more energetically at higher temperatures. (via robertlovespi)
Cornstarch Monsters
[original media no longer available]
Shaking a fluid surface often results in standing waves known as Faraday waves, but with a non-Newtonian fluid like oobleck, at some frequencies it’s possible to incite other behaviors. Oobleck is shear-thickening, meaning that its viscosity increases when force is applied. This is what allows it to develop finger-like protrusions under high frequency vibrations.
Carboy Combustion
Lighting a thin layer of ethyl alcohol in a jug produces some beautiful pulse jets and a moving wall of flame that shifts and flows according to the changing pressures inside the jug. Like the video’s author, we do NOT recommend trying this combustion demo yourself.
As for the video’s questions, firstly, blowing into the jar helps the flame because humans do not exhale pure CO2. With regard to the second question, the interior of the jug is initially thinly coated in ethyl alcohol vapor. Combustion starts at the top of the jug and the sheet of flame moves downward as the fuel at the top is spent. As that flame moves downward, however, it’s heating the air inside the jug, which expands and is forced out the opening. When the flame goes out in the upper part of the jug, that does not mean all of the fuel has combusted, simply that the ratio of air/fuel is insufficient for continued combustion. I suspect the flame persists at this opening because the air/fuel mixture is concentrated at that point. Any residual ethyl alcohol in the container is forced out through that narrow opening, and the resulting concentration of fuel there may be high enough to keep the flame burning there. (idea submitted by davidbenque #)
Shuttlecock Flow Viz
The flow around a shuttlecock is visualized in a water channel using fluorescent dye illuminated by laser light ultraviolet LEDs. Note the recirculation zone on the upper shoulder. Experimenters can match flow characteristics in water to that in air by matching the Reynolds numbers. (Photo credit: Rob Bulmahn)
Updated, thanks to information from the photographer. Thanks!
Starting Vortices
Whenever a wing stops or starts in a fluid, it produces a vortex. This 2D numerical simulation shows an airfoil repeatedly starting and stopping, shedding a vortex each time. Note how the line of vortices drifts downward in the wake; this is an indication of downwash. (submitted by jessecaps)
