Tag: flow visualization

Wingtip Vortices
Wingtip vortices are the result of high-pressure air from beneath a wing sneaking around the end of the wing to the low-pressure area on top. They trail for long distances behind aircraft, and are, most of the time, an invisible hazard for other aircraft. If you’ve ever sat in a line of airplanes waiting to take off and wondered why there is so much time between subsequent take-offs, wingtip vortices are the answer. The larger a plane, the stronger its vortices are and the greater their effect on a smaller craft. Much of the time between planes taking off (or landing) is to allow the vortices to dissipate so that subsequent aircraft don’t encounter the wake turbulence of their predecessor. Crossing the wake of another plane can cause an unexpected roll that pilots may not be able to safely correct, a factor that’s contributed to major crashes in the past. (Image credits: flugsnug, source video; submitted by entropy-perturbation)
February 11, 2015
The Earth in Infrared
The motions of Earth’s atmosphere are often invisible to the human eye, but fortunately, we’ve built tools to reveal them. This timelapse video shows the Earth in infrared light, first from a satellite view centered on the Pacific Ocean and second from a satellite centered on Central America. The water vapor in clouds is an excellent insulator, so clouds appear dark in this video. Warmer areas look brighter. The large-scale motion of the atmosphere and the wind bands that cut east and west across the world are apparent in the first half of the video, largely because they are not being interrupted by any land masses. In the second half of the video, the western coast of South America is intermittently visible. This is because the Andes Mountains disrupt air flow, pushing warm, moist air upward and causing it to condense into the dark-colored clouds that recirculate over the Amazon. Look further south along the coast and you’ll see the Atacama Desert flashing white each day as it heats up. (Video credit: J. Tyrwhitt-Drake/NASA; submitted by entropy-perturbation)
February 4, 2015
Interrupting Sediments
The pier at Progreso extends 6.5 kilometers into the Gulf of Mexico, creating an artificial obstruction to ocean flow and sediment transport near the shore. The first 2 kilometers of the pier are built on arches that allow some flow through, but the newer sections do not. Prevailing winds act from the east-northeast, driving flow roughly right to left in the image. The sediment traces flow around the pier and reveals the complicated flow-shadow downstream of the newer parts of the pier. (Image credit: NASA Earth Observatory)
January 7, 2015
Simplified Schlieren Set-up
Schlieren photography offers a glimpse into flows that are usually invisible to the human eye. With a relatively simple set-up–a light source, collimating mirror(s), and a razor blade–it becomes possible to see differences in density. The technique lets one visualize temperature-driven flows like the buoyant convection from a flame or other heat source, and it can also be used to visualize shock waves and sound. The video above has several neat schlieren demos, including some non-air examples using hydrogen (lighter than air) and sulfur hexafluoride (denser than air), both of which are transparent to the naked eye. (Video credit: Harvard University, via Jennifer Ouellette)
December 18, 2014
Phytoplankton Flow Viz
Nutrient-rich waters off Patagonia in South America blossom with phytoplankton in this satellite image. When present in large quantities, these microscopic photosynthesizers lend a green hue to the water. They act as seed particles in the flow, highlighting the currents and flow that carry them. If you check out the full resolution version of the photo, you can admire the rich detail in the whorls of ocean mixing. There even seem to be Kelvin-Helmholtz-like instabilities creating trains of vortices along the interface between separate bands. (Photo credit: NASA/ASU; via SpaceRef; submitted by jshoer)
December 15, 2014
Vertical-Axis Wind Turbines
Vertical-axis wind turbines (VAWT) are an alternative to traditional wind turbine designs. Unlike their more common cousins, VAWTs rotate about a vertical axis and are omni-directional, meaning that they do not have to be pointed into the wind to produce power. While their size allows VAWTs to be packed much closer to one another than traditional turbines, a clear understanding of the flow around the turbines is needed in order to place the turbines for effective and efficient operation. The images above show the complicated and turbulent wake of a three-bladed VAWT when stationary (top) or rotating (bottom). The flow is visualized using a gravity-driven soap film (flowing left to right in the images) pierced by a model VAWT (seen at the left). The wakes contain many scales from simple, periodically-shed vortices off a blade to very large-scale vortical structures forming downstream of the turbine. This work originally appeared as a poster in the Gallery of Fluid Motion at the 2014 APS DFD Annual Meeting. (Image credit: D. Araya and J. Dabiri)
December 10, 2014
Filter-Feeding
Sponges are filter-feeding marine animals that rely on water flow to obtain their nutrients and remove waste. By injecting non-toxic fluorescein dye at their base, one can visualize the flow they induce in the water. Only seconds after the dye is introduced, the sponges have pumped it in, through, and out. Different parts of the sponge filter particles of various sizes for food. Oxygen and carbon dioxide are transported, respectively, into and out of cells via diffusion. In this way, the sponge’s pumping fulfills digestive, respiratory, and excretory functions. (Image credit: Jonathan Bird’s Blue World, source video; submitted by Jason C)
December 8, 2014
Light Paintings
Photographer Stephen Orlando uses programmable LEDs to create light paintings. Here floating LEDs illuminate a track down a waterfall. In flow visualization terms, this is a pathline because it records the trajectory a particular particle followed through the flow. Streamlines, streaklines, and pathlines are all important concepts for interpreting fluid flow through visualization. To see more of Orlando’s light paintings, including some wonderful portraits of canoeing and kayaking, be sure to check out his galleries. (Photo credit: S. Orlando; via Colossal)
December 5, 2014
Colonial Life
Hydroids are small underwater animals that often live in colonies made up of individual polyps. The colony is interconnected through the gastrovascular system, which is responsible for both digestion and respiration. In the images above, a single polyp in the colony has been fed food dyed with a fluorescent tracer. The polyp serves as a circulating pump and, as the food is digested and the tracer released, more and more of the colony becomes visible. Watch the full video and read more about the experiment. (Video credit and submission: L. Buss Lab)
November 19, 2014
Von Karman Vortex Streets
The wake of a cylinder is a series of alternating vortices shed as the flow moves past. This distinctive pattern is known as a von Karman vortex street. The speed of the flow and the size of the cylinder determine how often vortices are shed. Incredibly, this pattern appears at scales ranging from the laboratory demo all the way to the wakes of islands. Von Karman vortex streets can even be seen from space. (Image credit: R. Gontijo and W. Cerqueira, source video)
November 6, 2014