Computational fluid dynamics and supercomputers can produce some stunning flow visualizations. Above are examples of turbulence, the Rayleigh-Taylor instability, and the Kelvin-Helmholtz instability. Be sure to check out LCSE’s website for more; they’ve included wallpapers of some of the most spectacular ones. (Photo credits: Laboratory for Computational Science and Engineering, University of Minnesota, #)
This photo collage shows vortices shed off a backward-facing step. The flow is left to right. Here the flow is visualized using dye released in water. Initially, the vortex forms near the bottom of the step in the recirculation zone. Because flow over the top of the vortex is much faster than the flow beneath the vortex, a low pressure zone forms over the vortex and gradually draws it up toward the top of the step. Eventually the vortex will rise to the point where the upstream flow pushes it downstream and the process begins anew. (Photo credit: Andrew Carter, University of Colorado)
Flow visualization is a powerful design tool for engineers. When Google was interested in determining optimal configurations for their heliostat array, they turned to NASA Ames’ water tunnel facility to test upstream barriers to deflect flow off the heliostats. In each photo, flow is from left to right and fluorescent dye is used to mark streamlines and reveal qualitative flow detail. Upstream of the obstacles, the streamlines are coherent and laminar, but after deflection, the flow breaks down into turbulence. In this case, such turbulence is desirable because it lowers the local fluid velocity and thus the aerodynamic loads experienced by each heliostat, potentially allowing for a savings in fabrication. For more, see Google’s report on the project. (Photo credits: google.org)
In this video, schlieren imaging is used to make visible the flow field around a mussel. Mussels are filter-feeders, drawing nearby water in to obtain their food and expelling the unneeded fluid once they’ve gathered the plankton they eat. Normally this process is invisible to the naked eye, but schlieren imaging reveals changes in density (and thus refractive index) that make it possible to visualize the outflow from the mussel. The technique is also commonly used in supersonic flows to reveal shock waves. (Video credit: Stephen Allen)
Maple tree seeds flutter and spin as they descend. The above video, which shows flow visualization of a freely falling seed, demonstrates that the so-called helicopter seed’s autorotation creates a vortex along the leading edge. Watch as the seed’s “wing” sweeps through and you will notice the vortex along the upper surface. This leading edge vortex generates high lift on the maple seed, allowing it to stay in the air more effectively than other seeds, thereby increasing the maple’s reproductive range. (Video credit: D. Lentink et al.; see also Supplemental Materials)
Ink released into water shows the swirling motion inside a vortex ring as well as its deformation and breakup upon stagnation against a wall. Although humans are known to make such vortex rings with smoke or bubbles, they are common in nature as well. Buoyant plumes often feature vortex rings at their head; dolphins and whales play with bubble rings; volcanoes blow smoke rings; and mosses use them to distribute spores.
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.
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)
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)
Researchers used computational models of ocean currents to produce this video visualizing worldwide ocean surface currents from June 2005 through December 2007. Dark patterns under the ocean are representative of ocean depths and have been exaggerated to 40x; land topography is exaggerated to 20x. Notice the wide variety of behaviors exhibited in the simulation: some regions experience strong recirculation and eddy production, while others remain relatively calm and unmoving. Occasionally strong currents sweep long lines across the open waters, carrying with them warmth and nutrients that encourage phytoplankton blooms and other forms of ocean life. (Video credit: NASA; submitted by Jason S)
