The flames surrounding a burning tree stump flicker and billow in this image from photographer Serdar Ozturk. The chaotic motion of the flames is indicative of turbulence, a state of fluid flow known for its many scales. Note the range of lengthscales and structures in the fire. In turbulent flows, kinetic energy cascades from large scales, like the width of the top of the plume, down to the small scales, which may be even smaller than the wisps of flame at the edges of the fire. At the largest scales, the structures and behaviors we observe are all flow- and geometry-dependent, but theory predicts that, at the smallest scales, all turbulent flows look the same. (Photo credit: trashhand/Serdar Ozturk)
Tag: turbulence
Ink Drops
This super high resolution video (check the original on YouTube) by filmmaker Jacob Schwarz features slow motion diffusion of ink into water. The subtle differences in density between the ink and the water promote instabilities such as the Rayleigh-Taylor instability and its distinctive cascade of mushroom- or umbrella-like shapes. The mixing of two fluids seems like a simple concept, but the reality is beautiful, complex, and always fascinating. (Video credit: J. Schwarz; submitted by Rebecca S.)
Dropping Through Strata
When a droplet falls through an air/water interface, a vortex ring can form and fall through the liquid. In this video, the researchers investigate the effects of a stratified fluid interface on this falling vortex ring. In this case, a less dense fluid sits atop a denser one. Depending on the density of the initial falling droplet and the distance it travels through the first fluid, the behavior and break-up of the vortex ring when it hits the denser fluid differs. Here four different behaviors are demonstrated, including bouncing and trapping of the vortex ring. (Video credit: R. Camassa et al.)
Mixing Physics
When a dense fluid sits above a lighter fluid in a gravitational field, the interface between the two fluids is unstable. It breaks down via a Rayleigh-Taylor instability, with mushroom-like protrusions of the lighter fluid into the heavier one. The image above comes from a numerical simulation of this effect well after the initial instability; the darker colors represent denser fluids and lighter colors are less dense fluids. The flow here has progressed to turbulence, and the authors of the simulation are exploring the statistical nature of this flow breakdown relative to the classical case of isotropic, homogeneous turbulence. (Photo credit: W. Cabot and Y. Zhou)
Plasma Jets
Jets of high-energy plasma and sub-atomic particles explode outward from the Hercules A elliptical galaxy at the center of this photo. The jets are driven to speeds close to that of light due to the gravitation of the supermassive black hole at the center of the elliptical galaxy. Relativistic effects mask the innermost portions of the jets from our view, but, as the jets slow, they become unstable, billowing out into rings and wisps whose turbulent shapes suggest multiple outbursts originating from Hercules A. (Photo credit:NASA, ESA, S. Baum and C. O’Dea (RIT), R. Perley and W. Cotton (NRAO/AUI/NSF), and the Hubble HeritageTeam (STScI/AURA); via Discovery)
Phytoplankton and Sediments
Pale sediments are carried out to sea by the rivers of the Mergui Archipelago of Myanmar. Dark blue ocean waters mix with the sediment, creating turbulent swirls in this natural color satellite image. With the sediment comes valuable nutrients for plant life in the ocean, which can prompt the formation of phytoplankton blooms. (Photo credit: Michael Taylor/Landsat/NASA)
A Colorful Rinse
In this image a jet of water (clear/white) is rinsing a solution of polyacrylamide (PAM; blue) off a silicon surface. In the center, a hydraulic jump marks the interface where fast-moving laminar flow changes to a slower turbulent one. At the same time, the water, which is less viscous than the PAM, creates viscous finger-like protrusions into the blue liquid as it rinses the surface clean. (Photo credit: T. Walker, T. Hsu, and G. Fuller)
Swirling Jets
In fluid dynamics, we like to classify flows as laminar–smooth and orderly–or turbulent–chaotic and seemingly random–but rarely is any given flow one or the other. Many flows start out laminar and then transition to turbulence. Often this is due to the introduction of a tiny perturbation which grows due to the flow’s instability and ultimately provokes transition. An instability can typically take more than one form in a given flow, based on the characteristic lengths, velocities, etc. of the flow, and we classify these as instability modes. In the case of the vertical rotating viscous liquid jet shown above, the rotation rate separates one mode (n) from another. As the mode and rotation rate increase, the shape assumed by the rotating liquid becomes more complicated. Within each of these columns, though, we can also observe the transition process. Key features are labeled in the still photograph of the n=4 mode shown below. Initially, the column is smooth and uniform, then small vertical striations appear, developing into sheets that wrap around the jet. But this shape is also unstable and a secondary instability forms on the liquid rim, which causes the formation of droplets that stretch outward on ligaments. Ultimately, these droplets will overcome the surface tension holding them to the jet and the flow will atomize. (Video and photo credits: J. P. Kubitschek and P. D. Weidman)
The Beauty of the Great Red Spot
Jupiter is home to one of the most famous storms in the solar system, the Great Red Spot, which Earth observations place at a minimum of 180 (Earth) years in duration. Some evidence suggests that it may have been observed by humans as early as 1665. The magnitude of such a storm is almost unimaginable. At its narrowest point, the storm is still as wide as our entire planet and observations from the Voyager crafts indicate that the storm has 250 mph winds. The scale of mixing and turbulence around the storm, seen in photographs, is stunning and beautiful. (Photo credits: NASA/Voyager 1 and Michael Benson; submitted by oneheadtoanother)
Fluidic Public Art by Charles Sowers
Artist Charles Sowers creates exhibits and public art focused on illuminating natural phenomenon that might otherwise go unnoticed, and much of his work features fluid dynamics directly or indirectly. “Windswept” and “Wave Wall” are both outdoor exhibits that show undulations and vortices corresponding to local wind flow. Other pieces explore ferrofluids through magnetic mazes or feature foggy turbulence. My own favorite, “Drip Chamber”, oozes with viscous fluids whose dripping forms patterns reminiscent of convection cells. Be sure to check out his website for videos of the exhibits in action. (Photo credits: Charles Sowers; submitted by rreis)
