Sediment swirls in Bear Lake caught the eye of an astronaut aboard the International Space Station last year. Bear Lake is situated in the Rocky Mountains, on the Idaho-Utah border. The eddies in the center of the lake are each about 3 km across and are likely the result of inflow from the lake’s tributaries. Silt and sediment picked up by the rivers and streams gets deposited into Bear Lake, revealing the turbulent mixing of tributary waters with those already in the lake. (Image credit: NASA; via NASA Earth Observatory)
Tag: turbulent mixing
Mixing Fresh and Salty
Earth’s oceans are a complex and dynamic environment, but fortunately, we can simulate some of their physics on a smaller scale in the laboratory. The time series of images above show how fresh and salty waters mix. On the right side of the image is fresh water with its top layer dyed green. On the left is salty water dyed pink. Initially, the fresh water spreads horizontally toward the salty region in a smooth and laminar fashion. As the fresh water picks up salt, it gets denser and starts sinking, ultimately forming a turbulent plume that will push all the way back across the tank. For more images, check out the full poster. (Image credit: P. Passaggia et al.)
“Heavy Metals”
Photographer Alberto Seveso’s “Heavy Metals” series builds on his previous works capturing fluid dynamics. By dropping mixtures of ink, liquids, and metallic powder through different fluids, he creates ethereal, billowing forms that turn the processes of diffusion and turbulent mixing into something one could almost touch. Be sure to check out the rest of the series and his online portfolio for more examples. (Photo credits: A. Seveso; via Colossal; submitted by jshoer and @catnogood)
Supernova Core Collapse
A core-collapse, or Type II, supernova occurs in massive stars when they can no longer sustain fusion. For most of their lives, stars produce energy by fusing hydrogen into helium. Eventually, the hydrogen runs out and the core contracts until it reaches temperatures hot enough to cause the helium to fuse into carbon. This process repeats through to heavier elements, producing a pre-collapse star with onion-like layers of elements with the heaviest elements near the center. When the core consists mostly of nickel and iron, fusion will come to an end, and the core’s next collapse will trigger the supernova. When astronomers observed Supernova 1987A, the closest supernova in more than 300 years, models predicted that the onion-like layers of the supernova would persist after the explosion. But observations showed core materials reaching the surface much faster than predicted, suggesting that turbulent mixing might be carrying heavier elements outward. The images above show several time steps of a 2D simulation of this type of supernova. In the wake of the expanding shock wave, the core materials form fingers that race outward, mixing the fusion remnants. Hydrodynamically speaking, this is an example of the Richtmyer-Meshkov instability, in which a shock wave generates mixing between fluid layers of differing densities. (Image credit: K. Kifonidis et al.; see also B. Remington)
Greening the River
Every year Chicago dyes its river green in honor of St. Patrick’s Day. This timelapse video shows this year’s dyeing, including several passes from a boat distributing the green dye. The color is remarkably slow to diffuse. The boat’s passage does little to affect the motion of the dye already in the river. This is because the boat mainly disturbs the surface and most of the color comes from dye spread throughout the water. It’s like if you tried to stir milk into your coffee just by tapping the surface with your spoon. Instead, the slower, large-scale turbulent motion of the river distributes the dye. For more St. Patrick’s Day physics, be sure to check out Guinness physics and why tapping a beer makes it foam. (Video credit: P. Tsai; submitted by Bobby E.)
Mixing Flows
Turbulence is an excellent mixer. Here two fluorescent dyes are injected into a turbulent water jet. Flow is from the bottom of the image toward the top. The dyes are quickly mixed into the background fluid by momentum convection, their concentration decreasing with increased distance from the source. Large-scale structures like the eddies visible in this image drive this convection of momentum in turbulent flows. In contrast, consider laminar flows, where momentum and molecular diffusion dominate how fluids move. In such laminar flows, it’s even possible to unmix two fluids, a feat that cannot be accomplished in the jet above. (Photo credit: M. Kree et al.; via @AIP_Publishing)
Salinity Near the Amazon
This numerical simulation shows the variation of salinity in the Atlantic Ocean near the mouth of the Amazon River over the course of 36 months. The turbulent mixing of the fresh river water and salty ocean shifts with the ebb and flooding of the river. Salt content causes variations in ocean water density, which can strongly affect mixing and transport properties between different depths in the ocean due to buoyancy. Understanding this kind of flow helps predict climate forecasts, rain predictions, ice melting and much more. (Video credit: Mercator Ocean)
Worthington Jet
A drop of sugar syrup falls into a pool of methylated spirits, producing a Worthington jet and several ejected droplets. Although surface tension holds the jet in a smooth shape, the refractive index of the spirits reveals the turbulent mixing within the jet. (Photo credit: Rebecca Ing)
Brazilian Barrier Islands
Barrier islands are in a constant state of flux due to the currents, tides, and winds that surround and shape them. This satellite image of islands off the Brazilian coast shows meandering waterways and the mixing of sediment from the land into the sea. Often, secondary flows are responsible for shaping of these sorts of geographic features. #
Combustion
Fluid dynamics are vital to combustion. Like here, many practical flames–such as those responsible for internal combustion in automobiles, jet engines, and rockets–are turbulent. The turbulence aids mixing of the fuel and oxidizer, resulting in more complete combustion and greater efficiency. #
