Photographer Janet Waters uses liquids and bubbles to create her fascinating abstract macro art. Check out this interview with the artist and her portfolio for more. (Photo credits: Janet Waters)
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How the Sun Drives the Earth
This video describes how the sun’s energy drives wind and ocean currents on earth. As solar winds stream forth from the sun, our magnetosphere deflects the brunt of the impact (creating auroras at the poles) while the atmosphere, land masses, and oceans absorb thermal energy from the sun’s light. Because of our cycles of day and night and the differences in how land, water, and ice absorb heat, temperature differentials around the earth drive a massive heat engine, causing the circulation of water and wind all around our world. Numerical simulations like the ones underlying this video are vital for the prediction of climate and weather, as well as for developing models and techniques that can be applied to other problems in science and engineering. (Video credit: NASA; via Gizmodo)
Martian Lava Coils
NASA’s HiRISE spacecraft has sent back images of lava coils left on the surface of Mars. These features form when lava flows of different speeds move past one another; they’re essentially Kelvin-Helmholtz waves–like the ones often seen in clouds–in the lava flow that have solidified into solid rock! On Earth these coils appear about a foot wide; the Martian versions are 100 feet across. (Photo credit: NASA/JPL/University of Arizona; via Wired; submitted by Brian L)
Particle Patterning
Here a container filled with a suspension of neutrally buoyant polystyrene beads and fluid is rotated. As the container rotates, a thin layer of fluid and bunches of particles get drawn up onto the wall by capillary forces capable of holding the particles in place even if the container stops rotating. The density and patterning of the particles on the wall depends on the container’s rotation speed and the volume fraction of particles. (Video credit: J. Kao and A. Hosoi)
Reader Question: How to Get Started in Fluid Dynamics
unboundid-deactivated20131116 asks:
Hi. I’m a freshman engineering student at UCSD, and I was hoping to get more into fluid dynamics. Could you possibly give a quick shake-down of what I should look into if I’m just kind of starting? I want to either work in studying specifically fluid dynamics or in studying interactions of oil and petroleum.
Glad to hear that you’re interested in fluid mechanics! I usually answer these kind of questions privately, but I’m going to go ahead and publish my answer here because I think the advice is useful for any undergraduates interested in fluids.
First of all, most engineering courses of study won’t cover fluid mechanics–outside of pipe flow–until the junior or senior-level courses. This is because, unlike many other engineering topics, fluid mechanics relies heavily on foundational material in other subjects. Although fluid mechanics is still essentially F = ma, writing and manipulating the fundamental equations requires advanced calculus. So you will definitely benefit from paying a lot of attention in your math courses, especially vector calculus and differential equations. I also highly recommend learning to solve differential equations numerically using tools like Matlab or Mathematica. These are super useful skills for just about any form of engineering, but they can really pay off in fluid mechanics.
Now, while this classroom work is very important, you don’t have to wait until you’ve finished four semesters of calculus and physics before getting into fluid mechanics. Look up the professors at your school and the research they do. Find some topics/projects you want to learn more about, and go meet with those professors. In my experience, professors are willing to have undergraduates–yes, even freshmen–volunteer in their labs. I can’t guarantee that you’ll get paid, but I can tell you that you will learn a lot, especially from the graduate students you will probably be assisting. As you gain experience, you’ll gain responsibility. Right now, my research group has a sophomore preparing to be the lead on a new data collection campaign in one of our best research wind tunnels.
Many professors recruit their future graduate students this way. And, if it turns out that you don’t want to work in that lab through graduate school, you will still have a leg up getting into grad school because you’ll have significant research experience and a professor who can write you a strong recommendation, having seen your work. You could even have co-authorship on a publication, and that sort of achievement is going to look good on your resume, whether you pursue graduate school or an industrial job.
In short: talk to professors about their research and find a lab where you can become a part of that research. The earlier you do this, the more impressive the results by the time you graduate. Good luck!
Artificial Fins in Tandem
For this image, two artificial fish fins are placed side-by-side and flapped in phase. Flow in the image is upward. The wakes of the fins interact in a complicated vortex street. Researchers hope that studying such flows can help in designing the next generation of autonomous underwater vehicles. (Photo credit: B. Boschitsch, P. Dewey, and A. Smits)
Particle Jets
During explosions, solid particles and liquids packed around the explosive charges can form jets, making a blast wave appear more porcupine-like than spherical. The instability mechanisms that cause this behavior are not well-understood, but researchers suspect the jets are formed due to perturbations in the particle bed on the timescale of the initial shock propagation. The presence of these jets can affect the blast wave’s subsequent growth as well as the mixing in its wake. The number of jets produced depends on many factors, including particle type, the geometry of the charge, the ratio of explosive to particles, and even whether the particles are wet or dry. Note the very different natures of the explosions in the video when shown side by side. (Video credit: D. Frost et al)
Particle Image Velocimetry
One common experimental technique for measuring velocity in a flow is particle image velocimetry (PIV), shown above. Special particles are introduced–seeded–into the flow. Typically, these particles are small, neutrally buoyant, and have a refractive index significantly different from the background flow. One or more lasers are used to illuminate a section of the flow–a plane for 2D measurements or a cube for 3D. Rather than operating continuously, the laser is pulsed, producing very short exposure times of the order of hundreds of nanoseconds. A camera (or more than one camera for 3D measurements) captures a pair of images separated by this short exposure. The time between frames is so small that the particles will not have moved much between frames. Researchers can then correlate the two frames and derive velocity data from the motion of the particles.
Wave-Particle Duality in Bouncing Droplets
A droplet atop a vibrating pool is prevented from coalescing by the constant influx of air into a thin lubrication layer between it and the pool. But that is not the strangest aspect of its behavior. Researchers have found that this system demonstrates some aspects of the mind-bending wave-particle duality at the heart of quantum physics. (Submitted by Dan H.) #
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)