FYFD

Year: 2014

  • “Milky WaY”

    “Milky WaY”

    Photographer Paulo Stagnaro uses milk and food coloring in his series “Milky WaY”. Despite the simple ingredients, the photos illustrate the enormous variety of shape and form in fluid dynamics. Surface tension, diffusion, and intentional mixing create abstract and ephemeral portraits of fluid motion. For similar work, see Pery Bruge’s art or just try browsing through FYFD’s “fluids as art” tag for more examples of science and art intersecting. (Photo credit: P. Stagnaro; submitted by Stephanie M.)

  • Von Karman Vortex Streets

    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)

  • Turbulence and Star Formation

    Turbulence and Star Formation

    Galaxy clusters are objects containing hundreds or thousands of galaxies immersed in hot gas. This gas glows brightly in X-ray, as seen in the Perseus (top) and Virgo (bottom) clusters above. Over time, the gas near the center of the clusters should cool, generating many new stars, but this is not what astronomers observe. New research suggests turbulence may prevent this star formation. The supermassive black holes near the center of these galaxy clusters pump enormous amounts of energy into their surroundings through jets of particles. Those jets churn the gas of the cluster, generating turbulence, which ultimately dissipates as heat. It is this turbulent heating astronomers think counters the radiative cooling of the gas, thereby keeping the gas hot enough to prevent star formation. You can read more about the findings in the research paper.  (Image credits: NASA/Chandra/I. Zhuravleva et al.; via io9)

  • Iridescent Clouds

    Iridescent Clouds

    Look up at the clouds on the right day and you may catch a glimpse of a rainbow-like phenomenon known as cloud iridescence. These colors occur when sunlight is diffracted through small water droplets or ice crystals. For the effect to be apparent, the cloud must be optically thin, meaning that most of the rays of sunlight must pass through only a single droplet or ice crystal. This means the effect is usually visible only near the edges of clouds or as new clouds are forming. You can see more photos of the phenomenon here, and there’s a great video where cloud iridescence makes an appearance during a rocket launch in this previous entry.  (Photo credit and submission: C. Havlin)

  • Featured Video Play Icon

    The Hidden Complexities of the Simple Match

    Striking a match and blowing it out seems rather simple to the naked eye. But with high-speed video and schlieren photography, the act takes on new complexity. Schlieren photography is an optical technique that is incredibly sensitive to changes in density, which makes it a prime choice for visualizing flows with temperatures variations or shock waves. Here it shows the hot gases generated as the match is lit. Once the match ignites, the flow calms somewhat into a gently rising plume of exhaust and hot air. When someone enters the frame to blow out the match, the frame rate increases to capture what happens next. The flow field around the match becomes very complex as the air and flame interact. The range of length scales in the flow increases, from scales of several centimeters down to those less than a millimeter. This complexity and range of sizes  is a hallmark of turbulence. (Video credit: V. Miller et al.)

  • FYFD at APS DFD 2014

    I’m excited to announce that I will be attending the American Physical Society Division of Fluid Dynamics meeting in San Francisco next month. This year I will be co-teaching a workshop on communicating science to general audiences. Here’s the lowdown:

    Scientist-Reporter Workshop: How to tell your science story

    Want to share your research with the public? Five experts lead a workshop on ways to draw attention to your research. Join science journalist Flora Lichtman, whose work has appeared on NPR, and in The New York Times and Popular Science; Jason Bardi, writer and Director of Media Services at AIP; Nicole Sharp, creator of “F! Yeah Fluid Dynamics”; Rachel Levy, creator of “Grandma got STEM” and biomechanic David Hu for a workshop on disseminating your research to news outlets.

    To learn more or register to attend, check out: http://apsdfd2014.stanford.edu/?q=content/special-events

    We’ll have a follow-on to the workshop at Sunday night’s banquet. For those who can’t make it to the conference in person, never fear: we will be taking to the Internet, too. More on that at a later date.

    So who all is coming?

  • Momentary Crown

    Momentary Crown

    When a drop falls on a liquid film, its impact drives a thin liquid sheet called the ejecta upward and outward from the point of impact. Within  milliseconds, tiny perturbations develop in the ejecta and begin growing exponentially. These become the distinctive spikes of the crown. The momentum from the impact drives the ejecta and spikes further outward until it overcomes surface tension’s ability to hold the liquid crown together. Tiny droplets escape the crown before the ejecta comes crashing down. The whole process takes only a few hundred milliseconds from start to finish.  (Photo credit: S. Jung et al.)

  • Kelvin-Helmholtz Clouds

    Kelvin-Helmholtz Clouds

    When differing layers of fluid move past one another, friction between them causes shear. This shear quickly transforms a simple flat interface between fluid layers into a wavy unstable boundary that resembles a series of breaking ocean waves. This effect is known as the Kelvin-Helmholtz (KH) instability. In the atmosphere, this instability causes air layers with differing temperatures and moisture content to form wave-like clouds where the two layers meet. Other examples of the effect are widespread. On earth, many ocean waves are generated by wind shearing the water; elsewhere in our solar system, the cloud bands of Jupiter are lined with spinning eddies from the KH instability. (Photo credit: H. Bondo)

  • “Courants et Couleurs”

    Although flow visualization is a scientific technique, there is very much an art to it. Flow structures are, by their nature, ephemeral. To capture them, one must design an experiment that introduces dye into regions of interest without altering the flow significantly and without either ignoring or obscuring important physics. One of the great masters of this scientific art was Henri Werlé, whose extensive flow visualization work at France’s national aerospace lab is documented in the short film above. The film includes examples of simple geometries, full aircraft models, subsonic flow, shock waves, and more. eFluids has a whole gallery of Werlé images, too. Take a few minutes to enjoy the mesmerizing beauty of these experiments and appreciate the talents of those who made them possible. If you have questions about specific clips, feel free to ask! (Video credit: H. Werlé/ONERA; via J. Hertzberg)

  • The Kaye Effect

    The Kaye Effect

    Those who have poured viscous liquids like syrup or honey are familiar with how they stack up in a rope-like coil, as shown in the top row of images above. What is less familiar, thanks to the high speed at which it occurs, is the Kaye effect, which happens in fluids like shampoo when drizzled. Shampoo is a shear-thinning liquid, meaning that it becomes less viscous when deformed. Like a normal Newtonian fluid, shampoo first forms a heap (bottom row, far left). But instead of coiling neatly, the heap ejects a secondary outgoing jet. This occurs when a dimple forms in the heap due to the impact of the inbound jet. The deformation causes the local viscosity to drop at the point of impact and the jet slips off the heap. The formation is unstable, causing the heap and jet to collapse in just a few hundred milliseconds, at which point the process begins again. (Image credit: L. Courbin et al.)