Search results for: “art”

How Are Sea Waves Created?
There are many different kinds of sea waves, some of which have fluid dynamical origins and some of which don’t. For example, tsunamis are caused by the sudden displacement of the ocean floor caused by earthquakes and the tides are caused by the pull of the moon on Earth’s oceans. But many of the waves we are accustomed to seeing are caused by the wind moving across open water, whether in the ocean, in a lake or a sea, or even a river or pond. When the wind blows across the free surface of the water, the difference in velocity between the two fluids causes shearing and the development of surface waves as a result of the Kelvin-Helmholtz instability. (Incidentally, this is why other examples of the K-H instability look so much like ocean waves.)
These wind-generated waves can take several forms. Ripples–or capillary waves–remain visible only as long as the wind is blowing. But under steady conditions, or after the wind has affected a large enough area, waves can form that will persist at the surface even if the wind stops blowing. At that point, even though the wind generated the waves, it is gravity that allows them to persist. This is the source of most of the waves we see on large bodies of water. (Photo credit: Travis Weins)
May 1, 2012
Convective Cells
Convective cells form as fluid is heated from below. As the fluid near the bottom warms, its density decreases and buoyancy causes it to rise while cooler fluid descends to replace it. This fluid motion due to temperature gradients is called Rayleigh-Benard convection and the cells in which the motion occurs are called Benard cells. This particular type of convection is essentially what happens when a pot is placed on a hot stove, so the shapes are familiar. Similar shapes also form on the sun’s photosphere, where they are called granules.
April 26, 2012
Reader Question: Fire as a Fluid?
Reader David L asks:
I understand that fire is a form of energy rather than a fluid in the physical/tangible sense. However, is it possible for fire to exhibit fluid-like behaviours to a certain extent.
In other words, could the dynamic properties of fire be described with pseudo-variables analogical to variables that describe a physical fluid (i.e. viscosity, density, Re, etc.)?
Actually, combustion is a major topic of research among fluid dynamicists. Since the part of fire that we identify as visible flame is a reacting mixture of gas and some solid particles, it moves according to the same equations of motion as any other gas. However, when studying combustion thermodynamical equations and chemical reactions must also be tracked in addition to mass and momentum, which makes modeling fire very difficult. Combustion plays a major role in internal flows like those in car, jet, and rocket engines. (Photo credit: master.blitzy)
April 23, 2012
“Ferroux”
In this video, artist Afiq Omar mixes ferrofluid with soap, alcohol, milk, and other liquids to create a surrealistic fluidic dance. In addition to using different fluid mixtures, I suspect he accomplishes many effects using several different permanent magnets and electromagnets to vary the magnetic fields around the ferrofluid mixtures. (Video credit: Afiq Omar; via Wired)
April 18, 2012
Frozen Fluid Illusion
This video creates the illusion of a jet of water frozen in mid-air. The effect is achieved by vibrating the water at the frequency of the speaker, then filming at a frame rate identical to the vibrational frequency. Thus the water pulses at the exact rate that the camera captures images, making the water appear stationary even though it is moving. (submitted by Simon H)
April 11, 2012
Rogue Wave Recreated
For years, mariners have reported occurrences of rogue waves–sudden, isolated waves many times larger than the surrounding surface waves. Until 1995, when a rogue wave was first measured, debate raged as to whether such waves even existed. Scientists have since agreed that nonlinear models of wave interaction are the most likely source of the amplification necessary to create rogue waves. Since the Navier-Stokes equations that govern hydrodynamics are so difficult to solve, scientists have looked to simpler nonlinear wave equations, like the nonlinear Schroedinger equation that governs optics, to generate rogue-wave-like behavior. While the equation gives insight into how a given wave system will evolve, it is still necessary to determine what initial conditions can lead to the formation of a rogue wave. All manner of random conditions exist in the ocean, but to recreate the behavior in a simplified system, we must know which initial conditions are the right ones. Akhmediev et al presented a theoretical perspective on the initial conditions that might lead to rogue wave amplification, and now, for the first time, researchers have been able to create a rogue wave in a wave tank. That little blip that sinks the Lego pirate ship is a great accomplishment toward understanding a phenomenon whose very existence was in question less than twenty years ago. (Video credit: A Chabchoub, N Hoffmann, and N Akhmediev; via Gizmodo; for more, see APS Viewpoints and Akhmediev et al)
April 9, 2012
Brine Shrimp Swimming
For small creatures, swimming is dominated by viscosity. Here researchers use particle image velocimetry (PIV) to explore the flow field around brine shrimp. Its motion is divided into two vorticity-generating phases–the wide power stroke where the shrimp generates most of its forward motion and the recovery stroke where the shrimp returns its starting position while generating as little motion and drag as it can. (Video credit: B. Johnson, D. Garrity, L. Dasi)
April 5, 2012
Granular Eruptions
Granular flows, which are made up of loose particles like sand, often display remarkably fluid-like behavior. Here researchers explore the behavior of granular flows when a solid impacts them at high speed. The sand, unlike a fluid, does not have surface tension, yet we still observe many of the same behaviors. Like a fluid, the sand splashes and creates cavities and jets as it deforms around the fallen object. The sand even “erupts” as submerged pockets of air make their way back to the surface.
April 4, 2012
Science Off the Sphere: Liquid Lenses
Astronaut Don Pettit delivers more “Science Off The Sphere” in his latest video. Here he demonstrates diffusion and convection in a two-dimensional water film in microgravity. He notes that the viscous damping in the water is relatively low and that, left undisturbed, mixing in the film will continue for 5-10 minutes before coming to rest, which tells us that the Reynolds numbers of the flow are reasonably large. The structures formed are also intriguing; he notes that drops mix with mushroom-like shapes that are reminiscent of Rayleigh-Taylor instabilities and cross-sectional views of vortex rings. It would be interesting to compare experiments from the International Space Station with earthbound simulations of two-dimensional mixing and turbulence, given that the latter behaves so differently in 2D.
March 23, 2012
Reader Questions: What Majors Study Fluids?
squky asks:
Your blog has truly inspired me to want to major in the field of fluid dynamics, and for that I wholeheartedly thank you. But I’m having some confusion over which discipline (major) it falls under. Would it fall under physics or engineering? And if engineering, which type? (My two-year college doesn’t have an engineering department or much of an upper-level physics department, so there’s little guidance on the particulars.) If you can give me some clarification it would help me a lot.
Firstly, that’s awesome! I’m thrilled that FYFD has been inspiring as that is one of its goals. The study of fluid dynamics is remarkably interdisciplinary. Researchers who study it can be found most often in physics, engineering, theoretical mechanics, and mathematics departments, though also in meteorology, chemistry, planetary science, or even biology. Which one is most likely depends on the school.
Traditionally, fluid mechanics falls under the topic of classical physics but many physics departments focus on modern physics instead. Mechanical and aerospace engineering departments are the most common places to study fluid dynamics–unlike physicists who moved on to quantum mechanics and relativity, engineers have to understand fluid dynamics due to its practicality and applications. Chemical and civil engineers may also study fluid mechanical topics for these reasons. And because the mathematics of fluid dynamics are so rich and full of unsolved problems, mathematicians are also drawn to the subject.
I would recommend looking into the research interests of the professors in your physics and mathematics departments and see if there’s anyone studying fluid dynamics there already. Even if there isn’t, take what courses you can in physics, calculus, partial differential equations, and numerical methods. All of those will stand you in good stead when looking for further programs down the line.
March 23, 2012

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