Celebrating the physics of all that flows with Nicole Sharp, Ph.D.
- Profile
May the Fourth Be With You
It only seems appropriate to share this little bit of schlieren photography today. May the Fourth be with you all. (Video credit: M. Hargather and J. Miller)
Vibrating on a Subwoofer
[original media no longer available] Vibrating a liquid droplet produces some awesome behavior. The video above shows a water droplet vibrating on a subwoofer at real-time speeds. The behavior and shape of the droplet shifts with the frequency of vibration, which we hear as a change in pitch. To see more clearly the shapes a…
Abstract Fluids
Janet Waters’ abstract photography is full of effects created with fluid dynamics. Diffusion merges different fluids, and gradients in surface tension drive interfacial flows. Changes in density and viscosity produce fingers and streaks and all manner of forms. Be sure to check out her photostream for many more examples of fluids as art. (Photo credits:…
Granular Jet
Sometimes the similarity between fluid flow and granular flows is quite striking. This video shows a stream of sand falling down a tube and impacting a rod. (Note: the view is rotated 90 degrees counter-clockwise, so down points to the right.) As the sand strikes the rod, it’s deflected into a conical sheet, very much…
Inside a Splash
When a droplet strikes a pool, a thin, fast-moving sheet of liquid expands outward from the region of contact. These ejecta sheets come in many forms depending on surface tension, viscosity, air pressure, and droplet momentum. When the ejecta sheet curls downward to touch the pool, it can spray microdroplets outward or trap a layer…
Cavitation in a Bottle
This high-speed video shows the cavitation that occurs when a bottle of water is struck. The impact accelerates the bottle downward, generating localized vacuums between the glass and the liquid. These are cavitation bubbles, which expand until the pressure of the water surrounding them is too great. This outside pressure triggers an implosion of the…
Island Vortex Street
Von Karman vortex streets are a pattern of alternating vortices shed in the wake of a bluff body. They’re commonly associated with cylinders and can be demonstrated in simulation and in the lab. (They even show up in supersonic flows.) But they also show up in nature quite frequently, like in this cloud pattern off…
Viscous Fingers
Viscous liquid placed between two plates forms a finger-like instability when the top plate is lifted. The photos above show the evolution of the instability for four initial cases (top row, each column) in which the initial gap between the plates differs. Each row shows a subsequent time during the lifting process. As the plate…
Bursting a Bubble
Though seemingly instantaneous to the naked eye, the bursting of a soap bubble is fascinating when slowed down. Here it is at about 2200 frames per second. Initially, the bubble is approximately spherical – its shape determined by a balance between surface tension, gravity, and pressure. The prick of a pinpoint disrupts the balance, and…
Instability
[original media no longer available] Many systems can exhibit unstable behaviors when perturbed. The classic example is a ball sitting on top of a hill; if you move the ball at all, it will fall down the hill due to gravity. There is no way to perturb the ball in such a way that it…