Celebrating the physics of all that flows with Nicole Sharp, Ph.D.
- Profile
Faces from Laminar Mixing
These images show the laminar mixing that occurs when a flat plate moves up and down in an otherwise motionless fluid. Each face-like snapshot represents a different point in time. The longer the plate oscillates, the more elaborate the “faces” become. (Photo credit: S. Brunton)
Wingtip Vortices in Ground Effect
[original media no longer available] If you’ve ever watched airplane contrails fade, you’ve probably observed the Crow instability, which causes the trailing wingtip vortices of the plane to interact and distort. The same effect is explored in the video above with the addition of ground effect. The first clip shows a pair of counter-rotating vortices…
“Oil in Water”
There’s beauty even in something as simple as two immiscible fluids–oil and water–colliding. (Video credit: Shawn Knol)
Aeroelastic Flutter
Flutter is a rather innocuous term for a potentially dangerous phenomenon that can occur for any flexible structure in a moving flow. Aeroelastic flutter occurs when aerodynamic forces and a structure’s natural modes of vibration get coupled: the surrounding flow causes the object to vibrate, which alters the nature of the aerodynamic forces on the object, which,…
Transition to Turbulence
Smoke introduced into the boundary layer of a cone rotating in a stream highlights the transition from laminar to turbulent flow. On the left side of the picture, the boundary layer is uniform and steady, i.e. laminar, until environmental disturbances cause the formation of spiral vortices. These vortices remain stable until further growing disturbances cause…
High-Speed Ferrofluid
High-speed video captures the behavior of a ferrofluid trapped between two magnets. Ferrofluids contain tiny ferromagnetic particles suspended in a carrier fluid like oil or water. The distinctive peaks and valleys of a ferrofluid subject to a strong magnetic field is due to the normal-field instability and is a result of the fluid minimizing its…
Diesel Ignition
In a diesel engine, ignition of the injected fuel occurs due to the heat caused by the compression of the fuel/air mixture. (In petrol/gasoline engines, spark plugs are used for ignition.) The subsequent expansion of gases drives the pistons of the engine downward, creating mechanical energy. This high-speed video shows the in-cylinder combustion within a…
Playing Pac-Man with Water Droplets
The vibrations of a plate in the horizontal and vertical directions can be used to control the motion of a drop placed on the surface. Here a droplet of water on a superhydrophobic surface is controlled by joystick a la Pacman. For more, see papers here and here.
Viscous Fingers
A Hele Shaw cell is little more than two glass plates separated by a thin layer of viscous fluid. The cell serves as a good test bed for viscous, low Reynolds number flows such as those found in microfluidics. Here a less viscous fluid is injected into the center of the cell, causing the finger-like protrusions of…
Visualizing Fish Wakes
This novel flow visualization technique uses dilute solutions of the tobacco mosaic virus (TMV). These rod-shaped particles align with shear and produce a birefringent interference pattern visible when viewed between crossed polarizing filters. The intensity of the light is related to the magnitude of shear. The technique is benign to the fish but enables researchers…