Earlier work done at CNLD

Couette-Taylor Vortices Over a century ago, Maurice Couette created a simple device to measure the viscosity of a fluid. He placed the fluid between two concentric cylinders and measured the amount of torque required to turn the inner cylinder. As one increases the rotation rate of the inner cylinder, more torque is required. However, at a certain rotation rate, the variation of torque with cylinder speed changes abruptly. This occurs at the onset of an instability, the sudden change of the pattern of fluid flow as a parameter is varied. In this case, a series of circulating cells known as Couette-Taylor vortices emerge in the fluid flow . The presence of this instability places limits on the utility of Couette's viscometer. At the Center for Nonlinear Dynamics, we study fluid instabilities and pattern formation in many fluid systems.

Turbulent patterns in 2D soap films
Because soap films are very thin (about 0.0001 cm thick), they are often used as experimental models of two-dimensional fluid flows. Furthermore, the vibrant colors on a soap film can conveniently be used to track the flow. We study the flows in a flat, horizontal soap film driven into motion by conveyer belts running near, but not actually touching the film. These belts induce an air flow which in turn drives the film, just as you can drive a flow on a soap bubble by blowing on it. We observe the resulting flow by watching the swirling variations in film thickness. When the film is forced using belts moving in alternating directions, a transition from large flow loops to an array of small vortices is seen (Fig. 1). Our work shows that flows in a soap film cannot be simply treated as two-dimensional flows, due to the drag of the surrounding air on the film. [John Burgess, Chris Bizon]

Figure 1: A black and white picture of vortices in a horizontal, flat soap bubble driven beyond the onset of flow instability. The variations of brightness in the image correspond to variations in film thickness.

Figure 2: Couette-Taylor Pictures

Flow in a Couette-Taylor Geometry
In addition to primary instability mentioned above, the Couette-Taylor fluid system exhibits many secondary instabilities, creating a small zoo of fluid patterns. The Couette-Taylor system can also exhibit turbulence at high rotation rates, creating an ideal system for study of this difficult problem.

Concentration Driven Convection in 2D
When a fluid is heated from below, the lower fluid becomes less dense than the higher fluid. The light fluid rises, leading to a convective flow pattern. For large differences in temperature, this flow pattern becomes extremely complicated, i.e. turbulent. Turbulent convection is important in both solar and planetary atmospheres. We studied turbulent convection in between two flat vertical glass planes. This allowed us to completely visualize the flow patterns. Experimentally, this pattern was driven using salt, rather than heat, to induce the density difference that causes the patterns. In addition, we performed high resolution numerical simulations to compare to the experimental results. In both cases, the transport of concentration (or heat) was due to powerful plumes. Fig. 4 shows a comparison between experiment and simulation of these concentration plumes. [Alexei Predtechensky, Chris Bizon]

Figure 4: A false color image of turbulent convection plumes in an experiment and in a computer simulation.

Page maintained by Matthew Thrasher
Last modified: 03/27/2006 14:40:04 -0600


Turbulent patterns in 2D soap films Because soap films are very thin (about 0.0001 cm thick), they are often used as experimental models of two-dimensional fluid flows. Furthermore, the vibrant colors on a soap film can conveniently be used to track the flow. We study the flows in a flat, horizontal soap film driven into motion by conveyer belts running near, but not actually touching the film. These belts induce an air flow which in turn drives the film, just as you can drive a flow on a soap bubble by blowing on it. We observe the resulting flow by watching the swirling variations in film thickness. When the film is forced using belts moving in alternating directions, a transition from large flow loops to an array of small vortices is seen (Fig. 1). Our work shows that flows in a soap film cannot be simply treated as two-dimensional flows, due to the drag of the surrounding air on the film. [John Burgess, Chris Bizon]	Figure 1: A black and white picture of vortices in a horizontal, flat soap bubble driven beyond the onset of flow instability. The variations of brightness in the image correspond to variations in film thickness.

Figure 2: Couette-Taylor Pictures	Flow in a Couette-Taylor Geometry In addition to primary instability mentioned above, the Couette-Taylor fluid system exhibits many secondary instabilities, creating a small zoo of fluid patterns. The Couette-Taylor system can also exhibit turbulence at high rotation rates, creating an ideal system for study of this difficult problem.

Concentration Driven Convection in 2D When a fluid is heated from below, the lower fluid becomes less dense than the higher fluid. The light fluid rises, leading to a convective flow pattern. For large differences in temperature, this flow pattern becomes extremely complicated, i.e. turbulent. Turbulent convection is important in both solar and planetary atmospheres. We studied turbulent convection in between two flat vertical glass planes. This allowed us to completely visualize the flow patterns. Experimentally, this pattern was driven using salt, rather than heat, to induce the density difference that causes the patterns. In addition, we performed high resolution numerical simulations to compare to the experimental results. In both cases, the transport of concentration (or heat) was due to powerful plumes. Fig. 4 shows a comparison between experiment and simulation of these concentration plumes. [Alexei Predtechensky, Chris Bizon]	Figure 4: A false color image of turbulent convection plumes in an experiment and in a computer simulation.