Rayleigh-Taylor Instability Experiments

About the Experiment :

   Rayleigh-Taylor instability is a very fundamental fluid instability that occurs whenever a heavier fluid is placed on top of a lighter fluid in a constant gravitational field. It is of importance to a wide variety of applications ranging from oceanography to inertial confinement fusion. The instability can most easily be demonstrated by simply inverting a stably-stratified system (by for example turning over a glass of water). However, the disruptive effects produced by the inversion process make this method unsuitable for studying the instability in a controlled laboratory environment.

   Rayleigh-Taylor instability is generated in our experiments by accelerating a tank containing the two fluids downward at a rate greater than the earth's gravitational acceleration. The experimental apparatus consists of a tank that is mounted to a linear rail system and attached by a cable to a weight and pulley system. The bottom half of the tank is filled with a heavy liquid and the top half with a lighter liquid. The filled container is then hoisted to the top of the rail system and then oscillated in the horizontal direction giving the interface a sinusoidal initial perturbation. The tank is then released allowing the weight to pull it downward at a rate approximately twice that of the earth's gravitational field which produces a net gravitational pull approximately equal to that of the earth's but oriented upward. Thus, the initially stably-stratified system becomes unstable.

   The fluids are visualized in these experiments using Planar Laser Induced Fluorescence. A fluorescent dye is mixed in one of the liquids and then illuminated with a sheet of laser light passing through the top of the container. The resulting fluorescent images are captured by a CCD camera which travels with the moving container. Pictures below shows a sequence of images captured during one of these experiments. In these views the effective gravity pulls the lower heavier fluid upward as if the tank had been inverted but without the disrupted effects of actually turning over the tank.

Pictures:

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