Abstract-
Recent results from two experimental apparatuses will be presented. The first is a vertical shock tube in which a well controlled interface is generated by flowing a light and a heavy gas from opposite ends of the driven section. The second apparatus is an incompressible experiment in which an impulsive acceleration is given to a box containing two miscible liquids by bouncing it off of a fixed spring. In both experiments a single mode initial perturbation is the given to the interface by oscillating the fluids in the horizontal direction. Both apparatuses provide particularly well visualized images of the instabilities far into the nonlinear regime and yield amplitude measurements that are in very good agreement with linear stability theory as well as existing nonlinear models. New results will be presented which extend the observation time of these experiments. These late time images show the development of a secondary instability of the vortex cores that eventually results in a transition to turbulence. The dimensionless time of appearance of this instability is found to be well correlated with the value of the Reynolds number based on the vortex circulation.
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