An experimental study of turbulent mixing by Rayleigh-Taylor instabilities and a two-fluid model of the mixing phenomena

A simple experiment has been used to quantitatively investigate turbulent mixing at an unstable interface when the interface is subject to a large two-dimensional disturbance. The introduction of a small amplitude long wavelength does little to alter the early time development of a planar mixed region, but at late times causes a large overturning motion that tends to thin the planar mixed region and accelerate the overall mixing process. Data have been collected from the experiment by way of image analysis of experimental photographs. These data serve as a source of information for the development of a open-quotes two-fluidclose quotes model of the mixing process. A open-quotes two-fluidclose quotes model has been developed to describe the turbulent mixing by Rayleigh-Taylor instabilities of the two different density fluids investigated in the experimental study above. A one-dimensional model was employed for the planar mixing experiments; here attention is focused on the development of a physically plausible equation to describe the length-scale development within the mixed region. The one-dimensional model was then extended to two-dimensions for the overturning experiments, and terms are added to account for thinning of the mixing region at late times. Data collected from the experiments are used to validate the model and to determine several model constants. The two-fluid model successfully simulates the experimental results and is recommended for further application to turbulent mixing processes in buoyant environments