Spectral measurements of Rayleigh–Taylor mixing at small Atwood number

Temperature measurements have been made in a buoyancy driven mixing layer created by an unstable temperature gradient in water. Experiments were performed with a temperature difference of 5 °C, with a corresponding Atwood number of 7.5×10−4. Two types of analyses were used to determine density fluctuation correlations. The first analysis determined density fluctuation correlations from the mean density profiles, which is sufficient for a two-fluid distribution of the density where there was no molecular mixing. The second analysis used measurements taken from a continuous distribution of density, and thus included molecular mixing associated with heat diffusion. The thermocouples used for temperature measurements enabled the collection of large sample sizes and thus a detailed examination of molecular mix fractions, spectral properties of the density fluctuations, and probability distributions of the density through the mixing layer.