Experiments on the Expansion Wave Driven Rayleigh-Taylor Instability

摘要

In the present study of Rayleigh-Taylor turbulent mixing, an expansion wave is used to generate a nonconstant acceleration of the interface between two gases. It has been shown that a very large acceleration of the interface can be achieved using this technique. An air/SF_6 gas combination is used that gives the initial Atwood number of A = 0.67. Measurements of the time history of the acceleration are found to be well predicted by 1D theory and simulations. The large acceleration of the interface leads to the rapid growth of the finite amplitude stochastic perturbations imposed on the interface that in turn results in the rapid development of RT turbulent mixing. The mixing layer growth rate is evaluated using the methods of Read and Youngs and Zaytsev et al., and an average growth constant a ≈ 0.1 is obtained. This value falls outside of the range usually reported in previous studies. However, additional effects that would affect the mixing rate such as dilatation of the mixing region and decrease in the Atwood number due to the expansion wave must be taken into consideration. Finally, it should also be noted that the use of an expansion tube allows one to easily study compressible fluid combinations with very large Atwood numbers, for example He/SF_6 would yield A - 0.95.