Mixing enhancement by expansion waves in supersonic flows of different densities

Abstract

When expansion waves pass through an interface between compressible fluids of different densities, the interface is Rayleigh–Taylor unstable if the low-density fluid is accelerated into the high-density fluid by the pressure gradient associated with the expansion waves. Numerical simulations of the evolution of interface structures interacting with expansion waves launched by a piston receding from the interface show rapid growth of mushroomlike structures from small disturbances. This is an indication of a strong Rayleigh–Taylor instability on the interface. In order to study the application of this concept to mixing enhancement in supersonic flows, simulations of a shear layer formed by supersonic flows of different densities passing through expansion waves have been performed. It is found that this instability enhances mixing by creating vorticity when the expansion waves generate a negative scalar product of the density and pressure gradients in the interface region.