Variable density ratio simulations of miscible Rayleigh-Taylor instability

Abstract

Knowledge of density ratio effects in miscible Rayleigh-Taylor instability is limited. Density ratio and species diffusion both have the potential to affect flow dynamics. We report results from direct numerical simulations of miscible Rayleigh-Taylor instability at three density ratios: 5/3, 3, and 7. The flow is assumed to be incompressible and density variations are due to changes in composition. A variable coefficient elliptic pressure problem is solved to enforce the velocity divergence constraint and permit simulations at high density ratio. Particular attention is given to the selection of flow parameters in order to minimize the effects of initial conditions. At the lower density ratios, the simulations achieve outer-scale Reynolds numbers of at least 3500, but the high density ratio case is limited to about 1700. As in the immiscible case, increasing density ratio leads to asymmetric bubble and spike growth. This directly affects mixed-fluid composition.