Fluid mixing due to Rayleigh-Taylor instability in a time-dependent acceleration field

The large-eddy simulation is used to study fluid mixing due to Rayleigh-Taylor instability in a time-dependent acceleration field. The numerical results show that the two fluids in the mixing layer move back towards their initial position if the acceleration has a sudden change in the direction during evolution process. If the direction inverse happens at the earlier stage while the amplitude of perturbation remains quite small, the two fluids may roughly resume their initial state. However, if the inverse happens at a rather late time and the instability has already evolved into the nonlinear stage, the two fluids can no longer be separated from each other, and there is no distinct interface between them.