Density dependence of Rayleigh-Taylor and Richtmyer-Meshkov mixing fronts

We propose a pair of ordinary differential equations to describe the motion of the two edges of a Rayleigh-Taylor (RT) or Richtmyer-Meshkov (RM) mixing zone. These model equations give a simple physics - based description of the RT and RM mixing rates. The equations are in agreement with all available experiments, including the recent LEM RT and RM experiments for spikes as well as bubbles. In particular, the model equations predict that the scaling constants alpha(s) --> 0.5 and theta --> 1 as the Atwood number A --> 1. (C) 2000 Elsevier Science B.V. All rights reserved.