Validation of Rayleigh-Taylor turbulent mixing simulations for real fluids

Summary form only given. Turbulent mixing displays experimentally universal growth rates, but simulations in most cases disagree with experiments by a factor of 2 or more. We report on a new class of simulations based on (a) an improved front tracking algorithm and (b) inclusion of real fluid effects which agree with experiment. Here the real fluid effects are surface tension for immiscible fluids and mass diffusion for miscible fluids. We document significant dependence of the mixing rate on both physical scale breaking effects (surface tension, mass diffusion and compressibility) and on numerical artifacts such as numerical mass diffusion (for untracked simulations). We conclude that modeling of turbulent mixing is sensitive to details of transport, surface tension, and to their numerical analogues. We also consider the problem of closure for the averaged equations. The numerical data base resulting from experimentally validated simulations is an invaluable resource in providing a rational and systematic way to evaluate proposed closures. We compare some leading closure models and find an approximate agreement, but in some cases, regions of disagreement