RAYLEIGH TAYLOR MIXING AND ENTRAINMENT NEAR SHARP DENSITY INTERFACES J. M. Redondo 1,2 1 Department of Applied Physics, UPC-Barcelona Tech. Universitat Politecnica de Cataluña, Campus Nord B5, 08034, Spain. 2 DAMTP, Cambridge University, Wimberforce Rd. Cambridge, U.K. Abstract Turbulence affects the dynamics and the evolution of the turbulent mixing layer and its complex configuration is studied taking into account the dependence on the initial modes at the early stages and its spectral, self-similar information. Most models of the turbulent mixing evolution generated by hydrodynamics instabilities do not include any dependence on initial conditions, but in many relevant physical problems this dependence is very important, for instance, in Inertial Confinement Fusion target implosion. We discuss simple initial conditions with the aid of a numerical model developed at FIAN Lebedev which was compared with results of many simulations. The analysis of Kelvin-Helmholtz, Rayleigh-Taylor, Richtmyer- Meshkov and of accelerated instabilities is presented locally, and seen to dominate the turbulent cascade mixing zone differently under different initial conditions. Simulations and multi-fractal and neuron network analysis of Turbulent Mixing under RT and RM instabilities are presented for the different experiments and numerical simulations, further analysis on the numerical model is presented using wavelet preprocessing of the simulation results and neuron network presentation of the data. The aspect ratios of the bubble induced convective cells are seen to depend on the boundary and initial conditions applied to the front. The evolution of the Rayleigh-Taylor instability develops into a turbulent mixing front that may be investigated further using the information that the fractal dimensions or Kolmogorov Capacities give as the flow evolves in time. The basic self-similar characteristics of the flow are compared and the evolution of the multi-fractal dimensions of density, velocity and vorticity contours provides indication that most mixing takes place at the sides of the dominant convective blobs. In the context of determining the influence of structure on mixing ability and determine the regions of the front which contribute most to molecular mixing. Keywords: Mixing, Rayleigh Taylor scales, Overturning layer, Shock turbulence 1 Introduction The Evaluation of mixing efficiency in overturning flows is characterized by a strong efficiency in the mixing process (Redondo 1990, Linden and Redondo 1991) Showed values of up to ½ which were much higher than previously thought, We discuss how these overturns produce small-scale turbulent mixing due to local buoyancy which is of great relevance for many processes ranging from medium to local scales. Unfortunately, measuring at those small scales is very difficult. To overcome this disadvantage it is interesting to use theories and parameterizations which are based on larger scales because they are more easily measured with conventional instruments.