Mixing generated by gravitational acceleration and the role of local turbulence measured through multifractal methods is examined in numerical experiments of Rayleigh-Taylor and RichtmyerMeshkov driven front occurring at density interfaces. The global advance of the fronts is compared with laboratory experiments and Nusselt and Sherwood numbers are calculated in both large eddy simulation (LES) and kinematic simulation KS models. In this experimental method, the mixing processes are generated by the evolution of a discrete set of forced turbulent plumes. We describe the corresponding qualitative results and the quantitative conclusions based on measures of the density field and of the height of the fluid layers. We present an experimental analysis to characterize the partial mixing process. The conclusions of this analysis are related to the mixing efficiency and the height of the final mixed layer as functions of the Atwood number, which ranges from 9.8 × 10 −3 to 1.34 × 10 −1 .

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Turbulence affects molecular mixing in a large variety of physical processes both in the environment, in astrophysics and in industrial situations. In some events it is interesting to enhance the transport of mass, heat, humidity and pollutants, while sometimes it is interesting to reduce mixing. Here we analyse some turbulent descriptors which reflect the mixing processes in the compressible induced instabilities that take place in shocks, such as Richtmyer-Meshkov and Rayleigh-Taylor (RM and RT). We present results related to both instabilities and discuss their spatial and temporal variability during the advance of a mixing front, and also their relationships with other scaling arguments. Two types of experiments were used in this study: Mixing generated by gravitational acceleration in low Atwood number incompressible experiments using fluids; and the full compressible shocktube experiments using interfaces between different density gases. The role of local turbulence has mostly relied on advanced visualization measurements through multifractal methods. Comparisons with numerical experiments of shock driven fronts occurring at density interfaces are also relevant. The global advance of the fronts is also measured and fractal descriptors are calculated in both Large Eddy Simulation (LES) and Kinematic Simulation KS models.