1. Experimental and Numerical Investigation of Buoyancy-Driven Hydrodynamics Nicholas Mueschke Texas A&M University Malcolm J. Andrews Los Alamos National Laboratory Oleg Schilling Lawrence Livermore National Laboratory This work has been supported by the Department of Energy as a part of the High Energy Density Science Grant Program under Contract No. DE-FG03- 02NA00060. This work was performed under the auspices of the U.S. Department of Energy by the University of California Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48. Rayleigh-Taylor instability occurs when the density gradient opposes the pressure gradient. Small perturbations grow to form bubbles which rise in the direction of gravity and spikes which fall in the direction opposite to gravity. As the perturbations grow in time, a turbulent mixing layer is formed that grows as Linear Growth Nonlinear Growth Turbulent mixing layer Overview of Rayleigh-Taylor Instability The modeling of hydrodynamics phenomena that occur in ICF applications remains a grand challenge to the turbulence community due to the complex nature of Rayleigh-Taylor and Richtmyer-Meshkov flows. In addition, the inclusion and understanding of the effects of initial conditions on turbulence models, i.e. Reynolds-Averaged Navier-Stokes (RANS) and subgrid-scale (SGS) models, is currently not well understood. This research aims to provide a basis for validating turbulence models used to study the implosion characteristics of ICF shell designs. Motivation Measure initial density and velocity perturbations of a small Atwood number, Rayleigh-Taylor driven mixing layer Quantify perturbations in both streamwise and spanwise directions Measure time-evolution of density statistics, spectra, and molecular mixing parameters Examine early-time transitional dynamics of mixing statistics Perform direct numerical simulations (DNS) Research Goals Statistically-stationary Rayleigh-Taylor mixing layer formed by positioning a denser fluid over a lighter fluid. Hot and cold water flow downstream, initially separated by a thin splitter plate. Experimental Parameters: Temperature Diff.  T  5  C Mean flow velocityU m  4.5 cm/s Prandtl NumberPr   7 Atwood number Overview of Experiment Experimental DiagnosticsImage of Mixing Layer Downstream distance converted to time by Taylor’s hypothesis Dimensionless time Streamwise interfacial perturbations were measured using high resolution thermocouples Evolution of molecular mixing parameter  on centerplane of evaluated to examine transitional dynamics of mixing layer. Streamwise Density Measurements Streamwise Velocity Measurements Streamwise initial velocity perturbations measured using PIV. Early-time evolution of the mixing layer driven by initial velocity conditions. Spanwise Interfacial Measurements Spanwise interfacial perturbations measured using planar laser-induced fluorescence (PLIF). Negligible velocity perturbations measured in transverse direction. Portions of this poster have been previous reports: UCRL-PRES-205960, UCRL-PRES-208016, and UCRL-PRES-207125 Image of Spanwise Perturbations Spectrum of Spanwise Perturbations RMS Vertical Velocity in Wake of Splitter Spectrum of Vertical Velocity Fluctuations