Effect of initial conditions on the development of Rayleigh-Taylor instabilities
Peart, Freeman Michael
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There are two coupled objectives for this study of buoyancy-driven turbulence. The first objective is to determine if the development of a Rayleigh-Taylor (RT) mixing layer can be manipulated experimentally by altering the initial condition of the experiment. The second objective is to evaluate the performance of the Besnard, Harlow, and Rauenzahn (BHR) turbulent transport model when initialized with experimentally measured initial conditions. An existing statistically steady water channel facility at Texas A&M University and existing experimental diagnostics developed for this facility have been used to measure the turbulent quantities of buoyancy-driven turbulence. A stationary, bi-planar grid with a high solidity ratio, ?, has been placed immediately downstream of the termination of the splitter plate, perpendicular to the flow direction, to generate a turbulent initial condition. The self-similar growth parameter, ? , for the RT mixing layer has been measured using a visualization technique to determine if the initial conditions affect the development of the RT mixing layer. The self-similar growth parameter, ? , decreased from a value of 0.072 ? 0.0003 with the fine grid to values of 0.063 ? 0.0003 and 0.060 ? 0.0003 with the medium and coarse grids, respectively. With the results from the first objective, a unique opportunity arose to evaluate the performance of the variable density, RANS-type, BHR turbulent transport model. Measurements of velocity statistics necessary to initialize the model accurately have been obtained using particle image velocimetry (PIV). The performance of the BHR model was evaluated through comparison of the experimentally measured and BHR modeled self-similar growth parameter, ? , from the penetration height of the bubbles/spikes and the self-similar growth parameter, K ? , of the turbulent kinetic energy at the centerline of the low Atwood RT driven turbulent mixing layer. When initialized with the experimentally measured initial conditions, the BHR model did agree with the experimental measurements of the penetration height growth parameter, ? , as well as the centerline turbulent kinetic energy growth parameter, K ? , in the self-similar portion of the flow.