CAREER: Towards understanding and modeling Turbulent Buoyant Flows

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1056142 Blanquart Rayleigh-Taylor instabilities appear when a heavy fluid is placed on top of a light fluid. The light fluid rises as a result of buoyancy forces, and in many cases, the flow transitions rapidly to turbulence. Due to their intrinsic nature, Rayleigh-Taylor instabilities are found in a large diversity of engineering applications and natural phenomena (inertial confinement fusion, furnaces, accidental fires, heat transfer within stars, supernova formation, underwater hot vents, oil spill). A lot of work has been done on the initial and long term growth of Rayleigh-Taylor instabilities. However, little is known about the structure of the turbulence inside buoyant mixing layers. A perfect example is the observed anisotropy of scales in direct contradiction with the well established Kolmogorov theory and which remains currently unexplained by any theoretical models. In order to gain access to the fine details of turbulence, Direct Numerical Simulations of various "con-trolled experiments" will be performed. These configurations span all regimes of turbulent buoyant flows, from weak buoyancy to buoyancy-dominated turbulence. The data will be used to analyze the growth of Rayleigh-Taylor instabilities, the emergence of scale anisotropy in buoyant flows, and the effects of Richardson and Atwood numbers. The outcome is multiple and includes the formulation of a novel theoretical framework unifying turbulent non-buoyant and buoyant flows. This first-of-a-kind model will correlate the anisotropy of scales and the energy spectra to the Richardson number of the turbulent structures. The project will result also in the development of new subgrid scale models specifically designed for Large Eddy Simulations of turbulent buoyant flows. This research project is integrated closely with an educational plan. Three key tasks have been chosen, and each task is targeting a real social problem. This includes performing hands-on experiments in middle school at a time when students lose interest in science. This includes engaging undergraduate students in research projects and providing them with the knowledge and skills to continue to graduate school. Finally, this includes reaching out to the general public to ensure that our work does not remain unknown. In addition, the research plan will ensure scientists across disciplines (engineering and non-engineering) benefit directly from the research project. In addition to establishing passive means of exchanging data, explicit collaborations have been initiated with personnel in other universities and national laboratories.