SUBGRID-SCALE TURBULENT MICROMIXING - DYNAMIC APPROACH

When numerically simulating the behavior of unsteady large scales in t urbulent mixing problems, subgrid diffusion of chemical species (turbu lent micromixing) requires a closure. A dynamic model is proposed to e stimate micromixing from the known properties of the resolved large-ed dy field. The dynamic procedure also provides a direct estimation of t he micromixing time. A reference scalar field is invoked in the closur e, and the physical model is based on basic properties of mass transfe r by diffusion. Direct numerical simulation (DNS) is utilized to valid ate the ability of the closure to capture the relaxation of probabilit y density functions for three-dimensional homogeneous freely decaying turbulence and a two-dimensional mixing layer The dynamic closure for diffusion is shown to reproduce DNS results, and then a standard test case for micromixing models is computed using large-eddy simulation.