High Fidelity Spectral-FDF-LES of Turbulent Scalar Mixing

The fidelity of the hybrid spectral-filtered density function (FDF) methods is assessed for large eddy simulation of turbulent scalar mixing. Both continuous and discontinuous spectral-element methods are considered on domains furnished by structured & unstructured grids. A parametric study is conducted of the effects of the spectral polynomial approximation ((Formula presented.)), the grid size ((Formula presented.)), and the LES filter width ((Formula presented.)). The simulated results are appraised via comparisons with high resolution direct numerical simulation (DNS) data. It is shown that the amount of energy resolved by LES depends on the magnitude of (Formula presented.), but the total energy is predicted reasonably well for all (Formula presented.) values. Also, for a fixed filter width, the LES results converge to DNS data with both (Formula presented.) - refinements. At lower (Formula presented.) values, the rate of convergence to DNS is faster as (Formula presented.) increases. Within the range of parameters considered, (Formula presented.) provides the optimum LES resolution. The consistency of the hybrid spectral-FDF for LES of complex flows is demonstrated; warranting future applications of the methodology for combustion engineering.