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Center for Nonlinear Studies |
Large Eddy Simulation (LES) is based on separation of variable of interest into two parts - resolved and unresolved, where resolved parts are obtained numerically using transport equations, and the effect of unresolved parts on resolved is modeled using subgrid-scale (SGS) models. This technique has been successfully applied to variety of problems including simulation of internal combustion engines. We shall present and discuss three new LES sub-grid scale (SGS) models for: - SGS scalar flux - SGS scalar dissipation - SGS energy dissipation The proposed models belong to a new family of SGS models - Dynamic Structure (DS) models. The DS models take the structure of the model term from the corresponding Leonard-type term, and a particular form of a scaling factor is then used. The models are evaluated a priori using available DNS data for a non-reacting mixing layer and decaying isotropic turbulence. The evaluation results compare well with viscosity and similarity models. During the a priori tests, the DS models were found do be robust and perform better than dynamic viscosity and similarity models under variety of conditions including different test-to-base filter size ratios and non-symmetric filters. To evaluate the models a posteriori, they are implemented into a high-order finite-difference code and two LES simulations are conducted: an LES of decaying isotropic turbulence and an LES non-reacting incompressible mixing layer. The results from both runs are compared with data available from the literature and DNS simulations.