This paper discusses three interrelated aspects of modeling scalar transport, mixing and combustion, in the context of large-eddy simulation (LES). In terms of passice scalar modeling, we find deom heated wake measurements that whereas the kinetic energy dissipation tensor tends towards isotropy at small scales, the SGS scalar variance dissipation anisotropic independent of filter scale in the presence of a mean scalar gradient. The eddy-diffusion model predicts isotropic behavior, whereas the nonlinear model reproduces the correct trends, but overestimates the level of scalar dissipation anisotropy. The results provide some support for mixed models. Applications of the dynamic models are also discussed. Initial tests on non-buoyant jet flows show that the Smagorinsky model with the standard coefficient-valuegenerates an entirely laminar jet, whereas the Lagrangian dynamic model very good results without the need to tune the Smagorinsky coefficient. In the context of applying the dynamic model to premixed combustion, or other physical processes with large scale-separations, we show that the dynamic determination of unknown scaling exponents instead of coefficients, is a more promising approach.
Citation: Proceedings of the IUTAM Symposium on Turbulent Mixing and Combustion
Pub Type: Journals
LES, modeling, passive scalar anisotropy, scale separation