Intermittent Fine Scale Structure of Vorticity and Dissipation Fields inTurbulent Shear Flows

摘要

Using results from direct numerical simulations of a planar turbulent jet, thesmall-scale dynamics and subgrid-scale interactions in turbulent shear flows has been investigated. Subgrid-scale energy transfer is found to arise from two distinct effects: one involving local energy exchanges between coherent vortical structures of size comparable to that of the cutoff wavenumber, the other involving nonlocal transfers of energy from the resolved to disparate subgrid scales of motion. In the physical space, the former gives rise to intense regions of forward transfer as well as backscatter of energy, while the latter results in a low intensity, background forward transfer of energy. A dynamic two-component subgrid-scale model (DTM), incorporating the dual character of subgrid-scale energy transfer observed in these studies, has been developed. The model predicts a spatial distribution of subgrid-scale dissipation in good agreement with results from filtered DN8 in a priori tests, and when applied to large-eddy simulations of transitional and turbulent flows it predicts statistics, spectra and structures in better agreement with data from direct numerical simulations than existing dynamic eddy viscosity models. The proposed model should enhance the utility of LES in the computations of complex engineering flows.