SPECTRAL-DYNAMIC MODEL FOR LES OF FREE AND WALL SHEAR FLOWS

Using EDQNM nonlocal spectral expansions, we have developed a spectral -dynamic model for LES of turbulence, allowing to account for kinetic- energy spectra steeper than Kolmogorov at the cutoff. In the case of a temporal mixing layer forced by a weak 3D isotropic while noise, a se lf-similar slate is reached, statistically in good agreement with labo ratory experiments, except for kinetic-energy spectra which behave lik e k(-2) at the cutoff, instead of k(-5/3). Th, pressure spectrum is co mpared with quasi-normal predictions, Concerning coherent-vortex dynam ics,the helical-pairing organization already found with the aid of DNS has been recovered. When the initial forcing is quasi 2D, no self-sim ilar state is reached. Coherent vortices consist then of quasi two-dim ensional Kelvin-Helmholtz billows with hairpin vortices stretched in-b etween, Afterwards, the model has been applied success fully to a turb ulent channel flow at h(+) = 204 and h(+) = 389, In the latter case, t he computing time is reduced by a factor of 100 with respect to DNS. T he model works also well for LES of a channel rotating about a spanwis e axis. Finally, we have proposed a generalization of the spectral-dyn amic model in physical space. (C) 1998 Elsevier Science Inc. All right s reserved.