Analysis of Subgrid Scale Models

We analyze the behaviour of several subgrid scale (SGS) models for large eddy simulations (LES) by means of an a priori test. For such a test, we make use of the results of a Fourier pseudospectral 512 × 512 x 512 direct numerical simulation (DNS) of a turbulent homogeneous flow at Reynolds number 1000 (courtesy of Meneguzzi). We compare the exact filtered quantities, obtained from the DNS data, to the same quantities as predicted by turbulent models. The filtering is done using the Fourier sharp-cut filter. For the SGS stress tensor we analyze the correlation coefficients and the alignment between the exact stress tensor and the modelled one. Since in LES it is very important to correctly represent the energy exchange between resolved and unresolved scales, the correlation coefficients are also computed for the energy dissipation and for the forward and backward scatters. The influence of the filter amplitude on the behaviour of the models is also tested. We next perform numerical simulations of a channel flow between two parallel unbounded plates, using a numerical code based on second-order centered finite difference. Two groups of simulations are performed at Reynolds numbers Reφ = 180 and 660, for which experimental data are available (at Re, = 180 we also dispose of DNS data. We shall focus the discussion essentially on the behaviour of the newest models.