On the role of subgrid-scale coherent modes in large-eddy simulation

The role of coherent and incoherent subgrid-scale modes in large-eddy simulation modelling is examined. The coherent/incoherent decomposition of the subgrid-scale stresses based on the wavelet de-noising procedure is introduced. A priori dynamical tests based on the perfect modelling approach are performed for decaying isotropic turbulence. The theoretical effects of coherent and incoherent subgrid-scale forces are dynamically evaluated during the simulation. The relation between deterministic/stochastic subgrid-scale models and coherent/incoherent subgrid-scale stresses is discussed. The main result is that in large-eddy simulations low-order statistics can be almost exactly reproduced when only the effect of the coherent subgrid-scale modes is accounted for, while the incoherent subgrid-scale modes have a negligible effect upon the large-scale dynamics and the energy transfer.