Large-eddy simulation of free-surface decaying turbulence with dynamic subgrid-scale models

This paper describes large-eddy simulations of decaying turbulence in an open channel, using different dynamic subgrade-scale models, viz. the dynamic model of Germane et al. [Phys. Fluids A 3, 1790 (1991)] (DSM), the dynamic mixed model in Zang et al. [Phys. Fluids A 5, 3186 (1993)] (DMM), and the dynamic two-parameter model of Salvetti and Banerjee [Phys. Fluids 7, 2831 (1995)] (DTM). These models are incorporated in a finite-volume solver of the Navier-Stokes equations. A direct numerical simulation of this flow conducted by Pan and Banerjee [Phys. Fluids 7, 1649 (1995)] showed that near the free surface turbulence has a quasi-two-dimensional behavior. Moreover, the quasi-two-dimensional region increases in thickness with the decay time, although the structure remains three-dimensional in the central regions of the how. The results of the large-eddy simulations show that both the DMM and the DTM are able to reproduce the features of the decay process observed in the direct simulation and to handle the anisotropic nature of the flow. Nevertheless, the addition of the second model coefficient in the DTM improves the agreement with the direct simulation. When the DSM is used, significant discrepancies are observed between the large-eddy and the direct simulations during the decay process at the free surface. (C) 1997 American Institute of Physics.