Modeling of Free Surface Effects Via Subgrid Scale Models

In large eddy simulation, the key to the reliability of the solution with relatively large mesh size (this is unavoidable for high Re flows) is to develop effective and physically correct subgrid-scale (SGS) models. The behavior of various SGS models in large eddy simulations (LES) of free surface turbulent flows is investigated. The anisotropy of the turbulence observed near a free surface even a sub-grid scales can not be realized by a standard Smagorinsky model (SMG). The SMG model is improved with free surface modifications. This model is verified on an open channel flow benchmark and then applied to the simulation of a surface ship wake. The turbulence features are studied and compared with the results of a simulation without free surface effects. The modifications in the SGS model damps the vertical velocity fluctuations as desired. This study provides a better understanding of SGS models, when applied to the case of the wake of a turning surface ship.