FILTERING EFFECTS OF FREE-SURFACE FLUCTUATIONS IN LES OF OPEN-CHANNEL TURBULENT FLOWS

Abstract

In an LES calculation of turbulent flows with a moving free surface, represented by an elevation function, new unknown subgrid-scale correlation terms arise from filtering of the kinematic boundary condition. Fundamental characteristics of these subgrid-scale terms and possible models have been investigated using the DNS data of fully-developed open-channel turbulent flow at subcritical Froude numbers. It is found that the magnitudes of the subgrid-scale terms are relatively small but can be important locally. The subgrid-scale model based on the scale similarity appears to be a good candidate, better than gradient-diffusion type model similar to the standard Smagorinsky model for subgrid-scale stresses.