LES OF OPEN-CHANNEL FLOW WITH FREE-SURFACE FLUCTUATION

Large-eddy simulation of fully-developed turbulent open-channel flow has been conducted allowing motion of the free surface. The shape of the free surface, and hence flow domain, is filtered along with the flow field itself. Filtering of the free surface position introduces extra subgridscale (SGS) terms. Two different models for these new SGS terms are proposed and incorporated in actual LES calculations. Calculations with and without the free-surface SGS terms indicate that the effects of these terms may not be overwhelmingly large in subcritical flows, but they make some differences in the mean-velocity profile near the free surface and in the Reynolds stresses. The effects can be much more in spatially or temporally varying flows at higher Reynolds and Froude numbers.