Author(s): Akihiko Nakayama; Satoshi Yokojima
Keywords: Turbulence model; Free-surface effects; Numerical calculation
Abstract: Recently available DNS data on open channel flows have been critically evaluated and it has been found that they contradict much of what was believed to be the free-surface effects. Based on this observation, a new method of modeling free-surface effects for the calculation of open-channel flows is proposed and its validation calculation has been performed. It can be incorporated in k-ε, k-εtype or similar two-equation models by introducing damping and structure functions which reflect the effects of the free-surface fluctuation and the intermittency of the largeeddy structure interacting with the free surface. The method requires the freesurface fluctuation and basic equations for it and the equations for the mean freesurface position are derived and modeled. The test calculation results agree with the trends seen in the DNS results as well as the experimental data at higher Reynolds and Froude numbers, and improve the prediction of the mean velocity, turbulent kinetic energy and the dissipation near the free surface.