Large eddy simulation of turbulent open-channel flow with free surface simulated by level set method

Turbulent open-channel flow over a two-dimensional laboratory-scale dune is studied using large eddy simulation. Free-surface motion is simulated using a level set method. Two subgrid scale models, namely, dynamic Smagorinsky and dynamic two-parameter models, are employed to assess model effects on the free surface. It is found that the two models have very similar performance in predicting the free-surface turbulence. Two flow depths are simulated to investigate the effects of water depth on flow coherent structures and turbulence statistics. In the deep-water flow, experimental data are used to assess for the numerical predictions of the mean flow field and turbulence statistics. They are found to be in good agreement. In the shallow-water flow, there is strong interaction between the free-surface and large-scale vortical structures emanating from the bed, increasing turbulence intensity and free-surface disturbance. The simulations predict streaky structures in the wall layer after flow reattachment in the deep-water flow, but not in the shallow-water case, suggesting that interaction between the free surface and the flow structures is significantly affected by the flow depth.