Free-Surface versus Rigid-Lid LES Computations for Bridge-Abutment Flow

Two separate large eddy simulations (LES) are carried out to investigate the effects of accurate computation of the curvilinear water-surface deformation of the flow through a bridge contraction. One LES employs the rigid-lid boundary condition at the water surface, while the other uses a highly accurate level-set method (LSM), which allows the water surface to adjust itself freely in response to the flow. The simulation with the LSM is validated with data from complementary physical model tests under analogous geometrical and flow conditions. Streamwise velocity, bed-shear stress and second-order turbulence statistics obtained from both simulations are compared, and it is shown that the turbulence structure of this flow is influenced strongly by the water-surface deformation. While bed-shear stresses and first-order statistics are very similar for both cases, the instantaneous turbulence structure and consequently, the second-order statistics, are distinctly different. The correct prediction of the water-surface deformation of such flows is deemed important for the accuracy of their simulation. (C) 2015 American Society of Civil Engineers.