Abstract
A direct numerical simulation (DNS) has been conducted to examine the near-wall structure of turbulence in rough-bed channel flow. It is intended to explore a better wall boundary condition in such simulation as Large-Eddy Simulation (LES) of open channel flows at high Reynolds numbers over rough bed. It is found that the instantaneous velocity profiles cannot be described by the instantaneous logarithmic-law similarity. The filtered velocity field is found to be closely related to the magnitude of the filtered temporal normal velocity near the bed. It agrees with the previous study based on experimental data and indicates that the near-wall velocity field over rough surface is related more to the sweep-ejection type modes of motion than the local and temporal values of the wall shear stress. A possible wall model using an assumed shear correlation is suggested.
