Direct numerical simulation and large eddy simulation of wind shear effects on non-stratified open channel flow

Abstract

In this study, direct numerical simulation (DNS) and large eddy simulation (LES) of turbulent channel flow beneath a flat surface with imposed wind shear stress are presented. An open channel with friction Reynolds number Reτ= 360 has been considered, while wind shear stresses were imposed as being aligned with the flow direction or not aligned with components in streamwise and spanwise directions. The results indicate that there are differences between wind-driven flow and the case with no wind shear stress. Streaks are present close to the surface in wind-driven flow and profiles of the mean velocity, TKE and mean shear production rate in wind-driven flow are different from those in the unsheared surface flow. Large eddy simulation of wind-driven flow was also carried out to evaluate the performance of sub-grid scale models. It is shown that the features of the flow observed in DNS are well simulated by LES with a relatively small difference near the surface due to shear stress boundary condition.