Turbulence damping of wave boundary layer flow over ripple covered bed

This paper mainly discussed the turbulence damping of wave boundary layer flow over ripple covered bed through flume experiment and theoretical analysis. Hydrodynamic experiments under current only and wave only were carried out in a wave flume with rippled bed. A PIV and ADV were employed to measure the near bed 2D vertical flow field and high frequency instantaneous velocity, respectively. The relationship between maximum turbulent intensity and bed shear velocity which can be derived from measured data was established to investigate the boundary layer turbulent characteristics. Furtherly, the turbulent characteristics under wave were theoretically explained by comparing the bed shear stress formulas under current only and wave only. The results showed that, the maximum turbulent intensity under current only and waves only can both be expressed proportional to the related bed shear velocity, but with different proportional coefficients. The coefficient under wave is much smaller than that under current, indicating a significant turbulence damping of wave boundary layer flow, which mainly results from the orbital motion-induced stress (uw) over tilde.