WAVE-INDUCED BOUNDARY-LAYER FLOWS ABOVE AND IN A PERMEABLE BED

In this paper, the oscillatory and steady streaming velocities over a permeable bed are studied both theoretically and experimentally. Three different sizes of glass beads are used to construct permeable beds i n laboratory experiments: the diameters of the glass beads are 0.5 mm, 1.5 mm, and 3.0 mm, respectively. Several experiments are performed u sing different wave parameters. A one-component laser-doppler velocime ter (LDV) is used to measure the horizontal velocity component inside the Stokes boundary layer above the solid and permeable surfaces. It i s observed that neither oscillatory nor steady velocity components van ish on the permeable surface. The 'slip velocities' increase with incr easing permeability. Based on the laminar flow assumption and the orde r of magnitude of the parameters used in the experiments, a perturbati on theory is developed for the oscillatory velocity and the steady wav e-induced streaming in the boundary layers above and inside the permea ble bed. The theory confirms many experimental observations. The theor y also provides the damping rate and the phase changes caused by the p ermeable bed.