OSCILLATORY BOUNDARY-LAYER FLOWS MODELED WITH DYNAMIC REYNOLDS STRESSTURBULENCE CLOSURE

A standard dynamic Reynolds stress model, with conventional coefficien ts, is applied to oscillatory boundary layer flows. With a grid resolu tion over the boundary layer thickness and wave period of the order of 100 and 600 respectively, well defined, grid-independent solutions ar e obtained. The available data are predicted in great detail. However, even with turbulence characteristics, the data from oscillatory flows do not appear to be very model discriminant. A model based upon a sta ndard (k-epsilon) closure also predicts them reasonably realistically. With sediment entrainment, giving stably stratified flow, the Reynold s stress model estimates that there is almost no turbulence above the mean velocity maximum. This is probably a reason why a (k-epsilon) mod el even predicts such flows accurately. Another reason is that the flo w is strongly forced (by the oscillatory pressure gradient) and is not , like for instance turbidity currents, decisively governed by the tur bulence. An oscillatory flow with sediment entrainment on a slope is p redicted to force a systematic turbidity current. At large enough slop e angles, the waves are predicted to trigger self-accelerated turbidit y currents.