Oscillatory boundary layer flows modelled with dynamic Reynolds stress turbulence closure

Abstract

A standard dynamic Reynolds stress model, with conventional coefficients, is applied to oscillatory boundary layer flows. With a grid resolution over the boundary layer thickness and wave period of the order of 100 and 600 respectively, well defined, grid-independent solutions are 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 standard ( k-ɛ) closure also predicts them reasonably realistically. With sediment entrainment, giving stably stratified flow, the Reynolds stress model estimates that there is almost no turbulence above the mean velocity maximum. This is probably a reason why a ( k-ɛ) model even predicts such flows accurately. Another reason is that the flow is strongly forced (by the oscillatory pressure gradient) and is not, like for instance turbidity currents, decisively governed by the turbulence. An oscillatory flow with sediment entrainment on a slope is predicted to force a systematic turbidity current. At large enough slope angles, the waves are predicted to trigger self-accelerated turbidity currents.