Wave-Induced Oscillatory Flow Over a Sloping Rippled Bed

Abstract

In this paper, the findings of an experimental analysis aimed at investigating the flow generated by waves propagating over a fixed rippled bed within a wave flume are reported. The bottom of the wave flume was constituted by horizontal part followed by a 1:10 sloping beach. Bedforms were generated in a previous campaign performed with loose sand, and then hardened by means of thin layers of concrete. The flow was acquired through a Vectrino Profiler along two different ripples, one located in the horizontal part of the bed and the second over the sloping beach. It was observed that, on the horizontal bed, near the bottom, ripple lee side triggered the appearance of an onshore directed steady streaming, whereas ripple stoss side gave rise to an offshore directed steady streaming. On the sloping bed, a strong return current appears at all positions, interacting with the rippled bottom. The turbulence is non-negligible within the investigated water depth, particularly when velocities were onshore directed, due to flow asymmetry. Turbulence caused a considerable flow stirring which, above a non-cohesive bed, could lift the sediment up in the water column and give rise to a strong sediment transport.

Steady Streaming Induced by Asymmetric Oscillatory Flows over a Rippled Bed

“…When symmetric ripples and oscillations induced by a sinusoidally varying pressure gradient are considered, the mean velocity far from the bed vanishes even though, as previously pointed out, a steady flow, which consists in recirculating cells, is present in the region close to the bed. When the ripples are asymmetric and/or the pressure gradient driving the flow is the sum of two or more harmonic components, as it occurs under asymmetric or skewed waves [13], the steady velocity component persists at the outer edge of the bottom boundary layer, even at low Reynolds numbers, and affects the flow in the entire water column [14,15]. This is due to the turbulence associated with flow separation at the ripple crests, which, in the cases mentioned above, causes a non-vanishing mean value of the Reynolds stress.…”

Orthogonal Wave Current Interaction Over a Fixed Rippled Bed: Preliminary Results of an Experimental Campaign

“…Moreover, some scale effects must be taken into account, as for as fixed rippled bed was considered, considering that wave and current characteristics were changed during the experimental campaign. However, the dimensions of fixed ripple profile (length λ and height η) were carefully chosen based on the results of previous experimental campaigns (Faraci et al 2012, 2019and Petrotta et al 2018, in order to be the most statistically frequent.…”