This study explores experimentally the turbulent flow in a laboratory flume, interacting with waves propagated against the flow. It focuses a region of 'wave-blocking' for which there is a stream-wise location on the water surface, where the wave propagation velocity vanishes. The observations are corroborated by finding a critical wave frequency for a particular discharge above which the waves are effectively blocked; and verified by the dispersion relation of monochromatic wave. The counter-current propagating waves show an evolutionary change in the flow with three segmented regions, viz, flow at the upstream, blocking at the mid-stream and waves in the downstream. The instantaneous velocity data were collected using 3-D Micro-acoustic Doppler velocimeter (ADV) along the flume centerline. This study addresses the changes in the mean flows, Reynolds stresses, eddy viscosity, turbulence kinetic energy fluxes and associated contributions of burst-sweep cycles to the total Reynolds shear stress due to addition of surface waves against a current. The velocity power spectral analysis shows the energy distribution over the whole profile from upstream to downstream. The quadrant analysis is also used to highlight the turbulent event evolutions along the flow; and shows that at the waveblocking and wave dominated regions, the contributions from ejection and sweep to the total shear stress are dominant. The changes in turbulence key parameters due to waveblocking may affect the sediment transport in coastal region.

Experiments are conducted in a laboratory flume on the propagation of a surface wave against unidirectional flow with a sediment bed. This article presents the spatial variation of bedforms induced by the wave‐blocking phenomenon by a suitably tuned uniform fluid flow and a counter‐propagating wave. The occurrence of wave‐blocking is confirmed by finding a critical wave frequency in a particular flow discharge in which the waves are effectively blocked and is established using the linear dispersion relation. The purpose of this work is to identify wave‐blocking and its influence on the development of bedforms over the sediment bed. Interestingly bedform signatures are observed at a transition of bedforms in three zones, with asymmetric ripples having a steeper slope downstream face induced by the incoming current, followed by flat sand bars beneath the wave‐blocking zone and more symmetric ripples below the wave‐dominated region at the downstream. This phenomenon suggests that the sediment bed is segmented into three different regions of bed geometry along the flow. The deviations of mean flows, Reynolds stresses, turbulent kinetic energy, and power spectral density due to the wave‐blocking phenomenon are presented along the non‐uniform flow over sediment bed. The bottom shear stress, bed roughness and stochastic nature of the bedform features are also discussed. The results are of relevance to engineers and geoscientists concerned with contemporary process as well as those interested in the interpretation of palaeoenvironmental conditions from fossil bedforms. © 2019 John Wiley & Sons, Ltd.

No abstract