Turbulence characteristics of wave-blocking phenomena

TL;DR

This paper experimentally investigates turbulence in wave-blocking phenomena in a flume, revealing how waves against a current alter flow dynamics, turbulence, and sediment transport, with implications for coastal engineering.

Contribution

It provides detailed experimental analysis of turbulence characteristics during wave-blocking, including velocity, Reynolds stresses, and spectral changes, advancing understanding of wave-current interactions.

Findings

Identification of a critical wave frequency for wave blocking.

Altered turbulence structures at wave-blocking regions.

Dominance of ejection and sweep events in shear stress contributions.

Abstract

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 streamwise 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 3D 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