Turbulence Statistics of Wave-Current Flow over a Submerged Cube

Abstract

This paper describes an experimental study carried out in a laboratory flume to investigate the interaction of a surface wave with a unidirectional current over a submerged cubic obstacle. The three-dimensional velocity field was measured using an acoustic Doppler velocimeter (ADV). The results highlight the changes induced in the mean velocity profile, turbulent intensity, and Reynolds shear stress in a plane of symmetry from the superposition of surface waves of different frequencies. Modifications in the mean velocities, turbulence intensities, and Reynolds shear stresses with respect to the flat surface case, in the vicinity of the cube, are explored. This study also investigates the dominant turbulent bursting event that contributes to the Reynolds shear stress in the near-bed flow influenced by the cube. The results show that near the boundary, the contributions to the total shear stress from ejection and sweep are dominant. However, away from the boundary, the outward and inward interactions illustrate the prominence of wave−current interacting flow over the cube, which differs greatly from the flow over a flat surface. The mean time intervals of the occurrence of bursting events are obtained from the measurements of the fractional contributions to the total shear stress. The distribution of these time intervals is found to change because of the superposition of waves. As the frequency of the surface waves in a unidirectional current changes, the results show variations in the mean flow and the turbulence statistics that affect the local sediment mobility in the flow region influenced by the submerged cube.