Bijoy S. Mazumder

Turbulence Statistics of Wave-Current Flow over a Submerged Cube

AbstractThis 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 interaction...

Changes in turbulent flow structure over rough-bed under combined wave-current motions

Abstract This paper presents the result of an experimental study carried out in a laboratory flume to investigate the interaction of surface wave and unidirectional current over cube-mounted rough-bed. The cubes were made of wood and were positioned at the channel-bed with different spacing. The study particularly focuses on the changes induced in the spatially averaged velocity profile, turbulent intensity and Reynolds stress due to the superposition of waves of different frequencies on current-induced flow. The spatially averaged velocity profile shows two distinct regions: the linear or exponential distribution below the roughness tops and logarithmic profile above the roughness top. The profile of streamwise turbulent intensity is similar to that of current-only flow except in the region near the water surface. In contrast, the profile of bottom-normal turbulent intensity is almost constant over the entire depth. Below the roughness crest, the form-induced stress changes significantly with switching from negative to a positive value with change in roughness spacing, but is not affected much by the presence of surface wave.

Higher order turbulent flow characteristics of oscillatory flow over a wall-mounted obstacle

Abstract The paper presents an experimental study in a laboratory flume to investigate the combined wave–current flow over a wall-mounted cubic obstacle. Detailed velocity data were collected using three-dimensional (3D) micro-acoustic Doppler velocimeter from upstream to downstream of the cube along the centerline of the flume. This study examines the spectra, co-spectra, and turbulence kinetic energy flux analysis under the influence of cube in the turbulent boundary layer. It is observed that stream-wise spectral and co-spectral energy distributions vary with the addition of surface wave. Particular attention is also given to understand the behavior of higher order moments to explicitly account for turbulent momentum transport characteristics over wall-mounted cube under wave–current interactions.

Turbulence study over submerged obstacles on waves and currents combined flow

Abstract The paper explores an experimental study carried out in a laboratory flume to investigate the interaction of surface wave and unidirectional current over a pair of hemispherical obstacles with relative spacing, L/d = 4 where L is center to center spacing and d is the obstacle height. The effect of surface waves and current interaction on the mean velocity profile, turbulence intensities and Reynolds shear stress of an open channel flow under the influence of two hemispherical obstacles has been presented in this paper. The components of velocity along three different directions were measured using 3D micro-acoustic Doppler velocimeter. The experiments were conducted for Reynolds number 58800. Quadrant analysis has been adopted to investigate the turbulence bursting events contributing to the Reynolds shear stress in the near-bed region. It is observed that closed to the top of the obstacles, the contribution to the total shear stress due to ejection and sweeping events changes with the superposition of waves.