Wave-Current Interaction at a Right Angle Over Rough Beds: Turbulence Analysis

Abstract

In the present work, an investigation on the hydrodynamics of wave-current orthogonal combined flow has been carried out. The work focuses on the effects of the oscillatory flow superposed on the current steady boundary layer, and on how the oscillatory flow affects the current velocity distribution. A laboratory experimental campaign of wave-current orthogonal interaction has been carried out in a shallow water basin at DHI Water and Environment (Horsholm, Denmark), in order to investigate the orthogonal combined flow in the presence of different roughness beds. Mean flow has been investigated by computing time- and space-averaged velocity profiles. Friction velocity and equivalent roughness have been inferred from the velocity profiles by best fit technique, in order to quantify the shear stress experienced by the current mean flow. Tests in the presence of only current, only waves and combined flow have been performed. Instantaneous velocities have been Reynolds-averaged in order to obtain turbulent fluctuations time series and compute turbulence related quantities, such as Reynolds stresses. The mean current velocity profiles have been also compared with a selection of analytical models in order to assess their validity for the case of wave-current orthogonal flow for the considered wave and current condition ranges. The analysis of the mean flow revealed a complex interaction of the waves and currents combined flow. Depending on the relative strength of the current with respect to the waves, the superposition of the oscillatory flow may determine an increase or a decrease of the bottom friction experienced by the current. Such a behavior is also strictly related to the bed physical roughness. Analysis of the turbulence Reynolds stresses seems to confirm the results of the mean flow investigation.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/GbtOgeLlVTU