Combined effect of wave and current in rough bed free surface flow

In this paper, detailed experimental results are reported to study the effect of the surface wave of different frequencies on turbulent characteristics of flow over a regular array of cubical roughness. The velocity time series of current-only and combined wave-current flow is analyzed to obtain the distribution of first and the second order turbulence statistics, turbulent kinetic energy production, turbulent dissipation and kinetic energy fluxes at a fixed Reynolds number. To highlight the changes due to combined wave-current flow, a comparative study was made between the velocity profiles for current-only flow and those measured for combined wave-current flow. As expected, the rough profiles are shifted downwards with the amount equivalent to the roughness function (ΔU+), which was obtained directly from mean velocity profiles. Further, the thickness of turbulent boundary layer increases with the superposition of surface wave compared to current-only flow. Particular attention is also given to understand the behavior of kinetic energy flux to explicitly account for turbulent momentum transport characteristics over roughness under wave-current interactions.