Spatially-averaged turbulent flow characteristics over ribbed surface in presence of unidirectional wave over steady current

The paper presents an experimental study on the characterization of the effect of surface-wave of different frequencies on spatially-averaged turbulent statistics over a rough bed. The model roughness comprised of periodically positioned, transverse square ribs that extended across the whole width of the channel. The three-dimensional turbulent velocity fluctuations were mapped by an acoustic Doppler velocimeter (ADV) in the flow domain at high resolution. These data were analyzed to examine time-space averaged turbulence parameters of the double averaged Navier Stokes equations and momentum transfer under the influence of the rough boundary. Further, Shannon entropy at different vertical position were also evaluated to develop insight into the energy transfer mechanism. Results show a reduction in the apparent roughness height and an increase of the intensity of turbulence under surface wave influence. Furthermore, the superposition of waves led to the increase in turbulence production and showed maximum values at the roughness layer as compared to buffer layer in current-only flow over plane bed.