Turbulence statistics of flow over scoured cohesive sediment bed around circular cylinder

The effect of clay content on the mean flow, turbulence intensities, Reynolds shear stress and conditional statistics of the Reynolds shear stress was investigated within and above the equilibrium scour hole around circular cylinder embedded in cohesive sediment bed having clay fractions 0.1 and 0.2. Detailed three dimensional velocity components were measured at three different cross-sections: upstream, sideward and downstream of the pier covering flow regions within and above the scour hole using 3D Micro acoustic Doppler velocimeter (ADV). It is observed that within the scour hole region the sweeping events play a dominant role at both the side and the front of the pier while the ejection events play a dominant role in the outer flow region. At the scour hole surface a thin layer of ejection dominant pocket is seen both at the pier front and the side. This resulted in kolk–boils phenomenon at the interface layer of sweep and ejection dominance which probably instigated the scouring process. In addition, the mean time interval of the turbulent bursting events within and above the scour hole is presented.

► Flow structure is reported for scoured cohesive sediment bed around circular cylinder.
► Mean flow and turbulence characteristic in scoured cohesive sediment bed is studied.
► Conditional statistics of Reynolds shear stress is evaluated within and above scour hole.
► Regions of ejection and sweeping dominance within and above scour hole is reported.