Numerical study of bed proximity effects on the wake characteristics of a circular cylinder

This study investigates the wake flow dynamics, turbulence characteristics, and vortex structures around a cylinder located near a bed at two gap ratios (G/D=0.25 and 0.50) at a Reynolds number of 8000. Using large eddy simulations, the evolution of velocity profiles, Reynolds stresses, and vortex shedding behavior is analyzed to elucidate the influence of bed confinement on wake development. Results reveal that the smaller gap ratio significantly suppresses vortex shedding and shear layer instabilities, leading to a longer recirculation zone and delayed entrainment of ambient fluid compared to the larger gap ratio. In contrast, the larger gap ratio case exhibits a well-defined von Karman vortex street, earlier shear layer transition, and a separated bed shear layer. Reynolds shear stress analysis highlights enhanced momentum transfer in the larger gap ratio case. In contrast, the smaller gap ratio shows stronger shear layer–bed coupling and vortex annihilation near the bed. Horseshoe-like vortices are identified along the cylinder span, forming sporadically through interaction with upstream bed-induced turbulent eddies. The formation and evolution of these horseshoe-like vortices depend strongly on the bed proximity and turbulent boundary layer dynamics. These findings provide critical insights into the complex interaction between confinement, turbulence, and vortex dynamics, with implications for flow control and sediment transport in near-bed bluff body flows.