Effect of gap on the flow characteristics in the wake of a bluff body near a wall

Abstract

a numerical investigation is carried out to evaluate the influence of the gap between the bluff body and the bed on the wake characteristics generated in shallow flows. a sharp-edge bluff body with a fixed gap from the bed is employed in the study, and the results are compared with the no gap case. a sharp-edged bluff body was chosen to minimize the effect of reynolds number and ensure fixed flow separation points. The transient three-dimensional Navier–Stokes equations are numerically solved using a finite volume approach with the detached eddy simulation turbulence model. The flow field in this study involves two different fluids, i.e. water and the air above it. The volume of fluid method is used for tracking the free surface separating the water and air. The fluid structures that are generated in the wake are identified using the λ2-criterion. The results reveal that the gap flow will develop a new structure near the bed, which enhances the upwash flow immediately after the submerged jet is about to turn upwards due to the weak hydraulic jump. This structure plays an important role in recovering the free surface to its original shape at a shorter downstream distance from the bluff body than when there is no gap.