Flow field around side-by-side piers with and without a scour hole

Abstract

The present study provides the experimental results of the flow pattern around two-circular piers positioned in side-by-side arrangement. The experiments were performed for two bed configurations (with and without a scour hole). Velocities were measured by an Acoustic Doppler Velocimeter (ADV). Flat bed and scour hole were frozen by synthetic glue to facilitate the performance of the experiments. The contours and distributions of the time-averaged velocity components, turbulence intensities, turbulence kinetic energy, and Reynolds stresses at different horizontal and vertical planes are presented. Streamlines and velocity vectors obtained from time-averaged velocity fields are used to show further flow features. Bed shear stresses at specific points around the piers are given. The results of power-spectra analysis are presented inside and outside the scour hole. It is shown that the horseshoe vortex is elongated further to the downstream of the gap between the two piers. The flow between the two piers is accelerated into the scour hole so that it influences the vertical and transverse deflections of the flow around and especially between the two piers. The maximum downflow was inside the scour hole near the base of the pier. Between the two piers, the magnitude of downflow and vertical turbulence intensity as well as turbulence kinetic energy are greater than that at the outer sides of the two piers. Bed shear stress has substantially large values between the two piers, as much as two times in comparison to the other sides of the piers. The flow pattern including the contracted flow and interference between the horseshoe vortices play an important role in the creation and formation of the greater scour depth between the two piers. The presence of scour hole changes the behavior of vortex shedding considerably. The present detailed measurements can also be used for the verification of numerical models.