Experimental Study of the Effect of Displacement of Vanes Submerged at Channel Width on Distribution of Velocity and Shear Stress in a ۱۸۰ Degree Bend

Shear stress is a parameter of high significance. Through knowledge of this parameter, assessment of scour or sedimentations at different points of bed is made viable. Therefore, this paper investigated alterations in shear stress along the bend, specifically around a bridge pier, under the influence of applying submerged vanes at the upstream side of the bridge pier. With the aim of modeling submerged vanes, vanes of Plexiglas with a thickness of ۲۰% of the pier diameter, a length of ۱.۵ times the pier diameter, and submergence ratio of ۷۵% were utilized. The vanes were installed at a distance equal to ۵ times the pier diameter from the pier center at a distance of ۴۰ to ۶۰% of the channel width from the inner bank at the upstream side of the bridge pier. Acoustic-Doppler Velocity velocimeter device was utilized for measuring three-dimensional velocity components. The experiments were conducted in a ۱-meter-wide flume with a degree of curvature of ۱۸۰. The results of the study suggested that upon reaching the bend apex, the maximum flow turbulence rate occurred in a transverse direction in the case of installing submerged vanes at a distance of ۴۰% of the channel width from the inner bank towards the inner wall; while in the case of installing submerged vanes at a distance of ۶۰% of the channel width from the inner bank, it occurred towards the outer wall, and it could be observed that the maximum longitudinal and vertical components of turbulence rate increased by ۱۶ and ۵.۵% respectively upon increase in the distance of submerged vanes from the inner bank. Furthermore, the values of and turbulence shear stresses at the outer bank in the case of installing the vanes at a distance of ۴۰% of the channel width from the inner bank were smaller than those in the case of installing the submerged vanes at a distance of ۶۰% of the channel width from the inner bank.