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Experimental Study of the Effect of Displacement of Vanes Submerged at Channel Width on Distribution of Velocity and Shear Stress in a 180 Degree Bend
Author(s): CHoonor Abdi, Mohammad Vaghefi
Keywords: Submerged Vanes; Position of Submerged Vanes at Width; Turbulence Shear Stress; Turbulence Kinetic Energy; The Secondary Flow Strength; 180 Degree Sharp Bend.
Shear stress is a highly important parameter. Through knowledge of this parameter, assessment of scour or sedimentation of different points of bed will be viable. Therefore, this paper addressed variations in shear stress under the influence of applyied submerged vanes, which were installed at the upstream side of a bridge pier and placed at a bend, specifically around the bridge pier. With the aim of modeling submerged vanes, vanes of Plexiglass as thick as 20% of the pier diameter with length of 1.5 times the pier diameter and 75% submergence were utilized. The vanes were installed at a distance equal to 5 times the pier diameter from the pier center at a distance of 40 to 60% of the channel width from the inner bank at the upstream side of the bridge pier. ADV velocimeter device was utilized in measuring 3D velocity components. The experiments were conducted in a 1-meter-wide flume with inclination angle of 180 degrees. The results of the study demonstrated that after 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 40% of the channel width from the inner bank towards the inner wall; while in the case of installing submerged vanes at a distance of 60% 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 16 and 5.5% 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 40% of the channel width from the inner bank were smaller than those in the case of installing the submerged vanes at a distance of 60% of the channel width from the inner bank.