امین محمودی

To reduce the trend of scouring, understanding the fow pattern around the bridge piers is necessary. By using hydraulic structures such as submerged vanes, it is possible to alter the fow pattern of water, thus scouring process and sediment transport in riverbeds. Since the scouring mechanism for pier groups difers from single pier, experiments were conducted in a 180° sharp bend channel in the laboratory to investigate the fow pattern around pier group and single pier under the infuence of 25% submerged vanes. Furthermore, a comparison was made between the fow patterns in single pier and pier group conditions. Three-dimensional velocities along the bend and diferent depths were measured using an Acoustic Doppler Velocimeter (ADV(. The results suggest that the maximum vorticity value at the apex position of the bend (location of piers) and the maximum secondary fow value, at the distance between the piers and the vanes, were found to be, 0.15 and 0.89, respectively. In the twin pier experiment, the maximum Reynolds shear stress value 휏yx decreased by about 36%, and the minimum value decreased by about 49% compared to the single pier experiment. The fnal results indicated that using submerged vanes obtained the maximum 휏yx and 휏zx near the vanes. Near the bed and mid-depth of the water fow, the geometric location of the maximum velocity also occurred around the vanes in both experiments. Therefore, the vanes are important in altering the water fow pattern, diverting the fow from around piers and consequently reducing the bridge pier scouring.