Experimental analysis of streamlines around single and double piers with submerged vanes in a sharp U-shaped flume

Abstract To understand the scouring mechanism around bridges, it is crucial to comprehend the flow pattern in their vicinity. The positioning of the piers along meandering rivers complicates the flow pattern and exacerbates scouring. Therefore, by employing hydraulic structures like submerged vanes to modify the flow pattern around the piers, scouring and further damage can be mitigated. This research investigated the streamlines around one pier and two transverse piers due to the installation of vanes with 25% submergence in a sharp 180° flume channel with a rectangular cross-section. The findings showed that the streamlines in the plan section at the pier locations, from the bed to about 50% of the flow depth at the inlet of the bend, directed towards the inner wall; then, from this level to the water level, the streamlines shifted towards the outer wall. In the plan sections, the maximum positive tangential velocity rose with distance from the bed surface. In the scour hole, radial velocities were negative, while tangential and vertical velocities were positive, resulting in the formation of clockwise vortices in these regions.