محمد واقفی

Scour is one of the important issues in the river engineering science, so this issue is considered as the main cause of failure of the riverine hydraulic structures. Bridge piers are among the structures that are influenced by the scour phenomenon. Therefore, the determination of the depth, formation and the development of scour hole, is one of the most important factors in hydraulic design of bridges. Accordingly, in this study the flow and scour patterns were investigated around bridge piers located in an experimental sharp bend flume. This experimental flume has 180-degree bend and the ratio of the central radius to the channel width is 2, which is classified within the sharp bends category. In these experiments, the form of piers group, direction of pier, and position of piers in the bend were studied in different conditions of flow in terms of scour pattern and in some states of flow pattern. The results showed that, the main secondary flow was established with clockwise direction, primarily at about 20 degree angle. Also, the second secondary flow was formed in the vicinity of the outer bank and near the water surface with an opposite direction comparing with the main secondary flow. The beginning point of the second secondary vortex in experiment of the bend without pier, convergent-vertival and divergent-vertical piers group, was observed at 40, 65, and 65 degree angles, respectively. In addition, in the scour pattern experiments, the maximum scour depth and sedimentation height occurred between two piers group around convergent-vertical piers group placing in 60-degree position and in the conditions of live bed that are equal to 128 and 88 percent of flow depth from the bed. In the divergent-vertical piers group, in two conditions of clear water and live bed, the changes of the maximum scour depth around piers altered from 60 degree to 90 and 120 degree positions, similar to the convergent-vertical piers group, and only their values were different. In clear