Three-dimensional Numerical Modeling of Flow in an Asymmetric Compound Channel at a River Bridge Site (Case Study: Khoresh Rostam Bridge in Khalkhal)

River bridges are among the most vulnerable technical structures of roads and railways in terms of flood risk. In the meantime, the characteristics of the river are effective in the flood that occurs and the damage that can be caused to the bridge structure. One of the common cross-sections, which is especially observed in rivers and natural streams, is compound sections. Asymmetric compound sections are one of the types of compound sections that cause flow conditions at the bridge site to be complicated. In this research, various dimensions of the problem have been investigated from a hydraulic perspective by means of three-dimensional numerical simulation of the flow at the bridge site. In this regard, FLOW-3D software has been used. After briefly introducing the software and explaining how to calculate important hydraulic parameters such as kinetic energy, energy loss and shear stress in the software, in order to ensure the proper performance of the aforementioned software, the results have been validated with a laboratory model. The model was used to simulate the flow at the Khursh Rostam Bridge in Khalkhal. The bridge is located in a narrow river span with an asymmetric compound cross-section with an elliptical water guide wall. The modeling results showed that although the use of an elliptical water guide wall on the right bank has protected the bridge abutment against severe changes in velocity and shear stress, the geometric shape of the river cross-section at the bridge site causes non-uniform flow distribution at the bridge piers. So that the shear stress around the piers, which is the main cause of scour and can cause bridge destruction, will vary by about 50 percent.
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