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In this work, the three-dimensional flow around piers in river meanders under rigid bed conditions was modeled. The software ANSYS FLUENT was used to perform the simulation. The study was carried out in a 180° curve accompanied by cylindrical piers with a diameter of 5 cm and a slope angle of 21° under rigid bed conditions. The results of the comparisons showed that this model can help simulate the flow pattern around inclined bridge piers in bended channels with acceptable accuracy. To analyze the flow pattern, the work was followed by studying the effect of the parameters that affect the physics of the problem: the relative radius of curvature of the curve, the location of the piers within the 180° curve, and the arrangement of the piers relative to the flow direction. The results showed that increasing the relative radius of curvature as well as the range of the bend reduced the tangential velocity values; the minimum tangential velocity value occurred at a relative radius of curvature of 5. With the pier group installed in the direction of flow, the maximum secondary flow power occurred at the 60° position at about 18.8%, while with the pier group installed across the flow, the maximum secondary flow power occurred at the 120° position at 14.2%. A comparison of the vorticity at the perpendicular and downstream positions showed that the vorticity values at the 60° and 120° positions were greater than the corresponding values at the 90° position in both cases.

In this research, the flow and scour patterns downstream of a rectangular Piano Key Weir (PKW) were studied experimentally and simulated by using the Flow-3D numerical model and with RNG turbulence model. It was found that the Flow-3D model simulates the scour downstream of a PKW with acceptable accuracy. Variations of the bed topographical downstream of type-A PKWs with different crest shape (i.e. standard crest and with zigzag indentations in various geometries, including: triangulate, half circular, sinusoidal, rectangular and fort crest) were investigated. The results demonstrate that the zigzag indentations of the lateral crest walls substantially influenced the geometrical characteristics of the scour hole including: scour depth at the weir toe, maximum scour depth, scour hole area and scour hole volume. The lowest value of maximum scour depth was occurred downstream of the PKW with the triangulation indentations, in this case a decrease of 10.5 and 17% in the longitudinal and vertical components of flow velocities, at the weir crest level and below the crest level, led to a reduction of 38% in the local scour, respectively. The higher energy of flow in the weir with the rectangular indentations caused the maximum scour depth location to occur at a farther distance from the weir toe. Also, the lowest upstream and downstream slopes of the scour hole were observed in the two weir models with rectangular and fort crest shapes.