High flow velocity near the free surface in rivers is due to the presence of shear stress near the bed and its absence on the free surface. This phenomenon results in unsteadiness of the vertical velocity profile. Moreover, secondary flows in river bends cause velocity variations, accordingly leading to changes in shear stress near the bed. The present study evaluates and analyzes the effect of streamlines variations, maximum velocity distribution, and secondary flow strength on bed shear stress distribution along a 180 degree sharp bend built in the Hydraulic Laboratory of Persian Gulf University. Results suggest of the occurrence of maximum secondary flow strength at the second half of the bend. The evaluation of bed shear stress distribution using the TKE, modified TKE, and Reynolds methods at turbulent boundary layer demonstrated that the maximum shear stress occurred from the entrance of the bend to the bend apex area near the inner wall. Moreover, comparison of the Reynolds shear stress method at distances of 5 and 15% of the flow depth from the bed indicated that the maximum shear stress occurring at the lower layer moved from the 40 degree cross section to 60 degree cross section at the upper layer.

Spur dikes are used for river training purposes. To meet the navigability of rivers, the mean annual flow is considered; hence, in terms of river flooding, spur dikes are necessarily submerged. Considering the importance of submerged spur dikes, this paper studied the effects of a T-shaped spur dike's submergence ratios on turbulent flow parameters in a 90° bend using the SSIIM as a commercial CFD model. The SSIIM numerical model solves the Navier-Stokes equations with the k-ε model on a three-dimensional, almost general, non-orthogonal grid. Submergence ratios of 0 (non-submerged), 5, 15, 25 and 50% were evaluated for parameters affecting the turbulent flow such as kinetic energy, pressure, eddy viscosity and the Froude number. It was observed that by increasing the spur dike submergence ratio from 0% (non-submerged) to 50%, in addition to changes in the values of pressure and kinetic energy, the Froude number changed in the bend and increased 2.1 times at the inner bank of the bend exit, and the eddy viscosity near the bed, which is the decisive factor of the turbulent flow, reduced by 42%. At the bed near the spur dike wing, the amount and range of kinetic energy reduced by increasing the submergence ratio. Near the bed, for all submergence ratios, the maximum pressure occurred at the upstream end of the spur dike.

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Numerous bridges are destroyed worldwide every year mostly due to the role of hydraulic factors including scour being ignored when they are designed. Therefore, examination of the scour phenomenon around bridge piers in rivers and identification of the parameters affecting them gain a great level of significance. Particularly, if the bridge piers are installed at river bends, the complicated nature of the flow in bends adds to complications already existent in analysis of flow and scour patterns around such structures, which indicates the need for further study. Hence, the present study has utilized SSIIM numerical model to analyze the three-dimensional flow and scour patterns around perpendicular pier groups (two series of triad parallel piers) at different positions of a bended channel (at the 60-, 90-, and 120-degree angles). The simulated bended channel is a 1-m-wide channel with a central angle of 180 degrees and a relative curvature radius of 2. These data are first compared and confirmed with data collected by acoustic Doppler velocimetry under similar conditions for validation of the numerical data. The results obtained from this model indicated that changing the position of the bridge piers in the channel does not have a significant effect on the maximum scour value; however, the amount of the maximum sedimentation increases by 12% after relocating the piers from the 60-to the 90-degree angle, whereas relocating them from the 90-to the 120-degree position leads to a 42% reduction in the maximum sedimentation.

This piece of research simulated the flow pattern around a T-shaped spur dike in the vicinity of attractive and repelling protective structures in a 90°bend using computational fluid dynamic (CFD) model. This CFD analysis has utilized RNG turbulence model to simulate turbulent flow field, and free surface variations were modeled through finite volume of fluid. A comparison between mean velocities in the main spur dike field was indicative of an acceptable precision of CFD model in simulating flow pattern along river bends in the presence of a spur dike. This numerical model mainly aimed at a scrutinizing study of the process of flow pattern around the T-shaped spur dike, the maximum velocity variations, the secondary flow strength, and the maximum stresses along the bend and the main spur dike field. Results demonstrated an increase in the maximum shear stress in attractive and repelling modes of the protective structure by 23.5 and 17.6%, respectively, in comparison with the vertical mode.

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