محمد واقفی

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.