علیرضا فیوض

Rivers’ bend routes are one of the most important areas for flow pattern investigation. Due to secondary flows existent in rivers’ bends, the alluvial bends morphology undergo many changes, and lead to erosion in the external bend. Spur dikes are simple hydraulic structures used in organizing rivers’ outer walls in the bend. In this research, a bend flume with a central angle of 180 degrees (with ratio of curvature radius to width of 2) was designed and built in the laboratory of advanced hydraulic structures in Persian Gulf University as the first 180 degree sharp bend flume in Iran in order to help better understand complicated flow pattern in a sharp bend. In conducting the experiments, Vectrino 3D velocity meter was used so as to measure velocity components and determine 3D flow pattern. The first step was to study average and turbulent flow patterns along the 180 degree sharp bend, and various parameters including turbulent stream lines, the Reynolds stress, the secondary flow strength, vorticity and kinetic energy were analyzed. The results of the experiment indicated that due to increase in the secondary flow strength at the bend apex, two clockwise vortexes were formed at the 90 degree cross section at distances of 5 and 38 percent of the channel width from the inner bank. The maximum bed shear stress also occured at the bend entrance, near the inner wall at the 40 degree cross section. Moreover, the amount of vorticity in the elements and the secondary flow strength reached their maximum at 60 and 80 degree positions respectively. The second step was investigating the spur dike’s effect on flow pattern variation in the 180 degree sharp bend. First, the effect of the length parameter of T-shaped and L-shaped spur dikes (in both upstream and downstream directions for the L-shaped spur dike wing) was studied. The results of such experiment demonstrated that a 67 percent increase in the spur dike length led to 26, 35 and 40 percent increase in the secondary flo