Impact of Vertically Constricted Entrance on Hydraulic Characteristics of Vertical Drop (Numerical Investigation)

Vertical drops are used in irrigation and drainage networks and surface run-off collection channels. In the present study, the impact of vertically constricted entrance on hydraulic characteristics of drops is numerically study utilizing FLOW-3D®. In the first step, for choosing the best model of turbulence, two types of turbulence models k -e and RNGk -e were used. In the next step, four constriction layouts of S/H=0.312, 0.500, 0.875, 2 (ratio of constriction distances to drop height) were utilized as long as the case without any constriction. The results showed that the RNGk -e turbulence model has less relative error percentage and RMSE in comparison with k -e model and more efficiency to simulate hydraulic characteristics on drops. Based on the obtained results, it was observed that the vertically constricted entrance would result in decreasing the relative depth of water in the pool, the depth of downstream water and normal residual energy by 42.31%, 47.23%, and 23.59%, respectively. Presence of entrance constriction results in increasing the velocity at drop edge and thus the kinetic energy decreases by flow turbulence increment caused by divided jet falls and production of more airwater mixing region. Some relations are proposed to calculate pond depth ratio, downstream depth ratio and normal residual energy with acceptable correlation coefficients which are in accordance with
those of other researchers.