عنوان مقاله [English]
Vertical drops reduce the flow velocity and increase energy loss in steep-slope areas. In subsurface networks, the upstream channels in vertical drops are generally circular and the flow regime is supercritical; thereby, the flow characteristics are significantly different from those of the rectangular vertical drops with upstream and downstream rectangular sections and the subcritical flow. The present investigation aims to model numerically and experimentally a vertical drop with an upstream pipe and downstream rectangular channel. A vertical drop of height 0.345 m is built in the Hydraulic Laboratory, Department of Civil Engineering, Isfahan University of Technology. The upstream pipe is 0.19 m diameter, and the width of the downstream channel is 0.4 m. A jet box is installed in the upstream pipe to create the free surface flow with different Froude numbers and to make the upstream flow fully developed. The flow is also numerically simulated using OpenFOAM software. The interFOAM solver has been used for solving the two-phase flow. This solver is a two-phase algorithm based on the volume of fluid (VOF) method. The brink, pool, and downstream depths and energy dissipation in supercritical flow with Froude numbers ranging from 1 to 3.8 and relative discharge of 0.25 to 0.5 are investigated. In the numerical model, fixed velocity is used for the inlet flow at the upstream boundary. For the bottom of the channel and the sidewalls, the non-slip boundary condition is applied. At the upper boundary of the simulation domain, the boundary condition of the atmospheric pressure is used. The downstream boundary condition is set as zero gradients for all parameters. The free surface is supposed to be an isosurface with a volume fraction of 0.5. Given that many parameters are calculated in numerical simulations, a code is written in the Octave programming language to facilitate calculations. The results show that the brink depth is about 80% of the upstream depth, and the difference increases with increasing Froude number. The pool depth is less than that of the rectangular vertical drop. Increasing the relative discharge, both the pool and the downstream depths increases. The relative head loss of the present model ranges from 50 t0 70% and is about 50% higher than that of the rectangular vertical drop. The numerical simulation results are in good agreement with the laboratory observations.