Numerical Modeling of Flow Over Trapezoidal Broad-Crested Weir

Abstract

Two computational fluid dynamics (CFD) codes, Flow-3D and SSIIM 2, have been used to calculate the water flow over a trapezoidal broad-crested weir. The two programs apply different algorithms for making the grid and computing the free water surface. Flow-3D uses the Volume of Fluid (VOF) method with a fixed grid, while SSIIM 2 uses an algorithm based on the continuity equation and the Marker-and-Cell method, together with an adaptive grid for the water surface. The results have been compared with measurements from a physical model study, using different discharges. The deviation between the computed and measured upstream water level was between 1.0 and 3.5%. The difference between the results from the two CFD models was in the range of 1–1.5%. The accuracy of the algorithms depends on the grid size. The computational time on one core of a CPU (Intel Q9650 3.00 GHz) was between 435 and 15,500 seconds, using between 6,350 and 10,000 cells.