The commercial CFD program STAR-CCM+ was used to compute the stage-discharge curve for the spillway of the Innerdalen Hydropower Dam in Norway. The spillway consisted of first a free overflow section and then a system of tunnels where the flow could be pressurized. Air entrainment and negative pressures caused the flow physics to be fairly complex.
The computer program solved the Navier-Stokes equations with the k-epsilon and k-omega turbulence model. A volume of fluid method was used to determine the water surface location. Several types of non-orthogonal unstructured grids were tested. The results were compared with experimental values from a physical model study. Parameter tests were done on roughness, turbulence model, time steps and grids. The results show that the numerical model predicts the free flow section very well, with an accuracy less than 5 %. For higher discharges where the tunnel is limiting the discharge, the accuracy is between 0 and 10 %.