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Numerical modelling of the capacity for a complex spillway, Page 1 of 2

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The stage–discharge curve for a complex spillway geometry has been computed with a three-dimensional numerical model. The model solved the Reynolds-averaged Navier–Stokes equations using the k– ε turbulence model. An orthogonal fixed grid was used, where the cells could be wet, dry or partially wet. A volume-of-fluid method was used to compute the location of the free surface in the grid. The spillway consisted of four partly separated free overflow chambers, with tunnel outlets. The four tunnels joined in a collection tunnel where free surface occurred in some sections and filled the tunnel in others. The resulting stage–discharge curve, therefore, showed two parts: one for low discharges with dominantly free surface flow in the tunnels and another part when the tunnels were filled. The results were compared with a physical model study. The deviation between the computed and measured values of the rating curve were under 2% for most of the curve, but rose to a maximum value of 10% where the flow was most complex. The findings indicate that a three-dimensional numerical model can be an accurate, inexpensive and rapid tool to predict the stage–discharge curve for complex spillways.