Tridimensional Computational Modelling of a Low-drop Spillway

ABSTRACT Usually spillways are controls of their discharge, which features are well known. However, the number of low-drop spillways grows each day. In this kind of spillway, the crest loses a great deal of its discharge capability, as it happened on HPP Belo Monte´s spillway. It´s shape had to be altered and the final solution, a non-conventional one, was only found after long studies carried out in a physical model with the goal of achieving the required discharge capability. The difficulties encountered led to the question whether a mathematical model could help optimize the path to the solution, since there are only few information regarding the validation of such tools. Therefore, this article searched to evaluate the capability of a mathematical modeling tool, FLOW 3D®, in properly reproducing the characteristics of the complex flow through such spillways. To fulfill this goal, a case-study was done with HPP Belo Monte´s spillway on which gate controlled operation was also analyzed. Discharge capacity, flow line and pressure distribution from both models were compared. The results of the free-flow simulations indicated a good representation of the flow by the mathematical model. But bigger differences in discharge capability for the gate-controlled simulations were found, mainly regarding small openings. The comparisons of pressure distribution showed a very good similarity between the models. The results indicate that the mathematical model is able to satisfactorily reproduce both types of flows since appropriate measures are taken regarding mesh quality to ensure the convergence of the simulation.