Complementary spillway of Salamonde dam. Physical and 3D numerical modelling

Abstract

Throughout the planning and design of hydraulic structures, engineers and researchers are increasingly integrating computational fluid dynamics (CFD) into the process. Despite reports of success in the past, there is still no comprehensive assessment that assigns ability to CFD models to simulate a wide range of different spillways configurations. The complementary spillway of Salamonde dam, located in the north of Portugal, is controlled by an ogee crest and two radial gates, followed by a free surface flow tunnel, with a rather complex geometry, and a terminal ski jump which directs the jet into the river bed. The present paper analyses the ability of a CFD model (FLOW-3D) to simulate the flows along this spillway. The spillway was primarily tested and developed in a physical model built in the National Laboratory for Civil Engineering (LNEC), where discharges and flow depths were measured in ten defined cross-sections for four different gate openings conditions. These results were used to calibrate the numerical model and to analyze the differences between physical and numerical models results. It is shown that there is an accurate agreement between physical and numerical model discharges. Concerning the flow depths, the FLOW-3D represents reasonably well the flow behavior, but slightly underestimates the flow depth in some points of the cross-sections. A sensitivity analysis for the conditions and parameters of the numerical model (e.g., 1st vs 2nd order momentum advection, turbulent mixing length TLEN, mesh size) was carried out. According to FLOW-3D results, for a certain reservoir level, spillway discharge and flow depth are highly dependent on mesh size. Conclusions about the most adequate FLOW-3D options to adopt are presented. The calibrated model was used to simulate the spillway design discharge and to assess the hydraulic behavior of the outlet structure and of the jet impingement characteristics. The pressure distribution in specific cross-sections was also assessed.