Author(s): Rita Carvalho

Linked Author(s):

Keywords: UAV; Spillway; Plunge pool flow; Turbulence; OpenFOAM

Abstract: The description of the flow over a dam spillway into a plunge pool stilling basin is complex and the flow patterns in the pool has great interest to better access the behaviour of the flow and improve their design. Foz Tua arch dam constructed in the Tua river, a right tributary of Douro river in Portugal, owned by EDP S.A. is a hydraulic infrastructure of this kind. The spillway is located in the central part of the dam with four separate spans controlled by gates designed for flood of 5500 m3/s and checked for the flood of 6500 m3/s. The plunge pool is located downstream of the dam 108 m height. The use of 3D numerical model becomes common in hydraulic water structure engineering as long as knowledge of the correct geometry is available. In this work, tools based on UAV images to construct a hydraulic infrastructure geometry to be used for numerical modelling are presented. The velocity, pressure field and surface profile of the flow from a reservoir, falling through a spillway into a plunge pool is investigated with OpenFOAM. UAV and aerophotogrammetry tools (Phantom 4 Pro, RTK Antena GPS D-RTK2, DJI Agisoft Meta Shape 1.53) allow referenced images acquisition from different points, which can generate 3D point cloud models, producing stl files ("Standard Triangle Language" or "Standard Tessellation Language"). Stl geometry after being checked against the project draws was used to construct meshes from different sizes and different combination of gate opening, using Salome 9.3.0, openFOAM blockMesh and snappyMesh, and paraview. The hydraulics of the real dam discharge over spillway was reproduced using OpenFOAM®v.18.12 within interFoam solver, which considers a Volume of Fluid (VOF) model that uses a single set of Navier Stokes equations for both fluids considered isothermal, incompressible and immiscible and an additional equation to describe the free-surface. The turbulence was described within RNG k-ε Reynold’s averaged Navier Stokes equation, which is known to be the best RANS modelling choice for predicting water elevation and velocity profiles. Each simulation was run for 100 s to reach steady state conditions. Simulations show the discharge crossing and leaving spillway with the movement of the trajectory in the air and the jet entering the water mattress downstream, generating strong turbulence. The velocity decreases when it penetrates the waterbed, but the jet remains strong, pushing the water away from the basin. Part of the kinetic energy of the water jet is converted into pressure energy, which extends to the bottom at the downstream limit of the basin. Case study allows to conclude that RANS CFD approach is an appropriate methodology to evaluate flow partition and energy dissipation from jet entering plunge pool to surface flow downstream dam.

DOI: https://doi.org/10.3850/IAHR-39WC25217119202270

Year: 2022