Characterization of two-phase flows in plunge pools

© 2018 7th IAHR International Symposium on Hydraulic Structures, ISHS. All rights reserved. The increasing magnitude of design floods has prompted re-evaluations of spillway capacity for large dams throughout the world. Current capacity of many spillways is inadequate. The overtopping creates new loading scenarios for the dam and raises questions about erosion and scour downstream from the dam. In this study, mean velocity was measured in different sections of the falling jet with optical fiber and with LS-PIV (Large Scale - Particle Image Velocimetry). Detailed studies of the submerged hydraulic jump downstream overflow nappe impinging jets are scarce. This work addresses such a situation, and compares numerical results against our own experiments. To advance the understanding of the phenomenon, instantaneous velocity was measured in the plunge pool with Acoustic Doppler Velocimeter (ADV) equipment, and mean velocities and air entrainment rate were obtained with optical fiber instrumentation. At the same time, transient numerical simulations were carried out with computational fluid dynamics (CFD) programs. Due to the variation of the air concentration in the plunge pool, optical fiber obtained valid velocities near to the impingement point, while ADV was used once the air concentration was small, allowing for the measurement of the velocity in the whole submerged hydraulic jump. In general, the CFD simulations provided results fairly close to the laboratory values measured, in spite of having used a simple two-phase flow model.