Importance of air cavity ventilation on pressures and forces on vertical structure subject to overflow

Abstract

This study investigates the dynamics of air-water flow and the resulting forces on a broad-crested weir with a vertical face under both ventilated and non-ventilated cavity conditions. The focus is on measured forces and flow characteristics across various upstream water depths and flume outlet heights, categorized by distinct groups based on flow regimes. The experimental setup incorporates measurements of air-water mixture density, air cavity pressure, cavity water depth, and velocity profiles in the recirculation pool downstream of the weir. Results indicate that under supercritical downstream flow conditions, the forces exerted on the weir are directly proportional to the upstream water depth, while the downstream flume depth has a minimal impact. Conversely, in subcritical downstream conditions, the downstream flume depth significantly influences stabilizing forces due to increased cavity water depth. Additionally, pressure profile estimations on the downstream-facing wall of the weir using hydrostatic, Bernoulli, and Navier-Stokes equations show that the hydrostatic assumption is inadequate for estimating pressures and sliding forces in non-ventilated cavities. This study offers crucial insights into air-water flow dynamics in weirs, underscoring the importance of incorporating dynamic factors into weir design and hydraulic modeling.