Numerical Simulation of Geysering Created by Air Pocket Release in an Upstream Vertical Shaft

Abstract

Over the past decade, the air-water interaction in pipes with rapid filling has been studied to understand its effect on the formation of geysering phenomena. Geysering phenomena involve the displacement of an air pocket that is pressurized inside a storm drainage system during extreme precipitation events. The entrapped air pocket can move rapidly and displace water in drainage structures, causing explosive release when the biphasic fluid reaches grade elevation. Previous experimental and numerical studies have attempted to investigate the mechanism of geyser formation, but have not considered a numerical study with a geometry in which the air pocket is released through the upstream end of the dropshaft vertical drainage system. The objective of the present work is to study geysering phenomena through numerical simulations by analyzing the pressure results over time and following the movement of the air pocket inside the pipe from the initial air chamber up to the release in the upstream vertical dropshaft. An upstream end geometry was implemented in the OpenFOAM Volume of Fluid model, and the results obtained were qualitatively compared with scaled geometry results from an experimental study. The presented results showed strong similarities when qualitatively compared with the experimental one. It is possible to observe the displacement of the air pocket on the vertical shaft up to the time of its release. When mesh refinement was imposed on the model, the maximum displacement of water in the vertical shaft was observed. Statistical analyzes demonstrate a tendency of convergence of the model as the mesh resolution increases, indicating the possibility of scaling the model to match the experimental setup.