Author(s): Roman Tijsseling; Janek Laanearu

Linked Author(s): Janek Laanearu

Keywords: No Keywords

Abstract: The simultaneous presence of air and water in a gravity-flow pipe—typical of a Water Collection System (WCS)—creates complex two-phase flow regimes. Ventilation is determined by the drag between the moving water interface and the air in the pipe headspace, resulting in air exchange through connected manholes. A critical knowledge gap exists in urban water engineering: There are currently no hydraulic formulae available for modelling the airflow in headspace and manholes, thus of ventilation of WCS. To address this issue, a custom-built numerical model was developed utilizing the open-source Computational Fluid Dynamics (CFD) library, OpenFOAM. This software uses a two-phase solver (interFoam), features fully custom geometry and meshing (using blockMesh) and appropriate boundary conditions to investigate the air-phase characteristics under varying conditions. The influence of three different pipe slopes on the air flux is investigated in a half-filled pipe located between two manholes with atmospheric top ends. The numerical solutions aim at the understanding the fundamental hydraulic principles of air-water stratified flow within gravity-flow pipes.

DOI:

Year: 2026