Author(s): Janek Laanearu

Linked Author(s): Janek Laanearu

Keywords: Ir-water interaction; Numerical modelling; Ventilation; Hydraulics; Sewers

Abstract: The dynamics of air-water stratified flow in the branched-pipes system with different diameters and restricted ventilation through manholes is studied numerically. It is shown that the air and water are strongly coupled in the underground gravity main not only by interfacial drag but also due to pressure, and therefore, the stratified flow in the partially filled underground gravity main is modified with the pressurized flow conditions. The flow in sewers is usually unsteady due to the water consumptions profiles of resident and industrial users. This type of consumption results essentially with the diurnal flow patterns in the hydraulic system. The changes in water level result in the adjustment of air-volume inside the pipe headspace and can lead to very intensive exchange of air or pressurization. It is explained how the different water levels and water-surface velocities drive the air exchange through several venting stacks of the large-scale sewer collector. It is demonstrated that the air-flow pattern in the venting stacks mounted at the top of deep underground chambers, which are located between differently elevated pipes is drastically changed due to the formation of air cavity inside the underground pipe. The water-flow quantities in the combined sewer are usually gained by the hydraulic models considering the quasi-steady flow conditions, but the modelling of air exchange through the gravity-main manholes is a more challenging task to study hydraulically. Therefore, the air-water stratified flow in the large-diameter collector pipe with minor slope is studied using the 3D numerical modelling software herein. The two-phase flow process is qualitatively analyzed in the reduced-size sewer-pipes system with chambers and manholes. Measurements information is used to facilitate an interpretation of the air-water flow processes using the CFD open-source software. This study demonstrates ability of the advanced numerical modelling tool to predict the turbulent air-water interfacial processes and associated air-flow pattern in the venting stacks.

DOI: https://doi.org/10.64697/978-90-835589-7-4_41WC-P1847-cd

Year: 2025