Air Pocket Modeling in Water Mains With an Air Valve

Abstract

Water mains filling events follow certain maintenance operations that require the complete or partial emptying of pipelines. These operational procedures are performed carefully in order to prevent air pocket formation, as such pockets may trigger damaging surges, as well impose blockages that reduce pipe conveyance. While previous research addressed the modeling of the pipeline filling events, the air phase within the conduits is in most cases either not included in the simulation, or its formulation is very simplified, not including air pressure gradients. This paper presents two modeling frameworks which couple a Two-Component Pressure Approach model to simulate water flow with models for the air phase flow within the conduits. The first is a discretized model for air phase based on the isothermal Euler equations and the second is based on the ideal gas law (as presented in [Zhou et al., 2002a]). Also, the results of an experimental investigation with an apparatus based on the experimental setup presented by [Trajkovic et al., 1999] without ideal ventilation which includes the essential features of a pipeline filling event are presented and discussed. Relevant and flow features characteristics during the filling event are analyzed such as the occurrence of interface breakdown. These experimental results as well as field data of the filling of an actual water main are used to calibrate and assess the model. A feasible modeling framework to simulate the filling of water mains accounting for air effects was presented. Also, it was demonstrated that lumped approach for air phase modeling has comparable accuracy with discretized model based on Euler equations at a much reduced computational effort.