A Quasi-Two-Phase Flow Model for Calculating Filling in Pipelines

This paper presents a quasi-two-phase flow model for simulating filling in water pipe systems. The model employs a shock-fitting algorithm for tracing the water column advancement during filling. The method of characteristics (MOC) along with discreet gas cavity model (DCGM) is utilized to capture the possible water column separation and induced water hammer pressures during filling. The state-of-the-art air valve boundary condition is improved to account for the two-phase flow usually established in the pipe on the downstream side of the air valve. The results show that the proposed model can (1) replicate the negative pressure and consequent water column separation; (2) reproduce the secondary transient pressure following the releasing of the air at air valve locations; (3) simulate controlled air release, a strategy usually employed for alleviating the severity of secondary transient events; (4) capture the final steady state flow condition even when the pipe system maintains both open channel and pressurized flow simultaneously; and (5) reproduce air binding and consequent flow reduction in the case that an air valve fails to release the air from the system.