Profile-Induced Column Separation and Rejoining during Rapid Pipeline Filling

Water column separation during rapid pipeline filling is numerically explored using a one-dimensional (1D) model that employs the method of characteristics to solve the governing equations and the well-known discrete gas cavity model (DGCM) to represent column separation. Extensive numerical experiments helped to identify the conditions under which column separation may occur during the rapid filling and to gain a physical sense of when the local rejoining pressures can be most severe. The major findings are that local V-shaped pipeline profiles following knee points are prone to the occurrence of water column separation and that the magnitude of the resultant overpressures markedly depends on the geometrical and hydraulic characteristics of the profile. Significantly, the propagation and reflection of the first pressure spike following column rejoining at a knee point can cause the onset of column separation in other parts of the pipe system. It is also found that short pipes must usually be steep to give rise to column separation during rapid filling, whereas longer pipes require much milder slopes; however, potential overpressures are significantly higher in short, steep pipes. Overall, the paper seeks to provide a physical interpretation of the numerical results to provide design and operational insight into this potentially important phenomenon.