Innovative Simulation of Unsteady Low-Pressure Flows in Water Mains

This work presents a new numerical-model approach to simulate abnormal operational conditions in water mains, including the transition between free-surface and pressurized flow-regimes and subatmospheric unsteady flows leading to cavitation. The method is based on the two-component pressure approach (TPA), which is modified to incorporate a variable acoustic wave-speed calculation that depends on the pipe elasticity properties and on estimated free-gas content. This modification represents an improvement over the original TPA method for water-main applications in that the celerity, originally treated as a simulation parameter, now varies with space and time as would be anticipated in actual conditions. The proposed method was tested in three different conditions that involved unsteady flows and vaporous cavitation, and its results were compared with the original TPA model, the method of characteristics discrete free-gas cavity model, and experimental data. The comparative analysis indicates that the modified TPA model be an interesting and useful alternative to simulate unsteady flows in water mains in cases in which flow-regime transition is anticipated.